groundwater development and survey methodsredciencia.cu/geobiblio/paper/2003_leslie_groundwater...

Groundwater Development

and Survey Methods l.f. molerio-león

UNESCO, 2003

Encyclopedia of Life Support Systems

GROUNDWATER DEVELOPMENT AND SURVEY METHODS 2

To the beloved memory of my parents, who guided me through life with love and courage

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ENCYCLOPEDIA OF LIFE SUPPORT SYSTEMS

GROUNDWATER DEVELOPMENT AND SURVEY METHODS1

L.F. Molerio-León Group of Terrestrial Waters, Institute of Geophysics and Astronomy, Cuba. P.O. Box 6219, CP 10600, Habana 6, Ciudad de La Habana, Cuba. E-mail: [email protected] Keywords: Aquifers, water wells, monitoring, groundwater development, speleology, karst, hard-rock aquifers, seawater encroachment, water quality, geophysics, tracer hydrology, mathematical modeling

GLOSSARY ................................................................................................................................ 6

1. INTRODUCTION .................................................................................................................. 7

2. SURVEYING .......................................................................................................................... 9 2.1. FACTORS CONTROLLING GROUNDWATER OCCURRENCE...................................................... 9

2.1.1. Geodynamic processes and factors. .......................................................................... 9 2.1.2. Morphodynamic processes and factors................................................................... 10 2.1.3. Climatic processes and factors ................................................................................ 11 2.1.4. Hydrodynamic processes and factors...................................................................... 12 2.1.5. Geochemical processes and factors ........................................................................ 13 2.1.6. Thermodynamic processes and factors. .................................................................. 14 2.2.1. Geologic indexes ...................................................................................................... 15

2.2.1.1. Lithology ........................................................................................................... 15 2.2.1.2. Tectonic structure .............................................................................................. 16 2.2.1.3. Stratigraphy and rock age.................................................................................. 17 2.2.1.4. Geomorphologic indexes................................................................................... 17 2.2.1.5. Climatic indexes ................................................................................................ 20

2.2.1.5.1. Extreme climates ........................................................................................ 20 2.2.1.5.2. Tropical climates ........................................................................................ 21

1 This is a single text comprising Topic Level 2.9.6. Groundwater Development and Article Level 2.9.6.1. Survey Methods of the Unesco’s Enciclopedia of Life Support Systems (EOLSS)

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mailto:[email protected]


2.2.1.6. Hydrodynamic indexes...................................................................................... 22 2.2.1.7. Geochemical indexes......................................................................................... 24

2.2. GEOLOGIC AND GEOMORPHOLOGIC EXPLORATION ........................................................... 27 2.2.1. Types of aquifers...................................................................................................... 27

2.2.1.1. Karst aquifers..................................................................................................... 27 2.2.1.2. Hard rocks aquifers............................................................................................ 28 2.2.1.3. Intergranular aquifers ........................................................................................ 28

2.2.2. Landscapes............................................................................................................... 29 2.2.2.1. Mountains .......................................................................................................... 29 2.2.2.2. Plains and Flatlands........................................................................................... 29 2.3.2.3. Small islands...................................................................................................... 30 2.3.2.4. Coastal zones, deltas and wetlands.................................................................... 30

2.2.3. Hydrodynamic types of aquifers.............................................................................. 31 2.4. GEOPHYSICAL METHODS................................................................................................... 34 2.5. TRACER HYDROLOGY....................................................................................................... 36

2.5.1. Types of tracers ........................................................................................................ 37 2.5.1.2. Suspended solids ............................................................................................... 38 2.5.1.3. Soluble chemicals .............................................................................................. 38 2.5.1.4. Dyes................................................................................................................... 38 2.5.1.5. Environmental isotopes ..................................................................................... 39

2.6. GEOCHEMICAL EXPLORATION........................................................................................... 39 2.7. PUMPING TESTS ................................................................................................................ 43

2.7.1. Planning................................................................................................................... 43 2.7.2. Well hydraulics ........................................................................................................ 44

2.7.2.1. Steady state equations........................................................................................ 46 2.7.2.2. Unsteady, transient, conditions.......................................................................... 47

2.7.3. Recovery tests ........................................................................................................... 48 2.7.4. Leaky aquifers.......................................................................................................... 48

2.7.3.1. Time –drawdown under unsteady conditions.................................................... 49 2.7.3.2. Steady state drawdown ...................................................................................... 49 2.7.3.4. Hantush solution................................................................................................ 49

2.7.5. Delayed yield solutions ............................................................................................ 49 2.7.6. Double porosity models ........................................................................................... 51 2.7.7. Solutions for turbulent, non-linear flows ............................................................... 52

2.8. SPELEOLOGICAL EXPLORATION ........................................................................................ 53

3. WATER DEMAND ASSESSMENT................................................................................... 56

3.1. WATER OFFER................................................................................................................... 56 3.2. WATER DEMAND............................................................................................................... 58 3.3. THE PROCESS OF HYDRAULIC PLANNING........................................................................... 62

4. WATER QUALITY ............................................................................................................. 65

5. WELLS AND TRENCHES ................................................................................................. 75

5.1.1. Penetration depth..................................................................................................... 76 5.1.2. Drilling method........................................................................................................ 77 5.1.3. Casing or tubing ...................................................................................................... 77

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5.1.4. Well diameter ........................................................................................................... 78 5.1.5. Well screen and filter pack ...................................................................................... 78 5.1.6. Well development ..................................................................................................... 79 5.1.7. Yield capacity and well efficiency ........................................................................... 80 5.1.8. Protection perimeters............................................................................................... 80 5.1.9. Maintenance ............................................................................................................ 81 5.1.10. Planning well drilling ............................................................................................ 81

5.2. TRENCHES AND INFILTRATION GALLERIES ........................................................................ 83 5.2.1. Gallery in slowly permeable material with minimum depth of water above stream bed ...................................................................................................................................... 83 5.2.2. Gallery in permeable riverbed or with minimum depth of water above the bed ... 84 5.2.3. Gallery in an ephemeral or intermitent stream channel with perennial underflow............................................................................................................................................ 84 5.2.4. Gallery for freshwater skimming ............................................................................ 84

6. STREAMFLOW RECESSION ANALYSIS ..................................................................... 86 6.1. GENERAL.......................................................................................................................... 86 6.2. GROUNDWATER RESOURCES ASSESSMENT........................................................................ 87 6.3. OVERLAPPING OF DIFFERENT SUB REGIMES ...................................................................... 89 6.4. WATER RESOURCES ASSESSMENT ..................................................................................... 90 6.5. VARIATION OF RESERVES AND STORAGE INDEX ................................................................ 91 6.6. TRANSMISSIVITY.............................................................................................................. 94

6.6.1. Alternative method for Transmissivity computation in karst aquifers .................. 96 6.7. EFFECTIVE INFILTRATION ................................................................................................. 98 6.8. DISTANCE TO THE WATER DIVIDES.................................................................................... 99

7. DESIGN, OPERATION AND OPTIMIZATION OF GROUNDWATER MONITORING NETWORKS.............................................................................................. 101

7.1 GEOMATHEMATICAL TECHNIQUES................................................................................... 103 7.2 METHODOLOGY FOR THE DESIGN OF HYDROGEOLOGICAL MONITORING NETWORKS...... 105 7.3 OPTIMIZATION OF HYDROGEOLOGICAL MONITORING NETWORKS .................................. 107 7.4 SELECTION OF THE OPTIMUM SAMPLING NET ................................................................. 111

8. MATHEMATICAL MODELLING ................................................................................. 113

8.1. PREDICTION MODELS ...................................................................................................... 114 8.2. IDENTIFICATION MODELS................................................................................................ 114 8.3. MANAGEMENT MODELS.................................................................................................. 114 8.4. STAGES IN MATHEMATICAL MODELING........................................................................... 114 8.5. MATHEMATICAL FORMULATION ..................................................................................... 115

8.5.1. Flow models ........................................................................................................... 115 8.5.2. Transport models ................................................................................................... 117

9. SPECIAL SCENARIOS AND FORTHCOMING GROUNDWATER DEVELOPMENT................................................................................................................... 119

REFERENCES ....................................................................................................................... 121

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GLOSSARY Productivity: Quantity of water that can be abstracted from an aquifer without affecting

its natural replenishment, quantity and quality. Karst: A particular kind of landscape and hydrogeologic media mainly developed

in carbonate rocks characterized by a high anisotropy of its hydraulic and geomechanical properties, taking its name after the Krs or Karst region, in ancient Yugoslavia. The presence of caves is one of the most important hydrogeological characteristics of these environments.

Aquifer: Water bearings rock formation capable of store and transmit water.

Hard-rocks aquifers:

A particular kind of aquifer developed in the joints of igneous and metamorphic rocks characterized by its low yields, a reason by which are also named as low-permeability aquifers.

Hydraulic properties:

A set of physical properties of rocks linked with their capacity to store and transmit water. Permeability, storage, transmissivity, specific yield are hydraulic properties.

Network Optimization:

In hydrogeology, the process of design, construct and operate a groundwater monitoring network with the minimum number of stations and measured at the largest time intervals, with the lowest operational costs without loosing information.

Geomathematics: The application of mathematical and statistical techniques to the interpretation and generalization of data on geologic and geophysical variables.

Speleology: The science of studying the geological, geomorphological, hydrological, biological and climatological variables of caves and its support system.

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1. INTRODUCTION

ccording to United Nations statistics, several millions of people annually die by water diseases. Most of them lives in Third World

countries with scarce economic resources or in territories were groundwater development is a difficult and expensive task.

A For example, the hard rocks or low permeability rocks cover huge regions of Africa and South America. Groundwater is usually scarce in these countries and is irregularly distributed in tectonic fractures with very low yield. Millions of inhabitants of these regions scarcely satisfy their needs with surface waters that are easily and, sometimes, highly polluted. Water supply has also been stressed by the growth of population. Sustainable development is seriously committed in countries that, until the year 2000, has experienced important rates of growth like Africa (75%), Latin America (65%) y southern Asia (55%). Therefore, in those countries is a high demand of water that will increase in the following years. Groundwater development is designed to satisfy a certain demand of water or to assess ground water resources of a watershed. Therefore it comprises three-four phases highly interrelated:

• Surveying; • Construction of abstraction systems; • Design, construction, operation and optimization of monitoring networks. • Mathematical modeling.

Surveying is the initial stage of any groundwater exploitation system and primarily deals with the identification of the perspective zones. Broad use of geological, geomorphologic, geophysical and special hydrological methods are made at this stage. Exploration boreholes are drilled and pumping and permeability tests are developed in order to obtain numeric indexes of groundwater potential. Chemical analysis of water and, sometimes, of rocks and sediments is also performed in order to clarify the process governing water composition and quality. Construction of abstraction systems where aquifer potential and water quality allows exploitation is usually the second stage. Wells, trenches and springs are then adequately built or adapted. Wells are built with the diameter, depth, casing and filters derived from the results of the surveying phase. Wells and trenches are tested again to define efficiency. In cases

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protection perimeters could be required, and computations for the proper design of them are performed. Maintenance program of the abstraction system is identified at this stage. Design, construction, operation and optimization of monitoring networks is the final stage of a groundwater development program but not necessarily or exclusively has to follow the preceding phase. In effect, when regional studies are performed or when controls of groundwater regime and quality are required, groundwater monitoring networks are designed, constructed and operated to prevent pollution, groundwater level depletion, undesirable side effects of groundwater exploitation or to control the effectivity of mitigation or rehabilitation measures. Mathematical modeling is required to manage groundwater resources. Therefore the construction of a mathematical model is commonly a phase of groundwater development linked with the design, operation and optimization of the monitoring network,. This stage is not always necessarily, while it can be implemented, in other stages, in order to save time and money, like in surveying, or in the reorientation of surveying, in well data processing, in geochemical hydrodynamics assessments, etc.

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2. SURVEYING

2.1. Factors controlling groundwater occurrence

roundwater occurrence depends upon the interrelation of several groups of factors. They control how ground waters are formed, move, gain its chemical composition, and vary in amount and availability. These factors are of different nature and involve

geodynamics, morphodynamics, climate, hydrodynamics, geochemistry and thermodynamics. G 2.1.1. Geodynamic processes and factors. Geodynamic factors are related with the processes forming the lithosphere or those whose action is expressed as or is a consequence of the composition, physical properties and relations among the rocks forming the earth crust. Factors of this kind are of the uppermost importance because is in the rocks lying under the earth’s surface that ground waters are. And also, the main types of aquifers are distinguished after the lithological composition of the rocks. Two main processes are then identified. One of them concerns to those involving the formation of rocks, v.gr. sedimentation, magma penetration, or the metamorphosis of rocks formed by one of the previous processes. This simple distinction allows the definition of three fundamental types of rocks: sedimentary, magmatic and metamorphic. But, at the same time, they constitute an initial, but not absolute, relative scales of aquifer potential, where sedimentary rocks are the most common and high productive aquifers. Metamorphic rocks use to be associated with low yield aquifers, the so-called low permeability or hard rocks aquifers that are often impermeable. The second group involves those processes governing rock fracturing and the displacement of the blocks in the rock matrix. They are grouped under the generic term of deformation of rheological bodies. Aquifer productivity depends upon the interaction of those processes and upon the space and time evolution of that interaction. For example, only in the case of sedimentary rocks the following processes interact:

• Geological evolution of the source of sediments • Oceanic circulation • Local circulation in the sedimentary basins • Wind induced turbulence • Sediment transport • Sediment accumulation and erosion • Compaction and diagenesis of rocks • Isostatic adjustment and subsidence of the sedimentary basin • External tectonic influence • Control of the local or regional base level of erosion • Depth of the basin

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With respect to the deformation processes it is necessary to consider a group of local and planetary factors. Among the most important are the following:

• Elasticity and plasticity properties of the rocks • System’s kinematics, dynamics and thermodynamics • Magnitude and direction of the stresses governing rock deformation • Thermal convection • Earth rotation • Rock folding and fracturing • Orogenic and magmatic cycles • Volcanism

These processes and factors build the scenario where the action of factors controlling groundwater occurrence began to act. Therefore, in second place morphodynamic processes will be examined. 2.1.2. Morphodynamic processes and factors These deal with rock modeling and, therefore with landscape formation. It should be taken into account that only in a small amount present landforms are recent or modern in the common meaning of these terms. Actually, the present landscape is much more the result of the evolution, at a geological time scale, of the action of several factors. Six main groups of processes govern landscape formation. They are, mainly, processes of erosion, v.gr. of rock dissagregation:

• Slope modeling • Fluvial erosion • Glacial erosion • Eolian erosion • Marine erosion and regional base level changes • Karstification

In slope modeling, the most important of all morphodynamic processes, the following group of control factors should be considered:

• Rock reduction • Spontaneous mass movement, like landslides • Denudation • Endogenetic effects

Fluvial erosion deals with the following elements:

• Fluids forces

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• Sediment transport • Interaction fluid-landscape-sediment transport • Gradation and basin slopes • Movement in river bends • Meander formation • Valley formation

Glacial erosion accounts for:

• Longitudinal movement of glaciers • Tridimensional movement of ice

Eolian erosion considers:

• Wind velocity and corrasion • Electric effects • Atmospheric diffusion

As far as it concerns to coastal aquifers and the sustainable development of the fragile ecosystems of coastal zones and small islands, marine erosion processes and sea level changes promotes the following:

• Isostatic readjustments or glacieustatic changes of sea level • Variations in the equilibrium profile • Formation of coastal lines, deltas and beaches

In carbonate terrains, karstification is the most important process and is governed by the following factors:

• Thickness of the carbonate rocks • Sources of carbon dioxide • Accumulation, movement and discharge of water

2.1.3. Climatic processes and factors In defining the occurrence of groundwater past and present climatic processes are of the outmost importance. These factors control the balance of precipitation, the primary and commonly, unique source of fresh groundwater formation and replenishment. Four main processes govern the formation and distribution of climate on the Earth. These are the following:

• Balance of energy and radiation • Heat transfer

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• Precipitation and evaporation • Climatic variations

The balance of energy and radiation is ruled by a set of factors, as follows:

• Astronomic factors, due to the Earth movements • Geographic, according to the latitude of the system • Meteorological, related with the weather of a certain basin

Heat transfer is linked with factors like diffusivity and thermal conductivity that also interacts with the processes of precipitation and evaporation and in turn is related with atmospheric diffusion, condensation and atmospheric circulation. Of special importance are the climatic variations, particularly those that took place in past geologic times, but mainly during Quaternary times. In many carbonate regions, one effect of these changes is the development of superimposed cave levels. When located in the saturated zone of the aquifer, these cave levels use to be very high productivity zones for water supply purposes. The most important factors controlling climatic variations are:

• The difference in radiation and energy balance in different latitudes during the recent geological evolution

• Readjustments in sources and sinks 2.1.4. Hydrodynamic processes and factors These processes and factors describe the mass transport in the system, particularly of the fluid and of the solutes moving with it. Therefore, the basic processes are the mechanical transport (advection), diffusion, dispersion and hydrochemical delay. These processes are so strongly related that in practice is very difficult to separate them. Among these factors the following could be specially distinguished:

• The saturated flow that takes place within the aquifer body, from the upper groundwater level to the impermeable bottom of the aquifer.

• The unsaturated flow that takes place in the unsaturated (vadose or epikarstic) zone; v.gr. the hydrodynamic sector extending from ground surface to the ground water level in unconfined aquifers.

• The alternatively saturated-unsaturated fluxes that takes place in the zone of seasonal fluctuations of groundwater level and, occasionally, near the surface under conditions of imbibition.

• The steady or unsteady flow conditions. • The mechanisms of accretion and hysteresis. • The velocity of ground water flow.

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• The distribution of potentials in the flow region, governing the direction of groundwater flow and the mass transport.

• The presence of other phase, because water is not always the only fluid and air and other gases or liquids could be entering or entrapped and water is not always the only fluid.

• The heat exchange due to friction and shearing stress derived from flowing water.

• The fluid transfer among the different constitutive spaces (pores, joints and

caves) of the aquifer (Figs. 1 – 2). 2.1.5. Geochemical processes and factors Geochemical processes and factors govern the acquisition of the chemical composition of waters. They are of extreme practical importance while they control the hydrodynamics of water quality and therefore, its capability to satisfy a specific demand (irrigation, drinking, and industry). For natural groundwater, geochemical processes are: • Stoichiometrical • Termochemical • Physico-chemical

Fig. 1. Rock pores

Fig. 2. Joint enlargement and cave development

Factors to be taken into account are the following: • Equilibrium among the different rock minerals where ground water flow takes place. • The kind and velocity of the chemical reactions and, in particular REDOX and Sulfate

reduction reactions. • The relative solubility of the different substances that are present or are produced by the

chemical reactions that take place. • The mixing of waters of different origin and chemical composition. • The temperature and partial pressure of carbon dioxide of groundwater, particularly in the

case of carbonate aquifers. • The chemical affinity of the reactions. • The diffusion and dispersion mechanisms. • The mineral precipitation and, particularly, the interstitial (in pores and joints) cementation;

as well as recristalization, mineralogical changes, dolomitization or dedolomitization of carbonate rocks and the formation of evaporites.

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2.1.6. Thermodynamic processes and factors. Thermodynamic principles govern the mass, energy and moment balance and the direction in which processes take place. By this reason, two main groups of processes should be taken into account: • The relation among forces and fluxes. • The variation of free energy. In the first the following factors should be considered: • Heat transfer. • Volumetric flux. • Electric conductivity. • Chemical reactions. In the second group, the following factors are important: • The self-regulation capacity of the system. • The entropy production. • The energy dissipation. 2.2. PRODUCTIVITY INDEXES The above-mentioned geodynamic, morphodynamic, hydrodynamic, geochemical and themodynamic factors provides the basis for identifying the productivity of aquifers in any region of the world. These are the most important but not unique sources of information. They should be complemented with historical, social and economical data before any prospecting should be developed. Selection of the adequate indexes is always linked with the type of aquifer, the goals of the development and the financial availability. As far as it concerns to the type of aquifer, it is necessary, first of all, to know about the geologic structure of the territory and the morphological expression of the potential productive rocks in the landscape. After it, the conditions for groundwater occurrence could be primarily inferred. Indexes are collected following particular techniques of documentation and inspection in the field and in libraries and archives. Inhabitants of the territory under consideration are always an important source of qualitative information as well as the local toponyms are excelent indexes of geologic, geomorphologic and hydrologic features. Therefore, the elements that could be considered as direct or indirect indexes of groundwater productivity are:

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• Geologic • Geomorphologic • Climatic • Hydrologic • Historic There are also indexes for groundwater quality, like: • Socio-economic level of development • Main economic activities • Medical history of the community 2.2.1. Geologic indexes Several geologic indexes are useful for a diagnosis of productivity. They should be accounted in the stage of development planning. The most important are: • Lithology • Tectonic structure • Stratigraphy 2.2.1.1. Lithology As it was mentioned earlier, according to the lithology, three main types of aquifers could be distinguished:

Fig. 3. Classification of carbonate rocks (after Folk,

1962)

• In carbonate rocks (Karst aquifers) • In igneous and metamorphic rocks

(Fissured -non-karstic- aquifers) • In granular rocks (Intergranular

aquifers) Carbonate rocks are sedimentary rocks mainly built by carbonate minerals forming three main types: aragonite, calcite and dolomite. Of all carbonate rocks, more than 600 types, limestone and dolomites are the most common. According to Folk (1962) carbonate rocks are genetically divided in two groups (Fig. 3): allochtonous and autochthonous, differentiated after the carbon content and the fractions of quartz or shales present. The most important post-

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sedimentary alterations in carbonate rocks is karstification (Fig. 4). Karst is almost a good indicator of productivity, particularly in the humid tropics. In some igneous and metamorphic rocks, like granites and diorites (igneous-intrusive), pegmatites and porfides (igneous –filonian) and magmatic like gneisses and some shales, fissured -non-karstic- aquifers are developed. In terms of their productivity, the rock type is not so important like the joint pattern, because these rocks are only productive along joints. Nevertheless it sdesigned as low-permeability rocks, because producticommonly included in this aquifers but they usually form Granular rocks are also sedimentary rocks but thhydrogeological purposes as unconsolidated, like sands, like sandstone. According to their degree of consolidatistorage or specific yield or permeability varies. Therefore, unconsolidated granular rocks usually existence, when linked with surface streams and rivers On the other hand, consolidated granular rocks arfracturing is a factor to be added to grain size wconsidering potential productivity of these rocks. Some volcanic rocks, like certain tuffs, are usuconsidered within this aquifers, while others like lava basalt are frequently considered within hard rocks aquife 2.2.1.2. Tectonic structure For the most karstic carbonate rocks, igneous, metamorand several consolidated granular rocks, the tectstructure, in terms of the fracturing pattern is the mimportant factor in defining their potential productivitygroundwater development. Fig. shows several fracplanes of rocks. In karst carbonate rocks, fracturing defines the preferedirections for groundwater flow. Those preferedirections are blocks or sectors of high transmissivity, anconsequence, of high yield among others of transmissivity or negligible transmissivity whose product

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Fig. 4. Sketch diagram of a karst system

hould be reminded that these are also vity is always very low. Basalt are very important aquifers.

ey are commonly differentiated, for pebbles and gravels, and consolidated, on important hydraulic properties like

form important aquifers and their is almost an indicator of groundwater. e also productive but, in this case, hen

ally and

rs.

phic onic

ost for ture

ntial ntial d in low ivity is alm

Fig. 5. Joints and blocks

ost null.

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The problem is more complex in the case of the hard rock aquifers where, definitely, groundwater flow only occurs in fractures. These could seem that groundwater development is easy but, on the contrary, makes it more difficult because not all fractures are capable to store and transmit water. Groundwater development in low permeability aquifers is particularly complex by the following facts: • Not all fractures of the same tectonic episode or the same genetic type are productive. • Not all fractures of the same family (orientation and dip) are productive. Therefore, a rigorous analysis of fracturing and of the physical connection among different joints has to be carried out in order to increase success and reduce expenses. 2.2.1.3. Stratigraphy and rock age For hydrogeological purposes, unless it can be recognized common features in rocks of the same age, like in several geologic formations, the position of certain groups of rocks in the stratigraphic scale is not so important. Age is most important while it is an indicator of what kind of processes like diagenesis, volcanism, flooding and fracturing could increase or decrease the water bearing spaces of the rocks: pores, fractures and caves.

Fig. 6. Evolution of permeability

2.2.1.4. Geomorphologic indexes The type of landscape is of fundamental importance in the assessment of the costs of groundwater exploration and development. The relation landscape-lithology-geologic structure defines the occurrence, extension and productivity of aquifers. From a hydrogeological point of view, landscape could be typified according to the following:

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Relief types Hydrogeologic index Mountains

1. According to their geologic structure 1. Homogeneous lithology 2. Heterogeneous lithology 3. Folded and faulted in simple systems 4. Folded and faulted in complex

structures 2. According to the degree of dissection of the relief

1. Alternation of erosion surfaces 2. a - High or b - low dissection degree

a - horizontal, or b - vertical (or both) 3. According to the development of the fluvial net and their hydrological activity

1. Forming suspended valleys 2. Drainage a - endorreic or b - exorreic 3. Drainage a - permanent, b - seasonal

or c - episodic 4. According to their altitude and geometric classification

1. High mountain 2. Low mountains and stockings 3. hills or isolated hills 4. Forming chains or plateaus

Plains 1. According to their genetic type or their current position in the geomorphic system

1. Coastal or deltaic 2. Marshy or lacustrine 3. Fluvial 4. Inland plains

2. According to their geologic structure 1. Sedimentary basins 2. Eroded anteclises and sineclises 3. Subsidence or uplifting areas 4. Lithology a - homogeneous or b -

heterogeneous with lateral or vertical facial changes

3. According to the degree of dissection of the relief

1. Alternations of erosion surfaces 2. a - High or b - low degree of

horizontal, vertical dissection (or both)

4. According to the development of the fluvial net

1. Forming suspended valleys 2. Drainage a: endorreic b:exorreic 3. Drainage a: permanent, b: seasonal,

c: episodic 5. According to their altitude and geometric classification

1. High mountain 2. Low mountains 3. Hills or isolated hills 4. Forming chains or plateaus

The geomorphologic features mentioned above could be conjugated in the way that is shown in Table 1 in order to assess the feasibility of a groundwater development.

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Table 1. Aquifer productivity matrix of geomorphologic features Morphological

feature High

productivity Medium

productivity Low

productivity Undefined or

negligible productivity

A.1.1 X A.1.2 X A.1.3 X X A.1.4 X X A.2.1 X

A.2.2 a.a X A.2.2.a.b X X A.2.2.b.a X X A.2.2.b.b X X

A.3.1 X X A.3.2.a X A.3.2.b X X A.3.3.a X A.3.3.b X X A.3.3.c X X A.4.1 X A.4.2 X X A.4.3 X A.4.4 X X B.1.1 X X B.1.2 X B.1.3 X X B.1.4 X X B.2.1 X X B.2.2 X X B.2.3 X X

B.2.4.a X X B.2.4.b X X B.3.1 X B.4.1 X

B.4.2.a X X B.4.2.b X X B.4.3.a X B.4.3.b X B.4.3.c X X B.5.1a X X B.5.1b X X B.5.1.c X X B.5.2 X

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2.2.1.5. Climatic indexes Precipitation is the main source for groundwater replenishment. Climatic factors are of outstanding importance to assess if a continuous source of groundwater recharge is available in a reasonable time span. In turn this defines whether or not groundwater could be exploited within the natural cycle of groundwater replenishment avoiding resources exhaustion. Groundwater prospecting and development is different according to the climate peculiarities of each territory. Particularly, according precipitation, the most important source for groundwater replenishment, the following types should be considered:

• Extremes: o Arid or semiarid o Polar, subpolar and tundra

• Tropical: o Permanent humid o Seasonally humid

Temperate

2.2.1.5.1. Extreme climates 20% of the emerged lands of the Earth is desert while another 20% is semiarid. These are developed at northern Africa and Australia, although similar, but less extensive zones are also found in the Caribbean, southern Africa and South America. In these regions precipitation is very low and generally does not surpass 200 mm yearly and natural recharge is practically negligible while evaporation rates are very high. These facts are of extreme importance for groundwater development. One of the most important is the replenishment rate of groundwater that is usually very low. In the Sahara this rate is estimated around 100 000 years in terms

of turnover time of groundwater, v. gr, the time span since water is recharged until it is discharged.

Fig. 7. Semiarid terrain

Most of the aquifers developed in these regions are very deep and groundwater was infiltrated in past geologic times. In modern geologic times, by the way, the hydrologic cycle of deserts show particular features which in turn defines the type of works that has to be built for groundwater development. Condensation, for example, is very important as a consequence of the daily difference in temperature and relative humidity; therefore water is collected in

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shallow horizontal galleries, named kanats, constructed since immemorial times to allow condensation. One of the best indexes of aquifer productivity in arid and semiarid zones is a kind of vegetation named phreatofites. Some grasses crops in places where water table is close to land surface, commonly at depths under three meters. Bushes and trees are usually associated with ground water depths between 10 and 30 meters. In permanent frozen zones (polar, subpolar and tundra) groundwater development is also very complex and expensive because the lack of clear indexes for aquifer development. Commonly prospecting tries to look to groundwater associated with non permanently frozen lakes, the location of hydrolacolites, clear indexes of permafrost and to the presence of trees of deep roots like poplars. Well construction, nevertheless, is complex and expensive because the depurate technology that requires, as well as the secure logistic needed and the reduced useful life of the wells, particularly when water wells need gravel filters or conduction pipelines are required at surface or close to it.

Fig. 8. Glacier

2.2.1.5.2. Tropical climates In tropical climates precipitation, expressed, as rainfall is not a limiting factor for groundwater recharge. On the contrary, it is so abundant that guarantees a steady replenishment of groundwater. These territories receive almost 50% of the world distribution of humidity; therefore geologic and geomorphologic factors become most important. It has to be stressed, however, that while rainfall is abundant and well distributed along the year, evaporation and evapotranspiration are also very important in the hydrologic balance. As a rule well and spring productivity should be assessed during the dry (or less humid) season in order to approach more unfavorable conditions of recharge and discharge. Most tropical regions are prone areas of extreme events of precipitation like hurricanes and heavy rains. High intensity rains depending on the recharge capabilities of the aquifer

could constitute important nodes of very high instantaneous natural recharge characterize these events. This feature has to be carefully accounted in groundwater development in these regions

Fig. 9. Flood

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because, according to the geologic type of aquifer their response to instantaneous recharge is differently expressed. For example, in unconsolidated granular aquifers of fluvial terraces of small basins, the net aquifer recharge is practically negligible. But in bigger basins it is usually very important. In karst aquifers, heavy rains could provoke subsidence phenomena associated to sediment conduit washout. In fissured non-karstic aquifers, heavy rains not seem to be an important source of natural recharge in fractures but in the weathering crust of these rocks. 2.2.1.5.3. Temperate climates Temperate climates are common in continental areas. The seasonal distribution of precipitation is clearly linked with the annual distribution of insolation and radiation. Rain and snow, with a clear distribution within the year, are the main agents of natural recharge to aquifers. Therefore, the seasonal components of precipitation, evaporation, runoff and infiltration could be better distinguished in continental temperate regions than in tropical climates. It is not insignificant that most of the empiric equations for evaporation, evapotranspiration and surface runoff have been described and validated in temperate climates and could be applied with some confidence in similar regions. 2.2.1.6. Hydrodynamic indexes A dozen of hydrogeologic processes and factors describing the overall mass transport were mentioned before. The way that they are expressed in the landscape suggests the potential groundwater productivity of a region. Three of them could be specially

mentioned:

Fig. 10. Spring

Fig. 11. Typical cross-section of a spring

• Springs • Permanent rivers and lakes • Water-filled caves in karst regions

Other indexes of reliable importance are:

• Lineaments of phreatophytes in metamorphic or igneous rocks, commonly linked with water bearing fractures;

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• Interior wetlands, mainly linked with high groundwater levels; • Existence of dug wells.

Indirect hydrodynamic and hydraulic information could be gathered from topographic maps or aerial photographs. Cemeteries indicate that high ground water levels do not reach ground surface or at least are deeper than two meters. Rural footpaths use to follow the dry zones along watershed divides and, in turn, can help in the determination of productive zones. The frequency and duration of floods in surface streams, particularly those occurring during the dry season, are an index of the self-regulation capability of the aquifer. The above-mentioned indexes are only a first approach to water development planning. In order to quantify aquifer productivity, more information has to be gathered. In the case of springs, for example, it is necessary to define:

• Genetic type of the spring. • Seasonal and annual flow

variability.

Fig. 12. Spring development

• Relation with other springs, wells or rivers

• Shape and dimension of the drainage basin, lithologic composition and geomorphology. • Transit time of groundwater and self regulation capability of the system • Shape, yields and duration of the floods.

These data allows hydrograph separation and, hence, to identify the spring base flow, somewhat equivalent to its safe yield and exploitation resources, the distribution of the most perspectives zones within the aquifer and the quality of ground waters.

Permanent lakes and rivers are clear evidences of the existence of groundwater sources feeding them. Observations of their regime provide the same information mentioned in the case of the springs. In karstic regions, freshwater filled caves are almost evidences of aquifer productivity. However, it is necessary to define whether they belong to an epikarst developed in the unsaturated zone or to the saturated zone of the aquifer (Fig. 13).

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When caves are filled by epikarstic or hypodermic flows, it must be clarified if it is a single, local phenomena or it is a seasonal or episodic event related with heavy rains, surface runoff or local perched aquifers. In cases where not associated to the aquifer system and exploitation should be only recommended after a special research effort. Nevertheless, when these caves are associated with local groundwater levels could be pumped directly without drilling wells. In the particular case of cenotes or casimbas, special care has to be accounted for water quality. However, in the case of caves, the following information has to be obtained:

• Genetic type • Hydrological position with respect to the local,

intermediate or regional flow system.

Fig. 13. Fresh water filled cave

• Input-output yields • Chemical composition of waters • Water level and yield variations • Hydraulic relation with springs, wells, rivers or lakes.

2.2.1.7. Geochemical indexes When properly related with spring or well yield, geochemical indexes are also hydrodynamic indexes in the sense that they offer valuable information regarding the processes governing the acquisition of the physical, chemical and bacteriological composition of waters. In this way, they define water quality and, hence, the use of water and, eventually, the treatment it has to receive to fulfill the requirements for a sustainable exploitation. Therefore, the knowledge of the processes governing water quality composition is of relevant importance. This process is strongly influenced by several factors acting from the recharge zone to the discharge zone along the flow paths. No matter where discharge zone is natural, like a spring, or man-made, like a well, the importance is the same. Among the factors controlling water quality, the following are especially important:

• The physical, chemical and bacteriological composition of atmospheric precipitation and, in particular of the recharge fraction.

• The looses by evaporation and evapotranspiration that takes place in shallow aquifers or that is produced on infiltration waters during its transit through the unsaturated zone.

• The acidity and degree of unsaturation of recharge waters and of ground waters, with respect to the basic minerals of the aquifer rocks.

• The availability of soluble rocks and the their solubility.

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• The solution rate of these rocks and the water-rock contact time. • The extent and intensity where pure hydrological processes like dilution by fresh

recharge waters or mixing of ground and surface waters exert their action. • The man-made processes affecting the natural composition of waters.

The most important geochemical indexes are the following:

• Temperature, pH and Specific Electric Conductivity • Dissolved solids • Dominant Chemical character • Dissolved Oxygen and REDOX potential • Isotopic composition • Age of waters

Temperature is a good index of movement conditions of groundwater. It depends on the initial temperature of precipitation, on the temperature in the different circulation scenarios and on the chemical reactions that take place in the aquifer and can add or rest heat. It is important to note that in temperate climates, unconfined aquifers show remarkable fluctuations of temperature within the year, while in confined or semi confined aquifers, those variations are of negligible importance. In many cases, temperature measurements in springs could help in the identification of when diffuse or concentrated flow conditions prevail within the aquifer or after a remarkable hydrological event. pH could contribute to define the relative concentration of solutions with respect to the prevailing minerals, the presence of mixed waters and, in conjunction with other indexes contribute to define the concentration of gases like CO2 , O2 , H2S, NH3 and the presence of algae or bacteria. The Specific Electric Conductivity (SPC) is the best indicator of salt concentration in waters. SPC depends directly on the load and mobility of ions and of their concentrations. Measurements of SPC and yield are successfully employed to define the chemical yield or the expected concentrations in several stations along the same flow line. Total Dissolved Solids (TDS) are directly related to SPC. For several prevalent chemical types empirical relations between them could be established. It is important to remark that the solutes present in ground waters are a direct consequence of the composition of precipitation waters, the mineralogical compositions of the aquifer rocks, of the chemical variations derived from hydrologic or geologic processes like evaporation, weathering or pollution. Indirect indexes of water mineralization are, for example, the travertine or tufa deposits at the discharge of springs. In fluvial beds, the presence of these deposits almost suggests the presence of waters of different chemical composition and reprecipitation by mixing waters. Weathering crusts of duricrust or caliche type almost indicates natural recharge deficits associated to evaporation of transit waters. The Prevalent Chemical Character (PCC) indicates the relative abundance of the different anions and cations present in water and allow to distinguish it according to their type and

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origin. There are several classifications for this purpose but they will not be mentioned. The most important remark is that the ions that use to be more abundant in any kind of groundwater are the following:

• Bicarbonate HCO3 -

• Sulphate SO4 + -

• Chloride Cl- • Calcium Ca ++

• Magnesium Mg++

• Sodium Na+ • Potasium K+

Concentrations of those major constituents are usually expressed in milligrams per liter (mg/l) or milliequivalents per liter (mEq/l). Commonly, type of waters are defined after the higher concentrations of cations and anions, in such a way that the usual denominations are “calcium bicarbonate waters”, “sodium chloride waters” and so on. The relations among those ions offer many indications on the groundwater regime, the geological composition of the terrain along circulation takes place, sources and losses, pollution sources and the transit time of waters. Therefore the composition of travertine or tufa deposits is a field index to characterize the PCC of the discharging ground waters. The teeth health and the complexion of the inhabitants of a certain place is also an index of the relative importance of calcium and fluor in drinking water. Renal diseases are also indexes of high concentration of iron in waters; keratosis always indicate high levels of arsenic; corroded pipelines indicates aggresivity of waters, and so on. Dissolved oxygen (OD) in ground waters is an important index of contamination. Potentially, the presence of residual sewers reduces the normal value of non-polluted waters that is usually of the order of the 8.25 mg/l of OD. REDOX potential can help to establish the degree of oxidation of the waters when the OD is below the detection limit. Fig. shows some common pairs of reactions of oxidation-reduction that can be useful under field conditions. The isotopic composition and the relative age of waters are very important indexes. Their determination, however, requires specific and expensive analysis mainly because, to be reliable, they require of at least an annual set of data on chemical and isotopic composition of groundwater and amount and isotopic composition of precipitation. However, there are not doubts about their success in the identification of an important group of hydrological processes. Examples of them are the time and spatial distribution of the evaporation and natural recharge, the transit or turnover time of waters, the renovation rate of ground waters and the process of horizontal and vertical mixing of the different aquifer horizons. Isotopic composition is also important to determine the sources of contaminants and the safe yield of aquifers. The environmental isotopes commonly used in hydrogeology are of two kinds: stable and radioactive. Among the first, deuterium (2H), the isotopes of carbon (12C, 13C) and of oxygen

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(18O, 17O, 16O). Among the seconds, the tritium (3H) and the carbon–14 (14C) generates β particles during the process of radioactive disintegration with a half time life, respectively, of 12.26, 5 and 30 years.

2.2. Geologic and geomorphologic exploration 2.2.1. Types of aquifers The different action, in space and time, of the processes and factors described above control the development of groundwater in the Earth’s crust. This differentiated action allows the distinction among different types of aquifers according to: • The geologic structure. • The geomorphologic features. • The hydraulic properties. Thus an aquifer is a flow system where the main fluid is water. From the geological point of view it can be defined as a tectonic unit absorbing, storing and transmitting and discharging water. Therefore, according to geology, the following types of aquifers could be distinguished: • Karst • Fissured • Intergranular or detritic 2.2.1.1. Karst aquifers

Karst aquifers are developed primarily, but not exclusively, in carbonate rocks, mainly limestone, but also in dolomites, gypsum, salt and marls among others. The are extended over more or less 20% of the Earth’s crust and its main characteristic is the development of a secondary porosity or permeability due to carbonate dissolution (Fig. 14). This process, known as karstification, enhances primary pores, joints and beds and varies completely the hydraulic properties of rocks. Anisotropy is the

main characteristic of these aquifers due to the presence of four interrelated spaces where flow takes place. After any measure of characteristic length or physical properties These constitutive spaces of karst aquifers were flow takes place (Molerio, 1985) are rigorously hierarchized.

Fig. 14. Karst areas of the world

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According to its geological and geomorphologic expression, these spaces are generically designed, in decreasing order, as caves, joints, pores and solid matrix. Karst aquifers exhibit a high dominating directional control of their physical and hydraulic properties, a strong dependence of the scale factor on the physical properties and the exclusively feature that groundwater and surface flow are highly interrelated. Karstification generates impressive and extensive subterranean drainage networks. These are the dominating aquifers in the Southern United States, the Gulf of Mexico and the Caribbean. The name comes from the typical limestone region of Karst in ancient Yugoslavia. 2.2.1.2. Hard rocks aquifers

Fig. 15. Hard-rock aquifers

Hard rock aquifers are developed in igneous and metamorphic rocks and covers between 20 and 30% of Earth’s surface (Fig. 15). These aquifers normally show a very low productivity and are also known in literature as of low permeability rocks. This is due to the fact that groundwater lies only in the rock fractures. They are developed in geological structures known as shields, like the Scandinavian, Brazilian, African or Canadian, and are built in rocks like granites, diabases, gabbros, serpentines and basalt. While water only circulates in a single space: the joints, hydraulic properties are highly dependent on direction and therefore, groundwater development in these aquifers is complex and expensive.

2.2.1.3. Intergranular aquifers These are the so-called porous aquifers, are developed in unconsolidated sediments like sands, pebbles and gravels of aluvial plains or fluvial terraces (Fig. 16) and in consolidated sediments like sandstone. Many aquifers of the weathering crust of different rocks are also of this kind.

Fig. 16. Fluvial terraces

Their extension is very variable and uses to be excellent aquifers in terms of their productivity. Geometrically, there is only one space for water occurrence: the pores of the rocks so their dependence on direction is practically negligible. Therefore they are commonly considered as isotropic aquifers.

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2.2.2. Landscapes All over the world the above mentioned rocks forms a variety of landscapes. As there is a relation among the relief and groundwater, geomorphology -the study of the morphology of the Earth- is a very important clue for groundwater exploration and development. Groundwater occurrence varies according to the morphological features of the landscape. Therefore the morphology of the rock-forming aquifers provides special features that have to be accounted for a successful groundwater prospecting. The following general landscapes will be discussed: • Mountains • Plains and flatlands • Small islands • Deltas and wetlands 2.2.2.1. Mountains In mountains (Fig. 17), aquifers are usually discontinuous and show limited extension and exploitable resources. Commonly, abstraction by wells is expensive and, in some cases, unavoidable and the exploitation of springs becomes the most common and cheap practice. Nevertheless, at the bottom of the valleys is common to find important aquifers linked with the river terraces.

Fig. 17. Mountains

Groundwater response to rainfall is very fast because of its small capability of self-regulation. This is due to the relatively small area of the catchments and the high vertical gradients derived from the sharp difference in head potentials, particularly between recharge and discharge areas. 2.2.2.2. Plains and Flatlands

Generally speaking, groundwater potential in plains and flatlands (Fig. 18) is greater than in mountains. This is due to the fact that hydraulic gradients use to be low, waters move slowly and the residence or turnover time of water is greater. Very large aquifers, some of them covering areas of thousands of square kilometers are not uncommon. Groundwater usually lies at shallow depths a reason that makes that the usual abstraction system is by wells, but also trenches and galleries are commonly found when groundwater is very close to surface, like in some coastal plains.

Fig. 18. Flatland

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Due to the low velocities of groundwater movement, these aquifers show a more slow response to natural recharge being its self-regulation capability much higher than in the case of mountain aquifers. In not few cases, nevertheless, this feature conspires against water quality because pollutants could remain long time in the aquifer allowing its broad dispersion within the system. Rehabilitation practices are then very expensive and in many cases abstraction has to be abandoned. Beneath these two main types of landscape, there are special environments where specific hydrogeological problems arise. The following have been specially selected as examples:

Fig. 19. Small island

• Small islands • Coastal zones, deltas and wetlands

2.3.2.3. Small islands Small islands (Fig. 19) could be of low relief or mountainous. But despite their morphological expression they show common hydrogeological features. Small islands are extreme fragile environments with limited natural resources and scarcity of arable farmlands. Commonly they are vulnerable to strong demographic stresses increasing water demand and the risks of pollution. The surrounding sea is always a risk of seawater intrusion. General water scarcity is a consequence of the very small recharge areas, a problem that becomes even worst in mountainous small islands because surface runoff is very fast and infiltration very slow. 2.3.2.4. Coastal zones, deltas and wetlands

In deltas and wetlands (Fig. 20) the most important risk to groundwater quality is seawater intrusion. Groundwater resources in deltas are almost related with the interrelation between surface and groundwater, v.gr. when and where surface waters recharge ground waters or viceversa, an interrelation varying in space and time.

Fig. 20. Wetland

In wetlands, linked or not with surface waters, similar problems are found. But there they are complicated by the proximity of groundwater level to surface. This fact introduces evaporation and evapotranspiration as additional mechanisms for salinization and water resources decrease. Commonly, the

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presence of wheat of different origin and its related expansion and contraction phenomena adds the problems of volume variation and relative storage variations to the water budget. 2.2.3. Hydrodynamic types of aquifers The third and last level for aquifer typification is the hydrodynamic type. This is related to the way groundwater flow is organized and developed. Four main types of aquifers are commonly defined (Fig. 21): • Unconfined aquifers • Semi-confined aquifers • Semi-unconfined aquifers • Confined aquifers

In unconfined aquifers, productive rocks are extended from ground surface down to an impermeable bed. Its upper limit is a free –unconfined- surface, more or less continuous, the water-table where the only acting force upon water is atmospheric pressure. This make water levels in wells to equilibrate at the same levels of aquifer ground water. Confined aquifers are those where a completely saturated permeable strata is vertically limited by two impermeable beds of so an areal extent that “confine” the aquifer that now is additionally under the influence of another force higher than atmospheric, the weight of the “confining” rocks. That is why, in some cases, groundwater elevates almost over the ground surface in wells drilled in these aquifers. These are the so-called artesian wells, named after the Artois region, in France. In these cases the term water table is substituted by piezometric level to denote that extra load.

Fig 21. Types of aquifers according to Krusemann and de Ridder (1974)

Semi-confined or delayed-yield aquifers are built in a completely saturated bed whose upper limit is not impermeable but semi-permeable. These semi-permeable beds are defined as those who shows a very low, but measurable, permeability or hydraulic conductivity. When the piezometric surface reaches the upper bed a circulation between the semi-confined bed and the aquifer is established. This circulation is mainly vertical because horizontal permeability or hydraulic conductivity is so low that the horizontal flow component is negligible. When piezometric level decreases, the upper bed starts to drain with a certain time delay. That is the reason why they are also called delayed-yield aquifers.

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In these aquifers, piezometers controlling groundwater level regime has to be installed not only in the aquifer but also in the upper and lower semi-permeable beds. Drawdown in the semi-permeable beds is almost lower than in the aquifer. Semi-unconfined aquifers are those where the pores of the semi-confining bed are so small and permeability so high that a horizontal flow component has to be considered. They represent an intermediate stage between an unconfined and a semi-confined aquifer. Carbonate karst aquifers show (Table 2) a more refined classification (White, 1988; LaMoureaux et al., 1984), according to the dominating flow conditions, the factors of hydrologic control and the associated types of caves. In karst aquifers, as well as in fissured non-karstic aquifers, where productive zones are associated with fractures and joints, two basic types of circulation depending on the hydraulic gradient and the effective diameter of flow conduits could be identified: diffuse and concentrated (Fig. 22).

Fig. 22. Basic types of circulation in karst aquifers.

In karst aquifers, these types could coexist both in the horizontal and vertical flow domain.

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Table 2. Carbonate aquifers according to the dominating flow conditions, the factors of hydrologic control and the associated types of caves.

Type of flow Hydrological control Type of associate caverns I – DIFFUSE FLOW (fine-textured permeability)

Shaley limestone, crystalline dolomites (high primary porosity or uniform distributed fractures)

Caves rare, small have irregular patterns.

II –FREE FLOW (coarse-textured permeability)

Thick, massive soluble rocks Conduits develop along bedding, joints, fractures or fold axes.

Integrated conduit cave systems.

A - PERCHED Karst system underlain by imopervious rocks near or above base level.

Cave streams perched – often have free air surface.

1- Open Soluble rocks extend upward land surface.

Sinkhole inputs; heavy sediment load; short channel morphology caves.

2- Capped Aquifer overlain by impervious rock.

Vertical shaft inputs; lateral flow under camping beds; long integrated caves.

B- DEEP Karst system extends to considerable depth below base level.

Flow is through submerged conduits.

1 – Open Soluble rocks extend to land surface.

Short tubular abandoned caves likely to be sediment-choked.

2- Capped Aquifer overlain by impervious rocks.

Long, integrated conduits under caprock. Active level of system inundated.

III. CONFINED FLOW Diffuse flow or free flow system stratigraphically bound between beds of low permeability.

A- Artesian Impervious beds that force flows below regional base level.

Rare, small irregular caves (diffuse flow). Inclined 3-D network caves (free flow).

B – Sandwich Thin beds of soluble rock between impervious beds.

Rare, small irregular caves (diffuse flow). Horizontal 2-D network caves (free flow).

In the diffuse flow component the main characteristics are low flow velocities due to a small hydraulic gradient and a high degree of physical connection among joints. These factors allow

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the development of a virtually continuous water table, sometimes very similar to intergranular aquifers. On the contrary, the concentrated flow component is almost characterized by high flow gradients promoting also high flux velocities along selective flow paths because a low degree of physical connection among the flow spaces. An individualized water table is also a characteristic of this component

2.4. Geophysical methods Geophysical surveys are often low cost techniques commonly applicable in conjunction with geologic and hydrogeological exploration and mapping, borehole drilling and water sampling (Fig. 23). Geophysical methods are based on the stimulation or identification of a group of physical properties of the rocks and groundwater that are helpful for the identification of several hydraulic parameters. Geophysics is based on the interpretation of variations in the measured response at surface of natural or induced forces. Surveys could be developed in surface or in wells. There are four basic surface geophysical methods widely used in groundwater surveying:

Fig. 23. Geophysical record form a borehole

• Seismic • Electrical Resistivity • Magnetometry or Electromagnetic methods • Gravimetry • Ground penetrating radar

Seismic surveys are based on the velocity distribution of artificially generated seismic waves. These waves can be generated from blows with a sledgehammer to dynamite explosions in boreholes. Seismic methods comprise refraction and reflection Because Electrical Resistivity is a well-defined physical property of rocks a differentiation between types of rocks could be made and, because it varies according to the moisture content of the materials is widely used in

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groundwater prospecting. Magnetometer surveys use the different magnetic properties of rocks affecting the Earth’s magnetic field. Finally, in gravimetric surveys, gravity is measured at selected stations along a traverse where gravity varies due to the contrast in density of rocks. Ground penetrating radar uses high frequencies of electromagnetic waves which are propagated in a straight line into the ground (USACE, 1999). Borehole geophysics is done after the lowering of a sensing device within a borehole for the determination of physical parameters of the adjacent rock and fluids contained in that rock (USACE, 1999). These allows the determination, in water bearing rocks of the following properties:

Fig. 24. Definition of rock porosity

• Lithology • Geometry • Resistivity • Formation factor • Bulk Density • Porosity (Fig. 24) • Permeability • Moisture content • Specific yield

Table 3 shows the application of various borehole geophysical methods. Caliper logs are used for the identification of lithologic horizons, location of fractures and fissures and for the borehole correction needed for other logs. Fluid conductivity logs are used to measure the conductivity of the fluid within the borehole that may or may not be related to the formation fluid or fluids. Spontaneous potential log is based on the measurement of the natural electric potential between borehole fluid and the formation and it is commonly used for lithologic identification. Resistance logging allows the measurement of the resistance of the rocks and, hence, a differentiation between different rocks is obtained. Resistivity is a physical property of rocks and of the fluids, therefore, resistivity logging includes the dimensions of the measured lithologic log and allows an estimation of parameters as the physical and chemical properties of fluids. Natural gamma logs are applied for recording the intensity of gamma radiation from the geologic materials and are useful for the identification of lithology, bulk density and rock porosity. Neutron logs are used for moisture measurements. Acoustic logs provide information on lithology and porosity in consolidated sediments.

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Table 3. Applications of borehole geophysical methods (after USACE, 1999)

Parameter Borehole Geophysical Method Stratigraphy and porosity Natural gamma log

Gamma-gamma log Acoustic log Neutron log Spontaneous potential log

Stratigraphy Caliper log Resistance log

Moisture content Neutron log Location of zones of saturation Spontaneous potential log

Temperature log Neutron log Gamma-gamma log

Physical and chemical characteristic of fluids Resistivity log Spontaneous potential log Temperature log Fluid conductivity log

Dispersion, dilution and movement of waste Fluid conductivity log Temperature log Gamma-gamma log

2.5. Tracer Hydrology One of the most important techniques applied to groundwater development is tracer hydrology. Its usually a convincing technique used even at court and its application varies from the simplest identification of the hydraulic relation between to points to the more refined isotopic water balance. Tracer hydrology is the black-box technique for interpreting the information derived from the introduction and recovery of a certain marker in water. Tracer hydrology is a refined and well-established technology where experiments has to be rigorously planned, executed and evaluated. Experiments with tracers can be qualitative or quantitative. The qualitative experiments are carried out with the objective of establishing only the hydraulic connections, in general between the recharge and discharge areas. The quantitative experiments are designed to collect series of data to identify and quantify the hydraulic characteristics of the system and predict its future behaviour. This experiments contributes among other, the following data (Fig. 25): • Average velocity of groundwater flow. • General direction of ground water flow. • Transit, turnover and residence times. • Storage capacity of the formation. • Geometry of the system.

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2.5.1. Types of tracers An ideal tracer is that who moves at the same velocity of water. But an ideal tracer should met the following properties (Custodio 1968): • It can not interact with the

aquifer rocks (v.gr. it should not be absorbed, depleted or exchange with the rocks).

• It has to be soluble in water (and does not be retained by mechanical filtration).

• The selected tracer has to be chemically and biologically stable in the water ti be traced (not oxidised, reduced or decomposed).

• It could be added to the water without altering its physical and chemical properties.

• It would not alter the aquifer permeability and porosity.

• The tracer can not contaminate permanently the aquifer and should disappear a short time after the test has been performed.

Fig. 25. Groundwater connections discovered by tracer methods

• It should be easily detected. There are another important properties of an ideal artificial tracer: • That could be effectively used in small quantities. • High solubility. • Quantitative detection in very low concentrations. • Easy to handle. • Non toxic. • Cheap and easy to obtain. • That doesn't exist in the water or only in very low concentration and should not be supplied

by the terrain. • Easy to be introduced or injected. The most common artificial tracers are the following: • Suspended solids. • Soluble chemicals (mainly strong electrolytic substances, like some salts).

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• Dyes. • Environmental isotopes (stables and isotopic) 2.5.1.2. Suspended solids Certain suspended solids could be used as tracers. The solid tracer in suspension have some application when water circulates through big cracks, like the case of very well developed karst conduits, but are commonly retained when water flows through siphons, a very common feature in karst conduits that limits the use of suspended solids as tracers. 2.5.1.3. Soluble chemicals The chemical soluble tracers should be identified easily after dissolved in water. The most common are the saline tracers. Saline tracer are highly soluble. The most used is those associated with the chloride ion, like the Sodium, Lithium or Potassium Chloride. These tracers are very close to the ideal tracer and in low saline waters could be widely used. Concentration could be directly measured after reading Specific Electric Conductivity because after injection, anions and cations are easily separated because of the polar action of the water and they move freely with flow. For the employment of saline tracer the following factors has to be considered (Zojer, 1988)

• Low salinity of the tracing waters. • Application in large quantities (specially

when NaCl and KCl are used) • Enough quantity of water available for the

test, a reason that restrict its use in areas with water shortage.

• Low concentration in the water to be traced. • Chemical Resistance. • Easy field detection with Specific Electric

Conductivity measurements. 2.5.1.4. Dyes Colouring chemicals (Fig. 26) are frequently used as tracers because they are easy to detect and waters usually does not have them in their composition or, in cases, they are at very low concentrations. They are not very advisable in rocks with a high clay content, because its molecular structure favouring its retention by clays, colloids and organic matter. Some of these substances can be altered or destroyed by change in pH or by certain micro-organisms.

Fig. 26. Dye experiment in a fluvial stream

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One of the most commonly used substance is the fluoresceine (C2OHL2O5) or a very soluble sodium derivate, the uranine (C2OHO4Na2). Other common dyes are: · Rhodamine B · Sulforhodamine · Losine · Amidorhodamine · Tipopal In sewage waters you can use the blue aniline and blue methylene could be used. The activated coal retains the fluoresceine, it is for it that is used for its detection, capsule perforated with active coal being placed, during the time that the experiment lasts in the place that is observed. 2.5.1.5. Environmental isotopes They are of two types of environmental isotopes that could be used as tracers: stable and radioactive. The use of isotopic stable tracers, as the 18O and the 2H does not suppose an artificially induced variation in the chemical or isotopic composition of the water, making tests highly reliable and accurate. Radioactive tracers like tritium, 3H are very important and show remarkable advantages over other types of tracers, but their handling, testing and assessment is more delicate and expensive.

2.6. Geochemical exploration Geochemical exploration is carried out not only is association with mine development or mineral ores prospecting. Geochemical exploration is the first stage of defining water quality, while water quality can not be properly understood and managed if a general background of the processes governing physical, chemical and bacteriological composition of ground waters are not identified. Precipitation is the main source of most ground waters. Chemical composition of rain and snow is the initial source of groundwater chemical composition and quality. As water precipitates and flows during the terrestrial phase of the hydrologic cycle, its physical, chemical, isotopic and bacteriological composition changes. These changes are due to the different physical, chemical, isotopic and bacteriological composition of the different scenarios were water flows through. Rocks are the mains responsible for changes in water composition because during groundwater flow water experiences different reactions associated with usually long residence times in the aquifer. But because land use is the most important source of lowering groundwater quality soils provide organic matter and major and secondary constituents, changes in pH, Base Exchange, and pollutants.

L.F. Molerio-León

39


In the chemical composition of groundwater (and surface water) four groups of constituents are recognized. Table 4 accounts for them. Table 4. Chemical constituents of groundwater

Group Average concentration (mg/l)

Components

Major or macro constituents 10 – 10 000 Bicarbonate, Sulfate, chloride, calcium, magnesium, sodium, silica.

Secondary constituents 0,01 to 10 Potassium, iron, strontium, carbonate, nitrate, nitrite, fluoride, boron.

Minor constituents 0,0001 to 0,1 Antimony, aluminum, arsenic, barium, bromide, cadmium, chromium, cobalt, copper, germanium, iodide, lead, lithium, manganese, molybdenum, nickel, phosphate, rubidium, selenium, titanium, uranium, vanadium, zinc.

Trace constituents Less than 0,001 Beryllium, bismuth, cerium, cesium, gallium, gold, indium, lanthanum, niobium, platinum, radium, ruthenium, scandium, silver, thallium, thorium, tin, tungsten, ytterbium, ytrium, zirconium.

The physical and chemical processes affecting ground water original composition are:

• Solution • Chemical attack • Changes of equilibrium • Reduction or oxidation • Base exchange • Concentration • Chemical filtration

There are several geologic, hydrogeological, chemical and biological controlling water composition and quality. The first two could be referred as the natural conditions and the last two as artificial conditions. The most important geologic conditions are the nature of the aquifer rocks, with independence of other geomorphologic or climatic influences. Therefore, siliceous, carbonate, carbonaceous,

L.F. Molerio-León

40


argillaceous, crystalline and metamorphic rocks and evaporites exert a different influence on water composition due to its own chemical composition and the degree of exchange water-rock. Siliceous rocks in consolidated intergranular aquifers, like sandstone, or unconsolidated, like sands, there are not many soluble substances to exchange. These waters are characterized by a low dry residue an low SO4 and Cl concentration and a sequence of the type rNa > rCa > rMg. Carbonate rocks, typically limestone and dolomite, produce large quantities of HCO3, Ca and Mg in low salt waters, where Cl, SO4 and Na are low concentrated. But in karst regions, Cl and SO4 are readily dissolved and increase their content in groundwater in such a way that a ratio of (rSO4 + rCl) > rHCO3 could be expected. Carbonaceous rocks like, peat, lignite, coal and other hydrocarbons supply specific physical and chemical properties to ground water, like low SO4 due to Sulphate reduction, iron precipitates associated with the oxidation of Fe2+ to Fe3+ and Fe(OH)3 and more or less presence of H2S. Argillaceous rocks supply different salt quantities depending on leaching and also may undergo base exchanges of the type: Na for Ca for Mg and Ca for Mg for Na; commonly (rCa + rMg) > (rSO4 + rCl) or rNa > (rSO4 + rCl). In crystalline and magmatic rocks such as granites and basalts where water circulation is mainly along fractures, major constituents show very low concentrations and a very small dry residue; deviations from this regularity are often associated with local sources of infiltration or evaporation or evapotranspiration. Common ratios are of the type (rNa + rCl) > (rSO4 + rCl) or rNa > (rSO4 + rCl). In metamorphic rocks a similar picture is obtained varying, nevertheless, in the high concentrations of SO4 and Fe due to the oxidation of pyrite. Finally, evaporites, like gypsum and anhydrite produce high salt enriched waters due to the great solubility of these rocks and, therefore, waters usually has large contents of CaSO4 and NaCl. Common ratios are (rSO4 + rCl) > rHCO3 or either taking Cl or SO4 separately. The most important hydrogeological conditions influencing groundwater chemical composition are:

• Soil composition and thickness. • The water travelled distance and the residence time. • Aquifer depth. • Paleohydrological evolution. • The presence of fossil and connate water. • Proximity to sea, salt lakes, ponds and other natural or man-made lakes. • Stream-groundwater relation. • Groundwater regime, in particular, water table fluctuations. • Presence of mineral deposits. • Climate.

L.F. Molerio-León

41


On the other hand, man-made or artificial conditions are responsible for the most important changes in the physical, chemical and bacteriological composition of groundwater, often causing pollution. Factors preventing or allowing contamination are the following:

• Soil or rock filtration. • Mixing with soluble substances. • Mixing with non-soluble liquids. • Solids transport. • Microorganisms, viruses and pathogens.

Ionic ratios provide information on the relations among the constituents of each water sample. The most important and useful ionic ratios are the following:

rCarMg

rClrSO4

rClrKrNarCl −−

rMgrCarNa+

rCarNa

rMgrNa

rClrKrNa +

34 HCOrSOrKrNarCl

+−−

The ratio rClrSO4 is typical for groundwater, where it is common that Cl concentration tends

to increase faster than the SO4 concentration, because the velocity of Cl dissolution is greater than that for Sulfates. Therefore if water tends to concentrate, the ratio decrease except in

Sulfate enriched rocks. If evaporation is present, the ratio also decreases. The ratio rCarMg is

L.F. Molerio-León

42


characteristic for waters flowing in the same lithological environment, changing according to dominating sources of Ca or Mg. Water from basalt is frequently distinguishable by high

rCarMg ratio due to olivine supply source of Mg. In evaporitic terrain, the ratio increases

while rClrSO4 decreases and in carbonate rocks values are different according whether are

limestone or dolomites present.

Relation between Na, K and Cl is of outstanding importance, and hence the ratio rCl

rKrNa +

mainly because the origin of water could be accurately assessed. Any difference rNa + rK –rCl suggest dissolution from sodium chloride, sodium Sulfate or sodium carbonate environments and even form calcium or magnesium chloride. In arid and semiarid environments, is usually tha rCl < rNa, but in the presence of seawater intrusion rCl > rNa. In crystalline rocks, rNa + rK

is always greater than rCl. A similar importance is derived from the ratio 34 HCOrSO

rKrNarCl+

−− .

It is important to notice some helpful regularities in geochemical exploration derived from the most general scheme for groundwater flow. Water circulation concentrates all major constituents except bicarbonates that use to remain

constant because the CO2 partial pressures. Ratios rClrSO4 and rCa

rMg do not change at the

beginning. The starting sequence is rHCO3 > (rSO4 or rCl) and rCa > rMg > rNa, followed by rCl > rSO4 > rHCO3 and rNa > rMg > rCa. If base exchange is present, the last sequence could be substituted by rCl > rSO4 > rHCO3 and rCa > rMg > rNa because of the addition of Ca.

2.7. Pumping tests 2.7.1. Planning Pumping tests are the most important “in situ” methods for determining hydraulic properties and aquifer yield. Hydraulic parameters such as transmissivity, specific yield, permeability or hydraulic conductivity, storage and well efficiency. These values are averaged over the entire influence area of the test and hence allow the assessment of the productivity of the water well when it is used as a supply source or its absorption capacity if it has been designed for infiltration purposes. A pumping test is an experiment consisting in pumping water from a well at constant or variable yield and measuring the drawdown in the pumped and surrounding wells. According to the designed relation between yield and drawdown there are three basic types of pumping tests:

L.F. Molerio-León

43


• Constant-rate • Step-drawdown • Recovery

Pumping a well at a constant rate for a given time performs constant-rate test. Time is usually selected between 24 and 72 hours but short tests could be performed in high productive formations. Increasing the pumping rate at regular intervals for short-time periods, not greater than 12 hours performs a step-drawdown test. They are commonly used as productivity assessment tests because provide information on the reduction of the specific capacity while yield increases. A recovery test measure the rebound of water levels after pumping and it is usually performed after any of the previous tests because provide comparative information on hydraulic properties. A pumping test is an experiment and should be properly designed, performed and assessed. The following steps should be followed in pumping tests design (slightly modified from USACE, 1999):

• Well preparation, which includes adequate well development and placement or selection of the observation wells in the area of influence of the test.

• Conceptual geologic model, because if no geologic information is available some assumptions should be needed from the lithologic composition and subsurface geologic structure.

• Conceptual hydrologic model, which includes the assumption or definition of the type and depth of the aquifer(s), expected water quality and expected range of hydraulic properties.

• Test objectives, because pumping tests are expensive and time-consuming is therefore very important that test objectives should be clearly established and priority should be given to the most careful definition of the experiment goals.

• Pumping rate must be properly defined because pumps are expensive, so pumping to the maximum expected aquifer or well yield seems to be the most useful technique while aquifer becomes highly stressed and hydraulic parameters are better defined.

• Test duration must be also carefully determined because this is one of the most important constraints for pumping tests but they can last from three hours to several months. It should be kept in mind that a similar time scheduled for the pumping test should be planned for recovery measurements.

2.7.2. Well hydraulics When discharge begins at least theoretically, water level in the web is lowered with respect to the previous undisturbed conditions. This change in head starts induced movement of groundwater from the surrounding aquifer to the well in a radial response to the head loss. This is the basic model of well hydraulics that describes the relationships between discharge and drawdown (Fig. 27). Two steady state equations describe these relationships for the extreme cases of confined and unconfined aquifers:

L.F. Molerio-León

44


KMrrQ

ssπ2

ln1

2

21

⎟⎟⎠

⎞⎜⎜⎝

⎛

=−

KrrQ

hhπ

⎟⎟⎠

⎞⎜⎜⎝

⎛

=− 1

2

21

22

ln

And in the unsteady case:

( )uWT

Qsπ4

=

As USDI (1977) points out, this relationship allows the following hypotheses:

• The drawdown at any point of the cone of depression, v.gr., the cone formed by the lowering of the water table or the piezometric level is proportional to Q.

• At a given discharge, the drawdown at any point on the cone of depression is inversely proportional to the log of r under both steady and unsteady conditions. At a given Q, drawdown decreases with increased values of transmissivity (Fig. 28). In the unsteady case, the drawdown is also inversely proportional to storativity (Fig. 29) and proportional to log t.

In the above equations, M is the thickness of aquifer, h1, h2, artesian head at r1 and r2 distances from the pumped well; s1, s2, drawdown at r1,r2; Q, discharge; T, transmissivity; K, permeability or hydraulic conductivity. Rearranging terms the resultant equation for well yield holds, for a confined or artesian aquifer:

( )

⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

w

e

rr

ssKMQln

2 12π

And for an unconfined aquifer:

Fig. 27. Typical time drawdown curves for different aquifers

( )

⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

w

e

rr

hhKQln

21

22

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45


In the above equations, re is the radius of influence and rw, the well radius. Here it is very important to remind that the yield is proportional to the

reciprocal of ⎟⎟⎠

⎞⎜⎜⎝

⎛

w

e

rrln .

2.7.2.1. Steady state equations The Thiem-Forcheimer or equilibrium equations are based on the following assumptions (USDI, 1977):

• Aquifer is homogeneous, isotropic, and of uniform thickness.

• The discharging well penetrates and receives water through the entire aquifer thickness.

Fig. 28. Definition of transmissivity

• Transmissivity and permeability or hydraulic conductivity is constant at all times and at all locations.

Fig. 29. Definition of storativity • Discharge has continued for a sufficient duration for the hydraulic system to reach a steady state.

• Flow to the well is horizontal, radial and laminar, and originates from a circular open water source with a fixed radius and elevation that surrounds the well.

• Rate of discharge from the well is constant.

For a confined aquifer the pertinent equations are:

( )21

1

2

2

ln

ssMrrQ

K−

⎟⎟⎠

⎞⎜⎜⎝

⎛

=π

( )21

1

2

2

ln

ssrrQ

T−

⎟⎟⎠

⎞⎜⎜⎝

⎛

=π

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46


For an unconfined aquifer:

( )21

22

1

2ln

hhMrrQ

K−

⎟⎟⎠

⎞⎜⎜⎝

⎛

=π

( )21

22

1

2

2

ln

hhrrQM

T−

⎟⎟⎠

⎞⎜⎜⎝

⎛

=π

Here, r2, r1, …rn holds for the horizontal distances from centerline of the test well to centerline of observation wells 1, 2, …n. 2.7.2.2. Unsteady, transient, conditions Transient equations are very important because allow the study of time varying aquifer conditions and involve storage. They are based on the following assumptions (USDI, 1977):

• Aquifer is confined, horizontal, homogeneous, isotropic, of uniform thickness, and of infinite areal extent.

• Pumping well is of infinitesimal diameter and fully penetrates the aquifer. • Flow to the well is radial, horizontal and laminar. • All water comes from storage instantaneously with decline in pressure. • Transmissivity and storativity of the aquifer are constant in time and space.

The Theis equation is the most widely used transient equation that is expressed as:

∫∞ −

=TtSr

u

udue

TQs

4

2

4π

Where s is the drawdown in an observation well of radius r, located at a certain distance at time

t since start of pumping; S, is the storativity of the aquifer, and TtSru

4

2

= is Theis Well

Function. For the solution of the equation Theis provided a graphical method that has been successfully applied to aquifer tests reasonably close to the boundary conditions described above. Jacob also provide a classical approximate solution for the non-equilibrium equation. In the domain of the time – drawdown solution it holds, for transmissivity, T, and storativity, S:

sQT

∆=

π4303,2

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47


2025,2

rTtS =

And in the domain of the distance- drawdown solution:

sQT

∆=

π2303,2

20

025,2r

TtS =

Where ∆s is the drawdown over one log cycle; t0, time at zero drawdown intercept and r, the distance from the test well to the observation well. 2.7.3. Recovery tests Recovery tests analysis is based on the concept of residual drawdown. The residual drawdown (USDI, 1977) at any time during the recovery period is the difference between the observed water level and the static water level. Hence, the graphical solution of the recovery equation:

sQ

tt

sQT

′=⎟

⎠⎞

⎜⎝⎛

′′=

ππ 4303,2log

4303,2

when the value t/t’ is chosen over one log cycle. Storativity can be computed by the following equation:

( )[ ]( )ss

ssrtT

S

p

p

′−∆

′−

′

= log

25,2 2

2.7.4. Leaky aquifers Where a confining layer separates two or more aquifers, pumping from one aquifer may disturb the mutual hydraulic balance and result in an increase or decrease in leakage between the aquifers. Therefore, under sufficient head even apparently impermeable rocks will transmit water (USDI, 1977). This is the so-called leakage or delayed yield phenomena. While leakage is a boundary condition, the area of influence of a discharging well expands until leakage into the aquifer induced by the well equals the well discharge (drawdown becomes constant because the area of influence stabilizes) and, conversely, if the discharge from a well in an aquifer balances the amount of leakage, the area of influence will stabilize. Graphical methods based on the Theis type curve was developed by Hantush and Jacob for several cases.

L.F. Molerio-León

48


2.7.3.1. Time –drawdown under unsteady conditions The solution of Hantush and Jacob (1955) for this case is based in the assumptions of a uniform aquifer of infinite extent penetrated by a well of infinitesimal diameter. These are the same assumptions of Theis but now supplemented by those of linear leakage, constant head of the ponded water supplying the leakage, and horizontal refraction of the leakage, as de Wiest (1971) pointed out. Therefore, following this author:

⎟⎠⎞

⎜⎝⎛=

bruW

TQs ,

4π

in which

∫∞ −−

=⎟⎠⎞

⎜⎝⎛

u

dxxB

rx

exb

ruW 2

2

41,

is the well function for leaky artesian aquifers in which TtSru

4

2

= .

2.7.3.2. Steady state drawdown It has been established that the steady state solution for the drawdown is proportional to

( )BrK0 , where Ko is the modified Bessel function of the second kind and zero order. In this

case the solution holds:

⎟⎠⎞

⎜⎝⎛=

BrK

TQs 02π

2.7.3.4. Hantush solution Leakance factor B can also be calculated by this graphical method where transmissivity T is obtained at the inflection point of the time drawdown curve, and:

⎟⎠⎞

⎜⎝⎛

′′

=

bKTB

2.7.5. Delayed yield solutions Delayed yield is the early response of an unconfined aquifer to a discharging well depending on the degree of isotropy (USDI, 1977). This means that tests of short duration in those aquifers could become unreliable because there is a delayed yield effect produced by

Fig. 30. Axis of anisotropy

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49


anisotropy (Fig. 30) identified by an S-shaped time-drawdown curve. Under certain circumstances delayed yield curves are similar to those from leaky aquifers. Those factors influencing the first part of the curve may be all or part of the following (USDI, 1977):

• Changing storativity caused by delayed drainage. • Expansion of water below the water table resulting from reduction in pressure. • Vertical flow components. • Thinning of the saturated zone as drawdown increases. • Observation well lag. • Aquifer heterogeneity.

Boulton has developed the following equations for the graphical solution of delayed yield:

⎟⎠⎞

⎜⎝⎛=

MruW

TQs ayπ4

TtSrua 4

2

=

TtSr

u yy 4

2

=

Type A curve equation is:

tuM

r

d a

4

12

⎟⎠⎞

⎜⎝⎛

=

And Type B curve equation is:

tuM

r

d y

4

12

⎟⎠⎞

⎜⎝⎛

=

In consistent units s, is the drawdown at time t since the start of a pumping test at a rate Q, and a distance r from the test well. S is the early time storage coefficient and Sy the true specific yield or storage coefficient; d, the reciprocal of the delay index; M, aquifer thickness and

⎟⎠⎞

⎜⎝⎛

MruW ay well function of u.

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50


2.7.6. Double porosity models Double porosity was first described by Barenblatt, Zheltov and Kochina in a classic 1960 paper devoted to fissured aquifers flow, but was extensively developed by Boulton and Streltsova in the early 70’s. Among various models and solutions the solution for the unsteady flow to a pumped well in a fissured water – bearing formation (Boulton and Streltsova, 1977) is illustrative of the conceptual model and the type of solutions. Double porosity conceptual models stands for a two-element aquifer with a highly transmissive fracture surrounded by a block of negligible or variable permeability. The concept is applicable to a huge set of initial and boundary conditions. In this case the general concept of fissured rock is that from Barenblatt et al. previously mentioned and considers the rock mass broken up into blocks of irregular size and shape by fissures. Replacing the actual system of block and fractures by a set or regular block-and-fissure units and assuming that:

• The block and the fissure are compressible. • The flow in the block is assumed to be vertical (the simplest assumption). • There is no contact resistance to seepage flow between the block and the fissure. • The abstraction well is lined along the block, the horizontal flow components in the

block towards the well thus being neglected. • The discharge per unit length of the unlined part of the abstraction well in the fissure is

constant. • The abstraction well is pumped at a constant rate from the instant t=0 and the radius of

the well is vanishingly small. • The depth of the fissure is small compared with that of the block; hence h/H is small. • The flow in the fissure is supposed to obey Darcy’s Law (low Reynolds number).

The drawdown equation in the fissure is:

dxxHrxJ

TQs

mm ⎥

⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛= ∑∫

∞

=

∞

100

11 2

ψπ

where

( )mmmmm

m

m cbHt

βββββ

κβψ 22

222

sectan5,0

exp1

++

⎟⎠⎞

⎜⎝⎛−−

=

and βm is a positive root of

( ) 2tan xcb mmm =+ βββ

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51


The equation describing the drawdown in the porous block is:

dxxHrxJ

TQs

mmm ⎥

⎦

⎤⎢⎣

⎡•⎟

⎠⎞

⎜⎝⎛= ∑∫

∞

=

∞

100

12 2

φψπ

where:

( ) ( )Hz

Hz

mmmm βββφ sintancos +=

In the above equations, subscripts 1 stand for the fissure and 2 for the porous block. The other symbols are: J0, Bessel function of the first kind of zero order; κn , Tn/Sn; Tn , transmissivity Sn , storage coefficient x , independent variable of integration c , T2/T1H , thickness of the porous block b , κ1/κ2 2.7.7. Solutions for turbulent, non-linear flows Although common solutions for radial flow to wells assume laminar, linear flow, in karst aquifers a non-linear component could be very important. As Perez (1982) stated, the drawdown in a pumped well is the sum of the linear and non-linear components of such drawdown. Deviations from the designed yield in cavernous limestone are, partially, due to the misunderstanding of this principle. For a confined aquifer:

np

n

pn rSn

mKQ −⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −= 1112π

For pure turbulent flow n = 0,5 and Kn = KT and, therefore:

( ) 21

2 ppT rSmKQ π=

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52


For an unconfined aquifer:

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

−

−+−

=−−

++

nn

nn

n

rr

hhnnKQ 1

1

2

11

1

11

1

11

2

112π

And, for pure turbulent flow:

21

21

31

32

1132

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛−

−=

rr

hhKQ Tπ

In the above equations, M, aquifer thickness; subscript T, refers to the turbulent conditions; subscripts 1 and 2 to wells 1 and 2, h is the unconfined aquifer thickness; S is the drawdown in the pumping well and the subscript p is referred to the pumping well.

2.8. Speleological exploration Speleology is the science of caves. Caves are a typical and common feature in karst regions and can be defined as fragments, truncated or not, of drainage networks (Fig. 31). Caves provide valuable hydrogeological information on the present and ancient hydrological conditions, flow direction, aquifer productivity and also on the local water balance. Caves are the conduction phase of water circulation in karst aquifers. Indeed, because in karst regions landscape and hydrology show the most strong relation and every morphological feature is

always related with a certain phase of water circulation. Fig. 31. Karst channel

The terrestrial part of the water cycle in karst regions is always associated with a group of landforms. In effect the cycle infiltration-transport-discharge could be recognized in the surface and subterranean relief in the so-called absorption-conduction-discharging landforms. To the absorption, infiltration or recharge step are associated most part of karst surface landforms, like the ponors, dolines, poljes, uvalas, vertical shafts and blind or closed valleys. Their morphology and evolution is associated with the action of infiltration waters and, in some cases of the joint action of surface and ground waters. These landforms are points of concentrated recharge and constitute the starting point of very local flow systems. Absorption forms have evolved as it was done by the whole hydrological system, and therefore

L.F. Molerio-León

53


fossil or hydrological inactive ponors or dolines, for example, could be recognized. Their inactivity is identified by a change of its hydrological function, v.gr. because of clogging, collapse, erosion or tapping, the karst landforms has stopped its function as a point recharge feature. But when hydrological active, absorption landforms are responsible of concentrated and fast recharge, a very important fact not only related with the replenishment of groundwater reserves but with the quality of groundwater because these are also point sources for groundwater contamination. This is also a particular hydrological feature of karst regions, the presence of two main sources of groundwater recharge: the fast, concentrated, point recharge associated with absorption landforms and the slow, non-point, diffuse recharge linked with the rock fissures, beds and joints. Absorption landform use to be connected with caves and, commonly constitutes the natural entrances to underground hydrological systems. Caves in karst regions are, mainly, the result of the action of dissolution and erosion processes in carbonate rocks. There are also caves formed by the erosive action of the sea in coastal carbonate zones. But as long as they are conduit systems for surface waters to the aquifer they show a variety of features of particular hydrogeological importance. Caves constitute the segment of conduction or transport of water through the aquifer or to the epikarst. Caves are formed by flowing groundwater in a favorable zone of the aquifer. While are always zones were flow concentrates, patterns of highly concentrated or diffuse flow could be recognized in the erosive features of cave floors, walls and ceilings. Caves could be of very variable length, from a few meters to hundreds of kilometers of interconnected passages, like the Mammoth Cave-Flint Ridge System in Kentucky, United States, the longest cave of the world. After flowing through caves, water emerges back to surface, in land or sea, and springs become the most common feature of the discharging phase of the terrestrial water cycle in karst regions. But water could also be discharged through vertical shafts or groundwater could return to the aerial phase of the hydrological cycle by means of evaporation of karst ponds, lakes, and cenotes or casimbas, a particular absorption-discharging feature. Particular and impressive discharge landforms are submerged caves known as blue-holes, typical in carbonate small islands, and associated both to fresh or brackish water absorption and discharge. Speleological exploration covers, actually, all landforms because of the strong relation among the different stages of water in the massif. Speleological exploration and documentation provide the following information:

• Mapping of the particular and local flow system formed by the associated set of absorption-conduction-discharging landforms; its extension, shape and associated morphologies.

• The hydrological evolution of the flow system: position and time and space evolution of the absorption-conduction-discharging, the record of climatic changes or, at least, the evolution of precipitation and temperature since the cave was formed, and some insight on the local water balance of the cave flow system.

L.F. Molerio-León

54


• The patterns of cave formation, in terms of the geologic, geomorphologic and hydrologic factors controlling cave formation and the position of the discharge zone, a very valuable information because hydrological active caves, v.gr. those permanently or seasonally filled with fresh water, are selected high transmissive and productive zones were groundwater development could be successfully carried out.

L.F. Molerio-León

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3. WATER DEMAND ASSESSMENT

he correct assessment of water demand is of remarkable importance. The maximum attention should be drawn to this subject. A correct estimation of the water demand defines the consumer's real needs and, in turn, allows the introduction of the appropriate

technology with the lowest costs of investment and maintenance and the maximum permissible efficiency for such a cost. A clear expression of the demand is fundamental for the consumer, being an individual or a community. Many authors consider that the assessment of the demand is not competition of the hydrogeologist. However, as a consultant for the community or the entity in charge of the construction of the water supply system, he has to certify that the design satisfies the actual needs. Furthermore, it has to be accounted that the satisfaction of the demand and the supply system does nt contribute to the deterioration of water quality or the exhaustion of the water resources.

T

The water demand is the volume of water fulfilling the necessities of social and economic development of a user. Its importance is variable depending on the basic needs, the social values and the cultural characteristics of the region. An appropriate characterization of the demand of water is based on:

• a precise knowledge of the local and regional offer of water • a characterization of the current and futures necessities of water

3.1. Water offer The water offer is defined as the capacity of the natural system to supply water. The offer is positive, when it is higher that the demand and negative when it is smaller. Therefore the natural water offer is of different kind: • Atmospheric waters: expressed as rain, snow, fog and environmental humidity. • Surface waters: component of surface runoff expressed in rivers, streams and lakes. • Ground waters: expressed in the volumes circulating underground and eventually appearing

at surface in the form of springs, caverns or natural wells. The knowledge of the real offer is of outstanding importance. The characterization of the variables of the water balance constitutes the water reserves of the territory. Such quantification is required in two basic scales, one with respect to its spatial distribution and another that corresponds to its distribution in time. Of not less importance is the quality of the water reserves and the energy level where it is located. The offer is characterized according to the following indexes:

Quantity Quality Opportunity Energy level

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Geometry Grouping

The quantity of water constituting the offer or the water reserves can be continuously or not distributed through the year. In such cases, the offer can be defined as discontinue when is abruptly or seasonally interrupted, as it happens with the rain and some rivers or streams and springs of episodic regime. The offer will be continuous in the case of permanent fluvial currents or groundwater systems. The quantity of available water constituting the offer, not necessarily means that it could be totally used. An offer numerically equivalent to the demand does not mean that the demand could be satisfied. It depends it on the available technology, the internal structure of the demand and several social and cultural factors commonly accentuated in rural communities. On the other hand, the physical, chemistry composition and bacteriological quality of the water offer have to be properly known and evaluated. In coastal areas important variations of salinity should be expected by the exchange between fresh inland waters and the sea. In rural areas should be expected that the underground and superficial waters show some degree of contamination from fertilizers or pesticides and, where some industrial development or population concentrates, industrial wastes or sewer waters produces variations in water quality. Water quality also varies seasonally and spatially and these variations have to be known properly. The term opportunity expresses the relation between the spatial and time distribution of the offer and the distribution, also in time and space of the demand. Opportunity is extremely important, because when the difference is very high or it is not synchronic, the phenomena of water scarcity appear. Artificial regulations are then needed to capture and store the offer, and for its use in times when the offer is discontinuous. The energy level of the offer is closely linked with the opportunity in the sense that, if storage is needed water should be captured at the highest possible hypsometric level to reasonably reduce the costs of water transfer. This is particularly important in the case of rain waters or surface runoff where high storage reduces the necessity of pumping waters. In the case of groundwater assessment it should take in consideration the additional energy that will always be required to elevate the water from the aquifer to the ground surface and, possibly, from there to the place where it is needed. The search of extraction alternatives of ground water should be considered to avoid or reduce the costs of the abstraction system. The geometry refers to the form that the offer is presented is what refers and it can be transformed when storage are built. The offer shows lineal geometry when it is presented in rivers, streams, channels, caverns and productive fissures; it is areal in the case of the rain and extensive aquifers, and of point geometry when it is presented in wells, shafts or springs. In terms of grouping, the offer can be dispersed or diffuse, or concentrated. Such a division is noticed clearly in the case of the rains, of the concentration of springs or of the structure of the fluvial or lake net of a territory.

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3.2. Water demand When defining water demand, one of the most important aspects is its distinction from consumption. Demand is the quantity of water of a given quality, in a certain moment and place required to satisfy a certain domestic, industrial, recreational, social or agricultural activity. Consumption is the quantity of water of a certain quality that, in a place and given time, is used or spent, actually, to develop such an activity. From these definitions, the demand can be characterized with the same time and space indexes than the offer. Such properties are this way the following ones:

Quantity Quality Opportunity Energy level Geometry

Space and time distribution

Grouping In terms of the quantity of water, the volumes required for the development of the social and economic activities has to be defined. For that reason, the water demand could be constant or variable with respect to time. The first case deals with domestic, industrial and husbandry supply. The second case is related to agricultural supply and it is expressed as the demand of the different crops, according to its biological cycles and the climatic characteristics of the locality. The concept of opportunity, is identical to that expressed earlier when discussing the offer. It is convenient to insist in the fact that demand could be continuous or discontinuous. The delay, in time and space, of the demand regarding the offer, is the pattern that defines the technology to be used to regulate the resource and to distribute it in the precise moment, in the appropriate place, and with the quality and quantity that it is needed. The energy level is especially important and, in this case, refers to the hypsometric relation between the supply source and the point where water will be used. Unless it is captured directly in the discharge of upstream springs the most common case is extracting from a certain depth. This will always require an energy consumption that will increase the costs of exploitation. For that reason –and to protect them from pollution-, whenever it is possible the supply sources should be placed upstream the site to be supplied, in order to lower the installation and maintenance costs and avoid pumping. As a rule, the greatest volumes of groundwater are not in the heads of the aquifer systems, but in their middle and lower regions. This fact implies that, commonly, the supply of elevated or upstream areas requires an increment in the costs of installation, operation and maintenance of the pumping systems.

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The geometry of the demand defines how it is distributed in space. The concept, itself, possess a tremendous importance for water deficit areas where, in association with the previous concepts and to the type of grouping, can be vital to guarantee the satisfaction of the demand. In other terms, in all the cases in that the supply takes place through wells it will have point geometry, if it is used for agricultural irrigation, the demand will be areal, and it could be redistributed in the space of the demand or in the space of the sources. If, on the contrary, it is sought to supply a community along a road, the geometry of the demand will be lineal. Geometry and grouping has to be properly managed to satisfy the necessities of water indeed. As grouping shows two extreme types: concentrated and dispersed, its influence on the costs of the investigation, construction, operation and maintenance, included the protection of the sources, is very variable. In general, towns, cities and farms could be considered as concentrated geometry and it is easier to satisfy their necessities. However, in rural communities the phenomenon of “dispersion of the demand” is always present bringing a systematic lack of satisfaction of the demand. This is due to the high costs of the initial investment, including research, and of the installation and maintenance of the exploitation technology. The local legal framework of certain countries favors the property of the waters limiting the satisfaction of the demand of other users with the same sources of water. It is evident that the dispersed demand reduces the effectiveness of any collective effort of improvement the quality of life derived from the appropriate use of the water, due to the high costs required to satisfy it globally. Tables 5 – 11 show some examples, collected from different sources. Table 5. Water consumption in m3 /Ha /year of some crops (according to UNESCO, )

Crop Requirement (m3 /Ha /year)

Fruit-bearing, vine, peach, pear 2000-2500 Cherry tree 3000-6000

Medlar 5000 Hazel tree and Almond trees 2000

Plum tree and peaches 4000 Wheat, barley 3000

Corn 7000-10000 Medic 11000 Cereals 2000 Cotton 6000 Rice 20000

(for two annual crops) Sugar cane 15000

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The demand for domestic supply is a function of the type of community and its present and future level of social and economic development. Therefore, endowment varies according the region. In some cases, consumption is calculated on a consumer basis but commonly as inhabitants per day basis is used. Domestic consumption in rural zones should not be less than 10 liters per day per inhabitant. In any case, domestic supply exhibits large daily and yearly fluctuations. In some urban locations maximum daily consumption could be as high as 240% daily average consumption. Most modern industries are commited by law to recycle part of their waters in order to reduce water consumption and increase their productivity. Several public or communal services should be considered when assessing water demand. Big consumers like military facilities, hotels, airports and fire extinction installations should be evaluated separately because their demand depends on several factors related with the technology available and the populations to be supplied. Inefficiency in water supply increases demand. In several cases this increment is greater than the actual capabilities of the sources and conducts to an unnecessary exhaustion or overexploitation. It is common that deficiencies in the water supply system require water volumes several times higher than the actual demand. Leakage volume is an important variable to be accounted and, usually, when losses are close to 40-50% is better to invest in the improvement of the distribution service than in the development of new water sources as it is a common and unsustainable practice in several countries. Table 6. Animal average consumption (in liters/day/head) (from different sources)

Animals Consumption Horses, Servant, Mule, Ox 35-70

Milkmaid vacates 50-100 Pig 15-30

(including area of the facilities) Sheep and Male goat 8-16

Hens 15-30 (for 100 hens)

Type of facilities Slaughterhouses 500

Dairies 5 liters / liter of milk

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Table 7. Demands of industrial water in m3/worker/day in Catalonia, Spain (according to Custodio, p. 2051)

Industry demands Paper production and cardboard 22

Paper, cardboard and graphic arts 0.05 Leather 0.05

Basic chemistry 17 Chemical products 0.25

Artificial and synthetic fibers 10-19 Textile (cotton, artificial and metallic fibers) 0.8

Textile (wool) 1.10 Textile (point gender) 0.10

Metallurgy (Metallic basic) 4 Metallurgy (metallic transformation) 0.20

Salt mining 12.3 Coal mining 1.5

Mining (other) 0.25 Foods 1.5

Non metallic mineral products 0.9 Wood and furniture 0.15

Construction 1 Table 8. Water demands in m3 / Rhyme of manufactured products (according to Custodio: 2051)

Industry type Demand Paper production 100-400 Basic chemistry 30-100

Coloring and paintings 20-40 Aromatic products and soap 10-40

Pharmaceutical products 50-125 Oil and fats 20-100

Fibers 500-1000 Textile (whiten) 50-100

Textile (tint) 50-100 Textile (others) 200-300

Textile (wool laundry) 150-250 Nutritious products 5-30

Beers 5-10 Alcohol 1-5

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Table 9. Endowment for urban use (in l / day / hab) (according to Custodio, p. 2048)

Inhabitants Endowment 50-1000 100

1501-6000 150 6001-12000 175 12001-50000 200 50001-250000 300

Greater than 250 000 400 Table 10. Demand of some public and communal services.

Type of service Demand Measure unit Schools 100 l / student / day

Sewer cleaning 25 l / lineal meter of sewer / dayWith intermittent discharge 20 l / square / hour

Laundries 1200 l / square / day Street cleaning 1 l / roadway m2 + 25

l / meter lineal sewer Garages 15 l / day / vehicle Car wash 40

70-100 l / vehicle of 2 wheels l / vehicle of 4 wheels

Hospitals Up to 400 l / day / bed

3.3. The process of hydraulic planning To conclude this epigraph it is convenient a brief comment about the process of hydraulic planning, as long as it constitutes the only way for balancing, at short, medium and long terms, the water offer and the water demand. Without a scientifically based approach about the current and perspectives necessities of water, very little will be able to satisfy the desired levels of life quality. The best approach to the solution of the problem is by means of the techniques of systems analysis of that allow a global approach to the problem. Considering the interaction of the different elements that exercise its influence on the current and perspective use of waters, they allow the management of alternatives, drive to the evaluation of risks, facilitate the construction of models, guide the prospecting and define the water resources research, use, management and protection.

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Table 11. Industrial demands in m3/occupied m2 according to the Resources Agency of California

Industry Demands (m3 / Rhyme) Meat products 145 Milky products 315

Fruits 100 Grains 40

Bakeries 40 Sugar 90 Drink 95

Preparation of foods 100 Dry cleaner's and textile finishes, except wool 125

Sawmills 80 Wooden products (several) 5

Cardboard factory 955 Paper derivatives, except boxes 35

Cardboard boxes 335 Organic and inorganic chemical industry 100

Plastic materials 25 Drugstores 20

Soap, detergents, cosmetics, etc 90 Paintings, varnishes, lacquers, etc 125

Several chemical products 25 Oil refineries 20

Tires 100 Several plastic products 75

Glassware 80 Glass products manufactured with glass 20

Hydraulic cement 30 Pottery and derived products 40

Plastic products 2 Cut and stone products 30 Iron foundry and steel 65

Secondary coalition and (not ferrous) 15 Foundries of non ferrous materials 40

Primary industries of the metal 35 Beat 20

Metallic structures 25 Motors and turbines 25

Machines tools and teams 20 Diverse machinery, except electric 20

Electric industry 25 Motor vehicles 50

Airplanes 25 Ships, construction and repair 10

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Such a process can be schematized in four big stages, following the recommendations of Project A.4.3 of the International Hydrological Program of the UNESCO: “The process of planning of the water resources. A systemic approach”: 1. Initiation of the plan and preliminary planning. 2. Data acquisition and processing. 3. Formulation and selection of project alternatives. 4. Development of the final study. The first three stages constitute the study of pre-feasibility, from where is derived the convenience of carrying out detailed studies during the last stage of the planning that conforms the study of feasibility. Starting from here, other stages begin, but already individualized as the detailed prospecting or the projection, construction and operation of the systems of supply of water. In the stage of plan initiation and preliminary planning the necessities of water are settle down for different sectors, the scope and the objectives of each one are defined of them and the main limitations to achieve them are assessed, driving to a preliminary formulation of the hydraulic plan. The following stage corresponds to the acquisition and processing of hydrological, economic, environmental, sociological, structural, legal, institutional and organizational data. After this stage is concluded, the formulation and selection of project alternatives allows the generation of variants by means of the interaction among hydrologists, manufacturers, planners, representatives of the authorized agencies, financial, governmental and not governmental organizations, authorities and decision makers and the representatives of the community. In this stage usually appear the use conflicts that require meticulous negotiations for its successful solution. Almost they drive to the reformulation of alternatives technological, economic and environmentally satisfactory and viable. In general, here is where the stage of pre-feasibility concludes. The last stage of the planning constitutes the study of feasibility. In this stage studies are driven for:

• A detailed formulation of the projects. • Construction of the models. • Evaluation of risk and analysis of environmental impact. • Evaluation of the relationship cost-benefit of each project alternative. • Definition of the regulations and operation models. • The design of parameters for the different structures takes place here.

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4. WATER QUALITY

he most important restriction for water use is water quality (Figs. 31-33). Requirements for water quality vary

depending on its use.

T Certain industries like canned foods or beverages need water with very specific properties. Water for swimming pools needs to fulfill another set of properties, while to be potable and adequate for human consumption water require other specifications.

Fig. 31. Uncontrolled landfill

To be economic and sustainable, a potential ground water source should be evaluated to satisfy a specific quality. This will avoid the depletion of the source and will not increase the costs of supplying water of less or higher quality. In its wider sense, the concept of water quality should involve not only the water for supply but also the wastewater issued after consumption. Although there are international

recommendations for water quality issued by the World Health Organization, there are international regulations, the ISO 9000 and ISO 14000 standards for specific uses of water and also, there are local regulations issued by the governmental authorities of each country or group of countries.

Fig. 32. Polluted stream

Tables 12-26 indicates such requirements of quality for different objectives.

Fig. 33. Contaminated soil

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Table 12. Sanitary requirements for the drinkable water according to the Cuban Standard NC 93-02-1985

Characteristic

Desirable Maximum

Concentration (CMD)

Acceptable Maximum

Concentration (CMA)

Physical indexes Turbidity (silica scale) 5 10

Color (platinum-cobalt scale) 5 15 Odour and flavor Pleasant Not unpleasant

Chemical Standards Mg/l Mg/l Total Dissolved Solids 500 1000

Sulfoalquilbencene 0.2 0.5 Mineral Oil 0.01 0.3

Extract of coal with chloroform 0.01 0.15 Phenol Compounds (referred to phenol) 0.001 0.002 Total hardness (as calcium carbonate) 100 400

Calcium 75 200 Chloride 200 250 Copper 0.05 1.0

Total iron 0.1 0.3 Magnesium 30 150 Manganese 0.05 0.1

Sulphate 200 400 Zinc 5 15

Sodium 50 200 Silver 0.05 0.05

Aluminum 0.05 0.2 Nickel 0.01 0.02

Inorganic Compounds Noxious To Health Mg/l Mg/l Arsenic absent 0.05

Cadmium absent 0.005 Cyanide absent 0.05

Total Mercury absent 0.001 Lead absent 0.05

Selenium absent 0.01 Barium absent 0.03

Total chrome absent 0.05 Chrome VI absent 0.05 Beryllium absent 0.0002

Molybdenum absent 0.5 Cobalt absent 1.0

Strontium absent 2.0 Vanadium absent 0.1

Boron absent 1.0 Fluoride 0.7 1.0

Ammonia absent 0.5 Nitrites absent 0.01 Nitrates absent 45

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Table 13. Pesticides concentration in drinkable water

Characteristic

Desirable Maximum

concentration (CMD)

mg/l

Acceptable Maximum

concentration (CMA)

mg/l Aldrin absent 0.03

Chlordanh absent 0.3 DDT absent 1.0

Dieldrin absent 0.03 Endrin absent 0.2

Heptachloride absent 0.1 Epoxide Heptachloride absent 0.1

Lindano absent 3.0 Metoxichloride absent 30

Hexachlorobencene absent 0.01 Toxaphen absent 5

Total pesticides absent 100 Table 14. Concentration of noxious organic components to human health in drinkable water

Organic component Desirable Maximum

concentration (CMD)

(g/l

Acceptable Maximum

concentration (CMA)

(g/l Organic nitrogen absent absent

Policyclic Aromatic Hydrocarbons absent 0.01 Benzene absent 10

Chloroform absent 30 Carbon tetrachloride absent 3

1,2 Dicloroethan absent 10 1,1, dicloroethylene absent 0.3 Tetrachlor ethylene absent 10 Trichlor ethylene absent 30

2,4,6 Trichlorophenol absent 10

Formaldehyde absent 500 Etilmercury chloride absent 0.1 Pentachlorophenol absent 10

Diethylmercury absent 0.1 Table 15 shows the values limit for some illnesses transmitted by the water.

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Table 15. Minimum concentrations of microorganisms to originate water clinical illness.

Microorganisms Quantity Shigellas 10-100

Escherichia coli 106 – 109

Salmonella typhi 103-105

Helmynthes eggs 1 unit Protozoon cysts 102

Table 16. General Standards of quality of water for the livestock and the wild fauna (according to the Inland Water Directorate of Ottawa, Canada)

Parameter Maximum Acceptable Concentration (CMA)

mg/l Aluminum 5

Arsenic 0.05 Bacterias Enterococci 40 No/dl

Boron 5.0 Cadmium 0.01 Calcium 1000

Chromium 0.05 Cobalt 1.0 Copper 0.5 Fluorine 2.0

Lead 0.05 Mercury 3 (g/l

Molybdenum 0.01 Nitrate + Nitrite as N 20

Nitrite as N 10 (alfa-radiation, total 0.02 Bq/l (beta-radiation, total 0.19 Bq/l

Selenium 0.01 Sulphate 1000

Total dissolved solids 2500 Vanadium 0.1

Zinc 25

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Table 17. Standards for the watering of acidic soils or continuous use in all soils (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Aluminum 5

Arsenic 0.1 Bacteria, Enterococci 20 No/dl

Bacteria, fecal Coliform 100 No/dl Berillyum 0.1

Boron 0.5 Cadmium 0.01 Chloride 150

Chromium 0.1 Cobalt 0.05 Copper 0.2 Fluorine 1.0

Iron 5.0 Lead 5.0

Lithium 2.5 Manganese 0.2

Molybdenum 0.01 Nickel 0.2

pH 4.5-9 (α-radiation, total) 0.02 Bq/l (β-radiation, total) 0.19 Bq/l

Selenium 0.02 Sodium Absorption Ratio(SAR) 6

Total dissolved solids 500 Vanadium 0.1

Zinc 2

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Table 18. Standards for the irrigationof alkaline soils or fine-textured soils (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Aluminum 20

Arsenic 2 Bacteria, Enterococci 20 No/dl

Bacteria, fecal Coliform 100 No/dl Berilio 0.5 Boron 1

Cadmium 0.05 Chloride 150

Chromium 1 Cobalt 5 Copper 5 Fluorine 15

Iron 20 Lead 10 Litio 2.5

Manganese 10 Molybdenum 0.01

Nickel 2 pH 4.5-9

(alfa-radiation, total ) 0.02 Bq/l (beta-radiation, total) 0.19 Bq/l

Selenium 0.02 Sodium Absorption Relation (SAR) 6

Total dissolved solids 500 Vanadium 1

Zinc 10

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Table 19. Standards for the brewing industiess (according to the Inland Water Directorate of Ottawa, Canada)

Parameter Maximum Acceptable Concentration (CMA) mg/l

Alkalinity as CaCO3 85 Bacteria, fecal Coliform 100 No/dl Bacteria, total Coliform 1000 No/dl

Bicarbonate Non detectable Calcium 100

Carbonate 50 Chloride 100

Color 5 TCU Fluoride 1

Total Hardness as CaCO3 250 Iron 0.3

Magnesium 30 Manganese 0.05

Nitrate 10 Odour Non detectable

pH 6.5-7 Silica 50

Sulphate 100 Total dissolved solids 1500

Turbidity Non detectable Table 20. Standards for food processing industries (according to the Inland Water Directorate of Ottawa, Canada)

Parameter Maximum Acceptable Concentration (CMA) mg/l

Arsenic 0.05 Alkalinity ase CaCO3 150

Bacteria, fecal Coliform 10 No/dl Bacteria, fecal Streptococci 1 No/dl Bacteria, total Coliformes 100 No/dl

Cadmium 0.01 Chloride 250

Chromium 0.1 Color 5 TCU

Fluoride 1 Total hardness as CaCO3 150

Iron 0.2 Manganese 0.2

Mercury 1 (g/l ) Nitrato+Nitrito, as N 10

Odour Non detectable pH 6.5-8.5

Phenolic substances, as phenol Non detectable Silica 50

Sulphate 250 Suspended solids 10

Total dissolved solids 500 Turbidity Non detectable

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Table 21. Standards for leather industries (general finishing and tanning, according to the Inland Water Directorate of Ottawa, Canada)


mg/l Alkalinity as CaCO3 130

Calcium 60 Chloride 250

Color 5 Total hardness, as CaCO3 150


pH 6-8 Sulphate 250 Turbidez Non detectable

Table 22. Standards for the industry of the iron and the steel (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Chloride 150

Total hardness, as CaCO3 100 Oil Non detectable pH 6-9

Suspended solids 10 Temperature 38ºC

Table 23. Standards for petroleum industries (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Calcium 75 Chloride 200

Total hardness, as CaCO3 350 Iron 1

Magnesium 25 pH 6-9

Suspended solids 10 Total dissolved solids 750

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Table 24. Standards for paper and pulp industries (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Alkalinity, as CaCO3 75

Calcium 20 Colour 5 JTU

Total hardness, as CaCO3 100 Iron 0.1

Magnesium 12 Manganese 0.03

Silica 20 Total dissolved solids 200

Turbidity 10 Table 25. Standards for textile industries (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Alkalinity, as CaCO3 50-75

Aluminum 2 Color 5 JTU

Copper 0.01 Total hardness, as CaCO3 25


Silica 20 Suspended solids 5

Total dissolved solids 100 Turbidity 15

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Table 26. Standards for recreational use (according to the Inland Water Directorate of Ottawa, Canada)


mg/l Arsenic 0.05

Bacterias, fecal Coliform 100 No/dl Bacterias, total Coliform 500 No/dl

Cadmium 0.01 Chromium 0.1

Color 100 Light Penetration 1.2 M

Mercury 0.001 Odour 16 RHYME

Oil and grease 5 pH 6-9

Radiation, total 0.37 Bq/l Surfactants 2

Temperature 30 ºC Turbidity 50 JTU

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5. WELLS AND TRENCHES

roundwater development, by means of wells, trenches (filtration galleries) or springs are the common methods for groundwater supply. The first two will be examined in this section. Those methods are substantially different in their design, construction,

maintenance, and the hydraulic laws that govern their productive capacity. G Wells are almost vertical constructions and are the most common and extended practice for groundwater abstraction with depths varying from o few meters to, in some cases, hundreds of meters, while trenches or infiltration galleries are horizontal and very shallow constructions. A water well (Fig. 34) is a hole or shaft, usually vertical, excavated in the earth for bringing groundwater to surface. According to its construction are distinguished the driven wells, generally very shallow, the bored wells drilled with machines specially designed for that purpose and those dug by hand. The drainage trenches or infiltration galleries are shallow horizontal conduits commonly built in arid or semi-arid regions or in coastal areas and small islands. These horizontal permeable conduits are designed for intercept and collect groundwater mainly by gravity flow (Todd, 1970). In low permeability aquifers they are usually useful to intercept a high number of fissures. A hybrid case exists between the vertical wells and the horizontal galleries. These are the wells with drains or radial galleries successfully used in some small carbonate or volcanic islands. This case will also be considered in this work. The direct abstraction or exploitation of springs is an ancient and peculiar type of water use. 5.1. Wells When such wells are drilled through all the aquifer thickness are designed as “of total penetration” or “perfect wells”, following the Soviet literature. When only a part of the aquifer is reached by the well is named as “of partial penetration” or “imperfect”. These two definitions imply, particularly in intergranular aquifers, a special distinction in the selection of the mathematical models describing flow to the wells, because in all formulae the aquifer thickness ios a variable of major importance.

Fig. 34. Water well

Corrections are almost needed in cases of partial penetration and also, a “partial penetration effect” has been described in the literature.

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Although most water wells are assumed as being vertically drilled or excavated, in certain cases, they can be designed with certain inclination, particularly in the case of fissured low permeability rocks; however, this is not the common case. It is also common that the term well is limited to the works of groundwater abstraction, but wells can also be constructed for the satisfaction of other objectives different from the domestic, industrial, recreational or public supply. Therefore they can be designed and constructed for several objectives like land drainage, increase of groundwater reserves or groundwater quality improvement, for the deep injection of wastewater or for groundwater monitoring. It is important to note that a well is an engineering work (Fig. 35) and, as such, it should be carefully planned, projected, protected, constructed, tested and preserved by means of appropriate maintenance. In this process the appropriate parameters of each well must be selected, in connection with: • The penetration depth in the aquifer. Fig. 35. Horizontal well • The drilling method. • The casing or tubing. • The well diameter or diameters. • The type of filters and screens. • The annular seals. • The placement of cement and grout. • The development techniques. • The techniques of calculation of their

productivity, abstraction regime and the well efficiency.

• The protection perimeter of the well, when it is used as a supply source for domestic use.

• The maintenance of the well. 5.1.1. Penetration depth The yields to be extracted and the aquifer under consideration define the penetration depth. In unconfined aquifers is classically recommended that wells should be completely penetrating. But it is not uncommon that the desired yields are reached at lower depths and becomes unnecessary and expensive drill deeper wells. Wells drilled manually, dug wells and driven wells are commonly very shallow. On the other hand, in confined or semi-unconfined aquifers where it is necessary to cross the upper impermeable layer, it is advisable to avoid the effect of partial penetration and reach the lower impermeable bed. In fissured rocks and in some karst aquifer, regardless if they are confined or unconfined penetration depths is specially important because productive flows are commonly associated with selected fractures or cave levels developed at determined depths. In such aquifers an

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increase in well depth is not necessarily associated to a proportional increase in well yield because dry fractures or cave levels could appear at greater depths drying or decreasing substantially well yield. 5.1.2. Drilling method The drilling method should be chosen appropriately, in attention to the designed depth, the well diameters, the lithological composition of the layers that will be drilled, the completion program, the geographical position of the developing area and the distance to the sources of logistical support to the perforation. The following well drilling methods are often use in groundwater development:

• Mud-water rotary with direct and reverse circulation

Fig. 36. Cable tool machine

• Direct and reverse circulation air – rotary with casing drive

• Hollow stem auger drilling • Cable tool method Rotary methods are widely used because they are very fast and show a lot of advantages in different geologic conditions. The term direct and reverse refer to the direction in which the drilling fluid (mud,

air, water) is circulated. When direct, the fluid circulates down the string of drill tools in the direction of drilling. When reverse, the direction of circulation is reversing that of direct drilling. While the first three methods are rotary and widely used in research or construction of observation wells, cable tool methods are not only the oldest, but of lower cost and able to drill into a variety of geologic conditions. They are worldwide used in the construction of water wells but have the disadvantage of being a very low process, specially in consolidated rocks.

Fig. 37. Mud-water rotary machine

5.1.3. Casing or tubing The selection of well casing (Fig. 38) depends on well diameter, aquifer lithology or the presence of aquifer horizons of bad water quality that has to be isolated.

Fig. 38. PVC well casing

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Well casing could be temporary or definitive. Its primary is to protect the walls of the well in the drilling process, in order to avoid detachments and blockade of the perforation tools. According to the nature of the rocks, the water quality and the well depth, casing is usually of the same diameter or of decreasing diameter, staggered according to a falling order.

The projection and selection of casing is a task of special importance and it should account for: the pipe diameter and its wall thickness. Diameter should be selected according to the installation depth and wall thickness according to the strength it will support. Casing should be enough resistant to the stresses during the drilling process (Fig. 39). 5.1.4. Well diameter

The diameter or the diameters of the well refer both to the hole itself and to the casing. The diameter is selected to accept a pump of a size enough to account for the lowering of the water table or the piezometric level. Well diameter does not needs to be necessarily uniform. In fact, in deep wells more than one diameter could be necessary to reach the desired depth. Again, according to the use of the well diameter should avoid interferences with its operation (pumping, water leve measurements, water sampling).

Fig. 39. Iron protection of a PVC well casing

5.1.5. Well screen and filter pack Well screen and filter packs (Fig. 40) are selected according to the aquifer rocks and, in particular, to the rocks of the productive horizon drilled. It also depends on the well yield, the permeability or hydraulic conductivity of the formation and even, in certain cases it should account to the corrosive or incrustant properties of groundwater.

Fig. 40. Horizontal well screen

The main objective of the placement of well screen and filter pack is to allow that groundwater pass into the well without suspended solids and with a minimum of head load loss. Not all wells need to be cased or filled with filter packs. For the appropriate selection or the construction of any filter type, the following indexes should be defined:

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• Longitude • Slot size • Diameter • Resistance This way, the longitude of the screen is defined considering the water level drawdown during the well operation and, in particular, of the hydrodynamic type of aquifer. In unconfined aquifers, screen the last half or 30% from well bottom; in confined aquifers it is recommended that most of the admission area should be built with a filter not smaller than 70-80% of the longitude of the productive section. Screens could be placed as an unique string or separated by intervals of tubes as it is common in stratified aquifers.

The appropriate selection of the slot size define will define well efficiency which in turn is a function of the filter pack gradation. Dimensions comprise parameters as slot size and the slot form (circular, rectangular, squared) that makes the well efficient and avoid collapse. These indexes are selected as a function of the required open area and should account for the hydraulic properties of the formation, like grain size, to minimize the hydraulic resistance of the

water entering the well.

Fig. 41. Grouting and sealing of a water well

The screen resistance should be physical and chemical. Screens should be placed balancing the required strength to hydrodynamic and static strain and stresses, well efficiency and resistance to corrosion or incrustation. The filter pack is necessary in some wells drilled in fine-grained aquifer formations to reduce the entrance of these fine sediments and to provide a high permeability zone around the well. Their proper design accounts for the formation porosity and the entrance velocity of water. Filter packs consists of graded sand or gravel and are also used when groundwater has incrustation properties or is necessary the use of a large screen slot size. Annular seals are commonly needed to isolate the productive some from the rest of the well. Sometimes there are needed to avoid mixing with undesired waters from upper horizons. Grouting (Fig. 41) is particularly important to prevent the entrance of surface of undesired quality and to protect casing from corrosion. Grouting is placed in the annular space surrounding the casing. 5.1.6. Well development Development consists in the removal of fine materials and impurities associated with the drilling process and to stabilize the formation eliminating the finest fractions so that thicker or

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more uniform grain sediments become better distributed around the filter pack or the screen. In many occasions poor attention is devoted to well development techniques. However, the election of the correct technology is fundamental to achieve the maximum well efficiency. Development techniques can be natural or artificial. A remarkable level of technological development has been reached for well development techniques making the extremely effective. Well development techniques involve pumping, surging, jetting, addition of chemical, hydraulic fracturing and the use of explosives. 5.1.7. Yield capacity and well efficiency The notables advances achieved in well hydraulics have produced a strong arsenal of analytic methods for the assessment of the productive capacity of wells, the definition of its abstraction regime and the evaluation of their efficiency. A well is designed and constructed to wield the required water with the minimum drawdown. After the geologic, geomorphologic and hydrodynamic knowledge of the well settlement and its influence area, computing techniques should be chosen and adjusted to the actual initial and boundary conditions. Sometimes yield is erroneously assessed because an inadequate selection of the analytic methods. In many cases, such errors are due to an incomplete knowledge of the geology, geomorphology, hydrogeology and, even, of the paleohidrology of the place. 5.1.8. Protection perimeters An adequate definition of the protection perimeters of water supply wells is vital for the preservation of the quality of the resource and of the user’s health or needs (Fig. 42). Commonly, these areas are determined based on the average life time of pathogen bacteria but, according to the case, they can extend to prevent the contamination from other sources of organic or chemical waste.

Fig. 42. Protection perimeters of a group of water supply wells

Table 27 shows some safe distances between domestic wells and sources of pollution.

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Table 27. Safe distances between domestic wells and sources of pollution (after Brown et al., 1977).

Source of pollution Distance (m) Septic tanks 15

Pipes with waterlight joints 3 Other pipes 15

Percolation zones 30 Sewage farms 30

Infiltration ditches 30 Dry wells 15 Cesspits 45

5.1.9. Maintenance Well maintenance is a process that should be always considered in groundwater development to extend the well useful life. Maintenance is specially necessary in the case of incrustant or corrosive waters, in horizons of fine sand, when very fine slots are used, or when the filter pack is composed of gravel. 5.1.10. Planning well drilling Well construction should be preceded by one or several field sessions of hydrogeological exploration in which the site groundwater potential is previously assessed, in terms of volume and quality of the water to be used, is assessed. For such reason, it is common that before preparing a water well exploration boreholes are drilled and tested. Therefore, well drilling is designed for the following hydrogeological purposes.

Hydrogeological Exploration

Water supply Artificial recharge

Monitoring Drainage

Agricultural drainage Storm drainage Car wash Septic systems Food processing Treated sewer effluents of Brines

Well construction

Waste Injection

Mine drainage

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Aquaculture Mine solutions Recovery of fossil fuels Experimental Reclamation

Water supply Artificial recharge

Monitoring Drainage

Agricultural drainage Storm drainage Car wash Septic systems Food processing Treated sewer effluents of Brines Mine drainage Aquaculture Mine solutions Recovery of fossil fuels Experimental

Cleaning and maintenance of works

Waste Injection

Reclamation Defining the number of exploration wells for groundwater supply is an extremely complex task. Only in very rich or well-known aquifers this Fig. could be acceptable approached. A relationship 1:1 between exploration wells and water supply wells are only obtained in those cases, but it can be as high as 10:1 in low permeability aquifers, where the success of water well drilling is very low. Table 28 shows a guide of the relationship among exploration wells and definitive water supply wells that could be useful to estimate the number of exploration wells that can be required in a given aquifer. Relations described in Table 28 are not absolute. Many times, the final quantity of water wells needed to satisfy a certain demand can nor be previously defined. Once again, it depends on the hydrogeologist skill and on the aquifer knowledge. Evidently these relationships are not absolute since also, many times, the number of receptions can be foreseen that are needed to satisfy a certain demand. All the wells, has to be tested to define their hydraulic properties, productivity and the water quality. In the current practice, all the modern drilling equipment are perfectly equipped for quick hydraulic tests. At the same time, portable kits allow field determinations of water quality.

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Appropriate equipment is fundamental when work has to be done in isolated communities or regions of high hydrogeological complexity and reduced accessibility, where the supply sources are very far. Table 28. Relationship between exploration wells and water supply wells.

Type of aquifer Relief type Karst Fissuredo non

karstic Intergranular

rocks Plain 2:1 5:1 2:1

Mountain 3:1 15:1 4:1 Small islands 2:1 10:1 2:1

Deltas 5:1 7:1 3:1 Wetlands 5:1 7:1 3:1

5.2. Trenches and infiltration galleries Wells are the most common constructions for groundwater exploitation, nevertheless trenches and infiltration galleries are used in many areas with particular hydrogeological conditions were wells could not be used. Therefore, in case of thin aquifers or thin fresh water layer underlain by saline waters, as is the case of most coastal zones trenches are often the only reasonable way to use groundwater. But while an infiltration gallery is considered by USDI (1977) a horizontal well or subsurface drain that intercepts underflow or infiltration of surface waters, methods of yield assessment and its design are quite different. Estimates of yield are made for each of the following cases. 5.2.1. Gallery in slowly permeable material with minimum depth of water above stream bed It is assumed that the river or lake has direct access to the gravel pack or backfill. The length of the screen, L, is computed as follows:

KHBQdL =

where: L, length of the required screen Q, desired discharge d, vertical distance between river bed and center of the screen K, permeability or hydraulic conductivity H, head acting on the center of the pipe

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B, average width of the trench backfilled with gravel 5.2.2. Gallery in permeable riverbed or with minimum depth of water above the bed In this case, L is computed by:

KHrdQ

Lπ2

2ln=

Where r is the radius of the pipe and H the minimum depth of water above the lake or channel bed. 5.2.3. Gallery in an ephemeral or intermitent stream channel with perennial underflow The yield per unit length of the gallery is computed by:

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛−−⎟

⎠⎞

⎜⎝⎛−+⎟⎟

⎠

⎞⎜⎜⎝

⎛−

=

Mr

Mr

TtSrerf

Mr

TtSr

MSKt

Ksqr

2exp

2expln2

44exp4

22 ππ

ππ

and the required length L is:

qQL =

5.2.4. Gallery for freshwater skimming

Trenches and infiltration galleries are common in coastal zones of shallow groundwater because they allow skimming freshwater from the top of a lens or saltwater wedge in seawater intruded aquifer.

Fig. 43. Ghyben – Herzberg relationship

The drawdown is basically conditioned by the position of the interface between fresh water and seawater, described by the Ghyben-Herzberg relationship Fig. 43):

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ffs

ss h

dddh−

=

where hs, is the distance below mean se level of the saltwater point ahead at the freshwater – saltwater interface; hf, distance from the top of the freshwater table to mean sea level or the point saltwater ahead; ds, density of saltwater and df, density of freshwater. For average densities of 1,027 and 1,000 for salt and freshwater, the relation holds . This relation is almost helpful for drawdown control.

fs hh 38,0=

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6. STREAMFLOW RECESSION ANALYSIS

6.1. General

n independent works published at the beginning of this century, two French investigators, J.

Boussinesq (1904) AND E. Maillet (1905), they deduced paths equations to characterize the descending branch of the curves of avenues in river hydrograph (Fig. 44). Boussinesq defined the descending branch following the peak flow to an expression of the type:

Fig. 44. Accumulation and recession branches in river flood hydrographs

I

( )Q Qtt

on=

+1 α

as long as Maillet stated that such a curve stops it could be adjusted perfectly to a falling exponential function of the type: ( )W W tt o= −exp α where, Wt: flow of the source at the end of time t Wo: flow in a moment previous to t α: a non-dimensional coefficient expressing the lag in the aquifer response to the compensation of t: time between αt and αo After these authors the decreasing branches of river or spring flow could be characterized when recharge stops. As recharge is usually a function of the precipitation, the equations allows to define the flow from the river to the end of any time t when natural recharge does not exist (Fig.

45).

Fig. 45. Decomposition of the recession curve

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Originally, such period, the recession period, was defined between two successive flow peaks but, for extension, the equation of Maillet, the most widely used, began to be applied in the hydrodynamic analysis of the flows of rivers and springs in periods of under or null contribution from precipitation. The importance of the method increases notably, since it is well-known that depending on the degree of penetration of a river in an aquifer this is able to maintain a certain flow when the recharge ceases and flow is due only to the contribution of groundwater. These yields, commonly denominated base flow it can be properly separated by this way. In karst aquifers (Fig. 46) this is one of the most valuable methods for assessing groundwater resources and safe yield with a considerable decrease in the research costs.

Fig. 46. Terms of the recession curve

The appropriate analysis of the recession curves allows, among other aspects: • the decomposition of the river flow hydrographs, • the determination of groundwater resources of the flow system drained by the river or

spring, • the determination, as regional variables, of the most important hydraulic properties, like

transmissivity, permeability or hydraulic conductivity, storage and diffusivity, in whose definition the scale effect is excluded.

• the computation, quite precise, of the effective infiltration, so that outlining the equation of balance appropriately, the value of the evapotranspiration can be determined in districts without another type of losses,

• at the same time, the distance to the water divide can be computed; • under appropriate conditions, in karst aquifers, the components of diffuse and

concentrated, or even retarded flow can be discriminated; • it is possible also to determine the components of hypodermic flow or interflow, those

flows organized in the unsaturated zone that usually appears like peak flows during the recession period;

• when flow control is accompanied by an appropriate chemical sampling some conclusions can be obtained on the internal chemical and physical mechanisms of the system;

6.2. Groundwater resources assessment The expression derived by Maillet has the following formulation:

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( )Q Q et ot to= − −. α

This way, the curve BC represents the recession of the aquifer (period of null effective recharge), and is designed, therefore, recession curve. The above equation represents the position of BC in the hydrograph, being Qo, the point B of the Fig. 47, and C the point at the end of the recession period. If Qa is the due net recharge to direct infiltration or insinuation as long as Qe is the flow drained by the river or the spring, or in other terms, the natural discharge of the aquifer, the infinitesimal change of volume (dV)t can be expressed as:

Fig. 47. Description of the recession curve ( )dV Q Q dta o= − In the recession period Qa = 0, then: dV Q dte= − For a time to, Qe = Qt, and (71) it can be written in the following way: - ( )Q e t t dt dVo o

− − =α

integrating under the condition that V = 0 when t = ∞:

( )

( ) ( )[ ]dV Q e dt V Q eV t

ot t

t ot t

tt

o o= = −∫ ∫ − − − −∞∞0

0 1α α

α

and

( )[ ]V Q et ot to= − − −1

0α

α

or

( )VQ

eto t to= − −

αα

If

( )Q Q et ot to= − −α

it can be concluded that,

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VQ

tt=

α

and therefore,

α =QV

t

t

The recession coefficient is also equal to:

( )α =−

−

log log,

Q Qt t

o t

o0 4343

Qt and Vt are closely related to each other and with the physical and geometric properties of the aquifer, especially with the transmissivity (T), storage (S) and the distance to the water divides (X). In karst aquifers the lag time in aquifer response can be represented better for the index τ, introduced by Singh and Stall in 1971:

τ =T

SLt2

instead of, T/S The coefficient of exhaustion α is also a function of the type:

( )( )α =f T

f S X,

similar expression to the obtained in 1960 by Rorabaugh for the discharge of a finite aquifer drained at the contact for a spring in laminar flow:

απ

=2

24T

X S

6.3. Overlapping of different sub regimes When recession begins the discharge of the aquifer takes place simultaneously through all the collectors, this is, following all the drainage paths. Although those of more diameter effective drain the small ones, drainage begins with those, and this, is clearly manifested in the changes in the slope of the recession curve. Recession

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Fig. 48. Shapes of the recession curve continues with a segment of less slope (smaller and T that the previous one and a higher S) that indicates the ceasing of the drainage of the big collectors and the prevalence of others of smaller diameter in the control of the discharge of the aquifer (Fig. 48). Recession concludes with a segment asymptotic to the time axis, the full recession period with and absolute control of storage on discharge. The following relationships are always valid for a constant recession, being 1, 2, 3 the different regimes:

For the coefficient of exhaustion α1 > α2 > α3………. > αn For transmissivity T1 > T2 > T3………. > Tn For the storage coefficient S1 < S2 < S3……… < Sn For the time of drainage of each collector t1 < t2 < t3. ….. .. < tn It is important to point out that the recession curve characterizes the discharge of the whole aquifer system that feeds the river or the spring under transitory, non-permanent, flow conditions of or even, in permanent regime.

6.4. Water resources assessment Groundwater resources assessment can be done processing recession curves. Accountig that: V Qtt = / α at to: Vo Qo= / α and, therefore, groundwater resources for the assessed period are: Wt V Vo t= −

or,

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Wt Qo Qt= −/ /α α for one subregime. For several subregimes it is easy to outline that

WQ Q Q Q Q Q

to o o o on

n t= + + +

⎛

⎝⎜

⎞

⎠⎟ −1

1

2

2

3

3

4

4α α α α α α..........

t

r

r

being Qt / αt = Vt, the final volume of water in the aquifer.

6.5. Variation of reserves and storage index The volume of stored water at the beginning of the aquifer recession can be expressed by the equations (11) and (24): The quotient of this volume divided by the area of the aquifer would express the head, in meters, discharged during recession (Fig. 49). Therefore, calling ∆r to the storage index, we have that when t = to, ∆r Vo Fo = / and for any t different from to, ot when t = tt, ∆r V Ft t= / and as the variation of reserves ∆R is the difference among the storage indexes of different subregimes:

Fig. 49. Variation of reserves

∆ ∆ ∆R ro t= − or, ∆ ∆ ∆R ro t= − being F the aquifer area. The storage coefficient can be computing processing piezometer data, accounting from the above described relations. Therefore, the variation of reservess ∆R and the change of groundwater levels of underground water ∆H in the aquifer. Being S the storage coefficient, then:

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S R= ∆ ∆/ H The storage coefficient should be calculated by intervals in each subregime. Their generalization can be made starting from the following analytic considerations. Defining Rt like the rate of storage change for two subregimes; for example, we would have that:

Q Rt ti

==∑

1

2

and the total value would be, then:

SR

RS

t

ti

t

ii

= =

=

∑

∑1

2

1

2

For one-dimensional flow (35) can be solved for S and T uniforms in two subregimes respectively. However,

Sht

Th

X∂∂

∂∂

=2

2

being h1 and h2 the heads in the two subregimes and (105) is represented by two differential equations of first order in t:

( )Sdhdt

TL

h h12 2 1

4= −

( )Sdhdt

TL

h22 1

4=

Solving by means of a lineal combination of h1 and h2 (Nutbrown and Downing, 1976; McCracken):

( )H h1 12 1= + + h2

( )H h h2 1 2 1= − + 2

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satisfying:

( )SdHdt

TL

H12 1

42 2= − −

( )SdHdt

TL

H22 2

42 2= − +

and the solutions for H1 and H2 are:

( ) ( )H t H o Kt1 1

1=

( ) ( )H t H O Kt2 2 2=

where

( )K e T SL1

4 2 2 2

= − − /

( )K e T SL2

4 2 2 2

= − + / inverting (108) and (109), then:

( )[ ]h H1 1

12 2

2 1= + − H2

( )[ ]h H2 1

12 2

2 1= − − H2

and the solutions are:

( )( ) ( ) ( ) ( ) ( )

h th h

Kh h

Kt t1

1 21

1 22

2 1 0 02 2

2 1 0 02 2

=+ +⎡

⎣⎢⎢

⎤

⎦⎥⎥

++ −⎡

⎣⎢⎢

⎤

⎦⎥⎥

( )

( )( ) ( ) ( ) ( ) ( ) ( )

h th h

Kh h

Kt t2

2 11

2 12

2 1 0 02 2

2 1 0 02 2

=− +⎡

⎣⎢⎢

⎤

⎦⎥⎥

++ −⎡

⎣⎢⎢

⎤

⎦⎥⎥

and the discharge is equal to:

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( )QTL

h tt =4

2

or Q A K A Kt

t t= +1 1 2 2 so that,

(122) ( ) ( )

( )α11

2

02 2

2 100

= − +⎡

⎣⎢⎢

⎤

⎦⎥⎥

Q hh

6.6. Transmissivity Transmissivity is one of the hydraulic properties where it is necessary to define: the geometry of the discharge area •

•• the type of aquifer the shape of the recession curve, in terms of the number of present subregimes.

Fig 50. Variation of the coefficient 2.25 /Π in the calculation of the regionalized transmissivity as a

function of the adjustment of flow lines to the morphology of the impermeable boundary in the

discharge area.

As in the discharge area flow is not radial, the derived coefficient of the classic term 2,25 / Π should be modified in correspondence with the geometry of the discharge area (Fig. 50). For remarkable angles, the value that should be taken is:

Π = 180º

Π/2 = 90º

Π/4 = 45º

Π/12 = 30º since it determines the corresponding adjustment of the flow lines at the discharge area (Fig.10).

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For the permanent or quasi permanent regime the exhaustion curves the commonly deduced methods can be applied keeping in this in mind. In a wider sense, recession can be compared with the pumping of an aquifer in transitory regime, and the values of ∆R are the successive drawdowns. Under those conditions, a function very similar to the general expression of Theis (1935) is obtained:

( )y a b x= +log log

∆ ∆H RQ

TT

X ST= = +

⎛⎝⎜

⎞⎠⎟

0 183 2 252

,log

,log

In the equation: a Q T= 0 183, / y R= ∆ x t= Plotting ∆R = f(log t), a straight line is obtained and after applying finite increments is possible to calculate to and T, since to, approximately belongs together with the first derivative of y(x):

( )0 183 2

2,

logQ

Tdydx

Rt

= =∆

As Mijatovic (1968) pointed out, the value is equal to ∆R in a logarithmic cycle, so that in an interval, log t = 1, t, 0 183, Q

TR C= =∆

and

TQ

C=

0 183,

Knowing the value of the storage coefficient, the value of T can also be obtained, substituting in (126), for a ∆R = 0.

SXtT

TQ

O o2

25,2log

183,0=

and by definition,

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0 1830

, QT

≠

then,

log,2 25

02

T tX S

o =

that is the same as, 2 25

12

, T tX S

o =

Therefore,

ST t

Xo=

2 252

,

and,

TX S

to=

2

2 25,

6.6.1. Alternative method for Transmissivity computation in karst aquifers This method (Molerio, 1997) modifies the solutions proposed by Abu-Zied and Scott (1963) and Aron and Scott (1965) for wells with decreasing flow during pumping. Considering an initial value of flow Qo that Qb falls in same intervals = Qo, in times t1, t2, t3,…, tn (Figs.51-52), the decrease of the water level in any point located at a distance r from the discharge point at a time tx , can be expressed by the general equation of Theis (1935):

Fig. 51. Curves of regular decreasing flow

⎥⎦

⎤⎢⎣

⎡ −= ∑=

n

iiuu WW

TQH

1)()(

0

4ε

π

where,

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∫⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛−

= uduu

iu eW )( Fig. 52. Graphic h/Q = f (log t)

is the Theis well function, and,

( )uni ttT

Sru−

=4

2

Value of ((or) and K

K ((or) K ((or) 1 1.000 6 0.245 2 0.614 7 0.213 3 0.445 8 0.189 4 0.350 9 0.169 5 0.228 10 0.153

For (u)i < 0,01, the approximate value of W(u)i is,

⎥⎦⎤

⎢⎣⎡ −

=−−≈Sr

TuW iniiu 2)(

)1(25,2lnln577,0 τ

and

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

−−

−

=∆

∑=

n

ii

n

Sr

TtnT

QH

1

2

0

)1ln(

25,2ln)1(4τε

επ

⎥⎦

⎤⎢⎣

⎡−+

=∆

∫0

1)(

0

)1ln(4 duWT

QH

nu τβγπ

When the time progresses,

β→∞ W (OR) ((

γ→0 Φ (µ ,τ)→0

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and

en

h

SrTtT

QH +=∆

2

0

25,2ln4πγ

6.7. Effective infiltration Discharging waters during recession could be a mixture of waters of different age, v.gr., with different turnover times in the aquifer. Böcker (1976) presented very simple synthesis:

• waters with brief time of residence (between hours and weeks) • waters with little time of residence (among months to one year) • waters with moderate time of residence (that varies between several years or decades) • waters with high time of residence (of some few hundreds to thousands of years), and, • waters with extremely high times of residence (with dozens of thousands of years).

The effect of natural recharge is manifested, in turn, in the river or spring hydrograph in these three ways: • a sudden elevation in the level of ground waters; • a gradual elevation in the level of ground waters; • a decrease in the recession rate. The first case is the simplest, since the discharge and the level increment could be compared directly with precipitation and infiltration could be accurately computed this way. In the second and third cases a direct comparison is more difficult, and often imprecise. The head increment due to infiltration between two successive measurements in any point of the aquifer would equal the evacuated head of the aquifer during the recession in that point. As this would be given by: h h eo o

dt

− − α

for to, ho, then h e hdt

1 1+ −α

This way, the change in head due to the infiltration at a time t, would be,

( ) ( )H h h h h e h h eo o o odtdt1

1 1= − + − = −− −α α1

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and with decreasing t:

( ) ( )H h h h e h h h eo odt

odt1

1 1 1 1= − + − = −− −α α Cumulative level Hn

o can be obtained applying:

H h en d

o

nn

0

1

1= − −

−

∑∑ α ht

h

and with falling t

H e hno

dtnn

= −−

∑∑α

0

1

1

whose average value will be:

( ) (H h e h eno

ndt dt

n

= + − +⎡

⎣⎢

⎤

⎦⎥∑ ∑+ −

−12

1 11 0

1α α )

and the effective infiltration is obtained applying:

Ii HpHe

no

no

=

or knowing the discharge volume, by means of,

AQI w

w =

6.8. Distance to the water divides Rorabaugh (1960) pointed out that recession, in base flow terms, could be represented by an equation of the type:

( )q T h L Tt Lo= −2 42 2/ exp /π S for values, Tt L S/ ,2 0 2>

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where L is the distance from the discharge area to the groundwater divide. For discharges q1, q2 in times t1, t2, the following equation is obtained:

( ) ( )log /,

q qx

TS

t tL1 2

2

2 1 24 2 3031

= −π

and if, q1 = 10 q2 being, t2 - t1 = ∆t then T L S t/ , /2 0 933= ∆ and the semi radial distance to the groundwater divide could be expressed as:

S,tTL

9330∆

=

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7. DESIGN, OPERATION AND OPTIMIZATION OF GROUNDWATER MONITORING NETWORKS

groundwater-monitoring network is designed, constructed and operated to gather data on the behavior of the aquifer. This data are

qualitative and quantitative and varies from water level data to temperature at a specific depth. Data is recorded manually or automatically and incorporated to the databases manually or automatically, including telemetry. Data is collected at specific time intervals, from a few seconds to several months (Fig. 53). Anyway, the network should be designed, constructed and operated for improve water management. Although initial investment is high the proper use of network data improves valuable economic, social and environmental benefits.

A Fig. 53. Water level control in an observation well

The conceptual model of any groundwater-monitoring network comprises:

• The network components (observation wells, springs, trenches, associated climatic and river gauging stations, exploitation wells and even tidal observations).

• The construction of the observation wells and, therefore, their adequate design (diameter, depth, casing, screen) and testing.

• The variables (Fig. 54) to be measured and observed (water level, chemical composition, physical parameters).

• The frequency which these variables will be measured.

• The instruments that will be used to measure those variables, assuring

its quality and systematic calibration (Fig. 55).

Fig. 54. Water sampling

Fig. 55. Water regime monitoring kit

• The adequate training of the observation team, comprising both the field personnel and the personnel in charge of data processing.

• The way or ways, in which data will be recorded, processed, stored and retrieved.

• The issues and the frequency of the different issues derived from the net operation and processing.

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• The use of the information derived from the network. When a groundwater monitoring net is designed is indispensable to define the basic aspects of their operation: 1. The objectives of the Net. 2. The spatial representativeness of the monitoring point. 3. The frequency of the observations, and 4. The type and number of variables to be measured. The classic techniques of projection of groundwater monitoring networks have been based on the application, more or less widespread, of the kriging spatial interpolation and, in less degree of the Kalman Filter to preexistent nets. Something more refined are those techniques derived from the application of the Observer's Theory or apply Combined Fuzzy Sets. Nevertheless, these applications presuppose that the observation stations whose spatial distribution and frequency will be optimized were correctly designed and, therefore, the measurements or observations that were carried out in them reflected the dynamics of the phenomenon to be studied. Until now, such techniques does not solves the problem of the optimal monitoring frequency neither the number of variables to observe in each point of the network. The geomathematical approach guarantees the operation of a hydrogeological monitoring network and of the consequent of hydrogeological forecasting system at the smallest acceptable cost. These techniques allowed the operation of a monitoring system with the minimum possible number of stations showing the maximum representativeness. In those stations the smallest number of variables will be measured at the longest time intervals, guaranteeing the maximum possible information effectiveness and the minimum uncertainty. These techniques, applied since the design stage, lead to a rigorous elaboration of the conceptual model of the hydrological system, in such a way that allow: • The identification of the natural or artificially induced factors, included those of

construction and operation of each monitoring station controlling the hydrodynamic regime of the aquifers as well as those factors governing the process of acquisition of the chemical composition and the quality of the waters;

• The appropriate regionalization of the aquifer systems and the definition of the structure and composition of the stations that will conform the hydrological prevention system in each one of the hydrogeological units, and,

• To specify the relationships in the regime and water quality of each monitoring station in order to define the optimum instants, sampling intervals and the variables to measure, in each station.

It is possible to achieve the following goals:

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• An increase in the knowledge of the internal structure and of the natural and artificial factors controlling the regime and geochemical hydrodynamics of the aquifer systems;

• To improve the systems of hydrogeological forecasting, making them more efficient, sure and dynamic,

• A decrease in the costs of acquisition, processing, conservation and recovery of the data derived from the operation of the network as a consequence of a more efficient design;

• To define the minimum number of monitoring stations that satisfy the requirements of maximum information effectiveness and lowest uncertainty at the minimum possible cost;

• To identify the construction parameters of the stations that eventually should complete the Net and their geographical position, guaranteeing the representativeness of the phenomenon that will be observed and of the variables that will be measured; and

• To identify the minimum sampling intervals and the frequency of the observations in each station of the Net, v.gr. the minimum frequency of measurements that be carried out in each one without remarkable loss of information effectiveness or, even, with gain of it, and the definition of the variables that has to be measured in such stations in each time interval.

7.1 Geomathematical techniques When hydrogeological observations are generalized or when the system’s properties are mapped errors of several sources are introduced (Agterberg, 1974; Brower, 1983; Bear, Zaslavsky & Irmay, 1968; Mardia, Kent & Bibby, 1979; Nawalany, 1983; Yevjevích, 1971; Molerio, 1983, 1984a, 1984b, 1985a, 1985b -, Jiménez and Molerio, 1997): • The uncertainty with which they were taken or measured, • Those that are characteristic of the methods that were used in their quantification, or • Those that correspond to the errors linked to the interpolation or extrapolation methods.

The variables that are measured directly in the field are not, neither, exempt of errors of different type: analytic, instrumental, and systematic, among others. Also, the spatial variability of the aquifer system properties introduces an important number of negative consequences in the evaluation of the available resources and in the decisions regarding the administration of the water resource. To the spatial variability (Fig. 56) , a direct consequence of the heterogeneity of the rocks and of the distribution of their system of collectors and conduits, should be added those caused by the anisotropy of the physical properties. It is also

expected a certain time dependence of some of the properties of the physical field and, obviously, those that characterize the chemical composition or the quality of the waters of the aquifers are variable that time influences in a decisive way. The geomathematical techniques (Matheron, 1965, 1970; Agterberg, 1974; Journel & Huijbregts, 1978; Delhomme, 1978;

Fig. 56. Variogram of hydrocarbon concentration in groundwater

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Molerio, 1992, 1997; Molerio & Portuondo, 1997; Molerio et al., 1996a, 1996b, 1977a, 1977b, 1997c, 1998; Obdam, 1983; Peck et to the., 1988; Reyment & Joreskog, 1993) are directed to the reduction of the sources of uncertainty in the representation and description of the system’s properties. The geomathematical method, based in the ideas of by Agterberg (1974), conjugates several the techniques: Information Theory, the Frequency Distribution Analysis of the Independent Random Functions, the Factor and Cluster Analysis, the Statistical Dependence, the Analysis of the Random Stationary Variables and Kriging, the Statistics of Oriented Data, the Harmonic, Autocorrelation and Spectral Analysis, the Fractal Mathematics and the Analysis of Spatial Variability in Multivariate Systems. Such techniques are applied to the time and spatial series of the hydrogeological monitoring networks. The observational matrix is built with geometric variables describing the construction parameters of each monitoring station and the topology of the station. The aquifer physical properties in each monitoring station are important data to be taken into account as well as some information on the actions over and from the system.

Fig. 57. Hydrocarbon concentration in groundwater mapped using kriging

P-1 P-3 P-4 P-6

P-5

PICKER

P-7 p-8

a.cura

meireles5

p-24

alcazabar

meireles7

gabin

meireles 6

355.00 355.50 356.00 356.50 357.00 357.50 358.00 358.50 359.00 359.50 360.00350.00

350.50

351.00

351.50

352.00

352.50

353.00

353.50

354.00

354.50

355.00

The working procedure allows to the definition of the most important elements in network design: • Number of wells that will integrate the initial Net or the Optimized Net; • The construction details of each of the wells; • The monitoring frequency; • The type and number of variables to be sampled in each monitoring interval. The methodology consists of the following steps: 1. Elaboration of the conceptual model of the hydrological system: its structures, governing

laws, actions on the system, response mechanisms and system inertia. 2. Identification of the current information effectiveness of the flow system. 3. Univariate and multivariate statistical processing of the time series. 4. Univariate and multivariate statistical processing of the spatial properties. 5. Multivariate statistical processing of the geometric variables.

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6. Regionalization of the system. 7. Definition of the monitoring frequency. 8. Identification of the complementary points and of those that should be eliminated from the

current Net. 9. Definition of the construction indicators of the complementary points and its geographical

position. 10. Validations of the designed or optimized monitoring network. 11. Computation of the information effectiveness of the designed or optimized monitoring

network. 12. Assessment of the operation costs and cost - benefit balance among the Net in operation

and the Optimized Network.

7.2 Methodology for the design of Hydrogeological Monitoring Networks The geomathematical techniques to be chosen for the initial design of a monitoring network depends on the availability of information regarding some of the variables that identifies the hydrodynamic regime of the system, such as piezometric levels and/or chemical composition of waters and of those who influence the hydrodynamic regime of the flow system. These geomathematical methods are very successful when applied to the evaluation of uncertainty and they allow to establish the reduction or amplification of the observation net, to reduce the interpolation errors and to define, among other, the representativeness of the data or of the stations of the net. The design and optimization of a groundwater monitoring net is based in the following approaches: 1. Optimum use of the historic information and of the data from the monitoring net in

operation. 2. Reduction of the number of points to monitor and of the frequency of the observations and

samplings regarding the current design. This reduction should account for the representativeness of the stations; the quality of the primary data; the perspectives of use of the surface and ground water resources and the objectives of the monitoring net.

3. Maximum elevation of the quantity of primary information derivable of the hydrogeological mapping reducing to a minimum the costs of drilling observation wells.

Practice has confirmed that an increase in the economic efficiency of hydrogeological research can be achieved whenever are available appropriate methods to evaluate, continuously, the use value of the groundwater monitoring networks. Its design should satisfy the following principles: 1. The monitoring objectives should be identified and quantified - as much as possible - for

each one of the hydrological systems, including the definition of certain measure of effectiveness. This is the most complex aspect in the design (and optimization) of the nets, since it could has different objectives for different users. These objectives include the estimation of the current state of quality, the long-term detection of tendencies, violations in

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the norms of quality of the groundwater or of the exploitation design, the mathematical simulation of the aquifer or the combined use of the surface and ground waters.

2. Identification of the hydrodynamic and the most important hydrochemical processes because they drive, in each case, the methods of research and data analysis.

3. Determination of the effectiveness of the information provided by the network or of the data specially collected to prepare the initial matrix of evidences. Such effectiveness can be related with such statistical concepts as the variance of the samples, the variance explained by means of the factor analysis, the probability of occurrence of any event or the interpolation error, among others.

4. Computation of the network cost and of the monitoring program. 5. Analysis of the cost-benefit or cost-effectiveness relationship, an aspect with a very

important subjective component. This should take into account the relative importance of the sampling stations and the variables to observe in each one of them. In practice, however, it is required a minimum level of effectiveness based on subjective approaches, economic and even political considerations. Unfortunately many times, they don't take into account the optimal monitoring minimum, built and operate exaggerated networks, or the real necessity of acquisition of the primary data is ignored or overestimated.

In case when time series of groundwater levels and/or hydrochemical composition or indicators of groundwater quality are available, the procedure is as follows: 1. Assessment and critical analysis of the information effectiveness and of the cost of

acquisition and processing of the basic data. 2. Statistical processing of the chronological series of each of the stations and validation of the

results of the operation of the eventual net. 3. Multivariate analysis and numeric classification of the aquifer geometric indicators and the

topology of the network stations, in order to determine the factors controlling the regime, the design parameters of the monitoring stations and the information effectiveness level of each one.

4. Comparison of the information effectiveness levels of each group of series according with the sampling frequency.

5. Categorization of the socioeconomic, politics and environmental importance of the aquifer systems to be monitored.

6. Validation of the results of the design for a most precise regionalization of the aquifer system.

7. Improvement of the conceptual model of the hydrological system. 8. Optimization of the Net. The most complex case is, obviously, when a monitoring net is designed for the first time. To solve this problem, it is required the preparation and processing of a matrix of evidences derived from the hydrogeological prospecting and mapping and from the digital processing of aero spatial images. Information should be added characterizing or identifying the possible impacts on the regime and quality of the waters that have promoted the design of such a net. In this case, it is common to proceed as follows: 1. Elaboration of the Conceptual Model of the Hydrological System.

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2. Digital processing of aero spatial images and elaboration of the geologic, geomorphologic and hydrographic regional base of the territory.

3. Definition of the accessibility, definition of impacts on the regime and the quality of the ground waters and preliminary evaluation of the cost of acquisition and processing of the basic data.

4. Field documentation including inventory, sampling and testing water stations. Geologic and geomorphologic mapping.

5. Definition of the seasonality of the stimulus to the system (rain, evapotranspiration, surface runoff) and the system’s response by means of combined techniques of statistical processing and field cartography.

6. Multivariate analysis and numeric classification of the aquifer geometric indicators in order to determine the factors controlling the regime, the parameters of design of the monitoring stations and the information effectiveness level of each of them.

7. Definition of a sampling cycle according to the same intervals of the seasonality of the stimuli on the most important hydrological or environmental system and its validation during at least at a complete cycle.

8. Comparison of the information effectiveness levels of each group of series according to the sampling frequency.

9. Validation of the results in a further more precise aquifer regionalization. 10. Improvement of the Conceptual Model of the Hydrological System.

7.3 Optimization of Hydrogeological Monitoring Networks The optimization of a hydrogeological monitoring network consists in adjusting its spatial distribution, monitoring frequency and number of variables to measure in such a way that, the same or higher information effectiveness can be obtained with less stations where the same or less variables are sampled in longer time intervals at the minimum acceptable operation cost. To optimize the spatial distribution, monitoring frequency and number and type of variables appropriately to be observed it requires of a certain number of observations of the variables that it is sought to optimize and of an improvement of the knowledge of the conceptual model of the aquifer system. It is necessary, also, to manage trustworthy information about the operation costs. In the practice it usually happens that it is required to optimize a net designed following other methods lower other methods or with a conceptual model that have not been validated. For optimization purposes, it is necessary to define: 1. The objectives of the optimized net. 2. The calculation of the effectiveness of the information of the net in operation and the

evaluation of uncertainty. 3. The definition of the factors controlling the hydrodynamic regime and of the processes that

intervene in the acquisition of the chemical composition and the quality of the ground and surface waters.

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A more detailed precision of the objectives of the optimized net defines the goals of the information processing, in particular, the corresponding to the chronological series of the hydrodynamic and hydrochemical variables. Some of these cases usually have to be faced: • To enlarge the objectives of the monitoring increasing it with new variables. It is

essential to define if, not having been measured previously, those new variables keep some relation with those observed during the operation of the net; this it is a case that, frequently, drives directly to the amplification of the number of stations of the net;

• Reduction of variables, when the causes or stimuli that caused their inclusion in the monitoring program have ceased, because of the retreat of some users or due to budget adjustments;

• Reduction of stations, generally obeying to financial considerations or the introduction of technological improvements.

The effectiveness of the information (E), derivable of the monitoring net can be evaluated (Schilperoort and de Groot, 1983) by a function of the sampling frequency, the number and localization of the sampling stations and the number and type of the variables to observe. The function can be derived knowing the time and spatial autocorrelation structure of each variable, and the cross-correlation structure among all the variables, also in time and spatial. This function is useful for the case of optimization of the one-dimensional variable net since it defines the relationship between a certain measure of effectiveness and the sampling frequency for fixed variables in fixed stations. The effectiveness of the information can be measured for different objectives:

• the estimation of the annual averages; • trends detection; • detection of violations in the standards of quality or exploitation, • reconstruction of the state of quality of the water as well as • the influence of the reduction of the sampling frequency on the effectiveness.

In practice, a black-box model is assumed for the correlation function, so that only the parameters have to be determined. This imposes less restrictions to the time series and facilitates the evaluation of the effect of an eventual increment in the sampling frequency. This relationship (Fig. 58) is described by means of an autoregressive first order model. For not correlated values another kind of processing is required. For decreasing intervals a limit is reached below which only values of marginal increment of effectiveness are obtained causing, therefore, an unnecessary increment of sampling but a sustained effort of basic data acquisition. As this value is high for closely correlated processes, the sampling frequency for other processes with low dynamic relationship can be reduced without remarkable loss of effectiveness. When violations of the standards of water quality or of exploitation of the ground waters, are sought to evaluate the measure of effectiveness is expressed (Schilperoort and de Groot,

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1983), like a relationship between the expected number of detected violations and the expected number of total violations. Finally, to evaluate the reconstruction of the state of quality of the waters from discreet measures during a certain period of time, E can be expressed as the half quadratic error of the reconstructed or interpolated data related with the sampling interval using the discreet form of the filter theory of Wiener-Kolmogorov. To evaluate the uncertainty of the physical properties they are especially useful, the autocorrelation functions, the semivariogram, the frequencies distribution and kriging. The autocorrelation functions characterizes the internal structure of the random processes and expresses the correlative dependence among the values of a process. The autocorrelation or the autocovariogram (Fig. 58) gives the information on the cycles within a temporary profile and, then, of the system’s memory, an equivalent to their inertial capacity regarding a stimulus as well as to the magnitude of their hydric potential.

Fig 58. Autocorrelation function of piezometric head in a karstic aquifer

Autocorrelation FunctionP22

(Standard errors are white-noise estimates)

1422. 0.0001422. 0.0001422. 0.0001422. 0.0001421. 0.0001420. 0.0001418. 0.0001416. 0.0001415. 0.0001415. 0.0001415. 0.0001414. 0.0001411. 0.0001407. 0.0001404. 0.0001399. 0.0001386. 0.0001360. 0.0001323. 0.0001275. 0.0001228. 0.0001181. 0.0001118. 0.0001028. 0.000915.6 0.000804.3 0.000704.0 0.000603.7 0.000479.1 0.000289.1 0.000 Q p

60 58 56

16 +.458 14 +.525 12 +.540 10 +.512

The periodogram and the variance spectrum (Fig. 59) allows to decompose the variance of the data in contributions on a range of frequencies. The spectral analysis consists on the decomposition of a sequence of data in sinusoidal components of different wave longitude that, added, reproduce the original series. In certain cases the analyses of cross-correlation and of cross-spectrum of variance are applied.

+.004 .0605-.027 .0610-.013 .0615

54 +.006 .0620 52 +.041 .0625 50 +.070 .0630 48 +.058 .0635 46 +.050 .0640 44 +.023 .0644 42 +.019 .0649 40 +.037 .0654 38 +.071 .0658 36 +.091 .0663 34 +.084 .0668 32 +.102 .0672 30 +.144 .0677 28 +.232 .0681 26 +.284 .0686 24 +.335 .0690 22 +.342 .0694 20 +.332 .0699 18 +.373 .0703

.0708

.0712

.0716

.0720 8 +.510 .0725 6 +.547 .0729 4 +.675 .0733 2 +.840 .0737Lag Corr. S.E.

-1 -0.5 0 0.5 1

Fig. 59. Spectral analysis of piezometric head in a karstic aquifer

Spectral analysis: P228No. of cases: 178

Hamming weights:.0357 .2411 .4464 .2411 .0357

Frequency

Spec

tral D

ensi

ty

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

The semivariogram (Fig. 60) allows examining the variance of the differences among the values of a spatial variable, measured in different stations, with the same time lag, in function of that lag. Without trend, the covariance function is the complement of the semivariogram regarding the variance.

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GROUNDWATER DEVELOPMENT AND SURVEY METHODS

L.F. Molerio-León 110

110

Fig. 60. Semivariogram types Assuming four hetereogeneity scales, one for each constituent spatial of the possible flow domains at each scale level i - it contains Neither units of the level i, and the total number of samples is N x N2 x N3 x N4, it can be carried out the analysis of variance of any physical variable including variance components of the properties of each space (solid matrix, pores, joints and caves) can be carried out. Table 1 outlines the corresponding calculation. When increasing spaces are involved, the rising increment of the relative distance among the sampling points diminishes the influence of the covariance of the different scales of heterogeneity, so that only the regional component prevails, like it is shown in Fig. 61.

The covariance function reproduces the curves of scale effect (Kiraly, 1975, 1978; Molerio, 1984a, 1988), indicating the orders of relative homogeneity (or heterogeneity) in the system and the dependence of the area rehearsed regarding the physical, real limits, of the representative elementary area of the system.

Fig 61. Covariance Function with effect of scale factor

Obdam (1983) extends such relationships to the study of the relationship cost-benefit of the monitoring net.


Table 29. Analysis of Variance. Significance test of Vi with respect to VI+1 :Vi/Vi+1 < F1-a (DGFi, DGFi+1) the case of Vi>Vi+1; for Vi+1>Vi the test is of Vi+1 with respect to Vi.Total variance is σstot2=s12+s22+s32+s42 (after Obdam, 1983)

Subdivision level

Degrees of freedom (DGF)

Squares sum Squares average (optimal

estimates)

Variance components

estimated after the squares

average 1 N1 - 1 S1= N2N3N4

Σ (xi - x)2

V1=S1/(N1-1) σ42 + N4σ3

2+ N3N4σ2

2 + N2N3N4σ1

2

2 N1 (N2 - 1) S2= N3N4 Σi Σj (xij - xi)2

V2=S2/(N1(N2-1))

σ42 + N4σ3

2+ N3N4σ2

2

3 N1 N2(N3 - 1) S3= N4 Σi Σj Σj(xijk - xij)2

V3=S3/(N1N2- (N3-1))

σ42 + N4σ3

2

4 N1N2N3 (N4 - 1) S4= N4 Σi Σj Σj Σk Σl (xijkl - xijk)2

V4=S4/(N1 N2 N3 (N4-1))

σ42

N1N2N3 N4 - 1 S= ΣI Σj Σj Σk Σl (xijkl - x)2

S/N1 N2 N3 N4-1

7.4 Selection of the Optimum Sampling Net Before proceeding to the optimization of the monitoring net, it is indispensable to validate the original conceptual model. As the net operation should have contributed to the improvement of the knowledge of the hydrological system, then the objectives of the net can be appropriately adjusted. The validation is carried out applying technical of multivariate analysis, pattern recognition, numeric classification, and, in general, of automatic generation of hypothesis. The basic approach of convergence, must be adjusted, once again, to the objectives of the net, the required information effectiveness and the available financing. The optimization has to incline to the decrease of the operation costs based in that, almost, the new net should contain fewer points and will measure fewer variables with longer time and spatial frequencies. In this sense, the convergence criteria that more frequently has shown to be enough rigorous and coherent to select the optimized Net consists in: 1. To obtain, with the Optimized Net, a piezometric configuration that doesn't oscillate in

more than 20% in gradient terms neither more than 10º in the flow direction with regard to identical periods of test with the not optimized Net.

2. That the Optimized Net show no information effectiveness loss with regard the Net in operation.

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In terms of the spatial distribution and composition of the Net, the following cases are given: 1. Net reduction; 2. Operate the current points and add other monitoring stations or 3. Eliminate some current points and add other stations. In frequency terms the following cases are given: 1. The current frequency stays in the old Net points to be conserved and in those that will be

added, or 2. The frequency of some points is varied. From the geomathematical analysis are derived which points can be eliminated and which are to be conserved. When the design characteristics are improved and to the representative wells are identified, it is possible to: 1. Improve the Hydrogeological Forecasting System 2. Improve the design of the wells that will remain in the Net and 3. Appropriately design the wells that will be incorporated. The validation process is carried out by means of different techniques of digital mapping (kriging, EOF, co-kriging, Fuzzy sets) and of conditional or not conditional simulation of the series of piezométric heads, chemical composition and quality of the waters (correlatory and spectral analysis, ARIMA, Monte Carlo, Kalman Filter, among others).

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8. MATHEMATICAL MODELLING

athematical models are a powerful tool to understand the behavior of groundwater flow systems. This understanding comprises evaluation, management, development and control of groundwater systems (Berkowitz, 1993). A groundwater model is a

replica of some real-world groundwater system (USACE, 1999). Models are characterized by:

M • An influence domain. • A set of governing laws. • A set of actions on the system. • A set of initial and boundary conditions.

Mathematical models, by means of numerical methods solves the differential flow and transport equations simulating the response of the real system to changes in the initial and boundary conditions, the governing laws or the actions on the system. Groundwater models are developed for the following purposes:

• Prediction • Identification (direct and inverse) • Management

Groundwater models are further distinguished between flow models and transport models. The first solve the differential equation for fluxes and the second solves the equations for mass transport after or simultaneously solving the correspondent flow equations. Flow models often express its results in changes in head and transport models in chemicals and pollutants concentrations in water. USEPA (1993) distinguishes the following groundwater models:

• Objective-based, like groundwater supply, well field design, parameter estimation, and education models.

• Process-based: saturated flow, unsaturated flow, contaminant transport, and flow path models.

• Physical-system-characteristics based: unconfined aquifer, confined aquifer, porous media, fractured rock, steady state, time varying, multi-layer, and regional scale models.

• Mathematical based: dimensionality of solution equations, analytical, numerical, empirical, deterministic, and stochastic models.

Models are solved analytically, by finite differences or by finite elements. Each method solves the governing equation of groundwater flow and storage differing in their approaches, assumptions and applicability to real world problems (USACE, 1993):

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8.1. Prediction models Prediction models are the most common and better-developed models. They are built and operated to predict the aquifer response to changes in recharge or pumpage. The most important flow problems solved by flow models are (Berkowitz, 1993):

• Long-term drawdown in the vicinity of a pumping well. • Long-term regional drawdown in an aquifer. • Short-term drawdown in the vicinity of a pumping well. • Short term regional drawdown in an aquifer. • Interference among pumping wells. • Reduction or increase in surface water flow and surface water levels or bodies as result

of groundwater pumping and recharge. • Changes in groundwater levels as a function of utilization of surface water sources. • Seawater encroachment as function of groundwater exploitation in coastal aquifers. • Engineering design of dams, drainage schemes, etc.

8.2. Identification models While the most common are the direct problems, v.gr. those where the input and operators are known and only response is unknown, inverse problems are also solved. Inverse problems are those where input and output are known and operators has to be identified. The most common case is the identification and/or estimation of the values of parameters and boundary conditions.

8.3. Management models These models are devoted to improve the decision-making process. They include information an stages of planning, implementation and control of policies relating to exploration, development ands exploitation of water resources. These models require rigorous formulation of management objectives and policy constraints and integrate numerical simulation models with optimization techniques (Barkowitz, 1993). Specially important are those models related with decision analysis under uncertainty. These models account for the formalization of qualitative information by fuzzy sets fully mathematically operational and also for uncertainty due to randomness and imprecision (Bogardy and Nachtenebel, 1994).

8.4. Stages in mathematical modeling The following stages are commonly recognized in mathematical modeling:

• Conceptual model. • Mathematical model. • Numerical model. • Computer code. • Calibration and sensitivity.

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Conceptual modeling is the first and most important stage. Here the most important cause-effect relations are defined, allowing the most complete qualitative description of the natural system. Im this phase the definition of the particular problem to simulate is identified and described by means of the pertinent mathematical formulation of the governing laws, initial and boundary conditions, number of spatial dimensions that will be accounted and the influence domain. Next stage is the mathematical modeling, where the above formulation is translated to an adequate representation of the flow system through the adequate mathematical partial differential equations describing mass, momentum and energy transfer, initial and boundary conditions. Usually the steady or unsteady solution alternatives are fully considered at this phase (Fig. 62). By means of the construction of the numerical model, the mathematical model is translated into numerical (finite differences, finite elements, boundary element) by the proper approximation of the continuos differential equations. Continuous variables are replaced by discrete variables and the corresponding differential equations are replaced by an adequate set of algebraic equations defining the convenient quantities at discrete points of the space discretized flow domain. The preparation of the computer code is the phase where the numerical model ins translated to computer language. This is the stage where the equations are conveniently solved and verification of the solution and model calibration is done. The verification of the solution is a basic point where the programmed computer solution is fully checked for the expected accuracy, numerical convergence and stability of the solution. The final stage is model calibration or validation. This process checks if the model reasonably satisfies its objectives, v.gr., if model predicts or identifies the intended behavior in a real groundwater system. A sensitivity analysis is often developed at this stage. In the calibration stage, model inputs, boundary conditions, system’s parameters, etc., are adjusted to achieve an adequate correspondence between simulations and the natural behavior. Calibration could be done by manual trial and error or by automated methods. Sensitivity analysis is a quantitative evaluation of the influence on model outputs from variations of model inputs (USACE, 1999) and helps the identification of inputs requiring more definition.

8.5. Mathematical formulation 8.5.1. Flow models Several general flow equations will be showed in this section.

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The general equation for three dimensional flow equation is (Peck et al, 1988):

***0 ρεβρραρ

µρ

wtP

tP

xzg

xPk

x jj

ij

i

+∂∂

+∂∂

=⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

+∂∂

∂∂

where ρ, fluid density; µ, dynamic viscosity; P, fluid presure; g, gravity acceleration; z*, elevation of the reference point above a standard datum; w*, volumetric source strength (positive for outflow and negative for inflow); ρ*, density of the source/sink fluid; α, vertical compressibility coefficient of the medium; ρ0, fluid density at a reference pressure; ε, effective porosity; β, compressibility coefficient of the fluid, xi, the Cartesian coordinates and t, time. The above equation, for two-dimensional flow in isotropic aquifers may be written:

bwthbS

xhbK

x sj

iji

*+∂∂

=⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

∂∂

or,

tHSQ

yHT

yxHT

x ∂∂

=+⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

∂∂

−⎟⎠⎞

⎜⎝⎛

∂∂

∂∂

−

where b is the saturated thickness, and the specific yield Sy for unconfined aquifers or storage coefficient S for confined aquifers is ; q, recharge; T, transmissivity; S, storage coefficient and H, aquifer thickness.

bSS s=

Fig. 62. Conceptual, mathematical and validation models

For confined conditions:

wthSb

xhT

x jij

i

+∂∂

=⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

∂∂

where w = w*b is the recharge or leakage to or from the aquifer, and the transmissivity, Tij= Kijb. For layered aquifers, the equation becomes:

( )tyxwthS

zhKB

zthT

yyhT

x zzcyyxx ,,+∂∂

=⎟⎠⎞

⎜⎝⎛

∂∂

∂∂

+⎟⎠⎞

⎜⎝⎛

∂∂

∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

∂∂

L.F. Molerio-León

116


where Bc is the thickness of the semi-confining bed and Kzz is its hydraulic conductivity. 8.5.2. Transport models Transport models (Figs. 63-64) for conservative constituents are based on a definition of the flow system that come from solution of the flow equations and the additional consideration of the mixing process due to dispersion (Peck at al., 1988; Bear, Tsang and de Marsily, 1993). The expression of the general equation for transport of a non-reactive single species driven by advection and dispersion is as follows:

*wcxcDcv

xtc

jiji

i

′−⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

−∂∂

−=∂∂ εε

where c, is the concentration of the dissolved chemical species; Dij, the coefficient of hydrodynamic dispersion; c’, the concentration of the dissolved chemical in a source or sink fluid; vi, the seepage velocity in the direction of xi, and ε, effective porosity.

Fig. 63. Simulated transport loads

Fig. 64. Cl/HCO3 ratio in an aquifer

448000 450000 452000 454000 456000 458000 460000 462000 464000 466000 468000

304000

306000

308000

310000

312000

314000

316000

318000

320000

322000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

RELACION CL/CO3H

Two-dimensional transport is:

εwcbcv

xxcbD

xtcb

ijj

iji

′−

∂∂

−⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

∂∂

−=∂

∂

Dispersion coefficients in almost every case are solved for a medium assumed isotropic (Peck at al, 1988) and only longitudinal (aL) and transverse (aT) dispersivity values are considered. After these authors, for two-dimensional transport these are

L.F. Molerio-León

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the dispersion coefficients:

vaD LL=

vaD TT =

( ) ( )

2

2

2

2

vvyD

vvxDD TLxx +=

( ) ( )

2

2

2

2

vvyD

vvxDD TLyy +=

( ) 2v

vvDDDD yx

TLyxxy −==

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9. SPECIAL SCENARIOS AND FORTHCOMING GROUNDWATER DEVELOPMENT

ater scarcity needs more and more refined techniques for surveying, exploration, development and management. Old scenarios will become in the near future, although many of them are now, highly stressed.

W Particular coincidences make situation more delicate. The growth of population in Africa, where low permeability hard rock aquifers are widely extended stressed groundwater development whilst untreated water and unprotected groundwater sources favors water resources quantity and quality depletion. Small islands and coastal zones have been always affected by salt water encroachment but, particularly in the Tropics, tourism development stresses abstraction systems and solutions for a sustainable development in these particular fragile environments requires appropriate technology for waste water treatment and reuse. Changes in water quality and quantity due to climatic changes should be bare in mind. Economic and social development in mountains, and even more in karstic mountains, diminishes water resources of downstream non-karstic environments and agricultural development, particularly in Third World countries produces downstream contamination of soil and water. The conjunctive use of surface and groundwater requires good skill but infrastructure and technology, v.gr. adequate financing. But the classical engineering (structural) measures associated to big waterworks have proved not been so efficient as it was dreamed. Big dams flooded agricultural lands and the expected productive response for food security never came. Water (groundwater) management becomes a new an important challenge whose first step is the application of adequate and in some cases, expensive, new methods for groundwater development and an improvement in non-structural measures (laws, standards, and development of local capabilities). But the legal infrastructure to be effective depends on technology. Therefore the cycle begins again and again. Forthcoming groundwater development is addressed to:

• Theoretical and practical development of well hydraulics, particularly in anisotropic, non homogeneus aquifers, v.gr. karstic and fissured non-karstic systems.

• More flexible and powerful mathematical models, particularly management models coupled with flow and transport models and to Geographical Information Systems to improve decision. The case of decision under uncertainty is particularly attractive.

• A sustained effort of technological development for waste water treatment, desalination and water reuse for irrigation and domestic purposes.

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• The application of information theory to water data will substantially improve, and it already has, water databases.

• Data logger and telemetry transmissions technology has reached unsuspected advances in quality, operational costs, amount of data and associated processing software involving more and more parameters. Portable kits have make possible, systematically, to reach remote places and gather adequate and precise information on groundwater occurrence.

• Geophysical techniques are more precise, compact and accurate and will be more in the near future.

• In its most wider sense, tracer techniques (environmental and artificial tracer hydrology) has improve and will better improve in the near future, our knowledge of arrival times of selected pollutants. In consequence, will improve water balances after knowing the position of recharge sources, turnover times and associated yields, travel time of pollutants.

• Transboundary aquifers have to be developed with adequate techniques and with an absolute respect of the rights of the people. This only can be done after the development of national capabilities.

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