HYDROGEOLOGY- GEOHYDROLOGY

Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers).

Hydrogeology, according to the Oxford English Dictionary, refers to the study of water at or below the earth's surface. Those who study it are hydrogeologists.

Geo-hydrology a science that deals with the character, source, and mode of occurrence of underground water. Geohydrology, according to the Merriam-Webster Dictionary, only deals with water that is below the earth's surface. Those who study it are geohydrologists.

Characteristics of rainfall that affect the amount and rate of runoff are:• intensity• depth• distribution over an area (spatial)• distribution over time (temporal).

Characteristics of rainfall that affect the amount and rate of runoff are:• intensity• depth• distribution over an area (spatial)• distribution over time (temporal).

• rainfall characteristics• catchment characteristics.

Rainfall -Precipitation• Single strongest variable driving hydrologic processes• Formed by water vapor in the atmosphere• As air cools its ability to ‘hold’ water decreases and some turns to liquid or ice (snow)

Values of Parameters for Intensity – Duration - Return Period RelationshipsThis relationship is known as Intensity – Duration – Frequency (IDF) relationship and can be expressed in the form of a formula or in the form of a graphic curve. Such a relationship can be developed by conducting an analysis of past rainfall records for this area under study.

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Hydrology.........an Introduction toGroundwater & Surface Water

Evapotranspiration: The loss water from the soil through both evaporation and transpiration from plants.Infiltration - The downward entry of water into the immediate surface of soil or other materialsPercolation -Vertical and Lateral Movement of water through the soil by gravity.Recharge: Groundwater supplies are replenished, or recharged, when water enters the saturation zone by actions like rain or snow melt.

Surface runoff: Water above the surface of the land, including lakes, rivers, streams, ponds, floodwater, and runoff.

Interflow, the water that infiltrates the soil surface and travels by means of gravity toward a stream channel (always above the main groundwater level) and eventually empties into the channel.

Groundwater flow is defined as the "...part of stream flow that has infiltrated the ground, has entered the phreatic zone.

Factors Affecting Water Movement in Soils

Surface Water – starts with

Infiltration capacity (how much rain can ground absorb before water runs off) determines what land will look like

HIGH –water sinks in LOW – water runs off

INFILTRATION

Infiltration is the term applied to the process of water entry into the soil.

If the rate of infiltration is limiting, the entire water balance in the root zone will be affected.

Infiltration Capacity- The maximum rate at which water can infiltrate into a soil under a given set of conditions.

Infiltration Rate- The rate at which water penetrates the surface of the soil and expressed in cm/hr, mm/hr, or inches/hr. The rate of infiltration is limited by the capacity of the soil and rate at which water is applied to the surface. This is a volume flux of water flowing into the profile per unit of soil surface area (expressed as velocity).

Water at various depths

Natural Recharge

NATURAL GROUND WATER RECHARGE ESTIMATION IN INDIA Chaturvedi Formula Based on the water level fluctuation and rainfall amounts (when rainfall exceeds 40cms). R = 2.0 (P - 15)*0.4 where, R = net recharge due to precipitation during the year, in inches P = annual precipitation, in inches

UP Irrigation Research Institute, Roorkee, formula is, R = 1.35 (P-14)*0.5

Amritsar formula ( rainfall between 60 and 70 cms. )R = 2.5 (P - 0.6)* 0.5 where, R & P both are measured in inches

Krishna Rao FormulaR = K (P - X) The following relation is stated to hold good for different parts of Karnataka; R = 0.20 (P - 400) for areas with P between 400 and 600mm R = 0.25 (P - 400) for areas with P between 600 and 1000mm R = 0.35 (P - 600) for areas with P above 2000mm where, R & P are expressed in millimeters

Drainage Divide separates basins

Policies need to be different for different types of drainage basins

Tributary – patterns as a result of Geology

Dendritic same rock type

Rectangular Jointed & faulted

TrellisBig stream cuts across anticline folds

RadialVolcano

Out from Center

Introduction to GroundwaterThe zone of saturation

occurs where water completely fills the open

spaces in the soil and rock.

The upper limit of this zone is called the water

table.

The zone above the water table is called the

zone of aeration.

How water gets into the zone of saturation (well

water)

Soil Formation

FACTORS AFFECTING SOIL FORMATION

1. Parent Materials (resistance, composition)2. Climate (precipitation, temperature)3. Biota (vegetation, microbes, soil fauna)4. Topography (slope, aspect, hillslope position)5. Time (period since parent material exposed)

http://www.physicalgeography.net

Silicate clays, ironoxides, aluminium oxides,and calcium carbonatesaccumulate (little organic matter)

Regolith (above bedrock)May be transported (ie., can be distinct from parent material)

Least weatheredpart of the soil profile

Good mix of mineraland organic particles (mainly mineral)

Partially decomposed organic material dominates

SOIL HORIZONS

ELUVIATION

ILLUVIATION

The exposed wall ofa soil pit or road cut is called the soil profile

E Horizonmay be present

Topsoil

•The organically-enriched A horizon at the soil surface in a cultivated soil•Most nutrient-rich portion of cultivated soils•Contains the majority of plant roots

Subsoil

•The soils that underlie the topsoil•Lower in most nutrients•Drainage properties important in determiningsusceptibility to waterlogging and soil moisture stress

SUITABLE SOILS

Particle Size Distribution

Porosity and Permeability

Porosity: volume proportion made up of voidsPermeability: connectedness of voids, dictating capacity to transmit flow

WATER MOVEMENT & SOIL STRUCTURE

Typical relationship between specific yield, specific retention, and total porosity for different soil types

A rock is an assemblage of minerals bound together

• Igneous (solidify and crystallize from molten magma)

• Sedimentary (settling)

• Metamorphic (altered under pressure)

The Rock Cycle

Igneous Structures• Flows• Veins • Dikes and Sills• Chilled or baked margins• Magmatic flow foliation• Flow tops marked by vesicles• Aa-aa vs. pahoehoe structure• Stocks and batholiths• Xenoliths or inclusions• Magmatic segregations

Sedimentary Structures• Bedding• Uncomformities• Cross bedding• Graded bedding• Ripple marks• Mud cracks

Secondary Geologic Structures develop after formation of the rock body

• Folds• Fractures and joints• Faults and breccias• Foliation and lineation• Metamorphic fabrics

like contact metamorphic aureoles and mylonitic S-C structures

Ground Water Movement in rocks

• Movement of ground water through pores and fractures is relatively slow (cms to meters/day) compared to flow of water in surface streams

– Flow velocities in cavernous limestones can be much higher (kms/day)

• Flow velocity depends upon:– Slope of the water table– Permeability of the rock or sediment

Aquifers and Aquitards

• Aquifer - body of saturated rock or sediment through which water can move easily – Sandstone– Conglomerate– Well-jointed limestone– Highly fractured rock

• Aquitard - rock/sediment that retards ground water flow due to low porosity and/or permeability

– Shale, clay, unfractured crystalline rocks

Unconfined Aquifer

Unconfined Aquifer • Has a water table, and is only partly filled with water

• Rapidly recharged by precipitation infiltrating down to the saturated zone

Confined Aquifers

• Confined Aquifer – Completely filled with water under pressure (hydrostatic head)– Separated from surface by impermeable confining layer/aquitard– Very slowly recharged

Wells• Well - a deep hole dug or drilled into the

ground to obtain water from an aquifer– Wells in unconfined aquifers, water level before pumping is the

water table– Water enters well from pore spaces within the surrounding aquifer

creating a cone of depression– Water table can be lowered by pumping, a process known as

drawdown

Insert new Fig. 11.8 here

The Water TableMaterial saturated with water lies below the

water table.

Materials that conduct water (are porous and

permeable) are aquifers.

Materials that do not conduct water (are well-cemented, unfractured, etc.) are aquicludes &

aquitards.

One inch of rain on one acre of ground results in 27,192 gallons of water (~100,000 L).

Groundwater returns to surfaceas baseflow to streams (in humid areas)

Groundwater: aquifers must be permeable and porous

• Any geologic unit through which water can move easily (i.e. it’s permeable)

• Porosity: how much water a geologic material can hold

Typical Values of Infiltration Rates

 Description Infiltration,

inches/hour

Sand and gravel mixture 0.8-1.0

Silty gravels and silty sands to inorganic silt, and well-developed loams

0.3-0.6

Silty clay sand to sandy clay 0.2-0.3

Clays, inorganic and organic 0.1-0.2

Bare rock, not highly fractured 0.0-0.1

Zones of underground water

Example Layered Aquifer System

Bedient et al., 1999.

Hydraulic Conductivity K

K represents a measure of the ability for flow through porous media:

• K is highest for gravels - 0.1 to 1 cm/sec

• K is high for sands - 10-2 to 10-3 cm/sec • K is moderate for silts - 10-4 to 10-5 cm/sec

• K is lowest for clays - 10-7 to 10-9 cm/sec

Q = K I A

K is hydraulic conductivityA is cross sectional area

I is hydraulic gradient

Groundwater Flow

BeforeRain

AfterRain &watermovesto streams

THE HOLY WATER OF ZAM ZAMAccording to Arab historians, the Zamzam Well, except for a few periods when it became dry or was buried under sand, has been in use for around 4000 years.

Structure and hydrogeology of the WellThe Zamzam Well is hand-excavated and is about 30.5 m deep, with an internal diameter ranging from 1.08 to 2.66 m. Hydrogeologically, the well lies within Wadi Ibrahim, which runs through the Holy City of Makkah, and taps groundwater from the wadi alluvium and, to a much lesser extent, the underlying fresh bedrock.

The upper 13.5 m of the well is excavated in the sandy alluvium of the Wadi Ibrahim, and the lower 17.0 m in the underlying diorite bedrock. In between lies a 0.5 m thick highly permeable weathered rock. Most of the alluvial section of the well is lined with stone masonry except for the uppermost 1m, which has a reinforced concrete collar.. The weathered rock section is lined with stone and it is this section that provides the main water entry into the well.

Research issues and objectives

Zamzam Studies and Research Center at SGS is to provide the required scientific solutions for effective monitoring and management of the aquifer feeding the Zamzam well and to ensure the purity and security of supply. The Center is currently focusing on the following aspects of management of the aquifer, the well and the Zamzam supply and distribution system:

Monitoring and managing demand to prevent depletion,Urbanization of the Wadi Ibrahim catchment and its effect on recharge,Management of storm drainage in relation to recharge,Maintaining groundwater movement and quality through building controls,Upgrading of the Zamzam pumping and storage system,Optimization of Zamzam supply and distribution,

Water balance of drainage basins

Net difference between precipitation and evaporation yields streamflow or groundwater recharge

MASS MOVEMENTS CLASSIFICATIONSpeed of movement and water flow.

On left have mass movement speed versus moisture content.On right have rates of travel for mass movements

Types of wells

Well installation methods

• Hand excavation / boring• Hand drilling

• incl augering and jetting

• Machine drilling • Rotary, percussion, down hole hammer

• Drilled wells• Reach greater depths• Penetrate wider range of rocks

CONE OF DEPRESSION

Salt water incursion in caostal aquifer

Saltwater Intrusion– upconing below cone of depression

Unconventional Measures for Source Strengthening

1. Bore-blast-technique.2. Jacket well -technique3. Stream blast- technique. 4. Fracture Seal Cementation5. Hydrofracturing to bore wells .6. Artificial recharge of bore well & dug well by flooding , Rainwater

harvesting , Rechage shaft etc.

Implemented as per location and Characteristics of the aquifers.

1.Jacket Well Technique (JW)

• Jacketing of well with the blasted bore holes increases effective diameter of the well thereby improves the storativity and transmissivity of the aquifer.

Hydrogelogical and Geophysical survey has to be carried out to know rock can be blasted to develop the cracks.

Bores are drilled in staggered pattern.

suitable explosives to be lowered in 2 to 3 sections for effective blasting.

2.Bore Blast Technique (BBT) :-

• Bore blast technique is adopted to create more storage space for groundwater in massive and crystalline hard rocks by fracturing.

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Bore Blast Technique

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Bore Blast Technique

Bore Blast Technique

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This technique is applied in areas where landforms are mostly hilly.

3. Stream Blast Technique ( SBT):-

The bores are drilled in the nala bed to a depth of open dug well.

These artificially created fractures get connected to the well and divert groundwater from nalla to the well.

Design Calculations.

• Calculate the volume of rock of each bore-hole to be fractured by blasting. • For example if,• Hard rock depth (h)= 7 meters,• Spacing between the bores = 4 meters • Radius = 2 mtrs. • Therefore volume of rock = ¶r2 x h• = 22/7 x22 x 7 = 88 m3 . • Quantity of explosives required is150 gms. per m3. • ( 0.150 Kg) • Therefore for 88 m3 rock quantity of explosive required • = 88 x 0.150 = 13.20 kgs.

The diameter of the bore-hole is 100-150 mm. Use 83 mm dia. slurry explosives (Class 2), the weight of each bag being 2.78 kg

Weathered Zone should not be charged.1.5 to 2.0 meters below the depth of weathered zone, explosive charge of 2.78 kgs. = 1 bag should be provided.Distance between two explosive charged @ section interval may be taken as 2-3 mBottom charge should be more.

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0 GL

10 m

Explosives charge2.78 Kgs

Explosives charge5.56 Kgs

Explosives charge 5.56 Kgs

Sand StemmingWeathered Zone

2 m

5 m

Hydrofracturing is a process in which pressurized water is injected into the bore well to increase the permeability of the consolidated material or a relatively impermeable unconsolidated material.

Which improves the yield of the bore well. Success ratio is about 65 %.

Hydrofracturing.

Hydrofracturing.

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HF is carried out bysealing a section ofB/w & pumping waterat high discharge rateinto the sealed offsection.So thatenormous pressure iscreated into theconfined space whichcreates the fractures.

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Line Diagram

Water Tanker

Booster PumpHigh Pressure water injection pump

(WOMA Pump)

Hydraulic Packer

HF Unit

High Pressure Hose.

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Tee

Drain valve

Pressure Gauge.

Then release outlet valve of tee to drain water under pressure in the B/w.When pressure of drainage water falls down release packers and set it to next section and repeat the process.

Schematic diagram of Reverse flow for recharge

Open well/Village tank/Percolation tank Siphon/Piping

Borewell

G.L.

Submersible pump

Siphon in action Dug well water is

recharged into the Bore well.

Siphon in action Dug well water is

recharged into the Bore well.