sourcebook of alternative technologies for freshwater augumentation in some countries in asia

8/13/2019 Sourcebook of Alternative Technologies for Freshwater Augumentation in Some Countries in Asia

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12/8/13 Sourcebook of Al ternative Technolog ies for Freshwater Augumentation in Some Countr ies in Asia

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3.10 Artificial Recharge of Groundwater

Technical Description

Artificial recharge is the planned, human activity of augm enting the amount of

groundwater available through works des igned to increase the natural

replenishment or percolation of surface waters into the groundwater aquifers,

resulting in a corresponding increase in the amount of groundwater available

for abstraction. Although the primary objective of this technology is to pres erveor enhance groundwater resources, artificial recharge has been us ed for many

other beneficial purposes . Some of these purposes include conservation or

disposal of floodwaters, control of saltwater intrusion, storage of water to

reduce pumping and piping costs, temporary regulation of groundwater

abs traction, and water quality improvement by removal of suspended solids byfiltration through the ground or by dilution by mixing with naturally-occurring

groundwaters (Asano, 1985). Artificial recharge also has application in

was tewater dispos al, waste treatment, secondary oil recovery,prevention of

land subsidence, storage of freshwater within saline aquifers,cropdevelopment, and streamflow augmentation (Oaksford, 1985).

A variety of methods have been developed and applied to artificially recharge

groundwater reservoirs in various parts of the world. Details of these methods,as well as related topics, can be found in the literature (e.g., Todd, 1980;

Huisman and Olsthoorn, 1983; Asano, 1985; CGWB, 1994). The methods may

be generally classified in the following four categories (Oaksford, 1985):

(1) Direct Surface Recharge Technique (ASANO, 1985).

(2) Direct Subsurface Recharge Technique.

(3) Combination surface-subsurface m ethods, including subsurface drainage(collectors with wells), basins with pits, shafts, and wells.

(4) Indirect Recharge Techniques.

Direct surface recharge techniques are among the simples t and mos t widely

applied methods. In this method, water moves from the landsurface to the

aquifer by means of percolation through the soi l. Most of the existing large scale

artificial recharge schemes in wes tern countries m ake use of this techniquewhich typically employs infiltration bas ins to enhance the natural percolation of

water into the subsurface (Dewan Mohamed et al., 1983). Field studies of

spreading techniques have shown that, of the many factors governing the

amount of water that will enter the aquifer, the area of recharge and length oftime that water is in contact with soil are the most important (Todd, 1980). In

general, these methods have relatively low cons truction cos ts and are easy to

operate and maintain. Direct subsurface recharge techniques convey water

directly into an aquifer. In all the m ethods of subs urface recharge, the quality of

the recharged water is of primary concern. Recharged water enters the aquifer

without the filtration and oxidation that occurs when water percolates naturally

through the unsaturated zone.

Direct subs urface recharge methods access deeper aquifers and require less

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an t an t e rect sur ace rec arge met o s, ut are more expens ve toconstruct and maintain. Recharge wells, commonly called injection wells, are

generally used to replenish groundwater when aquifers are deep and

separated from the land s urface by materials of low permeability. All the

subs urface methods are sus ceptible to clogging by suspended solids ,

biological activity or chemical impurities. Recharge wells have been used todispose of treated industrial wastewaters, to add freshwater to coastal aquifers

experiencing saltwater intrusion, and to force water under pressure into

permeable bedrock aquifers to arrest land subsidence resulting from extensive

withdrawals of groundwater, although with variable success (CGWB, 1994). In

many places, including the United States, Japan and Thailand, the use of

injection wells is still considered experimental (Dewan Mohamed et al., 1983).

Combinations of s everal direct surface and subs urface techniques can be us ed

in conjunction with one another to meet specific recharge needs.

Indirect methods of artificial recharge include the installation of groundwater

pumping facilities or infiltration galleries near hydraulically-connected surfacewaterbodies (such as streams or lakes) to lower groundwater levels and

induce infiltration elsewhere in the drainage basin, and modification of aquifers

or construction of new aquifers to enhance or create groundwater reserves. The

effectiveness of the former, induced recharge method depends upon the

number and proximity of surface waterbodies, the hydraulic conductivity (ortransmiss ivity) of the aquifer, the area and perm eability of the streambed or lake

bottom, and the hydraulic gradient created by pumping. Using the latter

technique, aquifers can be modified by structures that impede groundwateroutflow or that create additional s torage capacity. Groundwater barriers or dams

have been built within river beds in many places , including India, to obstruct anddetain groundwater flows so as to sustain the storage capacity of the aquifer

and meet water demands during periods of greatest need. Construction of

complete small-scale aquifers also seems feasible (Helweg and Smith, 1978).

Notwithstanding, indirect methods generally provide less control over the

quantity and quality of the water than do the direct methods.

Extent of Use

The concept of artificial recharge has been known for a long time. The practice

began in Europe during the early nineteenth century. However, the practice has

rarely been adopted on a large scale, with mos t large scale applications being

found in countries such as the Netherlands, Germany, and USA (DewanMohamed et al., 1983). Israel transports 300 million cubic metres of water

annually from north to south through the National Water Carrier System and

stores two-thirds of it underground (Ambroggi, 1977). The water is used to meet

high summer demands and offers a reliable source of supply during dry years.On the North Plain of China, which is prone to droughts, water from nearby

streams is diverted into underground s torage areas with capacities of about

500 million cubic metres. Several counties in Hebei Province are using

artificially recharged aquifers to combat sinking water tables (Widstrand, 1978).

In India, subsurface storage has caught on as a way of providing a reliablesource of irrigation water. A number of artificial recharge projects have been

carried out in that country (CGWB, 1994) (see Case Studies, Chapter 5).

Operation and Maintenance

To ensure the effective and efficient operation of an artificial recharge s ystem, athorough and detailed hydrogeological study must be conducted before

selecting the site and method of recharge. In particular, the following basic

factors should be considered: the locations of geologic and hydraulicboundaries; the transm iss ivity, depth to the aqui fer and lithology, storage

capacity, poros ity, hydraulic conductivity, and natural in flow and outflow of water

to the aquifer; the availability of land, surrounding land use and topography; the

quality and quantity of water to be recharged; the econom ic and legal aspects

governing recharge; and the level of public acceptance.

Level of Involvement

Because of the technical complexity involved in siting and regulating artificial


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, .

Costs

Rushton and Phadtare (1989) describe artificial recharge pilot projects in both

alluvial and limestone aquifers in Mehsana area of Gujarat, India. Recharge

was accomplished using spreading channels, percolation tanks and injection

wells. Table 11 presents a summary of the initial and operational costs for the

various s chemes. The m ost expensive scheme, an injection well feeding analluvial aquifer, had initial and operating costs per unit volume of recharged

water of $100/m3.

TABLE 11. Costs of Various Artificial Recharge Schemes in India ($/m3).

Artificial Recharge

StructureInitial Cost Running Cost

Injection well (alluvial area) 100 100

Spreading Channel

(alluvial area)9 10

Percolation Tank (alluvial

area)2 7

Injection well (limestone

area)6 21

Spreading Channel(limestone area) 7 6

It is apparent from Table 11 that injection wells in hard rock areas are less

expensive since they tend to be shallower and have a lesser risks of clogging.Percolation tanks appeared to be least expensive in terms of initial construction

costs; this would be the case in areas where the tanks already exist. In such

cases, the initial cos t only involves the cleaning of the bed of the tank. For

economic reasons, the main uses of artificially recharged water are likely to be

providing water for domestic needs, industry and environmental conservation.Because of its relatively high cost, recharged water is not generally suited for

irrigation for a total crop, but it can be us ed to provide supplem ental irrigation

water for rain-fed crops or to provide additional water to crops at a crucial growth

stage during periods of water shortage. As a general rule in this regard,

groundwater mus t be efficiently used and effectively applied such that the netbenefits from its use are maximized over time. Guidelines for the socio-

economic and financial appraisal of artificial recharge projects in developing

countries, necessary to assess these net benefits, are provided by CGWB

(1994).

Suitability

Groundwater recharge methods are s uitable for use in areas where aquifers

exist. Typically, unconfined aquifers are recharged by surface injection m ethods,

whereas confined aqu ifers are generally recharged through subs urface

injection. Surface injection methods require relatively flat or gently sloping

lands, while topography has little effect on subsurface recharge methods.

Aquifers bes t suited for artificial recharge are those which can absorb and

retain large quantities of water. In temperate humid climates, the alluvial areaswhich are bes t suited to artificial recharge are areas of ancient alluvium, the

buried fossil river-beds and interlinked alluvial fans of their main valley andtributaries. In the arid zone, recent river alluvium m ay be more favourable than in

humid zones. In these areas, the water table is subject to pronounced natural

fluctuations. Surface recharge methods are best s uited to these cases . Coastal

dunes and deltaic areas are als o often very favourable areas for artificial

recharge schemes. Dens e urban and industrial concentrations in such areasmay render artificial recharge schemes desirable, generally using subsurface

recharge wells to inject surface water into the aquifers.

When the quantity and availability of recharge water is highly variable, such as in

an intermittent stream, any of the surface application methods are suitable.

Basin and pit techniques have the greatest advantages because they can be


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es gne o accommo a e expec e oo ows . n con ras , s a s an we s

have little s torage capacity and, therefore, require a more uniform supply ofwater. Indirect methods, such as induced recharge, are virtually unaffected by

changes in surface water flows because the rate of recharge is controlled by

extraction rates (Oaksford, 1985).

The physical, chemical and biological quality of recharge water also affects the

selection of recharge m ethod. If suspended s olids are present, surface

application techniques tend to be more efficient than subsurface techniques

where they can result in clogging of injection wells. It is also im portant that therecharge water be chemically compatible with the aquifer material though which

it flows and the naturally occurring groundwater to avoid chem ical reactions thatwould reduce aquifer porosity and recharge capacity. Toxic substances must

not be present in the recharge water unless they can be removed by

pretreatment or chemically decomposed by a suitable land or aquifer treatmentsystem. Similarly, biological agents, such as algae and bacteria, can cause

clogging of infiltration surfaces and wells , limiting the subs equent use of the

recharged water.

Effectiveness of the Technology

Various artificial recharge experiments have been carried out in India by

different organizations, and have established the technical feas ibility of the

artificial recharge of unconfined, semi-confined and confined aquifer systems.

However, the m ost important, and somewhat elusive, iss ue in determining the

utility of this technology is the economic and ins titutional as pects of artificialgroundwater recharge. Experiences with full-scale artificial recharge operations

in India and elsewhere in Asia are limited. As a consequence, cost information

from such operations is incomplete. The available data, from certain

hydrological environs in which recharge experiments have been initiated and/or

are in progress, suggest that the cost of groundwater recharge can varysubstantially. These costs are a function of availability of source water,

conveyance facilities, civil constructions, land, and groundwater pumping and

monitoring facilities (CGWB, 1994).

Advantages

As s urface water augm entation methods, such as dam s and divers ions , havebecome m ore expensive and less promising in terms of environmental

considerations, the prospects of storing surplus surface water underground

and abstracting it whenever and wherever necessary appears to be more

effective technology. In urban areas, artificial recharge can maintain

groundwater levels in s ituations where natural recharge has become s everelyreduced.

Disadvantages

There are a num ber of problems ass ociated with the use of artificial recharge

techniques. These include disadvantages related to as pects such as recoveryefficiency (e.g., not all of the added water may be recoverable), cost

effectivenes s, contamination risks due to injection of recharge water of poor

quality, clogging of aquifers, and a lack of knowledge about the long term

implications of the recharge process. Hence, careful consideration should be

given to the selection of an appropriate site for artificial recharge in a s pecificarea.

Cultural Acceptability

Cultural considerations, s temming from socio-economic concerns, often enter

into the selection of a recharge method and site. The availability of land, landuses in adjacent areas, public attitudes, and legal requirements generally play

a role in defining the acceptability of artificial recharge in a given setting. In

urban areas, where land availability, costs and us es in adjacent areas may

pose restrictions, injection wells, shafts or small pits requiring highly controlled

water supplies and little land area may be preferable to larger scale, surfacespreading recharge methods. Surface recharge facilities generally require

protected property boundaries, regular maintenance, and continuous


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.

Further Development of the Technology

The recharge process is extremely complex, and, due to the numerous factors

affecting the process, is only partly unders tood. The studies on artificial

recharge techniques are mostly site-specific and descriptive in nature, which

gives little insight into the potential success of implementing this technology in

other locations. Thus, there is a need for further research and development ofartificial recharge techniques for a variety of conditions . In addition, the

economic, managerial and institutional aspects of artificial recharge projects

need to be studied further.

Information Sources

Contacts

ProfessorAshim Das Gupta, Water Engineering and Management Program,

Asian Ins titute of Technology, Post Office Box 4, Klong Luang, Pathumthani,Bangkok, Thailand, Tel. 66 2 516 0110, Fax: 66 2 516 21 26, E-mail :

[email protected].

Bibliography

Ambroggi, R.P. 1977. Underground Reservoirs to Control the Water Cycle,

Scientific American, 236(5):21-27.

Asano, T. 1985.Artificial Recharge of Groundwater. Butterworth Publishers,Boston, 767 pp.

CGWB (Central Ground Water Board) 1994. Manual on Artificial Recharge of

Ground Water. Technical Series-M, No. 3. Ministry of Water Resources,

Government of India, 215 pp.

Helweg, O.J. and G. Smith 1978. Appropriate Technology for Artificial Aquifers.

Groundwater, 16(3):144-148.

Huisman, L. and T.N. Olsthoorn 1983.Artificial Groundwater Recharge. PitmanPublishing Inc., Massachusetts, 320 pp.

Oaksford, E.T. 1985. Artificial Recharge: Methods , Hydraulics, and Monitoring,

In:Artificial Recharge of Groundwater, T. Asamo, editor. Butterworth Publishers,Boston, pp. 69-127.

Rushton, K.R. and P.N. Phadtare 1989. Artificial Recharge Pilot Projects in

Gujarat, India, In: Groundwater Management: Quantity and Quality, IAHS

Publication No. 188, pp. 533-545.

Todd, D.K. 1980. Groundwater Hydrology. Second Edition. John Wiley & Sons,

New York, 535 pp.

Widstrand, C. (Editor) 1978.The Social and Ecological Effects of Water

Development in Developing Countries. Pergamon Press, New York.

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