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<Sourcebook of Alternative Technologies for Freshwater Augumentation in Some Countries in Asia> 3.10 Artificial Recharge of Groundwater Technical Description Artificial recharge is the planned, human activity of augmenting the amount of groundwater available through works designed 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 preserve or enhance groundwater resources, artificial recharge has been used 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 abstraction, and water quality improvement by removal of suspended solids by filtration through the ground or by dilution by mixing with naturally-occurring groundwaters (Asano, 1985). Artificial recharge also has application in wastewater disposal, waste treatment, secondary oil recovery, prevention of land subsidence, storage of freshwater within saline aquifers, crop development, 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 methods, including subsurface drainage (collectors with wells), basins with pits, shafts, and wells. (4) Indirect Recharge Techniques. Direct surface recharge techniques are among the simplest and most widely applied methods. In this method, water moves from the land surface to the aquifer by means of percolation through the soil. Most of the existing large scale artificial recharge schemes in western countries make use of this technique which typically employs infiltration basins 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 of time that water is in contact with soil are the most important (Todd, 1980). In general, these methods have relatively low construction costs and are easy to operate and maintain. Direct subsurface recharge techniques convey water directly into an aquifer. In all the methods of subsurface 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 subsurface recharge methods access deeper aquifers and require less land than the direct surface recharge methods, but are more expensive to construct and maintain. Recharge wells, commonly called injection wells, are generally used to replenish groundwater when aquifers are deep and separated from the land surface by materials of low permeability. All the subsurface methods are susceptible to clogging by suspended solids, biological activity or chemical impurities. Recharge wells have been used to dispose 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 several direct surface and subsurface techniques can be used 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 surface waterbodies (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 (or transmissivity) of the aquifer, the area and permeability 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 groundwater outflow or that create additional storage capacity. Groundwater barriers or dams have been built within river beds in many places, including India, to obstruct and detain 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 most large scale applications being found in countries such as the Netherlands, Germany, and USA (Dewan Mohamed 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 storage 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 reliable source 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 system, a thorough 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 hydraulic boundaries; the transmissivity, depth to the aquifer and lithology, storage capacity, porosity, hydraulic conductivity, and natural inflow 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 economic 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 recharge, this technology is generally implemented at the governmental level. 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 schemes. The most expensive scheme, an injection well feeding an alluvial 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).
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 cost 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 used to provide supplemental 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 must be efficiently used and effectively applied such that the net benefits 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 suitable for use in areas where aquifers exist. Typically, unconfined aquifers are recharged by surface injection methods, whereas confined aquifers are generally recharged through subsurface injection. Surface injection methods require relatively flat or gently sloping lands, while topography has little effect on subsurface recharge methods. Aquifers best suited for artificial recharge are those which can absorb and retain large quantities of water. In temperate humid climates, the alluvial areas which are best suited to artificial recharge are areas of ancient alluvium, the buried fossil river-beds and interlinked alluvial fans of their main valley and tributaries. In the arid zone, recent river alluvium may be more favourable than in humid zones. In these areas, the water table is subject to pronounced natural fluctuations. Surface recharge methods are best suited to these cases. Coastal dunes and deltaic areas are also often very favourable areas for artificial recharge schemes. Dense urban and industrial concentrations in such areas may 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 designed to accommodate expected flood flows. In contrast, shafts and wells have little storage capacity and, therefore, require a more uniform supply of water. 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 method. If suspended solids 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 important that the recharge water be chemically compatible with the aquifer material though which it flows and the naturally occurring groundwater to avoid chemical reactions that would 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 treatment system. Similarly, biological agents, such as algae and bacteria, can cause clogging of infiltration surfaces and wells, limiting the subsequent 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 feasibility of the artificial recharge of unconfined, semi-confined and confined aquifer systems. However, the most important, and somewhat elusive, issue in determining the utility of this technology is the economic and institutional aspects of artificial groundwater 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 vary substantially. 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 surface water augmentation methods, such as dams and diversions, have become more 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 situations where natural recharge has become severely reduced. Disadvantages There are a number of problems associated with the use of artificial recharge techniques. These include disadvantages related to aspects such as recovery efficiency (e.g., not all of the added water may be recoverable), cost effectiveness, 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 specific area. Cultural Acceptability Cultural considerations, stemming from socio-economic concerns, often enter into the selection of a recharge method and site. The availability of land, land uses 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 uses 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, surface spreading recharge methods. Surface recharge facilities generally require protected property boundaries, regular maintenance, and continuous surveillance if they are to be acceptable to the public. Further Development of the Technology The recharge process is extremely complex, and, due to the numerous factors affecting the process, is only partly understood. 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 of artificial 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 Professor Ashim Das Gupta, Water Engineering and Management Program, Asian Institute of Technology, Post Office Box 4, Klong Luang, Pathumthani, Bangkok, Thailand, Tel. 66 2 516 0110, Fax: 66 2 516 21 26, E-mail: remc@ait.ac.th. 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. Pitman Publishing 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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