Describe the methods adopted for artificial recharge of ground water Jan 2013 Dec 2013

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Describe the methods adopted for artificial recharge of ground water. (Jan-2013) (Dec- 2013)?

Describe the methods adopted for artificial recharge of ground water. (Jan-2013) (Dec- 2013)



By:Rajiv

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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.

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Shikhil

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