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  Ministry Of Water Resources 
Govt. of India
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|Mandate| |Recharge|

  
 

TECHNIQUES OF ARTIFICIAL RECHARGE TO GROUND WATER

             Artificial recharge is the process by which the ground water is augmented at a rate much higher than those under natural condition of replenishment.The techniques of artificial recharge can be broadly categorized as follows:

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A.SURFACE (SPREADING) METHODS

            These methods are suitable where large area of basin is available and aquifers are unconfined without impervious layer above it. The rate of infiltration depend on nature of top soil if soil is sandy the infiltration will be higher then those of silty soil. The presence of solid suspension in water used for recharge clogs the soil pores leading to reduction in infiltration rate i.e. recharge rate. Water quality also affects the rate of infiltration. The various spreading methods are as below:-

 

1. Flooding

           This method is suitable for relatively flat topography. The water is spread as a thin sheet. It requires a system of distribution channel for the supply of water for flooding. Higher rate of vertical infiltration is obtained on areas with undisturbed vegetation and sandy soil covering.

2.Basin & Percolation Tanks

           This is the most common method for artificial recharge. In this method, water is impounded in series of basins or percolation tank. The size of basin may depend upon the topography of area, in flatter area will have large basin. The most effective depth of water in basin is 1.25 m (Baumani New York) because lesser or greater depths resulted in reduced rate of infiltration. This method is applicable in alluvial area as well as hard rock formation. The efficiency and feasibility of this method is more in hard rock formation where the rocks are highly fractured and weathered.

3. Stream Augmentation

         Seepage from natural streams or rivers is one of the most important source of recharge of the ground water reservoir. When total water supply available in a stream / river exceeds the rate of infiltration, the excess is lost as run off. This run off can be arrested through check bunds or widening the steam beds thus larger area is available to spread the river water increasing the infiltration. The site selected for check dam should have sufficient thickness of permeable bed or weathered formation to facilitate recharge of stored water within short span of time. The water stored in these structures is mostly confined to stream course and height is normally less than 2 m. To harness maximum run off, a series of such check dam may be constructed.

4. Ditch & Furrow system

         In areas with irregular topography ditches or furrow provide maximum water contact area for recharge. This technique consists of a system of shallow flat bottomed and closely spaced ditches / furrow which are used to carry water from source like stream /canals and provide more percolation opportunity. This technique required less soil preparation and is less sensitive to silting. Generally three pattern of Ditch & furrow system are adopted (i) lateral (ii) dendritic & (iii) contour. In area of low-transmissibility the density of ditch & furrow will be high.

B. SUB-SURFACE METHOD

         In this method the structure lies below the surface and recharges ground water directly. The important structures commonly use are Recharge wells, Recharge shaft, Dug wells etc.

1.Recharge Well

        Recharge wells can be of two types - (a) Injection well, where water is “pumped in” for recharge and (b) Recharge well, where water flows under gravity.

         The Injection wells are similar to a tube well. This technique is suitable for augmenting the ground water storage of deeper aquifers by “pumping in” treated surface water. These wells can be used as pumping wells during summers. The method is suitable to recharge single aquifer or multiple aquifers. The recharge through this technique is comparatively costlier and required specialized technique of tube well construction and maintenance to protect well from clogging. It is better if an abandoned tube well is used as a recharge well which will be a cost-effective structure.

         The recharge well for shallow water table aquifers up to 50 m are cost effective because recharge can take place under gravity flow only. These wells could be of two types, one is dry and another is wet. The dry types of wells have bottom of screen above the water table. In such wells excessive clogging is reported due to release of dissolved gasses as water leaves the well and on other hand redevelopment methods have not been found effective in dry type of wells. The wet type of wells are the wells in which screen is kept below water table. These wet type wells have been found more successful.

2.Pits & Shafts

         In area where impervious layer is encountered at shallow depth the pits & shafts are suitable structure for artificial recharge. These structures are cost effective to recharge the aquifer directly. The diameter of shaft should normally be more than 2 m to accommodate more water. A silt free source water can be put into recharge shaft / pit directly through pipes, if this pipe is kept above water table there are chances of choking of the aquifer by air bubble with water therefore it is always advisable to lower the injection pipe below the water level.

           On other hand in the areas where source water is having silt the shaft / pit should be filled with boulder, coarse sand from bottom to have inverted filter or the source water should be passed through a separate filter chamber before it enters the shaft / pit.

            The advantage of shafts / pits structure is that they do not require large piece of land like percolation tank & other spreading method and there are practically no losses of water in form of soil moisture and evaporation like other methods of spreading.

3 Dug wells

        In alluvial as well as hard rock areas there are thousand of dug wells have either gone dry due to considerable decline of water levels. These dug wells can be used as recharge structure storm water and other surplus water from canal etc. can be diverted into these structures to directly recharge the dried aquifer. The water for recharge should be guided through a pipe to the bottom of well to avoid entrapment of bubbles in the aquifer. The source water should be silt free.

C. INDUCED RECHARGE

        It is an indirect method of artificial recharge involving pumping from aquifer hydraulically connected with surface water such as perennial streams, unlined canal or lakes. The heavy pumping lowers the ground water level and cone of depression is created. Lowering of water levels induces the surface water to replenish the ground water. This method is effective where steam bed is connected to aquifer by sandy formation.

Basic Requirement for Artificial Recharge

        The basic requirement for recharging ground water is Source water availability. The availability of source water is basically assessed in terms of non-committed surplus monsoon run off. This component can be assessed by analysing the following:

a. Monsoon Rainfall pattern

b. Its frequency

c. Number of rainy days.

d. Maximum Rainfall in a day.

e. Its variation in space & time.

        Broadly, to calculate monsoon surplus, the 50% of monsoon rainfall (i.e., July, August and September) can be considered as monsoon run-off.

RAIN WATER HARVESTING

           The rain water in urban area can be conserved through Roof Top Rain Water Harvesting Techniques for artificial recharge to ground water. This technique requires connecting the outlet/drop pipe from roof of the building to divert the rainwater to either existing wells/ tube wells / bore well or specially designed structure.

The advantages of Rain Water Harvesting are:

1. Rainwater is bacteriologically pure, free from organic matter and soft in nature.

2.It will help in reducing the flood hazard.

3.To improve the quality of existing ground water through dilution.

4. Rainwater may be harnessed at place of need and may be utilised at time of need.

5.The structures required for harvesting the rainwater are simple, economical and eco-friendly.

  

ROOF TOP RAIN WATER HARVESTING