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Ground water recharge in Rural areas

In rural areas, rain water harvesting is taken up considering watershed as a unit. Surface spreading techniques are common since space for such systems is available in plenty and quantity of recharged water is also large. Following techniques may be adopted to save water going waste through slopes, rivers, rivulets and drain line

Gully plug

Gully plugs are built using local stones, clay and bushes across small gullies and streams running down the hill slopes carrying drainage to tiny catchments during rainy season.

Gully Plugs help in conservation of soil and moisture. The sites for gully plugs may be chosen whenever there is a local break in slope to permit accumulation of adequate water behind the bunds.

Contour bund

Contour bunds are effective methods to conserve soil moisture in watershed for long duration.

These are suitable in low rain fall areas where monsoon run off can be impounded by constructing bunds on the sloping ground all along the contour of equal elevation.

Flowing water is intercepted before it attains the erosive velocity by keeping suitable spacing between bunds.

Spacing between two contour bunds depends on the slope, the area and the permeability of the soil. Lesser the permeability of soil, the close should be spacing of bunds.

Contour bunding is suitable on lands with moderate slopes without involving terracing.

Gabion structure

This is a kind of check dam commonly constructed across small streams to conserve stream flows with practically no submergence beyond stream course.

A small bund across the stream is made by putting locally available boulders in a mesh of steel wires and anchored to the stream banks.

The height of such structures is around 0.5 m and is normally used in the streams with width of less than 10 m.

The excess water over flows this structure storing some water to serve as source of recharge. The silt content of stream water in due course is deposited in the interstices of the boulders. With the growth of vegetation, the bund becomes quite impermeable and helps in retaining surface water run off for sufficient time after rains to recharge the ground water body.

Ground water recharge in urban areas

In urban areas, rain water available from roof tops of buildings, paved and unpaved areas goes waste. This water can be recharged to aquifer and can be utilized gainfully at the time of need. The rain water harvesting system needs to be designed in a way that it does not occupy large space for collection and recharge system. A few techniques of roof top rain water harvesting in urban areas are described below.

Percolaiton Tank

Percolation tank is an actually created surface water body, submerging in its reservoir a highly permeable land, so that surface runoff is made to percolate and recharge the ground water storage.

Percolation tank should be constructed preferably on second to third order streams, located on highly weathered rocks, which have lateral continuity down stream.

The recharge area down stream should have sufficient number of wells and cultivable land to benefit from the augmented ground designed for storage capacity of 0.1m to 0.5 MCM. It is necessary to design the tank to provide a ponded water column generally between 3and 4.5m.

The percolation tanks are mostly earthen dams with masonry structure only for spillway. The purpose of the percolation tanks is to recharge the ground water storage and hence steepage below the seat of the bed is permissible. For dams upto 4.5 m in height, cut off trenches are not necessary and keying and benching between the dam seat and the natural ground is sufficient.