The prime importance in the Rain Water Harvesting is the identification and selection of suitable sites for the artificial recharge project. The site is selected depending upon the local topographic, geological and soil conditions. Obviously the basic requirement is the maximum percolation rate of the surface water and sustenance of recharged water in the ground water bodies and aquifers.

In unconsolidated formation, it needs the presence of unsaturated/partially saturated formation or top granular zone suitable for percolation, whereas in hard rock terrain, the surface water percolation depends on the presence of weathered or highly fractured rock system with appreciable thickness of unsaturated portion at the top.

A successful infiltration recharge system needs following aspects to consider:

Surface soil must be sufficiently permeable to maintain high infiltration rate Vadose zone must be permeable and free from clay layers or other fine materials that could restrict downward flow of water. Aquifer must be unconfined, permeable and thick enough to avoid excess amount of ground water mounts There should be sufficient unpolluted surface water supply for percolation tanks.

The selection of recharge site involves the consideration of following:

Availability of land and topography Hydrological condition Possible source of water for recharge Operational maintenance Economic consideration

The underground dams have following advantages over the surface dam structures:

No evaporation from storage takes place No siltation in the reservoir takes place The potential disaster like collapse of dam is not there