Annexure 05:Water Harvesting
STANDARDS FOR RAINWATER HARVESTING SYSTEM
The storage of rain water on surface is a traditional technique and the structures used were underground tanks, ponds, check dams, weirs etc. Recharge to ground water is a new concept of rain water harvesting and the structures generally used are:
(i) Pits: Recharge pits are constructed for recharging the shallow aquifer. These are constructed 1 to 2 meter, wide and to 3 meter deep which are back filled with boulders, gravels, coarse sand.
(ii) Trenches: These are constructed when the permeable stream is available at shallow depth. Trench may be 0.5 to 1 meter wide, 1 to 1.5 meter deep and 10 to 20 meter long depending up availability of water. These are back filled with filler materials.
(iii) Dug wells: Existing dug wells may be utilized as recharge structure and water should pass through filter media before putting into dug well.
(iv) Hand pumps: The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Water should pass through filter media before diverting it into hand pumps.
(v) Recharge wells: Recharge wells of 100 to 300 mm. diameter are generally constructed for recharging the deeper aquifers and water is passed through filter media to avoid choking of recharge wells.
(vi) Recharge Shafts: For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 meter diameter and 10 to 15 meter deep are constructed and back filled with boulders, gravels and coarse sand.
(vii) Lateral shafts with bore wells: For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 meter wide and 10 to 30 meter long depending upon availability of water with one or two bore wells are constructed. The lateral shafts are back filled with boulders, gravels and coarse sand.
(viii) Spreading techniques: When permeable strata start from top then this technique is used. Spread the water in streams/Nalas by making check dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed.