RAINWATER HARVESTING IN WATERSHED
The watersheds of the country have different characteristics such as rainfall, soil and climate and hence cultivations are also different in different watersheds.
Based on cultivations and other requirements, the amount of water to be harvested is different. Again, as the rainfall is not perennial and it is erratic, temporal and spatial, both rainwater and run-off have to be harvested to maintain the water requirements of the watershed. Depending on the rainfall intensity, pattern, crops growth and their seasons and harvesting techniques, methods also vary from watershed to watershed and region to region.
There are both indigenous and scientific methods of water harvesting.
Based on sources of water supply, water harvesting techniques are classified into various types :
Rainwater Harvesting from Rooftop
In Situ Rainwater Harvesting
Stream Flow Run-off Harvesting
Subsurface Flow Harvesting
Harvesting for Micro Watershed
Run-off Inducement by Surface Treatment
1) Rainwater Harvesting From Rooftop :
It involves direct collection of rainwater falling on the roof or onto the ground without
passing through the stage of surface run-off on the land.The gutter efficiently collects the rainwater and discharges it to the collecting tank below as shown. It an ideal practice in regions where groundwater provision is inadequate. The rainwater is bacteriologically pure and free from organic matters. The rooftop used may be galvanized iron, asbestos sheet, clay tiles or made of concrete. The gutter should have a uniform slope of about 5%. Shape of the collecting tank may be cylindrical, square, rectangular and made of ferrocement, galvanized iron, brick masonry or concrete. It should be big enough to accommodate the annual rainfall on the roof. The tank may be overground or underground or partly overground partly underground
2) In Situ Rainwater Harvesting :
This harvesting is done by contour bunding and terracing, contour ditching graded border strips, land levelling, vegetative contour barriers, contour farming, contour trenching, cover crops and mulching and tillage and deep ploughing.
3) Run-off Harvesting :
Run-off water produced as a result of rainfall are harvested by dugout ponds or storage tanks, khadins, ahars and bundhies, havelis, diversion bunds, diversion channels, water spreading, etc.
4) Stream Flow Run-off Harvesting :
Stream or river flow run-off is harvested by check dams, bandharas or weirs, water harvesting dams and embankments, percolation tanks and ponds, water diversions and nadis.
5) Subsurface Flow Harvesting :
Subsurface water may be harvested by dams, barriers, subsurface bandharas and earth dams with diaphragms dams.
6) Harvesting for Micro Watershed :
Harvesting for micro watershed is done by interterracing, conservation bench terracing and micro plotting.
7) Run-off Inducement by Surface Treatment :
It is the process of harvesting run-off by treatment of surfaces to reduce loss of water to minimum. Surface treatment is done by metal, use of cover materials such as plastic and rubber use of chemical for waterproofing, water repelling, etc.