Rainwater harvesting is the art and science of collection and productive utilization
of runoff from rooftops and ground surfaces as well as from intermittent
watercourses. Rainwater harvesting, though an old-age practice, is emerging as a new paradigm
in water resource development and management due to the recent efforts of both
government and non-governmental organizations to promote water harvesting and
groundwater recharge in urban and rural areas.
The principle of rainwater harvesting is to conserve rainwater where it falls
according to the needs and geophysical conditions. Benefits of rainwater are lost if the
runoff-stored water is not properly recycled and efficiently utilized. In-situ water conservation is a more feasible and practical proposition under most situations. The amount and
effectiveness of in-situ water conservation is a function of an interaction between the climate, soil
and plant properties. In-situ rainwater harvesting can be achieved by increasing in the
filtration rate with the help of deep ploughing, profile modifications, vertical mulching,
keeping soil surface rough, contour cultivation, inter terrace land treatments, etc., thereby
allowing more infiltration opportunity time. In-situ moisture conservation measures include
graded bund, drop structures, contour trench, staggered trench, catch pit, V-ditch, jalkund, micro catchments, slanting trench, tick ditch, pits with crescent bunds and pitcher
irrigation systems.
The ex-situ rainwater harvesting technologies include roof top collection, dug
out ponds, storage tanks, nala bunding, gully control structure/check
dams/bandharas (weirs), water harvesting dams, percolation tanks/ponds, subsurface dams/barriers, etc.
Having said so, these technologies are highly location-specific, and practices appropriate for
a particular region may have a limited application on other regions. In areas, where
soils are heavy in texture with low infiltration rate and land slope ranges from 0.5 to 2%
with erratic rainfall distribution, dugout type of water harvesting structure has
been recommended. Small gullies are plugged by stone plugs with height usually not
exceeding 1.2 m slope of nearly vertical in upstream and 1:4 in downstream for temporary
water harvesting. In areas with crystalline rocks, percolation tanks may be constructed to
raise water table. Appropriate technology in terms of catchment area, volume of storage
and capital investment for the region need to be refined/modified, incorporating
indigenous experience/technology to suit the local needs. |
