Broadly the rain water can be harvested by two methods :
Any rain water harvesting will have four elements :
The choice and effectiveness of any particular method is governed by local hydrological and soil conditions and ultimate use of water. Methods of Rainwater Harvesting in Urban Cities.
Rain Water Harvesting / RWH
Need for Rain water harvesting :
Nature replenishes the ground water resources annually through rainfall; by way of infiltration though soil layers. Due to urbanization, the soil surface exposed to natural recharge gets reduced. Therefore, natural recharge is diminishing, resulting in drying of wells. Ground water source has the benefit of availability where water is needed and during emergencies and scarcity period, the public at large or NGOs should take measure to improve the ground water recharge by rain water harvesting to maintain the reliable and sustainable ground water resource for supplementary domestic and industrial needs by ground water balance use.
Rain water Harvesting Aims and Objectives & Scope :
Rainwater harvesting may be defined as process of augmenting the natural infiltration of rainwater or surface run off into the ground by some artificial methods. The methods suggested are recharge through pits, trenches, bore wells shafts by directly diverting run off water into existing or disused wells or conserving the rain water by artificial storing and using the same for human use.
Catchments area :
The catchment is the area or surface, which receives rainfall directly. It can be any surface such as paved area like a terrace or courtyard of building or an unpaved area, like Lawn or open ground. Temporary structures like sloping sheds can also act as catchment. Run-off factor determines the quantity of water which will be available from the catchment run-off factors for wooded or grassy land is very less say 10% rest is absorbed by percolation, whereas run-off factor for paved or terraced area is 70 to 80% as most of the rainwater is available for recharge or storage except for water lost due to evaporation.