Rainwater Harvesting Introduction

What is Rainwater Harvesting?

In a short term, RWH is the technique of collection and storage of rainwater at surface or in subsurface aquifers, before it is lost as surface run-off. The augmented resources can be harvested in the time of need.

To do this, there are certain needs which arise over the period of time -

To overcome the inadequacy of waters to meet our demands.
To arrest the decline in ground water levels.
To enhance availability of ground water at specific places and time and utilize rainwater for sustainable development.
To increase infiltration of rainwater in the subsoil which has decreased drastically in urban areas due to paving of open areas.
To improve ground water quality by dilution.
To increase agriculture production.
To improve ecology of the area by increase in vegetation cover, etc.

There are various advantages to do RWH -

Cost of recharge to subsurface reservoirs is lower than surface reservoirs.
The aquifer serves as a distribution system also.
No land is wasted for storage purposes and no population displacement is involved.
Ground water is not directly exposed to evaporation and pollution.
Storing water underground is environment friendly.
It increases the productivity of aquifers.
It reduces flood hazards.
Effects rise in ground water levels.
Mitigates the effects of drought.
Reduces soil erosion.

There are some important aspects to design a rain water harvesting system -

Hydrogeology of the area including nature and extent of aquifer, soil cover, topography, depth to water level and chemical quality of groundwater.
The availability of source water, one of the prime requisite for ground water recharge, basically assessed in terms of non-committed surplus monsoon runoff.
Area contributing run off like area available, land use pattern, industrial, residential, green belt, paved areas, roof top area etc.
Hydrometeorological characters like rainfall duration, general pattern and intensity of rainfall.

Potential Area -

Where groundwater levels are declining on a regular basis.
Where a substantial amount of aquifer has been de-saturated.
Where availability of groundwater is inadequate in lean months.
Where due to rapid urbanization, infiltration of rainwater into subsoil has decreased drastically and recharging of groundwater has diminished.

There are important methods and techniques to do RWH in urban areas -

In urban areas, rain water is available from roof tops of buildings, paved and unpaved areas goes waste. This water can be recharged to aquifer and can be utilized gainfully at the time of need. The rain water harvesting system needs to be designed in a way that it does not occupy large space for collection and recharge system. A few techniques of roof top rain water harvesting in urban areas are described below.