Rain water harvesting & Artificial recharge of ground water

What is rain water harvesting?

In scientific terms water harvesting refers to collection, storage, preservation of water and also other activities such as harvesting surface water, extracting ground water, prevention of losses through evaporation and seepage. Rain water harvesting is capturing of rain water from where it falls or capturing the run off and keep the water clean from contamination and induced recharge of ground water. It can be undertaken in a variety of ways such as capturing run off from roof tops, from local catchments, seasonal flood waters from local streams and conservation of water through water shed management.

The Concept of 'Zero Run Off"

This is the hypothetical situation wherein there will not be any surface run off and the total rainwater is going either as underground water or lost through evaporation back to the atmosphere. Through rainwater harvesting or artificial recharge to ground minimizes the surface run off which in turn slows down the fast run off. The slow run off enables round the year availability of fresh underground water, causes dilution of underground water and prevents saline water intrusion in the off season of rains.

RWH in urban areas is relatively a new concept evolved once the underground water in urban areas reduced substantially. It was made mandatory with building permits in cities like Madras, Delhi, Jaipur etc and nowadays it is made compulsory in all new constructions in most of the states as per the directives of the ministry of urban development and subsequent amendment of the building rules of the state governments. The RWH practices in urban areas

. Provides drinking water
. Increases ground water recharge
. Reduce storm water discharges and urban floods
. Reduce overloading of sewage treatment plants
. Reduce saline water intrusion in coastal areas etc

Artificial recharge of ground water

Recharge of ground water aquifers. Design considerations

Three most important components to be evaluated for designing the rainwater harvesting structures are

. Hydrogeology of the area including nature and extent of aquifers, soil cover, topography, depth of water level and chemical quality of ground water
. The area contributing for runoff, land use and general built up pattern of the area
. Hydro meteorological characteristics such as general pattern, intensity and duration of rain fall.

Artificial Recharge Structures

a. percolation or absorption pit
b. percolation well
c. percolation well cum bore pit
d. artificial recharge through injection well