Rain Water Harvesting and Artificial Recharge to Ground Water

The rain water as it passes through the atmosphere; picks up dissolved gases. When it comes in contact with the earth, picks up the suspended & dissolved matter. Thus the main impurities in the water can be broadly classified as under:

What is Rain Water Harvesting:
The principle of collecting and using precipitation from a catchments surface.
An old technology is gaining popularity in a new way. Rain water harvesting is enjoying a renaissance of sorts in the world.


Artificial Recharge to Ground Water:
Artificial recharge to ground water is a process by which the ground water reservoir is augmented at a rate exceeding that obtaining under natural conditions or replenishment. Any man-made scheme or facility that adds water to an aquifer may be considered to be an artificial recharge system.

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Why Rain Water Harvesting:
It is essential because surface water is inadequate to meet our demand and we have to depend on ground water.
Due to rapid urbanization, infiltration of rain water into the sub-soil has decreased drastically and recharging of ground water has diminished.
As you read this guide, seriously consider conserving water by harvesting and managing this natural resource by artificially recharging the system.

 

Rain Water Harvesting Techniques:
There are two main techniques of rain water harvestings.
Storage of rainwater on surface for future use.
Recharge to ground water.
The storage of rain water on surface is a traditional techniques and structures used were underground tanks, ponds, check dams, weirs etc. Recharge to ground water is a new concept of rain water harvesting and the structures generally used are :-


Pits :- Recharge pits are constructed for recharging the shallow aquifer. These are constructed 1 to 2 m, wide and to 3 m. deep which are back filled with boulders, gravels, coarse sand.

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Trenches:- These are constructed when the permeable stram is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long depending up availability of water. These are back filled with filter. materials.


Dug wells:- Existing dug wells may be utilised as recharge structure and water should pass through filter media before putting into dug well.

Hand pumps :- The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Water should pass through filter media before diverting it into hand pumps.

Recharge wells :- Recharge wells of 100 to 300 mm. diameter are generally constructed for recharging the deeper aquifers and water is passed through filter media to avoid choking of recharge wells.

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Recharge Shafts :- For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are constructed and back filled with boulders, gravels & coarse sand.


Lateral shafts with bore wells :- For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon availability of water with one or two bore wells are constructed. The lateral shafts is back filled with boulders, gravels & coarse sand.

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Spreading techniques :- When permeable strata starts from top then this technique is used. Spread the water in streams/Nalas by making check dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed.
Computation of artificial recharge from Roof top rainwater collection :
Factors taken for computation :
Roof top area 100 sq.m.for individual house and 500 sq.m. for multi-storied building.
Average annual monsoon rainfall - 780 mm.
Effective annual rainfall contributing to recharge 70% - 550 mm.

 

Individual
Houses

Multistoried
building

Roof top area

100 sq. m.

500 sq. m.

Total quantity available forrecharge per annum

55 cu. m

275 cu. m.

Water available for 5 member Family

100 days

500 days

  

Benefits of Artificial Recharge in Urban Areas:

Improvement in infiltration and reduction in run-off.

Improvement in groundwater levels and yields.

Reduces strain on Special Village Panchayats/ Municipal / Municipal Corporation water supply.

Improvement in groundwater quality

Estimated quantity of additional recharge from 100 sq. m. roof top area is 55.000 liters.

 

Harvesting Rainwater Harnessing Life:
A NOBLE GOAL - A COMMON RESPONSIBILITY
Ground water exploitation is inevitable is Urban areas. But the groundwater potential is getting reduced due to urbanisation resulting in over exploitation. Hence, a strategy to implement the groundwater recharge, in a major way need to be launched with concerted efforts by various Governmental and Non-Governmental Agencies and Public at large to build up the water table and make the groundwater resource, a reliable and sustainable source for supplementing water supply needs of the urban dwellers.

 

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