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Rain water harvesting and ground water recharge



Background
Ground water levels in some areas are falling at the rate of one meter per year and rising in some other areas at the same rate.The major cause of this is over exploitation of the ground water.
1.The number of wells and borewells for irrigation in the country has increased five fold to 175 lakhs during past fifty years.
2. There are 25 to 30 lakh wells and borewells for drinking, domestic and industrial uses.
3. More than 80% of rural and 50% of urban; industrial and irrigation water requirements in the country are met from ground water.

This serious situation can be rectified through harvesting rain water for the purpose of ground water recharge

More than 65000 litres of rain water in Delhi can be captured and recharged from a 100 meter size roof top and meet drinking and domestic water requirement of family of four for 160 days. Central Ground Water Board implemented the first Water Harvesting and Recharge Project in 1976 in Haryana, 1980 in Gujrat and 1988 in Kerela


GROUND WATER RERSOURCES
Annually replenishable are assesed as 432 billion cubic meter (BCM). By adopting water harvesting, an additional 160 BCM shall be available for use.

Causes of fall in Ground Water Levels
1. Over exploitation or excessive pumpage either locally or over large areas to meet increasing water demands.
2. Non availability of other sources of water. Therefore, sole dependance is on ground water.
3. Unreliability of municipal water supplies both in terms of quantity and timings, driving people to their own sources,
4. Disuse of ancient means of water conservation like village ponds, baolis, percolation tanks and therefore, higher pressure on ground 5. water development.

The Effects Over Exploitation of Ground Water Resources
1 Drastic Fall in water levels in some areas.
2 Drying up of wells / borewells.
3 Enhanced use of energy.
4 Deterioration in ground water quality.
5 Ingress of sea water in coastal areas

OBJECTIVES OF RAIN WATER HARVESTING
10 Restore supplies from the aquifers depleted due to over exploitation.
2 0Improve supplies from acquifers lacking adequate recharge.
3 0Store excess water for use at subsequent times.
4 0Improve physical and chemical quality of ground water.
5 0Reduce storm water run off and soil erosion.
6 0Prevent salinity ingress in coastal areas.
7 0Increase hydrostatic pressure to prevent / stop land subsidence.
8 0Recycle urban and industrial waste waters etc.
9 0Rehabilitate the existing traditional water harvesting structures like village ponds, percolation tanks,baolis, tankas etc.
10 With minor scientific modifications and redesigning, convert the traditional water harvesting structures into ground water recharge 111facilities.
11 Use the existing defunct wells and borewells after cleaning and also the operational wells as recharge structures.

METHODS AND TECHNIQUES
1 Roof top rain water harvesting and its recharge to underground through existing wells or borewells or by constructing new wells, 1.borewells, shafts or spreading basins.
2 Capturing and recharging city storm water run-off through wells, shafts, spreading basins, storm water drains.
3 Harnessing run off in the catchments by constructing structures such as gabions, check dams, bhandaras, percolation trenches, 3..sub-surface dykes etc.
4 Impounding surplus run-off in the village catchment and watersheds in village ponds and percolation tanks.
5 Recharging treated urban and industrial effluents underground by using it for direct irrigation or through recharge ponds, basins or 5. wells, etc.

EXPECTED BENEFITS
1 1Rise in ground water levels in wells.
2 1Increased availability of water from wells.
3 1Prevent decline in water levels.
4 1Reduction in use of energy for pumping water and consequently the costs.
5 1Reduction in flood hazard and soil erosion.
6 1Benefiting in the water quality.
7 1Arresting sea water ingress.
8 1Assuring sustainability of the ground water abstraction sources and consequently the village and town water supply systems.
9 1Mitigating the effects of droughts and achieving drought prrofing.
10 Reviving the dying traditional water harvesting structures and their rehabilitation as recharge structures.
11 Effective use of lakhs of defunct wells and tubewells as recharge structures.
12 Upgradation of social and environmental status.etc

For Rain water harvesting to be successfull on a massive scale government should have some policy measures

PROPOSED POLICY MEASURES
1 Provide at least one roof top rain water harvesting structure for every 200 square meter plot in urban areas.
2 Revive / rehabilitate all village ponds.
3 Subject to technical feasibility, provide atleast one check dam / KT weir / subsurface dyke in each streamlet with a catchment of 1 1to 3 sq km.
4 Provide all drinking water wells with a recharge structure.
5 Ban construction of irrigation wells / tube wells within a distance of 200 m or less (depending on scientific criteria) of the drinking 5. water supply well.



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