SUSTAINABILITY OF AN ARTIFICIALLY RECHARGED AQUIFER THROUGH RAINWATER HARVESTING IN INDIA

Dr. S.K. Sharma, GRI, 24 National Road, Dehradun 248001, India E-mail : [email protected]

Abstract: About 85% of rural and 55% of urban India's drinking water needs are met from ground water but indiscriminate pumping of water from deep aquifers is leading to rapid depletion of ground water resources in the country. It is in this context that the roof top rain water harvesting in India assumes an importance for artificially augmenting the recharge. A scheme to recharge the part of urban area of Delhi, the capital city of India, where the natural recharge to ground water is very low and the water table is registering a continuous decline with time due to increased urbanization, is conceptualized, implemented and presented in the paper. The surplus run-off generated during monsoon which otherwise is lost to flow is proposed to be conserved through roof top rain water harvesting technique involving the connection of outlet pipe from rooftop of a dwelling site in Kishangarh in East Delhi having 150 sq. m. roof top area to divert collected water to dug well to augment the existing ground water level thus raising the water table level by artificial recharge. Except for the initial capital outlay and creating additional surface installations like settling tanks for silt removal and chlorination / UV radiation treatment plants to meeting the acceptable standards of potable water, the scheme of roof-top rain water harvesting for augmenting ground water storage is feasible, eco-friendly and beneficial. Key Words: Rain water, Harvesting, Ground water, Aquifer, Dry Season

In many parts of Delhi including Kishangarh, increasing population and limited water resources require more storage of water for potable purposes.

Unit configuration The water table in Kishangarh is found to be at 5.5m in the hand pump of the dwelling unit which goes further down to about 7.0 m or beyond during dry season. Given that the building has 1 50 sq. m. of roof top area, a recharge trenches of 4 m long, 3 m wide and 3 m deep called "collection and filtration pit" is constructed in the same campus of dwelling unit (Figure 2). The trench is filled with boulders at the bottom followed by pebbles and sand at the top This infiltration pit is directly connected to the existing bore well. The roof-top rain water is channelled through 10 cm diameter pipe to the existing bore hole of the hand pump which is used here to act as the recharge shaft that ends into the aquifer under gravity flow conditions through collection and filtration pit (to make it silt free) and recharge pit.

Results During monsoon period of June to August, 2001, the scheme was put to use and it was observed that the hand pump which used to remain dry even after the monsoon period started flowing in the month of September, indicating a rise in the water level of the aquifer. This option of roof-top rain water harvesting is found to be the most appropriate for augmenting local groundwater level in the dwelling unit of congested Kishangarh residential area in East Delhi as the recharge in the area is considerably reduced due to increased urban activities and not much of land is available for implementing any other artificial recharge measure. The structure of trenches and the pipes for conserving rain water are simple, economical and eco-friendly. It requires only one time large investment and subsequently with proper maintenance, the entire system can run forever. Such local initiatives have reduced the dependence on imported water.

Benefits/ Drawbacks The following benefits are accrued from the scheme 1. Limited additional regular water supply in the area during dry season. 2. Land surface, installations and working entirely unaffected. 3. The basic infrastructure is expected to last indefinitely and is suitable for any further expansion. 4. However, the only drawback or short coming is that it attracts large initial capital expenditure and requires additional surface installations for chlorination / UV radiation treatment plants for making the collected water acceptable standard potable water. In addition, collection and filtration pit also requires periodical cleaning after rainy season.

Conclusions and recommendations Based on the available hydrogeological conditions and data, the roof-top rain water conservation through injection technique is found to be most suitable in the present site of investigation at Kishangarh in East Delhi where land availability was limited due to very high population density and the aquifer was deep and overlain by the impermeable strata. The water level depletion during summer is very common problem throughout the country specially the mega cities with rapid urbanization like New Delhi, the capital city of India. With encouraging results from the present experimentation, it is recommended that the scheme be extended for implementation in Group Housing Societies where large rooftop surface area will be available to conserve rain water so that it could be tapped judiciously when needed. It is need of the hour as well as the Government before we reach the last drop of the water.