RAINWATER AVAILABLE FOR HARVESTING Total area - 12,500 square metres (Sq m)
Average annual rainfall in Delhi - 611 millimetre (mm)
Total volume of water harvested - 6491.8 cubic metre (m³) or 64,91,875 litres
This is 85 per cent of total rainwater harvesting potential.
WATER SUPPLY SOURCE
The organisation's water requirement is fulfilled by two tubewells and is supplemented by Municipal water supply. Approximately 15,000 litres of water is used for potable and non-potable purposes.
RAINWATER HARVESTING SYSTEM
Rooftop rainwater and runoff water from paved and unpaved areas:
The rooftop rainwater from the northern portion of the UNDP building is diverted to a recharge well located near the existing borewell through a network of pipes and collection chambers. The recharge well is 2m in diameter and 3.5 m deep, with a recharge bore which is 100mm in diameter and 5m deep. The rooftop rainwater runoff from the southern part of the UNDP building is collected in a chamber and diverted to a 1m x 1m x 1m recharge well with a recharge bore of 100mm diameter and 5m deep. A layer of pebbles and sand filled inside the recharge well acts as filtering media, ensuring the quality of water being recharged.
Surface water harvesting:
Surface runoff from paved and unpaved sources and part of the rooftop rainwater are trapped by constructing recharge troughs near Gates I, III, V and VI. These troughs are 5m long, 0.7m wide and 1.5m deep. Each trough is provided with recharge bores that are 100mm in diameter and 5m deep.
Implementation of the system was completed on November 2000 and the water level on February 2003 was recorded at 9.80m below ground level (bgl).
The cost of the entire rainwater harvesting system was Rs 4 lakh.
Water level data
This project clearly showed that was possible to arrest declining water levels through rainwater harvesting. The water level at the Ford Foundation premises stood at 14.7 m below ground level (bgl) in April 2003. Concerned with the sharply declining water levels in the area, authorities of the United Nations Development Program (Ford Foundation) decided to take up rainwater harvesting in the main building.