Delhi forest dept planning 80 check dams in Asola Bhati to check soil erosion

New Delhi: In a major move to check soil erosion and replenish groundwater levels to significantly improve vegetation in the Asola Bhati Wildlife Sanctuary here, the Delhi forest department is planning to build 80 check dams in what is considered to be the lungs of the city, officials here said on Tuesday.

During the monsoon months, the runoff from the rains cascades downhill with high velocity, washing away much of the soil and seeds into the city's drainage system.

These barriers being built by the Delhi government will inhibit the surface runoff by capturing and preventing sediment from flowing downhill along with the rainwater, Deputy Conservator of Forests (South), Amit Anand said. It will help improve soil quality, which in turn will improve vegetation, and increase the rate of groundwater recharge in the area, he said.

Spread over 4,845 acres, the sanctuary is located on the Southern Ridge, a part of the northern terminal of Aravalli Hills, one of the oldest mountain ranges in the world. It is a potential shelterbelt against desert storms and the shifting sand dunes. Also, the Southern Ridge, with an annual recharge potential of 20 million cubic metres, is capable of providing natural mineral water for the entire city.

Freed from the grip of illegal sand miners, the sanctuary is returning to its glory. But, in the absence of good soil-moisture content and silt, only small trees can grow there. "We start from the top level of the ridge and gradually go down, slowing down the rainwater enough at the top itself, assisting percolation into the soil," one official said, adding that this would allow nutrient-rich silt to be deposited from the top itself.

The forest department has planned a series of check dams on each monsoon stream. "The first of these has been completed in the forest area behind Sangam Vihar. We are planning more dams near the Neeli Jheel and Shahurpur area," Anand said. He added that if enough check dams are built, seasonal streams could possibly be turned into perennial sources of water over a period of time, which would improve soil moisture regime and groundwater table.

Sohail Madan, the centre manager of Bombay Natural History Society, which has been assisting the government in the project, said due to the steep slopes in the Asola Bhati area, the rainwater is forced downhill, often at high speeds. "So, we have identified a number of streams, some as long as nine kilometers, for the construction of check dams," he said.

Three types of check dams, gabion structures, embankments, and grass dams are being built on each stream and by the time water flows down from the gabion structure to the grass dam, its velocity is reduced substantially. "The idea is to inhibit the runoff at places, for it to percolate down in the forest only for groundwater recharge," Madan said.

"We have created grass dams at the end, so it makes a grassland. We undertook a pilot project last year, where we used lots of grass dams. A good grassland has developed because of that," he added.

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