By Gaurav Saini
New Delhi, Aug 4 (PTI) The Delhi forest department is building 80 check dams in Asola Bhati Wildlife Sanctuary to check soil erosion and replenish groundwater levels to improve vegetation in an area considered the lungs of the city, officials said Tuesday.
During monsoon, when it rains, the runoff cascades down with high speed, taking soil and seeds along into the city's drains. The barriers will inhibit the surface runoff by capturing and preventing sediment from flowing downhill, 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 considered the lungs of Delhi and 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, could provide 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," the official said.
"It means that the nutrient-rich silt will start depositing from the top itself," he said.
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.
"If we are able to create enough check dams, we can turn these seasonal streams into perennial sources of water over a period of time, improving soil moisture regime and groundwater table," he said.
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 Asola Bhati area, the rainwater doesn't stay at one place and flows down rapidly into the sewage.
“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.
“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 said. PTI GVS ABH