Check dams breathe life back into Delhi’s Asola wildlife sanctuary

Besides retaining rain water and preventing soil run-off, these dams help in regeneration of trees.

More than 60 check dams built by the Delhi forest department along the natural rain-fed streams at the Asola wildlife sanctuary, also called one of the green lungs of the capital, over the past year have helped improve the ecology in the area, experts and officials have said.

A view of a check dam at Asola Wildlife Sanctuary, in New Delhi.(Sanjeev Verma/HT PHOTO)

Besides retaining rain water and preventing soil run-off, these dams help in regeneration of trees. The seeds in the soil that would otherwise flow out of the forest with the rain water, are now being stored in the dams itself. These seeds will then be collected and sowed by a process called dibbling --- making shallow holes for the seeds to grow into plants, which experts believe is a more ecologically sound method of growing trees, as it allows natural regeneration of the forest, unlike mass plantation.

Check dams are small dams that are built across a water channel or a drainage ditch (depression) to counteract erosion by reducing the velocity of the flow of water. It prevents the soil from eroding during rains and allows water to be retained in the form of small pools or waterholes where wild animals can drink and bathe.

Earlier, the top soil layer along with its nutrients was lost every year during monsoon. Though there were two big dams, they did not help retain water along all the seasonal streams. Now, the rain water is being held within the dams, which is then being used for ecological purposes.

Sohail Madan, an ecologist and centre manager of the Bombay Natural History Society (BNHS) Conservation Education Centre at the Asola sanctuary, said this is the first monsoon after these small dams were introduced, and its effects arereflected in terms of regeneration of the forest. “Dibbling helps in regeneration of trees. “So far the surface run-off during the monsoon would take away all the seeds and nutrients along the top soil. As per our study of the area, now with the dams holding the water and soil, a lot of run-off has stopped. The seeds fall into the holes and grow over time. This is the most natural way of functioning for a forest,” said Madan.

He added that the streams are along critical wildlife habitats and migration routes thus helping the birds and animals to find enough water within their habitat. For instance, in between two such streams, there is the breeding ground for the painted sandgrouse, a ground-dwelling bird that is considered fairly uncommon, Madan said.

“It is crucial for wildlife habitats to have water in the vicinity. Though it will take some years for these dams to hold water all the year around, having them in place is a step in the right direction. Also, the dams are of immense help in retaining soil and moisture at a place like Asola, which has steep slopes where the water and the silt run down fast,” he said.

According to forest officials, the dam sites are being surveyed regularly to assess their impact. “These dams are built along eight seasonal streams ranging from 6km to 11km. With two good spells of rainfall received so far this month, these have been able to retain rain water to a large extent and prevent soil erosion,” said Amit Anand, deputy conservator of forest (DCF), south division.

The ongoing study by forest officials also shows an increase in the capacity of groundwater recharge. With the dams coming up, one of the streams that flowed like a waterfall outside the forest, has been able to retain water. “Now only a little water flows out while most of it is retained and seeps into the ground allowing the aquifers to recharge. This will help keep the soil moist during the dry months,” said Madan.

CR Babu, professor emeritus and head of the Centre for Environmental Management of Degraded Ecosystems (CEMDE) at Delhi University, said check dams play an important role in retaining moisture and seeds for plant growth. Some of these dams made of grass also serve as grassland habitats enriching the overall biodiversity of a forest.

“These dams are a traditional method of rain water harvesting in larger landscapes such as forests which have bigger surface drainage channels. They help in increasing the capacity of groundwater recharge and allowing the water table to rise even in the nearby areas. Some of the streams, which are deeper, serve as a water resource even during the dry season,” said Babu.