Why can’t we desilt our dams like others do?

The narrative in Barvi — where silt accumulation reduces the dam capacity, which is then followed by the bad choice of raising the dam’s height, causing another round of submergence of forests and displacement of villagers — is not an isolated one.

This is a story that cruelly plays out along most water sources which are dipping to unusable levels. India can no longer draw water from 81 of its most important dams and reservoirs as levels have fallen to muddy lows.

Central Water Commission data shows that dams across India have never been de-silted, leading to a decrease in their water holding capacity. Mumbai’s Upper Vaitarna reservoir’s capacity has been reduced by 22%, the capacity of Maharashtra’s biggest dam, the Koyna, has been reduced by 26.5%, while the capacity of one of India’s biggest dams and certainly its most silted, the Hirakud, has come down by 27.25%.

British engineer, Dr Rodney White, who has written Evacuation Of Sediments From Reservoirs, says “about 1,500 cubic km could be lost before the middle of the century. Intensifying climate change could hasten this loss with an increase in the severity of storms which worsen erosion.” According to him, deforestation is a major contributing factor. “The levels of erosion from hillsides planted with crops can be 150 times higher than from similar forested land.”

“To build dams, forests are cut down. This leads to erosion and silting. As the capacity reduces and demand for water rises, either the height of the dam is raised or newer dams are planned, which means more deforestation and silting. This is a vicious cycle in emerging economies where urbanisation-led migration is making the problem chronic,” he explains.

In fact, a United Nations Environment Programme (UNEP) report has expressed concerns over water wastage in developing countries since 2001. “About 60% of the water used for irrigating crops is wasted or used inefficiently, and 50% or more of the water distributed in cities is lost through leaks and poor management,” says the report, which had named India the top water waster followed by Brazil and China.  “Six thousand children die every day because of inadequate water and poor sanitation. The poorer you are, the more you have to pay for water,” it adds.

“The amount of money it costs us to clean dams and reservoirs will be enough to make a new one,” MIDC CEO Kshatrapati Shivaji told DNA. The de-silting technology which will be used here is the same that countries like Taiwan (Jhungua, Mingtan and Zengwun dams) and Italy (Punt Dal Gall and Cingino dams) have successfully used.

The Imperial Dam across the Colorado River in the US was built with three sections; the gates of each section hold back the water and help divert it towards the de-silting plant. Three giant de-silting basins and seventy-two 230 m scrapers hold and de-silt the water; the silt removed is carried away by six sludge-pipes running under the Colorado River that dump the sediment into the California sluiceway, which returns the silt to the Colorado River.