A lifeline for the residents of Ranchi, its three water reservoirs — Hatia, Kanke and Rukka dams — have two things in common. One, that they were all commissioned “as an alternate to groundwater sources” in the city, as the rocky beds render the water table unreachable at times. Second, they have lost around 10 to 20 per cent of their depth due to silting!
It’s an unbelievable but well-known fact around here that these dams have not been de-silted even once since they were commissioned. Kanke Dam, for instance, was commissioned in 1956 and is more than five decades old. The remaining two are also more than four decades old and about to expire.
Engineer-in-chief of drinking water & sanitation department Shardendu Narayan admits, “There has been neither any de-siltation of dams in Ranchi, nor have we such plans in the near future.” However, he recalls, “Once there had been direction to de-silt the Kanke Dam. But for some reason or the other, it could not be done.”
De-siltation is the process of removing suspended silt, including mud and sand, from water bodies. Non-removal of the silt in these dams has resulted in huge accumulation over the years, along with other harmful material, on the dam beds. It’s much like not brushing teeth results in a layer of plaque.
“Water in dams helps in recharging ground water over a large area since the bases of dams spread over large geographical regions. On an average, around 1-2 cm water percolates into the ground and recharges the water table. However, if silt sits on the beds of dams, percolation is blocked and hence, the water table recharge is stopped,” explains director of Ground Water Directorate SlS Jageshwar, showing how silt plays the demon in lowering the water table.
There has been no exact data on the depth of siltage in the dams, but there is apprehension that it is no less than four feet.
A retired officer who was posted at Kanke Dam during his service and has witnessed the changes dams had undergone in the last 30 years, estimates that Kanke Dam might have lost more than 6 feet of its depth to silt.
“There used to be times when water in the dam was fresh. But for a few years now, the water has developed a stench. This has happened because of decomposition of organic silt present on the beds. In past few years, the dam has been comparatively more frequented by people. They throw in plastic, edibles and leftovers, all of which affect the water adversely,” he says.
Environmentalist Nitish Priyadarshi adds, “The three dams have been commissioned more than four decades ago. The way the population has increased, even with the lowest pace of accumulation of silt, the depth of siltage will not be less than four feet.”
This year, Ranchi and all of Jharkhand is experiencing a normal monsoon, a time when the water level in dams rises. However, Jageshwar said the rise in water level is a mere spectre since dams have already lost massive storage capacity to silt.