Experts raise doubts over Mettur dam’s storage capacity

With the Mettur dam brimming with 120 ft of water for over a week now, the farming community in the State could not have asked for anything more.

However, opinion is quite divided among water management experts whether the dam is actually holding 93.47 thousand million cubic feet (TMC), its designed capacity.

Considering the age of Stanley Reservoir, which was commissioned in 1934, the experts are of the view that the dam has suffered a substantial amount of capacity loss.

Degree of loss

The only point of divergence is over the degree of loss. WAPCOS, a Central government agency, is said to have submitted a report to the State government quantifying the loss to be around 20%.

A. Veerappan, former special chief engineer of the Water Resources Department, said that as per his estimate, the loss would be up to 25%. A few years ago, when the State government commissioned sedimentation studies on five dams including Mettur, sections of the media had mentioned the figure at 30%.

A senior PWD official said that the report from WAPCOS was being studied, and at this stage, it was premature to comment on the extent of loss of capacity.

Another official, a long-standing observer of the Mettur dam, strongly disputed the contention that the loss could be as high as 30%. Had it been so, the current phase of heavy flows would have exposed the vulnerability, he argued, adding that the way the flows had been managed only showed that the extent of siltation was not as high as it had been made out to be.

Logistical constraints

Over the years, the PWD has not been keen on removal of silt from the dam.

The department has been of the view that considering the logistical constraints in disposing the removed silt and the cost of transportation, the whole operation may not be worth undertaking.

But Mr. Veerappan dismissed the contention. “Let the government permit highways and building contractors to remove silt at their cost. The contractors need the material for their works. So, one does not have to worry about the likely reception from them. Also, since the concentration of silt is in the middle of the dam bed, there need not be any concern about the likelihood of causing any damage. But, the government should first take a decision in principle.”

Referring to the government’s move of allowing farmers to remove silt, clay and gravel from the beds of tanks, channels and reservoirs, a PWD official confirmed that the Mettur dam had also been included in the list.

However, the amount of silt taken out from the dam bed would have been negligible to make any impact, as the farmers themselves had to make arrangements for transportation.

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