AP awaits nod from CWC to take up dewatering and resume D-wall works

VIJAYAWADA: The Andhra Pradesh government is awaiting a nod from the Central Water Commission to go ahead with its dewatering plans and resume works on the scoured portion of the diaphragm wall of the Polavaram irrigation project at Polavaram in Eluru district.

Water resources authorities are facing the biggest challenge of dewatering nearly 450 acres of work area located between both the upper and lower cofferdams to take up vibro compaction – an exercise to solidify the filled sand at scoured portions of D-wall.

Once this is done, the authorities will go ahead with the D-wall works either by constructing a new parallel wall or by taking up the construction of portions of the walls, replacing the damaged ones. Then only, the main earth-cum-rock-fill dam works will be taken up on the D-wall as it serves as a foundation.

With the Godavari river facing floods with a discharge of nearly 16 lakh cusecs of water from the Sir Arthur Cotton barrage recently, the work area was filled with water due to seepage from the coffer dams -- to the level of over 22.5 metres. It gradually came down to nearly 16 metres, with the water level in the river coming back to the normal level.

Water resources authorities have come up with two plans -- one to use a pump under rocky strata at the work area to take up dewatering through gravity. Secondly, they want to fix 10,000 hp capacity motors to pump out the remaining water.

A proposal to that effect has been sent to the CWC and to Polavaram Project Authority, seeking their approval recently. As CWC is the technical agency that studies the plans thoroughly and gives its approval based on technical feasibility, the water resources authorities are waiting for its approval to go ahead with the works.

Moreover, with backwaters from the Sir Arthur Cotton barrage, the water level at the lower cofferdam was recorded at 14 metres. The water resources authorities have no alternative other than to dewater the entire work area for taking up such works.

Meanwhile, with the Godavari river witnessing floods during every rainy season and seepage of water from both the cofferdams and natural oozing of water from the riverbed to cause work the area filled with water.

The authorities are planning to dewater the work area to ensure no interruption in regular work as they have to take up the D-wall works once its designs are approved by the CWC, the Dam Design Review Committee and other agencies. It may take a year or so to construct the D-wall.

Polavaram project superintendent engineer Narasimha Murthy said, “Once we get the permission, we will execute the plans to dewater the area and resume the works.”