Ponda: Water resources department has been planning to fill underwater ravines in Khandepar river basin with concrete cubes or blocks to protect Opa barrage. Officials fear the scouring could affect the barrage at Opa Water Works.WRD executive engineer Mario Rebello said the cubes would be placed inside the ravines with the help of synthetic mesh — geosynthetic membrane — to prevent displacement by the water current.WRD had this plan to level the river basin before the onset of the monsoon; however, the task was deferred as they couldn’t empty the river basin due to tidal water.“The work to place the cubes will start once the water current recedes,” Rebello said.He said they had prepared square concrete blocks measuring one cubic metre to place where soil inside the water basin had washed away, creating deep ravines.Soil washing away with the water current is a natural phenomenon. During monsoon, when the barrage gates are opened to release excess rainwater, the water runs with a high current, washing away river bed soil and leading to the development of the ravines, Rebello said and added that in such conditions, the concrete blocks are placed inside the ravines to level the river bed.“However, due to tidal water, the river basin couldn’t be emptied fully to place geosynthetic membrane that maintains the concrete blocks stable. Each cube weighs around 1.5 tonnes,” he said.After finding that a major part of the Khandepar river was eroded near the barrage at Opa Water Works, WRD had taken up construction of a retaining wall to prevent further erosion.A retaining wall has already been constructed along Khandepar river basin on the downstream side of Opa barrage.Rebello said they would extend the retaining wall by another 110sqm. The project has already been sent for administrative approval, he said.The tender for the earlier retaining wall and concrete blocks was allotted to Unique Construction, Quepem, at a cost of Rs 5 crore.“WRD does not open the first and last gates of the barrage during overflow in monsoon to avoid further erosion of the river bank,” Rebello said.
