A flood diversion channel could be built along Outer Ring Road and linked to Kosasthalaiyar river to reduce inundation in surrounding areas of Adyar river. This was one of the multiple flood mitigation strategies suggested for the city by the Centre for Water Resources, Anna University.
Titled ‘Investigation of multiple flood mitigation strategies for an urban catchment using semi-distributed hydrological modelling’, the study analysed various solutions for flood mitigation during extreme events. It suggested that the 25 m-wide median space of the ORR could be used to carry flood water. The new channel may intersect the Chembarambakkam surplus course near Thirumudivakkam bridge and be linked to Kosasthalaiyar river near Minjur. The natural topography of the area would allow flow by gravity.
G. Ravikumar, professor, Centre for Water Resources, who co-authored the study published in Arabian Journal of Geosciences, said the project, though expensive, would be efficient. It would help transfer about 14,000 cubic feet per second of water (cusecs) during floods and reduce the flood volume by 23.48% in Adyar river and its streams.
Waterbodies may be developed on either side of the road to harness the flood water as the channel would also ensure inter-basin water transfer from Adyar river to the Cooum and Kosasthalaiyar basins.
Different scenarios of flood control measures and its reduction of peak discharge were analysed. The peak flood discharge in the Adyar sub-basin at Tiruneermalai watershed was calibrated to be 95,000 cusecs in 2015, Mr. Ravikumar said.
Some of the other solutions offered were: increasing the capacity of the tanks such as Nemam and Manimangalam by 10% or 20%, quicker construction of Orathur reservoir and increasing greenery and construction of check-dams across minor channels.
D. Elanchezhiyan, a research scholar and co-author of the study, said the efficiency of various measures suggested depended on different factors, including land acquisition cost, extent of urbanisation and slope of the watershed. A combination of flood mitigation works, be it better green cover, Orathur reservoir and new channel, would help in reducing the floods by a minimum of 34.07%.
While mitigation of extreme flood events was hydrologically possible, there might be constraints such as lack of undeveloped areas to execute projects. Proper flood management policies need to be in place, he added.
