To reduce formation of sand bars
The Water Resources Department (WRD) proposes to construct groynes to reduce formation of sand bars near the mouths of Adyar, Cooum and Kosasthalaiyar rivers.
Of the three major waterways that join the sea in and around the city, Cooum river already has groynes running to a total length of nearly 250 metres. The opening between the groynes is about 170 metre and it is to facilitate tidal action. The impact of high tide bringing in sea water was felt for nearly 3 km in the river.
Officials of the WRD said Adyar and Kosasthalaiyar rivers do not have groynes. The problem of sedimentation was not severe as the Adyar's width near Thiru.Vi.Ka.bridge is nearly 480 metre that enabled tidal effect into the waterway for about four km.
However, it was essential to provide groynes to keep the river mouth open for adequate width and prevent inundation during monsoon.
Sand bars are formed due to silting near the river mouths and provision of stone groynes would help control the movement of sea water in the river. The sedimentation also caused stagnation of sewage in the waterways and resulted in breeding of mosquitoes, the officials said.
At present, the Cooum has to be periodically cleaned to prevent sand deposits. At least two machines are involved in clearing the deposits near the mouth below the Napier bridge. About 80,000 cubic metre of sand were removed in the past one year.
The National Institute of Ocean Technology (NIOT) is studying the impact of tidal effect at the Cooum and the toxic nature of the sediments. Similarly, a detailed study is under progress at the WRD's Institute of Hydraulics and Hydrology in Poondi for Adyar river.
Following the detailed report, the WRD would seek funds from the State government for the project.
The immediate concern for the authorities is the accumulation of solid waste at the mouth of the Cooum river. The waste had been washed away during the recent rains and the priority is to clear it at the earliest, officials said.