CHENNAI: Indian Institute of Technology Madras (IIT-M) researchers who studied flooding in and around Chennai have proposed the construction of ‘straight training walls’ at the mouth of Ennore Creek in order to significantly minimize the risk upstream.
The study was commissioned by Kamarajar Port (formerly Ennore Port) in Chennai to propose solutions to reduce flooding around the banks of the Kosasthalaiyar river, said a statement from the institution on Monday. It was undertaken by K Murali, SA Sannasiraj and V Sundar from the Department of Ocean Engineering, IIT Madras.
The study focused on extreme storm surge scenarios and high tide levels along with flooding in the river. It found that heavy siltation in the creek mouth and narrow opening of the mouth posed a floodthreat to areas adjoining the river.
The study showed straight training walls at the creek mouth and regular desilting of the river will improve the situation and minimize the flood risk significantly in North Chennai. It also showed that an alternative proposal of curved training walls proposed earlier will worsen the situation by blocking the free exchange of seawater with the creek, thereby increasing the flood risk.
Sannasiraj said, “The proposal has been made to construct a pair of training walls extending perpendicular from the shore up to a water depth of -5m on either side of the creek.”
He said a straight structure with sufficient height is essential. "Further, the straight training walls would act in complement with the present series of groynes which were designed by IIT Madras for shore protection too," he said.
In the history of flooding in and around Chennai, the three creeks - Adyar, Cooum and Ennore - remain as major bottlenecks due to sand bar formation at their mouths. This results in significant flooding over the settlement along its banks, impact on coastal villages, disruption in fishing activity, industrial network on the upstream, road encroachments and illegal waste disposal.
In a well-balanced ecosystem, the mouth of the inlet should remain open and continuous exchange of water has to be ensured. Owing to the large volumes of sediments transported along the bed as well as suspended in water, such inlets act as a sediment sink resulting in sand bar formation. Like a chain reaction, the hydrodynamics are altered, the inlet stability fails and flooding on riverbanksfollows.
The comprehensive report of IIT Madras examined different possibilities of extreme event cases both from the land and sea. The studies reveal that it could lead to an overflow in the region of
elevation less than 2.71 m with respective MSL. A detailed study for the Adyar and Cooum estuaries will also be taken up for investigation by IIT Madras, the statement said.