The Central Water Commission (CWC) has unearthed a significant finding regarding the severe Kerala floods that took place. The Vembanad Lake, despite being the largest lake in Kerala, was found to have contributed to the severity of the floods due to its congested carrying capacity. The Lake could only absorb a fraction of the water flowing into it from overflowing rivers, resulting in extensive damages, especially in districts like Kottayam and Allapuzha.
Limited Absorbency of the Vembanad Lake
Although the Vembanad Lake is the largest lake in Kerala, it could only absorb 0.6 billion cubic meters (BCM) out of 1.63 BCM of water caused by excessive rainfall. This resulted in 480 sq km of area being inundated as the lake expanded to nearly three times its original size.
Reasons for the Limited Capacity of the Lake
Certain factors were identified to be the reasons behind the reduced capacity of the lake. Firstly, siltation, a natural process, might have reduced the lake’s volume. Dredging, which could reduce siltation, was not allowed since the lake is situated in an eco-sensitive zone. Secondly, Vembanad being a coastal lake interacts with the backwaters. This interaction may have led to backflow as the outlet was unable to discharge the substantial water flow into the ocean. Lastly, high rainfall and lack of reservoirs in the upper reaches of the rivers draining into the lake also exacerbated the flooding.
Role of the Dams in the Flood
The CWC attributed the intense rainfall during August as the primary cause of the floods. It pointed out that the dams neither mitigated nor aggravated the floods. However, it was noted that the Idukki dam functioned as a flood cushion by absorbing much of the runoff. This resulted in a lesser outflow from the dam during the intense spells of rainfall.
Recommendations for Future Flood Management
Various recommendations were made to manage potential floods in the future. These include:
1. Increasing the capacity of the spillways through which rivers such as Pamba, Manimala, Achenkovil, and Meenachil drain into the lake.
2. Reviewing rule curves for reservoirs based on historical data, to determine the water release each month over the monsoon period.
3. Applying the Reservoir Regulation Procedure (Rule Curve), which governs the storage and release functions of a reservoir.
A Note on the Central Water Commission (CWC)
The CWC is the primary technical organisation in India dedicated to the development of water resources. It is an attached organisation of the Ministry of Water Resources and is responsible for initiating schemes for control, conservation, development, and utilization of water resources across the nation. These schemes cater to various needs such as irrigation, flood management, power generation, navigation, and more. The CWC works in consultation with State Governments to ensure effective water resource management across the country.