Malankara Dam in Kerala Loses Nearly Half Storage to Silt; Desilting Begins
The Malankara dam in Kerala's Idukki district, part of the Muvattupuzha Valley Irrigation Project (MVIP), has lost nearly half of its storage capacity to silt accumulation, according to a study conducted by the Kerala Engineering Research Institute (KERI). The findings, which were released in 2021, indicate that silt occupies 48.95% of the reservoir's total storage capacity, severely limiting the dam's ability to store water and manage downstream flows.
The dam, with a full reservoir level of 42 metres, primarily stores tailrace water discharged from the Moolamattom powerhouse, which generates electricity from the Idukki reservoir. It also receives inflows from two streams, making it a critical component in regulating water in the Thodupuzha and Muvattupuzha rivers. However, the reduced capacity has created significant challenges for MVIP officials, who must balance water storage with flood prevention during heavy rains.
An MVIP official explained that the dam's dependence on power generation at Moolamattom complicates water management. "The tailrace water and two other streams constitute the major inflows into the dam. During heavy rains, the inflow from the streams becomes uncontrollable, leading to excess water," the official said. "If water levels in the Thodupuzha and Muvattupuzha rivers are already dangerous due to rain, releasing more water from the dam can cause severe flooding." To mitigate this, MVIP has asked the Kerala State Electricity Board (KSEB) to reduce or halt power generation at Moolamattom, thereby limiting the volume of tailrace water entering the dam.
The official acknowledged that KSEB had cooperated during recent floods by keeping generation low, which helped avert a crisis. However, this approach is not always feasible. "When there is high power demand, we cannot ask KSEB to reduce or stop generation," the official added, highlighting the competing priorities of power supply and flood safety.
In response to the KERI study, MVIP has initiated a desilting project. The plan involves clearing silt from an eight-kilometre stretch upstream of the dam to Kanjar bridge. The project is expected to be completed within three years, and the contracting company will be allowed to retain the sand extracted from the reservoir as payment. This marks the first time silt is being removed since the dam was commissioned in 1994.
"Clearing the silt will restore the reservoir to a safe storage capacity level," the official said, expressing confidence that the effort will alleviate the current crisis. In the meantime, ongoing operations require careful monitoring. "Presently, five shutters of the dam are open. In recent days, these shutters have been raised and lowered to various levels to manage the low storage capacity and prevent flooding," the official noted.
The Malankara dam functions as a diversion dam, and its inflow depends largely on KSEB's power generation. Consequently, it does not operate under a strict rule curve. This makes the ongoing coordination between MVIP and KSEB essential for safeguarding downstream communities. The successful completion of the desilting project is expected to enhance the dam's operational flexibility and reduce flood risks in the region.
