Vembanad Lake growing shallower, say researchers | Kochi News

TC.SreemolKochi: The depth of North Vembanad Lake in Ernakulam district has declined by over 50% in the last 95 years, according to a study on underwater depth of waterbodies conducted by the Kerala University of Fisheries and Ocean Studies (Kufos). Researchers surveyed a 32km stretch of the lake from Bolgatty to Munambam for the study. Experts warn that the shrinking depth has significantly reduced the lake’s water-holding capacity, leading to deteriorating water quality, weakened flow dynamics, increased risk of flash flooding and serious threats to the ecosystem and livelihoods that depend on it. The study divided the stretch into two segments: Bolgatty to Cherai and Cherai to Munambam. In the Bolgatty-Cherai stretch, the lake’s depth ranged between 3m and 4.5m in 1930. By 1983, it had dropped to 2m–2.5m, and by 2026, it further declined to just 1.2m, a reduction of more than 50% over 95 years. The Cherai-Munambam stretch recorded an average depth of 3m to 6m in 1930, which fell to 2.5m–4m by 1983, and further to an average of 1.75m by 2026. The worst depletion was recorded in the Cherai and Kuzhupilly sub-sectors, where depths have fallen to less than 1m. To conduct the study, Kufos collaborated with the state govt’s hydrographic survey wing, deploying echo-sounding apparatus to measure lake depths across the surveyed stretch. North Vembanad Lake receives water from the Periyar and Chalakudy rivers before discharging it to the sea through the Kochi and Munambam barmouths. V N Sanjeeven, professor chair, centre for aquatic resource management and conservation, Kufos, stressed the urgency of understanding the lake’s shrinkage in the context of flood risk. “The 2018 floods mostly affected people living on both sides of the Periyar and Chalakudy rivers. We need to understand how the reduction in the lake’s depth, which receives water from both rivers, will impact lives when a flood situation emerges,” he said. Sanjeeven attributed the declining depth primarily to man-made disruptions affecting water flow. Rivers naturally carry sediment into the lake, but when obstructions reduce flow velocity, sediment settles on the lakebed rather than being carried further. “Encroachments, bridges, and debris deposits accelerate sediment accumulation by restricting water flow,” he explained. Kufos now plans to extend its research to assess how much the lake’s surface area has shrunk over the same period, measure current discharge levels from the feeder rivers, and evaluate the lake’s present storage capacity. The findings are intended to help identify the reasons of flooding and propose effective mitigation measures.