The director of the Central Water Commission (CWC), Sharad Chandra has praised the state of Kerala for its management of dams during the retreat of the Southwest Monsoon. At the end of September or October, when the Southwest Monsoon is on retreat, the authorities release dam water if not depleted. This causes flooding, especially in the low lying areas. In 2018, Kerala had witnessed abnormally high rainfall from 1 June 2018 to 19 August 2018 leading to severe flooding in 13 out of 14 districts in the State. The state authorities opened its dams overnight and caught people in low-lying areas unaware.
“Most dam authorities tend to fill the reservoir at this time up to Full reservoir level (FRL). If they are not pre-depleted, in wake of increased rainfall and inflow, there is no space to absorb it. Awareness has been generated in recent years regarding proper reservoir operation for flood moderation. Despite large excess rainfall in southern India this year, by and large, dam releases have been done in a judicious way. Kerala really managed its dam very well,” wrote Sharad Chandra on the microblogging site Twitter.
The dams are important in India owing to wide spatial and temporal rainfall variability which affect the water availability. It becomes important to have efficient reservoir operation from flood moderation point of view.
Small dams, if built for some other purposes, cannot provide the benefits of flood moderation as they quickly fill up during high intensity of rainfall. They are as good as some detention/ retention basin.
Large dams having no dedicated flood cushion and are more vulnerable to cause downstream flooding in event of heavy rainfall. However, by evolving a proper decision support system, these dams can utilise dynamic flood cushion.
“Reservoir operation remains a challenge in India as we have made multi-purpose dams with nearly no dedicated flood cushion. But we need to realise that saving lives need to given priority even at cost of losing some power production or irrigation benefits,” wrote Sharad Chandra.
The Central Water Commission monitors the live storage status of important reservoirs in India on weekly basis. As per the CWC website, India currently has 91 reservoirs.