Valvonti floods, a distress signal

by Nandkumar Kamat

The flash floods at night, which created a nightmarish situation for the people of Sattari and Bicholim, is natures’ warning that all is not well with the management of the catchments of the inter-state Valvonti river - an important tributary of the Mandovi river. Goa shares this river basin with Maharashtra. Valvonti, a 22-kilometre long river with tidal influence till Sanquelim town, originates near Virdi in Sawantwadi taluka and enters Goa at Shiroli. The Costi river joins it at Ghonteli, the Cudnem river at Karkhazan and the Bicholim river, which originates from Maharashra and enters Goa at Kudchirem, joins it at Karapur. By these floods the Valvonti river has sent out a distress signal.

Flood control requires an integrated understanding of hydrology and ecology of the Valvonti river basin. Controlling such floods in future needs joint monitoring and management of Valvonti’s inter-state catchments. There are natural and man-made reasons for the recent flash floods. Natural reasons may include higher rainfall intensity, bottlenecks in the silted streams feeding the tributaries and truncation of the normal flow channels. Man-made reasons could be several but the systematic destruction of the steep slopes of the Virdi hills by plantation owners in the catchment area of Valvonti is a major cause. The floods might have lasted for a few hours but the intensity and consequent damages were far greater this time than in the past. In Keri, Sattari such flash floods were experienced for the first time in 60 years, so the people were caught by surprise, especially as they took place in the night. The government thinks that longer, taller and stronger RCC embankments will control the floods. But these are of limited use if the flood water carries a heavy sediment load and acquires a higher momentum downstream. Embankments which fragment the natural flood plain could actually cause more havoc in the downstream areas.

France, England and Belgium have faced the consequences of permitting constructions on their river banks. The urban populations in these countries paid a heavy price when they reclaimed the river flood plains. People initially wanted to have a closer look of the scenic rivers. In the process large areas of the flood plains were systematically reclaimed. Hard constructions came up. Under normal precipitation conditions nothing happened. But when it poured heavily the rivers, in spate, tried to recapture their lost flood plains. Massive floods in Europe in recent times have started a debate there about the technological limits of flood control. Now the focus is to conserve and protect the natural flood plains.

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