CHANGES IN HYDROLOGY AND COASTAL SEDIMENTATION BY DAMS

CHANGES IN HYDROLOGY AND COASTAL SEDIMENTATION BY DAMS—A CASE STUDY

Abdu Rahiman, K. U. / Dwarakish, G. S. / Kawal, Babita M.

The sustainability of coasts depends on intermittent deliveries of sediments from rivers and streams. This fluvial sediment delivery has been greatly reduced by dams, which prevent the sediment from reaching the coast and nourishing the beaches naturally. Dams alter the downstream flow system of rivers. River hydrology were mainly affected by dams, through changes in the frequency, magnitude and timing of flows, ultimately creating a hydrologic system differing significantly from the pre- impoundment natural flow system. This paper describes the effects of 15 dams in Periyar river basin, Kerala, on river hydrology and sedimentation in Cochin coast. Hydrological, river sedimentation and reservoir sedimentation analyses of Periyar river were carried out using rainfall, discharge and sediment load data collected from India Meteorological Department (IMD), Central Water Commission (CWC) and Kerala State Electricity Board (KSEB). The results show that the net runoff of Periyar river is reduced by 41 % mainly because of the impoundment of dams. The net sediment transport of Periyar river towards Cochin coast during the 25 year period was also estimated. The total quantity of sediment trapped in all the reservoirs in Periyar river was calculated, by using Brune's curves. The results showed a distinct reduction in sediment load in Periyar river mainly due to the interference of dams. The total amount of sediment trapped in all the reservoirs in Periyar river up to 2006 is estimated as 205 million tons, which is nearly 27 times the total sediment load transported by Periyar river towards Cochin coast (7.545 million tons), during the 25 year period (1978 to 2002).