The Coleroon river flow and its effect on the Pichavaram mangrove ecosystem

The fresh water reaching an estuary fluctuates on many scales and the fluctuation in the flow over a time period is also due to the anthropogenic activities like construction of dams, diversions and upstream withdrawals. These fluctuations may have profound effects on the estuarine ecosystem, which usually has remarkable biological productivity and diversity. A desktop analysis is carried out by compiling historical records of discharge and other hydrological information to study the dynamics of the river Coleroon, a distributary of the Cauvery River, Tamil Nadu, India. Remote sensing analysis was carried out on images ranging from the years 1977 to 2008 and the changes in the Pichavaram mangrove areas adjoining the Coleroon were studied by comparing the results with the freshwater flow into the ecosystem. Environmental flow analysis indicates that the minimum flow needed for a healthy mangrove system in Pichavaram is 750.75 cumecs; however, this is currently achieved only 12 % of the time. The reduction in freshwater flow over the years has resulted in loss of species diversity and degradation of the mangroves; this needs to be corrected immediately to conserve the Pichavaram mangrove ecosystem.