ASSESSMENT OF ENVIRONMENTAL FLOW FOR A MANGROVE SWAMP ECOSYSTEM IN TAMIL NADU (INDIA)

Estuaries are areas of interaction between fresh an d salt water along the coasts. They are areas of remarkable biological productivity and div ersity. Due to anthropogenic activities like construction of dams, diversions and upstream withdrawals the amount of water that reaches the estuary viz. environmental flow undergo es many variations. This will have profound effects on estuarine conditions including changes in the hydrometeorological and hydrodynamic regimes that in turn will upset the ec ological balance. As there exist strong correlations between freshwater inflows and the sal inity gradients and between salinity and a wide variety of biological productivity, the health of the estuarine ecosystem is affected seriously. In this context, it is necessary to kno w the amount of freshwater reaches estuarine ecosystem and their natural variability by reflecti ng the monthly flow time series. This flow time series is referred to as the reference hydrolo gical time series. Pichavaram wetlands, which houses a vast diversity of mangrove species, is located in between the Vellar and Coleroon estuaries, drained by distributaries of th e Cavery River, Tamil Nadu, India. The total extent of the wetland is around 2300 ha, out of which only around 858 ha is covered by dense mangrove vegetation at present. Pichavaram receives freshwater mostly during the northeast monsoon season from October to November. In this area dry season is long, extending from February to September and correspondingly, the average salinity of the mangrove water is also high during the dry season, ranging from 35 to 45 ppt. This indicates the greater need for protecting the existing swamp and also for increasing the areal extent. This can be effected only by understanding the fact ors influencing the survival and growth of the different species, among which the quantity and quality of water flows is the most important. The paper focuses on understanding the p resent environmental flow reaching the estuary by desktop Environmental Flow Assessment (EFA) and reflecting the reference hydrological time series. And also Flow Duration Cu rves are obtained for the Coleroon river to upgrade the ecosystem to the desired Environment al Management Class.