INFLUENCE OF SALTWATER BARRAGE ON TIDES, SALINITY AND CHLOROPHYLL a IN

Thanneermukkam Barrage is constructed in the southern arm of Cochin estuary. It prevents salt intrusion to further upstream and regulates river discharge downstream. The characteristics of the estuary when the barrage was opened and closed are discussed. The analysis showed that the closure of the barrage caused amplification of tides in the immediate vicinity and up to 10 km farther downstream. When barrage was closed, the northern region of TB transformed from ebb dominant system into a flood dominant system. During high discharge period, the barrage was opened and salinity intrusion was exponentially dependent on river discharge. During dry period, the reduction in river flow compounded with the closure of barrage resulted in the increase of salinity concentration downstream. While the oceanic salinity was observed at ocean-end station, about 13 occurred at the river-end station when the barrage was closed. The hydrodynamic control on phytoplankton biomass was also evident. Higher surface chlorophyll a levels were observed at higher salinity during the barrage closed period and the residence time was estimated for 4 days during this period.