Flushing characteristics and pollution assessment of Purna River Estuary

Abstract

Tide dominated coastal plain Purna River Estuary was studied to evaluate its flushing characteristics and pollution status. The shallow estuary was generally well-mixed vertically with excellent flushing due to high seawater influx and strong tidal currents. The flushing time of < 2.5 tidal cycles, based on fraction of freshwater method, indicated that the load retained in the estuary after infinite number of tidal cycles was only 0.4 to 1.2 times the load introduced per tidal cycle. Although, spring tidal range of 1.5 m was observed at 30 km inland, the seawater component here at high tide was < 1%. The estuarine zone was characterised by high and variable suspended load due to the dispersion of bottom sediment into the water column by strong tidal currents. The wastewater streams entering the estuary were sampled periodically to quantify the pollution loads. Nutrients, <i>p</i>H and trace metal concentrations in water did not seem to have been grossly affected by the present wastewater inputs. Some influence was however observed on the dissolved oxygen content and BOD specially in the inner estuary.