Salinity Distribution and Effect of Fresh Water Flows in the Hooghly River

An examination of the hydraulic characteristics of the Hooghly river with particular reference to the pattern of salinity intrusion and the effects of fresh water flows has been made in this contribution. It is seen that the conditions prevailing are such that during the brief period of fresh water flows the problem of salinity intrusion is absent. The beneficial effect of fresh water flows in improving the navigable depths along the river is also shown. The cessation of fresh water flows causes the deterioration of navigable depths due to the landward movement of sediment; it also results in the upstream encroachment of salinity affecting the supply of drinking water to the City of Calcutta. It has also been shown that even during the period in the freshet when the salinity profiles exist the estuary remains well-mixed. The need for augmentation of fresh water flows for improving the conditions has also been brought out. A few remarks on the comparative features of Hooghly and other tidal rivers have also been added to spotlight on the vastly different characteristics of the Hooghly.