Anomalous inland influx of the River Indus, Gulf of Kachchh, India

Abstract

The Gulf of Kachchh is a funnel-shaped macrotidal water body located in the arid region of northwestern India with ∼50 cm annual rainfall and insignificant fluvial input. The Gulf waters, however, have high-suspended matter. Time series measurements of total suspended matter (TSM) and synchronous, validated hydrodynamic modeling have been used to decipher the dispersal pathways and the sources of the high turbidity. Contrary to the prevalent offshore reducing trend for most of the Indian Coast, the Gulf is anomalous for having an enhanced turbidity at the mouth with lower concentrations in the inland areas. The hydrography of the Gulf is dominated by strong, alongshore currents at the mouth which move in (out) during flood (ebb), and undergo cyclic, dynamic changes with tidal phases. The flood tidal currents amplify inland with propagating tides, pulling in the offshore waters and acting as a feeder of high saline, turbid offshore waters into the Gulf, most of which are trapped inland due to time lag of ebb and flood between the outer and the inner Gulf. Based upon the distribution maps of TSM and clays in the water column, it is deduced that a large segment of the Gulf is nourished by contributions from the Indus River.