Influence of the macrotidal environment on the source to sink pathways of suspended flux in the Gulf of Kachchh, India: evidence from the Ocean Colour Monitor (IRS-P4)

A series of tide-synchronous satellite images, obtained from the Ocean Colour Monitor (OCM) onboard the Indian Remote Sensing Satellite (IRS-P4), in situ measurements and hydrodynamic model simulations were used to describe dispersal pathways and sources of total suspended matter (TSM) in the Gulf of Kachchh, a macrotidal system with insignificant freshwater inputs. Strong alongshore currents are prevalent at the mouth that move in (out) clockwise during flood (ebb) and undergo cyclic, dynamic changes with the tidal phases. The Gulf, unlike other regions of the Indian coastline, has dynamic turbidity that is zonal (very high in the outer Gulf and in the creeks of the Gulf), particularly during flooding, and reduced in the central region throughout the entire tidal cycle. From this dynamic turbidity with regard to the prevalent currents, it is deduced that inland amplifying flood currents draw in TSM-rich offshore waters into the Gulf, and are the major source of turbidity in the outer regions of the Gulf. In the inner Gulf, because of these high-magnitude currents, scouring of the creek bed leads to resuspension to create higher turbidity. Most of the scoured flux sinks off the mouths of these creeks because of the fanning out of ebbing flows from the narrow creeks into the wider Gulf. The areas under specific influence of different sources of turbidity are delineated schematically.