ASYMMETRY OF TIDE AND SUSPENDED SEDIMENT CONCENTRATIONS OBSERVED AT THE NORTH-EASTERN PART OF THE MEGHNA ESTUARY

Abstract

Field investigations have been conducted at the north-eastern part of the Meghna Estuary to collect tidal water level, velocity and turbidity. It is found that strong vertical as well as horizontal tidal asymmetry exists around the highly accreting Urir Char Island of the Meghna Estuary. Along the northern channel of Urir Char Island flood velocity exceeds ebb velocity which would induce residual transport of coarse sediments towards land. Also duration of slack water duration before flood is much longer than that before ebb indicating residual transport of fine sediments. The phase lag between peak flood velocity and peak turbidity during the flood duration is about two hours, while it is less than one hour between peak ebb velocity and peak turbidity during ebb duration. A 'second peak' in the turbidity profiles is observed which appears to be caused by rundown of ebb tidal flow from the shallow intertidal mudflats around the Urir Char Island. A 2DH numerical model based on non-linear shallow water equations have been employed to explain the observation data. From the simulation results, it is evident that the horizontal advection pattern plays significant role in residual transport of suspended sediments.