Study on morphological change from Chandpur to Sandwip channel in the Meghna estuary

Abstract

The Meghna Estuary system is a very dynamic estuarine and coastal system. The sediment discharge from the lower Meghna River is the highest and the water discharge is the third highest among all river systems in the world. The changes in tidal flow direction, channel topography, the occurrence of new channels, accretion of new lands and abandonment of old ones are the unique features that exists in the Meghna estuary. These processes trigger changes in sedimentation and erosion rates which are directly related to the change in discharge and sediment content and bank line shifting In this study, Meghna Estuary has been taken as a test case to apply a newly proposed technique where Hydrographic maps prepared from field level data have been used as a substitute for Satellite images for studying the morphological changes. This newly applied technique will be a handy tool in detecting major morphological changes of a river bank and the estuary. From Previous Studies it has been revealed that accretion is a dominant process in the Meghna Estuary. Long term study carried out by EGIS shows that the accretion rate is 9.9 sq. km per year in this region. Recent findings from the Meghna Estuary Study carried out in the year 2000 have also revealed that the accretion rate has increased to 18.8 sq. km per year. In this study where a new technique has been applied to identify the morphological changes, accretion has been found to be the dominant process in the study period of the last 30 years (from 1978 to 2008) with nearly 15.5 sq. km. net area accreted per year. But it showed a sign of declination in net accretion in the later portion of the study period. It has been found out that during the period from 1978 to 2002 accretion was a dominant process but during the period from 2002 to 2008 erosion started to dominate and the net result has been found to be accretion as dominant in the last 30 years. Based on the results found from the newly applied method of estimating erosion/accretion and comparing it with other established studies it can be said that the new technique is suitable to calculate the morphological changes.