Analysis on River Bank Erosion-Accretion and Bar Dynamics Using Multi-Temporal Satellite Images

摘要

Dudhkumar River flows from upstream of India Border at Bhurungamari to the confluence with Brahmaputra River at Noonkhawa of Kurigram district having a stretch of 64 km in Bangladesh. Due to onrush of water from upstream in monsoon, erosion in Dudhkumar River takes a serious turn, threatening collapse of Sonahat Bridge in Bhurungamari, embankment on its right bank, dykes and several dwelling houses in recent years establishing the river as a destructive one. Thus study aiming at computing the long and short term bank line shifting along the river is of great significance. In this study, images of Landsat MSS and TM acquired from the year 1973 to 2015 have been used to investigate the riverbank migration pattern, accretion-erosion, rate of change of width, sinuosity and island dynamics of Dudhkumar River. For the short term analysis, migration rates are calculated from one Landsat image to the next. For long term analysis, the migration rates are calculated based on the difference between the 1973 image as the reference and subsequent images. From the short-term analysis, the mean erosion and accretion rate have been estimated as 128 m/y and 194 m/y on the left bank, and 141 and 176 m/y on the right bank indicating the accretion rate as greater than the erosion rate. Erosion rate has been found as greater in right bank rather than left bank and accretion rate is much more in left bank than the right bank. Due to high discharge, maximum erosion and accretion have been found as 349 m/y and 410 m/y respectively at left bank in 2013-2015 indicating the bank protection measures vulnerable. Computations on sinuosity of the river Dudhkumar River show that the sinuosity ranges from 1.36 to 1.53 showing significant increase in year 1989, 1997 and 2011 due to active erosion and deposition induced by monsoon flood. Analyses on island dynamics reveal that the island area started increasing after 1973 and maximum island area found in 2001. The analysis divulged that the Dudhkumar River is a highly meandering river with several critical sections where the river has been suffering enormously with erosion problem and shifting.The present study also identifies steadfast evidence on the dynamic fluvio-geomorphology of Dudhkumar River depicting urge for execution of erosion control schemes.