Tidal River Siltation and its Impact in the Coastal Parts of Bangladesh

Abstract

The study area is located in the south-western coastal part of Bangladesh and belongs to the lower deltaic plain of the Ganges delta system, which lies in the Rampal upazila of Bagherhat district. The area is more or less flat with elevation ranges from 1.0 to 2.0 m above mean sea level (MSL) and is blanketed with fluvio-tidal deposits of sandy silt, clayey silt and clay. Right now, water logging is one of the major problems in the area. The present paper is an attempt to expose the causes of water logging as well as its consequences. The satellite images of the last few decades, existing statistical records and simultaneous field checking were employed in this study, which reveals that natural as well as anthropogenic factors are responsible for water logging problem. The rivers and their link channels in the areas are influenced by tidal water regularly. The Water Development Board (WDB) was built embankments along the river courses as well as constructed sluice gates on the head of the tidal creeks to protect the area from regular tidal flooding and sea water intrusion. During monsoon, when rivers carry huge amount of water and sediments due to torrential rain, and these rising waters overtop the natural levees which were artificially modified and raised by coastal embankments. Consequently, the sediments drop down inside the channel and near channel bank rather in the nearby tidal plain. As a result, channels are gradually congested due to siltation, whereas tidal plain areas gradually lower due to subsidence and lack of sedimentation. Moreover, many sluice gates were constructed on the river courses in the coastal areas which also aggravate the situation. Daudkhali river is one of the main rivers in the study area. Image interpretation depicts that in 1977 the width of this river was nearly about 200 m all through its course and the river maintained this width up to 1990. But due to embankments the river starts to squeeze and the width of the river reached about 100 m in 2000. But in 2014, the river was nearly abandoned. A sluice gate was constructed on the course of the river about 30 years ago near Foila Bazar. The sediments carried by the river started to deposit in the mouth of the sluice gate which gradually choked the opening of the gate and now the gate is nearly blocked. During the rainy season, the river cannot carry excess water resulting flooding and water logging for long time. The presence of thick finer sediments in the subsurface as well as climate change further prolongates the situations. Finally, for sustainable development of the area,it is necessary to carry out different development activities with consideration of delta building processes.