Evaluation of an alternative way of river bank protection in the Meghna Estuary

Evaluation of an alternative way of river bank protection in the Meghna Estuary

De Jong, J.

Wang, Z.B. (mentor)
Louters, T. (mentor)
Van der Wal, M. (mentor)
Stive, M.J.F. (mentor)
De Vriend, H.J. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2000-08-01

After the disastrous floods in Bangladesh in 1987 the Flood Action Plan (FAP) was initiated. The FAP was a co-ordinated action to study the flood problems of Bangladesh. The Meghna Estuary Study (MES) was drawn up as a component of the FAP. The overall goal of MES is to ensure the physical safety and social security of the people living in the coastal areas and on the islands of the Meghna Estuary. This goal is to be realised by retaining and increasing knowledge of the hydraulic and morphological processes and by developing appropriate techniques for efficient land reclamation as well as effective river bank protection. In particular during the monsoon season erosion of the river banks occurs throughout the Meghna Estuary. The erosion causes direct land loss (including loss of livelihood and impoverishment) and, where embankments are eroded, results in flooding of homesteads and agricultural land. Looking at the planform development of the Lower Meghna it is expected that in future years the eastern river bank of the Lower Meghna river starting south of Chandpur up to Haimchar is going to be subject to severe erosion. The river banks are highly erosive due to the non-cohesiveness of the sediments, the small particle size and the high flow velocities. Previous studies carried out have shown that protection of the river bank using conventional river bank protection methods is not generally economically viable at the current level of economic development in Bangladesh. It is expected that at the current level of economic development in Bangladesh alternative Iow cost bank protection measures are the only viable option to protect the river banks against erosion on a large scale. Nevertheless it must be stated that the circumstances are severe and the possibilities and necessary know-how have to be assessed by further research and execution of experiments. Under MES several pilot projects have been executed to study alternative ways of river bank protection. In part I of this study the author has studied the application of flexible bottom screens in combination with permeable spurs. In part II the application of bottom screens to create a roughness field is subject of discussion. Both studies are conducted under the responsibility of the Technical University Delft. One of the pilot projects executed by MES is the Hanar Char erosion control pilot scheme in which flexible bottom screens and permeable spurs are applied as an alternative way of river bank protection. This pilot scheme was executed from March to July 1999 and is part of the proposed Haimchar erosion control pilot project, which covers the complete eastern river bank from Chandpur up to Haimchar. However, up till August 2000 only a part of the Haimchar erosion control pilot project has been executed. The objective of this study is to determine whether flexible bottom screens and permeable spurs are an effective way of river bank protection in the river dominated part of the Meghna Estuary. This is done by studying the available literature and the influence of the structures on the flow pattern and morphology. Flexible bottom screens Flexible bottom screens show great analogy with so called bottom vanes which are placed at a certain angle of attack with the flow. The vanes cause the passing flow to attain a circular motion downstream from it. The sediment-rich bottom flow is directed to the river bank and the erosive upper current is directed towards the centre of the river. In the available literature on bottom vanes the distinction is made between vanes placed at a small angle of attack with the flow and vanes placed at a high angle of attack with the flow.

bank protection
Bangladesh
Meghna
river engineering

http://resolver.tudelft.nl/uuid:5ea02e53-0988-4cfd-a2a0-c4155f7c3406

Student theses

master thesis

(c) 2000 De Jong, J.