Bank Erosion And Protection On The Brahmaputra (Jamuna) River
Free (open access)
A. B. M. Faruquzzaman Bhuiyan, M. M. Hossain & R. Hey
Bank erosion is a major problem for river and floodplain management along the Brahmaputra-Jamuna river system of Bangladesh. Considerable resources are spent protecting the river banks from erosion. Consequently an understanding of the erosion processes as well as the suitability of protection methods are important issues to be explored. In this paper bank erosion processes are examined considering the hydrogeological conditions with particular reference to the Jamuna river. The critical condition for bank erosion by mass failure can be defined by the critical bank height for cohesive soils and the critical slope angle for noncohesive soils. Basic analyses show that the critical condition for failure, and hence the critical bank height or critical slope angle, change considerably depending on the hydrogeological condition as affected by river and groundwater levels. A river bank that appears to be stable in the dry season may fail subsequently in the wet season without any significant change of bed levels in the river. This phenomena, combined with fluvial action, would explain the temporal variation of bank erosion rate on the Jamuna from pre-monsoon to post-monsoon period. To protect banks of the Jamuna river from widespread erosion several types of structural measures have been used. These include groyne and revetment type constructions. As evident from the variable degree of performance of such structures in this river, a critical evaluation should be undertaken before implementing such measures. The performance of the structures is drastically impaired by the generally unpredictable development of the multiple charnels in the braid belt and resulting damage to the structures by the combined effects of fluvial action and geotechnical instability. Based on the field evidence, important issues related to the design of bank protection structures are discussed.