Author(s): Soren Tjerry; Ranjit Galappatti

Linked Author(s): Søren Tjerry

Keywords: Tidal rivers; Bank erosion; Morphological modelling; Morphological hindcasting

Abstract: Four tidal rivers in the southwest region of Bangladesh were studied with emphasis on river bathymetry and bank line developments over medium timescales. Morphological hindcasting was used as a centerpiece in the model development. Bathymetry data was available for 2011 and 2019 for three of the tidal rivers, while one tidal river only had 2019 bathymetry data. Historical bank lines were obtained for 1988-2019 by using Landsat data. Boundary conditions were generated using a 1-dimensional hydraulic model of the Bangladesh southwest region. The dominating sediment in the rivers was silt, and calibration through hindcasting allowed adjustment of almost identical silt transport models in the four tidal rivers, while the same hindcasting also allowed almost identical bank erosion formulas adjusted for the four rivers. Bank erosion in the tidal rivers is slow and systematic, and banks that were eroding in 1988 were likely to also erode in 2019. Bank erosion rates in the tidal rivers are in the range of 5-10 m/year. The tidal discharges in the tidal rivers dominate compared to the monsoon discharges, which means that the tidal rivers do not exhibit significant imbalances between dry season and monsoon conditions, which when combined with cohesive banks results in slow and systematic erosion rates, which are not seen further to the east where the Lower Meghna can exhibit annual erosion rates orders of magnitudes faster. Bank line development over time in the tidal rivers has good predictability.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0344-cd

Year: 2023