Author(s): Maruf Dustegir; Munsur Rahman; Anisul Haque; Ashiqur Rahman; Hajime Nakagawa; Hiroshi Takebayashi; Zhang Hao
Linked Author(s): Hajime Nakagawa, Hiroshi Takebayashi
Keywords: No Keywords
Abstract: Having a catchment area of 530000 km 2 and draining discharge up to 100000 m3/s and sediment load up to 1160 MT/year, Jamuna is one of the largest braided river in the world (Immerzeel, 2008; Rahman et. al., in review). It originates at an altitude of 5100 m in the western part of the Tibet and flows through Bangladesh having a slope of 0.10 to 0.06 m/km (FAP24,1996; Jagers, 2003). The high seasonal variability in discharge and sediment (Figure 1) and complexities in fluvial regime determines Jamuna as one of the most complex and challenging fluvial stream to manage. We analyzed the historical sediment load and discharge in the Jamuna (Figure 1). From the historical data of the Jamuna, it is found that the total sediment flux is experiencing a downward trend of 6 MT/yr. Since 1958, total load decreases from 585 MT/year to 243 MT/year whereas bed load decreases from 200 MT/year to 30 MT/year. In the late 60s, where the ratio of the bed load to total load was approximately 0.3, in the recent years this ratio decreases to 0.12. Furthermore, from the historical satellite image analysis, it has been found that the braid in the Jamuna is also decreasing (Figure 2 and Figure 3). For determining Braiding Index using Brice formula (Brice, 1964), the Jamuna has been divided into three reaches. There is a clear notion that, the reduction of the bed load in the Jamuna governs its bed forms by decreasing its braid over the last few decades. It implies that, the transforming phenomenon from braided to meander by decreasing its braided index (Figure 3) as well as the hitherto lowering ratio of the bed load to total load determines the gradual stability of the Jamuna with time (Schumm, 1985).
Year: 2018