Sediment erosion and transporting from upstream basin is one of the main factors for natural alluvial channel bed degradation and aggradation. Downstream of river hydraulic structures crossing a channel such as dams and reservoirs, both the water and sediment supplies can be altered principal to adjustments in the river channel bed morphology. In case of a compounded double-cross sectional channel with floodplain, it is commonly observed that both dynamic responses of alluvial stream refer to channel bed degradation and aggradation. With the limited inflow sediment discharge, channel bed erosion and sediment deposition with vegetation are developed in main channel and in floodplain, respectively. In this study, alluvial channel bed degradation and aggradation due to different inflow sediment discharge were investigated using a movable bed physical model. A 0.6 m wide and 0.8m high rectangular section experimental flume was set with 20m long. A 20m long rectangular section (0.6 m wide and 0.8m high) experimental flume was used for the model. Medium particle diameter 1 mm of sand was covered with 0.15 m depth in the flume. To investigate hydraulic impact of inflow sediment discharge and channel slope on the channel bed elevation changes, three sediment discharges (0 %, 50 %, and 200 %) and three channel slopes (1/400, 1/500, and 1/1000) were tested over three different flow conditions of approaching uniform water depths (0.05 m, 0.10 m, and 0.15 m). Channel bed level changes were measured with surface topologic digital imaging system and generated three dimensional channel surface contour map. The results of the experiments showed that inflow sediment discharge gives a significant impact on alluvial channel bed geometry. Channel bed incising on the main channel was increased in proportion as test run time and for that reason, bed level divergence between the main channel and the floodplain was increased. It was found that alluvial channel dynamic transformation from a compounded double-cross section stream a single-section channel can be controlled with inflow sediment discharge.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1625 Geomorphology and weathering (0790;
- 1815 Erosion;
- 1847 Modeling;
- 4558 Sediment transport (1862)