MODELING BED LEVEL CHANGES AND SEDIMENT SORTING PROCESSES FOR POOL-RIFFLE SEQUENCES IN GRAVEL BED RIVERS

摘要

One of the main features of gravel-bed rivers is the pool-riffle sequence. Investigation on morphological changes in pool-riffle topography plays a key role in environmental engineering and river training practices. In the present work, the morphological response of a river to sediment input in a bed with pool-riffle sequence was simulated by Gstars4.0 computer code. Experimental data presented by Hassan et al. (2006) was first used to find the model capability in predicting sediment transport rate and bed composition changes in an alluvial bed. The model was then employed to simulate the experimental study of morphological changes conducted by Harrison (2007). Comparison of the observed and computed results demonstrated that the model was capable of predicting bed changes and grain sorting processes in the pool-riffle sequence of non-uniform sediments with satisfying agreement. Results from this study showed that though sediment was deposited in the pool first, as flow discharge increased, the pool-riffle topography approached its initial elevation. The results also showed a gradual coarsening of the bed sediment in the pool as well as the riffle region in higher discharges.