THE EFFECT OF THE SUSPENDED SEDIMENT TRANSPORT ON BED EVOLUTION DURING FLOOD STAGE

摘要

The transition from gravel river-bed to sand river-bed in Taiwanese rivers often occurs in several kilometers. Therefore, the effect on bed evolution of suspended load transport should be considered. This paper develops a two-dimensional depth-averaged mathematical model for bed evolution of alluvial rivers by solving convective-diffusion equations for suspended-sediment to obtain suspended load transport. Then, the effect of suspended load transport can be discussed. The applicability of the model can be performed by simulating the bed evolution in Pa-Chang River, which is one of the principle rivers in Taiwan, with and without suspended load transport during the period of Herb Typhoon (the peak discharge is 1650 cms) and 2-year frequency flood (the peak discharge is 476 cms). The apparent discrepancy in calculated results of bed variation during the flood stage is obtained when suspended load transport is considering in the numerical bed evolution model. The findings indicate that not only the quantitative effect is the influence of the suspended load transport on bed evolution but also qualitative effect. The comparisons of the simulated results show that it is necessary to consider suspended load transport in the simulation of bed evolution for alluvial rivers as bed material includes sand and silt.