Abstract

The paper is intended to account for the abnormal phenomenon that a flood peak increased in August.2004 along the lower Yellow River and studies its hydrodynamic mechanism. It is found that the flood peak increase was mainly due to decrease of channel roughness in the propagation of the high-concentrated flood carrying extra fine sediment which was discharged from the density current of Xiaolangdi reservoir. The mechanism of “04.8” flood is justified by the simulation with a quasi-2-D numerical model, which includes, among others, considers roughness change with concentration and sediment gradation. In addition, the paper shows that flood peak increase caused by reduction of roughness could endanger the security of flood control works along lower Yellow River, and emphasis should be laid more on it.

Keywords: river sediment; flood peak increase; roughness decrease for extra fine sediment; simulation; mechanism; justification