Author(s): Xudong Fu; Hongbo Ma; Dawei Guo; Liguo Zhang
Linked Author(s): Hongbo Ma, Xudong Fu
Keywords: Flash flood; Earthquake; Mountain stream; Numerical model; Longxi River
Abstract: Following the “May 12, 2008” Wenchuan earthquake, landslides and debris flows have occurred more frequently than before in the earthquake-hit mountain area of southwest China’s Sichuan Province. A huge amount of loose solid materials entered streams, resulting in abrupt changes in channel morphology and bed materials. This paper presents an investigation of the impacts of pulsed sediment input on flash floods in the Longxi River in the earthquake-hit region. A one-dimensional numerical model considering flood routing, bedload transport and bed elevation evolution was formulated. Flood hydrographs obtained from design rainstorms with different recurrence intervals were used as the boundary conditions at the inlet of computation domain. The results demonstrate that the peak flood stage can be significantly augmented due to the pulsed sediment input following the earthquake. Bed aggradation plays a dominant role in contrast to the extra flow resistance resulting from bedload transport. This suggests a significantly lowered threshold of rainfall for flash flooding. Meanwhile, the examination of two bed load transport formulae suggests the need of improving the understanding of bedload transport in flash floods.