Debris-Flow Peak Discharge Calculation Model Based on Erosion Zoning

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Earthquakes trigger large numbers of landslides that provide abundant material for rainfall-induced debris flows and hence increase the frequency and magnitude of post-quake debris flows. A physically-based model incorporating a quantitative function of how much landslide deposit transforms into debris flows is developed to calculate debris-flow peak discharge by dividing a catchment into non-erosion, hydraulic erosion, and gravitational erosion zones. The model was implemented with a distributed hydrological computation program, and applied to Qipan catchment that was strongly influenced by the 2008 Wenchuan earthquake and where the debris flow peak discharge in 2013 was more than 10 times that before the earthquake. Remote sensing images and digital elevation model (DEM) data were used to obtain the spatial distribution of the earthquake-induced landslides. In situ tests were conducted to measure the hydrological parameters of the landslides. Comparisons of field survey and simulation results were carried out to verify the model validity. At 14 cross-sections, the peak discharge errors range from 3 to 20%. Moreover, the error of the inundation area is 2.1%, which suggests that the model is highly applicable to hazard mapping.KeywordsDebris flowPeak dischargeEarthquake-induced landslidesDistributed hydrological computation