A calculation method for predicting the runout volume of dam-break and non-dam-break debris flows in the Wenchuan earthquake area

Abstract

The factors affecting debris flow runout volume changed considerably in the Wenchuan earthquake area. The main characteristic parameters for calculating the debris flow runout volume, namely, channelized landslide dam volume are first used to establish empirical models. A new empirical statistical model is established by applying a multivariate regression analysis to the runout volumes of dam-break and non-dam-break debris flows. Additionally, FLO-2D is used to simulate the debris flow runout volumes under the non-dam-breaking and dam-breaking scenarios. When the rainfall frequency is P = 1%, the predicted runout volumes in the Huaxi gully are 24.48 × 104 m3 under the non-dam-breaking scenario and 43.41 × 104 m3 under the dam-breaking scenario. The runout volume in the dam-breaking scenario is 6.07 × 104 m3 more than 1.77 times that in the non-dam-breaking scenario. The predicted runout range of the dam-breaking scenario is 1.16 times that of the non-dam-breaking scenario. The predicted alluvial fan areas and average accumulation depths in the dam-breaking scenario are larger than those in the non-dam-breaking scenario. The predicted runout volume of the dam-breaking scenario is 5.58 × 104 m3 which is less than the actual surveyed volume (48.99 × 104 m3). The relative error and accuracy of the numerical simulation results are −11.39 and 88.61% for the dam-breaking scenario. The new runout volume model was developed in catchments with abundant loose materials in the Wenchuan earthquake area and can thus be applied to debris flow gullies in meizoseismal areas with newly fractured regolith and abundant loose material to estimate runout volumes. The results of this study will help authorities select safe sites for future rehabilitation and relocation projects and can also be used as an important basis for debris flow risk management.