Predicting Volume and Runout of Single Gully Debris-Flow Using Hypsometric Integral Value in the Wenchuan Earthquake Area

Debris-flow volume and runout zone are estimated from empirical equations which are based on the most important morphometric characteristics of a catchment and have the limitation of requiring uncertain input parameters. In addition, due to extraordinary abundant loose solid materials and local short-time heavy rainfall by extreme climate in the Wenchuan earthquake area, large errors will occur if the existing empirical equations are directly used. In order to enhance the applicability of those empirical equations in this area, we use Strahler’s Hypsometric (area-altitude) analysis method to quantitatively describe the geomorphological conditions, develop models that quantitatively depict spatial distribution of mainly available loose sediment in debris-flow catchment and with integral values T, G 1 and G 2 as quantitative parameters of loose sediment’s spatial conditions. Grouping-occurring debris-flows triggered by the September 24, 2008 rainstorm in Beichuan County and the August 13, 2010 regional rainstorm in Qingping Town, Mianzhu County are selected. Applying multivariate regression analysis, Hypsometric integral value S is used in estimating debris-flow volume and runout distance models; and T, G 1 and G 2 are used as the coefficients of correction. The results showed that the hypsometric integral value S was suitable for the prediction of the debris-flow volume and runout zones in the Wenchuan earthquake area; the predicted results were more accurate when T, G 1 and G 2 are used. The introduction of S, T, G 1 and G 2 will enhance the applicability of existing empirical equations in Wenchuan earthquake area.