Statistical and probabilistic analyses of impact pressure and discharge of debris flow from 139 events during 1961 and 2000 at Jiangjia Ravine, China

Debris flows often cause catastrophic damage to communities in the downstream area, by direct impact and deposition. Theoretical predictions of impact pressure and volume of discharge, however, still remain very challenging, mainly due to inadequate understanding of the complex problems and limited field data at the local scale. In this study, the maximum impact pressure (P_max) and total discharge (Q_total) of 139 debris flow events that occurred during 1961 and 2000 in the "debris museum" of China (i.e., the Jiangjia Ravine) are reported and interpreted with statistical tests and probabilistic analyses. Four common probabilistic models (Normal, Lognormal, Weibull and Gamma distributions) are used to simulate the distributions of P_max and Q_total. The level of fitting of each model is assessed by performing two quantity-based statistic goodness-of-fit tests (Chi-square and Kolmogorov-Smirnov tests). The field data show that during the period from 1961 to 2000, the maximum values of P_max and Q_total are 744kPa and 1,751,537m³, respectively. It is suggested by the goodness-of-fit tests that the Weibull distribution is the only model (among the four probabilistic models) that is able to capture the distributions of P_max and Q_total of both surge and continuous flows. Using the verified Weibull distributions and Gaussian copula approach, univariate and bivariate exceedance probability charts considering P_max and Q_total are developed. Regression models between P_max and Q_total are also established.