PREDICTION FOR HAZARD ZONES OF RAINSTORM INDUCED DEBRIS FLOWS IN THE WENCHUAN EARTHQUAKE EPICENTERS

The rainstorm induced debris flows have entered a new active period after the Wenchuan Earthquake.Debris flows have huge energy to drain a large amount of sediments and their peak discharges have several times of the normal events.Such results are based on field observation of the rainstorm induced debris flows on 24 September 2008 in the Beichuan epicenter areas.This phenomenon is due to the huge loose materials of earthquake induced landslides in the debris flow watershed.Therefore,it has obvious errors if the existing models are applied to estimate the hazardous zones of debris flows in the epicenter areas.In this way,it needs to establish an appropriate model to predict possible hazardous zones of debris flows in the Wenchuan Earthquake epicenter.This study selects the 9.24 rainstorm induced debris flows as a typical case.It uses the high resolution aerial photograph and SPOT5 images to extract a set of data of landslide volume in debris flow drainage basin and also geometrical dimension of depositional fans.Applying the multivariate regression analysis,a mathematical model is established to estimate the maximum runout distance and depositional width.The validation and application show that the new model is suitable for predicting debris flow hazardous zones in the Wenchuan Earthquake areas.The intent of the study will help future decision makers in the selection of safe sites during the rehabilitation process and also be used as an important basis for landslide risk-management in the rehabilitation area.