The Hazard Assessment Of Lansslide And Debris Flow Under Different Rainfall Frequencies

The hazard assessment is one of the most effective soft measures in natural hazard prevention,and the base of hazard risk management,which can be contribute to the construction planning and prevention measure making.During several years after the May 12,2008 Wenchuan earthquake,heavy rain events induced massive landslides and debris flows resulting in many problems in the reconstruction of the earthquake-affected area,causing the deaths of people as well as serious damage to roads and the relocation areas for the earthquake-struck people.So many research results of hazard assessment were got,but there still has a defect.We don't consider the time scale of hazard assessment.So,the effective study system for the hazard assessment has not been formed.In this article,landslides and debris flows are regarded as research objects,based on GIS and Logistic method,landslides and debris flows hazard assessment would carry out.Then through FLO-2D numerical simulation method to study the hazard assessment of debris flows in the Miansi town area,which can promote the geohazard mitigation and other natural hazard risk assessment.Based on collected a large number of references,carried out detail field investigation and calculated the complex indoor works:Through the ENV14.8?ARCGIS10.0 and MAPGIS6.7 to revise and intensifies remote sensing images,resulting in improving image geometric accuracy and increase tonal characteristics.Landslide and debris flows inventories were carried out by deciphering of remote sensing data indoor,then compared with the on-the-spot field investigation,and improved the informations of landslide and debris flows inventories.Based on our earlier researches,6 major influencing parameters including lithology,seismic intensity,distance from river,distance from fault,slope gradient and elevation were prepared and analyzed with the mapped landslides,and created their evaluation layers.Topography informations(catchment elevation factor,gully density factor and main gully slope factor)of debris flows in study were got.In order to analysis sensibility assessment of landslides and debris flows.For the purpose of spatiotemporal context in hazard assessment,we established maximum daily rainfall distribution maps on different returm period(5%,2%,1%).First of all,we collected 32 rain gauge stations through Aba prefecture bureru of meteorogy,rain gauge stations distribute along with Minjiang River.Based on?Sichuan province small watershed storm flood calculation manual?,combine with Cs=3.5Cv curve-fitting,maximum daily rainfall of every rain gauge station was estimated.And then created maximum daily rainfal distribution map under different rainfall frequency(5%,2%,1%)by Co-criging method with elevation.First,an sensibility assessment method of geological hazard has been built.Because factors were standardized before the regression,the co-efficients of the logistical function indicate the apparent weight of each factor,which contributes to the landslide susceptibility.Then,we compared the results of logistic method to information value method,it is reasonable for logistic method to analysis landslide susceptibility.We also obtained the source activity of each catchment before calculate the probability of debris flow.And combined with topography informations of catchment,the probability of each debris flow could be calculated by the logistic regression coefficients.The result of debris flows susceptibility assessment was verificated by field investigation.Second,an space-time hazard assessment method of geological hazard has been built.The susceptibility model built above is capable of landslide predic-tion during a scenario event.In mapping landslide hazard,a return period for rainfall should be adopted.So,we combined the susceptibility maps of landslides and debris flows with maximum daily rainfal distribution maps under different rainfall frequency(5%,2%,1%)respectively through ARCGIS.Under different rainfall frequency(once every 20 years,once every 50 years,once every 100 years),the important debris flows near Miansi town were carried out numerical simulation by FLO-2D software.The velocity and depth of debris flow were got from numerical simulation result,then the damage capability of debris flow accumulation fan was substituted with the intensity index I(vd2),accumulation fan hazard hierarchy standard and hazard map were established in Miansi town area.Limited by research theory and sample size,some possible deviations are inevitable during applying the hazard assessment system.Even so,the results are expected to provide a reference to research in natural hazard risk assessment and its engineering application.