Hazard Assessment Of Debris Flow In Earthquakeregion And System Design For Warning And Mitigation

Hazard assessment of debris flow and early warning is an important part of riskmanagement，providing a powerful guarantee for people’s lives and property indisaster area."5.12" Wenchuan earthquake induced a large number of geologicaldisaster. According to the statistics, there are more than50000landslides and collapsesinduced by earthquake, potential geological hazard up to million and more than1000gullies with possibility of outbreak of debris flow. Landslides and collapses induced byearthquake provide a rich source for debris flow development. And debris flowoutbreak with high possibility under the condition of strong rainfall.Influenced byWenchuan earthquake, debris flow disasters would be active state for a long time.Therefore,the hazard assessment of debris flow and researchof early warning hasimportant scientific value and practical significance.Thesis research content and made innovations in the following areas:（1）Debris flow hazard assessment can be divided into regional hazardassessment and single gully hazardassessmentaccording to scale. In this paper,selectingBeichuanJianRiver and Hongchun gully as research object for regional debris flowhazard assessment and single gully debris flowhazard assessmentrespectively. Incurrent, regional debris flowhazard assessment always adopts calculated riskmethod toevaluate the dangers of the outbreakdebris flow. However, it cannotpredict the risk ofwithout debris flowsin this way.In this paper, based on GIS and RS,we got theinformation of debris flows to research the distribution of landslides and debris flows inthe region after "5.12" Wenchuan earthquake. And by using the high precision DEMand hydrological models, we obtained different threshold of catchment units. Finally,99evaluated catchment units were got by comparing and mergering with the actualterrain catchment units.The debris flow evaluation factors are gradient, curvature,seismic intensity, gully density, and Earthquake intensity.Among these factors,landform is the main influence factor.We consulted the information method to evaluateunits, and every catchment unit stands for a possibility of debris flows in this region.According to these units, the study area was divided into very high danger zone, high danger zone,mediumdanger zone and low danger zone. The final evaluation resultsshowed thatrelative density of debris flow were increasing from low to high risk zone.The evaluation results almost reflect the risk distribution of debris flowsand provide apossibility to forecast the outbreaks ofthe debris flows in this region.（2）The method of single gully debris flow hazard assessment uses empiricalformula for predicting maximum movement distance of mudslides,difficult toaccurately describe the range of activities.However, the numerical simulation can givevarious quantitative parameters and the area of accumulation areaof debris Flow forhazardassessment.―8.14‖Hongchungou gullydebris flowblocking Duwen road,rushedinto the Minjiang and blocked river. The water rushed intoYingxiu new town whichcaused tremendous damage to property. The study was carried out detailed work suchas field investigation.And based on the research of debris flow gully characteristic,formation mechanism and source, we adopted FLO-2D Model with rheologicalparameters to simulate Hongchungou gully debris flow.The debris flow is caused bylandslide dam outburst, which breakout at14th Aug2010when the debris flowbreakout,the landslide dam can not supportfluid pressure and break.Because ofamplification effect, the flow of debris flow is more than that of debris flow induced byrainfall. Therefore, it can not adopt commonly rainfall data.the process of landslidedam outburst is similar to that of dam break. According to the field investigation, wefound that the height of dam is4meters. The landslide dam break discharge hydrographgot by dam break,which was regarded as water discharge hydrograph for simulatingdebris flow. From the comparison of accumulation range between the simulation resultsand aerial photographs，we founded that the accuracy of simulation reached70.1%.And we simulated debris flow state of motion without dam break by using data on flowsin100years and50years, draw debris flow map intensity of different return period andfinally accomplish Hongchungou gullyhazarddebris flow zoning mapaccording tohazard results based on the strength distribution data and return period.（3）Themonitoring andearlywarningofdebris flowis animportant measure fordisaster prevention. At present, there are manly researches involved in warning ofdebris flowat home and abroad, including establishvarious warning modelsbasedoninducing factor and motion characteristics of debris flow. However, these models aresingle warning model and their prediction levelsare not high. In the paper, according tothe studies of preliminary rainfall and stimulate rainfall of debris flow in earthquakearea, Combining the rain-accumulated rainfall warning model which used oftencurrently with the traffic monitoring data of debris flow and group monitoring and prevention network to develop a multi-source debris flow warning system to improvethe early warning accuracy.In this article,using GIS technology, the Internet technologyand information transfer technology to set up debris flow monitoring and early warninginformation platform for disaster reduction,it could dramatically reduce the debrisflows threat to the people in disaster areas.Debris flow early warning and mitigationinformation platform integrated group monitoring and prevention network module,debris flows spatial information and attribute information data management module,monitoring and early warning module. After the rain of debris flow gullies, earlywarning information platform obtain real-time field monitoring data through the fieldstation, used early warning modelbuildby hours of Rain-cumulative rainfall andcombined with group monitoring and prevention network to monitor debris flow. Whilereaching the early warning condition, the system sends early warning information bySMS, radio, Internet and television. After the completion of the debris flow earlywarning information platform, based on the monitoring data, we will enhance the earlywarning model in order to improve the accuracy of early warning.