The Study Of The Early Warning Model And The Meteorological Early Warning System For The Debris Flow Hazards In The Nujiang State

The debris flow is the main geological disaster in Nujiang prefecture.Precipitation is the inducement of debris flow.It is a hot issue in the field of debris flow disaster how to bring about the debris flow early warning due to the precipitation.Web GIS is a combination of GIS and Internet,it is very powerful and it has been widely used.A system for the debris flow prediction based on Web GIS is an effective approach to improve the debris flow forecasts skill.So we plan to develop a system based on Web GIS to bring about the debris flow early warning,which has a very broad application prospect.The geological environment and topography features in Nujiang state are very special and complex.Every year a large number of debris flow disasters happened here because of the influence of human activities and precipitation,which would cause serious destruction of people's safety and prevent the local economic development.In the study,a debris flow warning system,which can realize rainfall analysis,disaster warning and data management,has been developed to improve the debris flow prediction and to minimize the losses caused by disasters.The system can shorten the time for officials to analyze data and heighten the work efficiency of the relevant departments greatly.At the same time,the system can release the debris flow risk forecast and provide the reference for the study of forecast of debris flow area.At first,the paper makes a preliminary analysis of the climate situation and the status quo of the geological disasters in Nujiang state and finds that the number of precipitation and debris flow occurred more frequently during the period from July to September.Secondly,two regional early warning models for rainfall-induced debris flow are selected,they are the geological and meteorological coupling model and geological rainfall coupling model.The debris flow susceptibility map is taken as one of the debris flow prediction indexes.In order to get the debris flow susceptibility map,the paper evaluates the probability of debris flow in Nujiang state.12 evaluation indexes such as fault,rock and soil type,elevation,slope,river vertical slope,river bend coefficient,drainage area,flow accumulation,NDVI,average annual precipitation,road and villages are used to evaluate the probability of debris flow in Nujiang state.The probability evaluation takes the small watershed as basic assessment unit and the weights of indexes are calculated by CF and multi factors superposition method.A debris flow susceptibility map is produced by grading the probabilities.Thirdly,this paper makes a preliminary analysis of 30 debris flows triggered by rainfall in the period 2012-2016 and finds that the precipitation on that day and the antecedent precipitation are the main factors causing mud-rock flows.So the paper takes the precipitation on that day and the antecedent precipitation as two other indexes of debris flow prediction.A database of 2 debris flows triggered by rainfall in the period 2012-2016 is used to validate the two kinds of models.The results indicate that the geological and meteorological coupling model for rainfall-induced debris flows has the higher rate of accuracy.Finally,this paper designs and develops the debris flow early warning system based on GIS,Asp.NET and ArcGIS Server.The system design includes the architecture design,the function design and the database design.The function includes map display,rainfall analysis,disaster warning and data management.