Study Of Flash Flood And Debris Flow Disaster Prediction And Early Warning System For Xiqugou Catchment,Fangshan District,Beijing

In northern part of China debris flow mainly has low frequency.People will suffer a big loss if they ignore preventing from the debris flow.In the mountain area of Beijing,people not only consider the debris flow disaster,but also they need to consider the flash flood.The flash flood is also a terrible natural hazard.This study processed a geological survey in Xiqugou catchment,Fangshan district,Beijing.Based on the geological qualitative understanding and evaluation,this study constructed a geological concept model of debris flow gully.Based on the previous researches,this study tried to distinguish the debris flow and flash flood in the aspect of sedimentary structure,destructional forms,and the intrinsic characteristics of the fluid(rheological properties,solid conservation and natural density).This study considered the form of debris flow,the capability of debris flow hazard,the development period and the grade of vulnerability.Combined with the evaluation factor and weights,this study assessed the Xiqugou catchment and its six first-level tributaries hazard degree.Moreover,this study also mapping the hazard,vulnerability and risk zoning of the Xiqugou catchment.And the field geological description,characteristics evaluation and risk assessment mapping are used as the judgment information of medium-long term prediction of debris flow of Xiqugou catchment.The field monitoring instruments are used as the support of the debris flow disaster warning system for Xiqugou catchment.On the concept of the ?one rainfall process?,this study modified the effective rainfall formula.Through the hydrological analysis module in ArcGIS software,this study calculated the rainfall accumulation of Xiqugou catchment and established the critical line of debris flow rainfall on the basis of the critical excitation rainfall threshold provided by the historical data.In order to achieve the purpose of classification warning,this study established four warning lines,including blue,yellow,orange and red lines.According to the rainfall information,cofferdam water changes,concentration in volume and other information,this study analyzed how to release the warning.Five-minute continuours warning is needed.By analyzing the ?one rainfall process? from July 12 to July 20,2016,this study verified the proposed model.The main contents and achievements of this study are as follows: 1.There are six first-level tributaries in the Xiqugou catchment.The slope from the sources area to transportation area changes from steep to slow.And the width changes from narrow wide.Materials rushed from the upstream suffer a lot of energy loss,then the materials is easy to accumulate in the transportation area.There is a large amount of unstable accumulation of coal gangue deposits in the catchment,as well as the loosening of the material caused by cutting slope,the erosion caused by the soil erosion etc.2.Flash flood and debris flow can be distinguished from the sedimentary structure,the destructional forms,and the intrinsic characteristics of the fluid.This study established a diagram to distinguish them.This study also clarified the basic geological processes of the two natural hazards chains and mechanics of interaction of flash flood and debris flow.It is concluded that both flash flood and debris flow are deposits of two-phase.From the destructional forms of trees,people can preliminary judge the type of the hazards.This study established a diagram to distinguish concentrated flow,pseudo-phase muddy flow,hyper-concentrated flow,dilute debris flow,transitional debris flow and viscous debris flow from the perspective of rheological properties,solid conservation and natural density.It also suggested that there were four geological processes in the process of continuous precipitation.The evaluation process of the flash flood and debris flow can be toughly summarized into three stages.3.The type of the Xiqugou catchment may be dilute debris flow.The comprehensive activity intensity is weak to strong.The disaster ability is weak to strong.The development stage is middle to old.The prone degree is light.Based on the influencing factors and weights,this study used the cloud model,extentic theory and gray correlation to evaluate the hazard degree of the Xiqugou catchment and its six tributaries.The Xiqu hazard degree is moderate.And the other six tributaries hazard degree are light-moderate.Based on 3S(Global position system,Remote sensing and Geographic information system)technology,this study used the analytic hierarchy process and ArcGIS software to mapping the hazard,vulnerability and risk zoning maps.The results showed that extremely high risk area was distributed in the four villages.The moderate-high risk was distributed in the farmland and orchard on the both side of the main channel.4.Based on the concept of ?one rainfall process?,this study calculated the total amount of effective rainfall and the total amount of short-term rainfall.Based on the historical rainfall data and debris flow disaster data,this study established the rainfall critical lines,and four warning areas.Through the rain data recorded by the rain gauge,the ArcGIS software hydrological analysis module is used to calculate the accumulation total amount of the cofferdam.It also drew the critical rainfall line of Xiqugou catchment and realized the continuous warning function based on ?one rainfall process?.By validating the rainfall data on July 19 and July 20,2016,this study showed its good prediction ability in debris flow early warning in Xiqugou catchment.