Research On Disaster Mechanism And Risk Assessment Method Of Highway Flood Disaster In Rizhao City

Rizhao City is located in the eastern coastal area.In recent years,affected by typhoons,it is prone to heavy rain in summer,which brings security risks to roads and facilities and causes serious losses to the economy and people’s property safety.There are many damage forms of washout,so it is of great significance to classify the type of washout,study on early warning and assess the risk.Based on the field investigation and data collection of washout,clarifing the occurrence conditions of washout,and dividing the types of washout,analyzing and the occurrence,development and damage mechanism.Two villages and a highway in a typical watershed were selected to identify the critical water level and critical discharge of washout.The rainfall analysis method was used to calculate the influence of rainfall on the flood damage under different antecedent precipitation index.The rainfall monitoring system was combined to give early warning and issue early warning signals in real time.Conduct risk assessment on Rizhao City based on grid units,adopt literature review method,select evaluation factors based on actual investigation,use ArcGIS software to extract,analyze and quantify evaluation factors,and ultimately clarify the risk units of water damage at all levels.The main research achievements achieved include:(1)Through the field investigation and data collection of washout in Rizhao City,counting the quantity and distribution of flood disaster.According to the terrain and conditions along the river,the washout is divided into three categories:flash flood washout,river washout and plain low-lying washout.Flash flood washout can be divided into hillside flood impact type and small watershed outlet flood impact type.River washout can be divided into subgrade water damage along the river,protection engineering water damage and bridge and culvert water damage according to the damaged parts.Plain low-lying washout can be divided into subgrade and pavement water damage,slope water damage,drainage facilities and ancillary engineering water damage according to the damaged parts.Flash flood washout is mainly affected by the flood impact on the hillside and flood erosion at the outlet of the basin.River washout is mainly caused by the erosion of the retaining wall,roadbed,bridge and culvert by the river.Plain low-lying washout is mainly caused by road surface inundation caused by insufficient drainage,blockage and destruction of small drainage facilities,slippage and collapse caused by rainfall infiltration slope.(2)In order to reduce the traffic danger and economic loss caused by flood damage,early warning research is carried out.Warning indicators can be divided into forecast warning and alarm warning,corresponding to yellow warning signal and red warning signal respectively.Through the investigation of water damage in the early stage,the critical condition of water damage is defined.Villages and typical roads in typical watershed were selected for calculation,the early warning period was selected and different previous influence rainfall was considered.Combined with the measured river data,the critical rainfall of early warning was obtained by using the backward extrapolation method of water level and discharge and the same frequency backward extrapolation method,and the rainfall data of historical washout was verified.The final verification results were reasonable.This method can play a positive role in the prediction and early warning of flood damage.Through rainfall monitoring,real-time warning signals can be issued,patrol can be strengthened,and disaster relief can be prepared in advance.(3)In order to accurately assess the risk of washout,the factors affecting the flood disaster were summarized through field investigation,and the risk assessment method suitable for Rizhao City was established.Four evaluation indexes of average annual rainstorm days,river network density,topographic slope,and historical flood disaster were selected.The weights of each index were calculated through analytic hierarchy process.ArcGIS was used to extract the indexes.The average annual rainstorm days are 6.45-9.85d,the river network density is 0～9.59km/km~2,the slope is 0～57.6°,and the historical flood disaster is 0～3n/km~2.The classification is carried out and the grid layer is formed,the weighted superposition is used to finally form the flood disaster risk unit partition.Risk levels are divided into low risk(level four risk),low risk(tertiary risk),medium risk(secondary risk)and high risk(first-order risk).And select a typical highway,overlay it on the risk assessment layer,make clear the level of the risk unit,make risk assessment on it,and put forward suggestions on construction.Through the above research,we can establish an effective prevention and early warning mechanism for washout in Rizhao City,and provide a safety basis for disaster prevention and mitigation.