Flood Simulation And Risk Analysis In Mountainous Areas Under Special Working Conditions

Flash flood is one of the frequent natural disasters in China,which often cause serious loss of life and property in disaster areas.In recent years,the frequency of extreme rainfall has been increasing,and hydraulic construction accidents such as bridge erosion have also appeared.There have been many flash floods in the history of Jiehe River Basin in Yantai City,Shandong Province,which have brought great losses to coastal residents.In this paper,taking the boundary river basin as an example,a one-dimensional and two-dimensional coupled hydrodynamic model is constructed to simulate the flooding in hilly areas under various special working conditions,and the impact and risk of floods under various working conditions are analyzed.The main research contents of this paper are as follows:(1)Construct one-dimensional and two-dimensional coupled hydrodynamic model.Through the measured peak data,the river roughness parameter required in the one-dimensional hydrodynamic model is calibrated and finally selected as 0.027;The coupled hydrodynamic model is verified by the measured flood mark data,and the relative error is less than 10%,and the simulation accuracy of the model is good.(2)The flow velocity of the main stream of Jiehe River is simulated,and the high probability position of special working conditions is determined according to the actual situation of the river.By modifying the parameters of one-dimensional hydrodynamic model,the flood inundation simulation of three special working conditions,namely river sediment deposition,bridge blockage(blockage rate is 75%and 50%)and bridge blockage and breach,is completed.The results show that the sediment deposition has the greatest influence on the area of flood inundation in the study area,the second condition is that the collapse condition after bridge blocking,and the condition that the bridge is blocked in different degrees(blocking rate is 75%and 50%)is the smallest,the flooded areas under the condition that encountering the once-in-a-century flood are 13.95 km~2,11.96 km~2,11.07 km~2and 10.9 km~2,respectively.(3)The influence and economic losses caused by flood caused by various working conditions were estimated by estimating.The results show that the economic losses caused by damage of household property and housing are much greater than those caused by the damage of arable land and roads,and with the increase of flood magnitude,the proportion of economic loss caused by household property and housing is increasing.Under the same recurrence period,the most economic losses are caused by collapse condition after bridge blocking,followed by bridge blocking(blocking rate is 75%,50%),and river silting is the least,the economic losses were 17.5 billion yuan,16.47 billion yuan,14.7 billion yuan,13.9billion yuan,respectively.(4)The flood risk under various conditions were analyzed based on the analytic hierarchy process(AHP),the weight of each index were determined by taking the grid of87×87 m~2as the calcaulating unit,and the flood risk calculation and analysis under 15different scenarios were completed by using the variant formula of data standardization,the standardized formula can be used to compare the risk of different working conditions.The results show that the flood risk areas are mostly distributed along the river course,and the risk areas perpendicular to the river course less,and the most of high risk areas are near the confluence of the mainstream of the Jihe and the tributary of Luoshan which located in the northern part of the city When the once-in a century flood occurs in the research area,the total area of high risk area and the more higher risk area is 1.98 km~2,2.51 km~2,2.23 km~2,2.44 km2,2.53 km~2,respectively under the condition of no special condition,sediment deposition condition,50%bridge blocking condition,75%bridge blocking condition and collapse condition after bridge blocking.The standardized formula can be used to compare the risk of different working conditions.