Flood Risk Analysis Of The Middle And Lower Reaches Of Hanbei River

Flood disaster has always been an important problem that puzzles the development of human society.In recent years,with the change of climate,extreme flood events occur frequently,resulting in the aggravation of disaster and loss,and the analysis of flood risk is also concerned.Among them,the flood disaster in the plain-Lake area of Hanbei is the main disaster.The upper part of Hanbei river is under the pressure of mountain flood in the hilly area,and the lower part is supported by the high water level of Hanjiang River and Yangtze River.When the flood comes,the water level along the river generally exceeds the design water level,and the coastal flood control situation is very tense.In this paper,the flood risk of the middle and lower reaches of Hanbei River Basin in Hubei Province is studied comprehensively from three aspects: flood magnitude encounter characteristics,flood overflow simulation and Bayesian network of risk transmission.In the analysis of flood magnitude encounter characteristics,copula function is used to establish the joint distribution of the annual maximum peak discharge of the main and branch flow,to obtain the magnitude encounter probability.In the risk analysis of flood overtopping and breakout,based on the embankment vulnerability curve,one-dimensional hydrodynamics is used to simulate the water level in the study area and analyze the embankment section Finally.By the encounter probability of flood magnitude and the probability of embankment risk under one-dimensional hydrodynamic simulation,the Bayesian network of embankment collapse and risk level of subarea in the middle and lower reaches of Hanbei river is established,and the risk analysis and risk transmission under various scenarios are studied.The main conclusions of this paper are as follows:1)In Archimedes copula family,Frank copula is the optimal joint distribution function of the annual maximum flood peak discharge of the main and branch streams,with a parameter of 5.553.The joint distribution characteristics show that the probability of heavy flood encounter decreases with the increase of the magnitude.In this paper,the node probability table of the Bayesian network provides the parameters.2)The vulnerability curve of embankment in the middle and lower reaches of Hanbei river is obtained.It is found that the higher superelevation of flood water level is,the greater the risk of embankment collapse is.The left embankment of Hanbei river is more likely to break than the right embankment.At the same time,the critical superelevation ofwater level from left embankmentof 1st section to 3th section increases.The embankment situation is integrated into the one-dimensional hydrodynamic simulation of the flood process in the middle and lower reaches of Hanbei River.The flood scenarios under three scenarios are simulated respectively,that is,without considering the scenario of Overtopping,the scenario of only overtopping and the scenario of collapse.Then the number of water level overtopping sections on the left and right banks and the risk of collapse are calculated.It is found that most of the sections of the left and right embankmenthave water level superelevation scenarios,and the left embankmentis more serious.However,under the scenario of overtopping overflow,the water level superelevation sections are significantly reduced.On this basis,although some sections of the embankment section have a certain risk of collapse,the highest risk probability is not more than 0.7.In the calculation of the flood volume,the overflow volume of the collapse scenario is obviously more than that of the only overtopping scenario.The embankment3 th section,which is more prone to the risk of embankment break,has a larger flood volume.In addition,it is also revealed that the risk of spillage in 3th subarea will be reduced when there is a large amount of spillage in 1st subarea and subarea 2nd.3)The Bayesian network of flood risk in the study area is established considering the risk of embankment collapse and the risk of subarea inundation.The risk of each embankment section is analyzed from the two scenarios of prior and posteriori experience respectively.The risk of overflow of the right embankment is relatively small,no risk of collapse,and the risk of overflow of the left embankment is relatively large.Among them,the left embankmentof 1st section is less likely to burst in the left embankment,and more likely to be affected by the main stream flood in 2008 type flood.The left embankmentof2 nd section and 3th section are more likely to be affected by the tributary flood in 1983 type flood,among which the 3th embankment section on the left bank is the highest risk among all embankment sections.In the post test analysis,the risk of other nodes in the state change of the left embankmentof 2nd section also changes,which also reflects the risk transfer of the embankment flooding.In the analysis of inundation risk,3th subarea is more likely to have high or medium risk than other subarea s.Adjust the flood scenario of3.33% of the main stream,and the risks of 1983 and 2008 type flood annual floods are different under this frequency.Among them,the risk of 1983 type flood to upstream 1stsubarea is smaller than that of 2008,but the risk of flooding to 3th subarea is larger,and the flood volume must be generated.In contrast,the risk of 3th subarea under 2008 type shows that there is no risk,which indicates that 2008 type flood has no risk.It is easier to generate the flood volume in the upstream subarea,and the risk transfer occurs.This Bayesian network,which can adjust the state of each node as input,can quickly analyze the risk of embankment collapse and subarea inundation in different scenarios,which provides a reference for flood risk analysis in the middle and lower reaches of Hanbei river.