Study On Waterlogging Causes And Risk Control In Coastal Cities

Under global climate change and rapid urbanization,extreme disaster weather is prone to occur frequently.For coastal cities,the rainstorm brought by typhoons leads to floods and severe urban traffic congestion,causing huge economic losses to the normal work,production and life of the city.Therefore,how to deal with urban waterlogging scientifically and effectively,so as to avoid or reduce the loss of life and property caused by waterlogging disaster,has always been a research hotspot in urban development.Taking Fengban River Basin in Fuzhou City as an example,this thesis constructed a refined urban rainstorm waterlogging model based on Infoworks ICM.The model parameters were determined by measured historical rainfall events,and the accuracy and effectiveness of the model were verified.The research simulates the surface waterlogging process under different return periods of designed rainfall,analyzes the causes of waterlogging,and explores the mitigation effect of urban waterlogging control and reduction measures on rainstorm waterlogging in the study area.The main research results are as follows:(1)By collecting the basic data of the study area,summarizing the drainage network and river system,and dividing the first-level sub-catchment area,a one-dimensional drainage network model,a river channel model and a two-dimensional surface overflow coupling model were constructed based on Infoworks ICM to realize the simulation of urban rainstorm waterlogging.Using the downhole liquid level data,the water depth data and the water range data of the surface water measurement station under the two measured rainstorm conditions of Typhoon Lubi in 2021,the parameter calibration and accuracy verification of the model were carried out.The results show that the peak occurrence time,peak relative error,Nash efficiency coefficient and water depth meet the error requirements of 30 min,25%,0.5 and 20% respectively.The simulation accuracy of the model is high,and the model is effective and feasible.(2)Based on the constructed waterlogging model,seven rainfall scenarios in different return periods are designed,and the node overflow,pipe network carrying capacity and surface inundation conditions under each return period scenario are simulated and analyzed.Results show that the once every five years and 5 years in a design under the rain,the study area overflow node number and the full number of pipe flow and hydraulic gradient is smaller than the pipe grade with getting return period increased when more than 5 years in a design rainfall,the overflow node number increase speed gradually slow,full flow and hydraulic gradient lower than that of the slope of the pipe number increases along with the return period.The reason is that when the designed rainfall return period is more than once in five years,the carrying capacity of the drainage network in the study area has reached the maximum limit and cannot accommodate more rain.Through scenario analysis,it can be seen that the design standard of rainwater pipe network in this region is low,local low-lying,impervious water surface expansion and high water level jacking of downstream river are the main reasons for its serious waterlogging disaster.(3)According to the causes of waterlogging,the thesis puts forward the waterlogging control reduction and reform measures from the aspects of pipe network layout,vertical adjustment and LID construction,and compares the waterlogging control and prevention effect of the city after the reform with the indicators of node overflow,pipe network carrying capacity and surface inundation.The results show that the reconstruction measures proposed by the research institute can effectively alleviate the waterlogging disaster in the study area,especially for the rainfall events with relatively low return period,the reduction effect of the number of overflow nodes and the waterlogging risk can reach 60%-100%For coastal cities,the heavy rain brought by typhoons leads to floods and urban traffic congestion,causing serious economic losses and affecting normal work,production and life.Therefore,how to deal with the problem of urban waterlogging scientifically and effectively,so as to avoid or reduce the loss of life and property caused by waterlogging disaster,has always been a research hotspot of urban development.