Construction Of Rain Flood Safety Pattern In Liuyang River Basin Based On Flood Regulation Service

Flood disasters are one of the major natural disasters in the south,posing a major threat to the safety of people’s lives and property.In recent years,China’s cities have expanded rapidly.Changes in the shape and imperm eability of the underlying surface have affected the hydrological process.The cities have also brought a high concentration of a large number of people and properties,resulting in increased losses from floods and waterlogging.In order to cope with flood disasters,China has formed a flood control system that combines engineering and non-engineering projects with "dykes as the mainstay,reservoir regulation,and storage and stagnation as the supplement",and has carried out the pilot construction of spong e cities.However,the current flood regulation service capacity of the ecosystem is not fully exploited,and the contradiction of flood regulation is still prominent.In addition,the focus of flood control work at different spatial scales is unclear,lac k of systematic connection,and the flood control at the meso-basin scale is the weakest.Therefore,it is very important to measure the supply of flood regulation services in the watershed ecosystem at the mesoscale,human society’s demand for flood regul ation services,and the matching relationship between service supply and service demand,for alleviating flood disasters and protecting the water ecological environment.This paper takes the Liuyang River Basin at the mesoscale as the research area,and co nducts research based on the measured data of extreme rainstorms in the middle and lower reaches of the Yangtze River in 2017.Large-scale extreme rainstorms have led to overburdens in the lower reaches of the Yangtze River,and the floods of the Xiangjian g River cannot be discharged.Therefore,seeking a balance between supply and demand of flood regulation services within the basin is an effective means to achieve rainwater safety.First of all,this paper classifies the service supply of the watershed ac cording to the current flood control system,calculates the actual supply composed of soil and water system through the SCS model and the water tank storage formula,identifies and selects depressions by the equal volume method and landscape index,etc.,a nd calculates the potential supply of depressions.quantity.Secondly,according to the flood risk assessment,the service demand is classified,the rainfall is the total demand,the medium to high risk area is the rigid potential demand,the lower and low risk areas are the elastic potential demand,and then the respective demand is calculated.Finally,the quantity matching and spatial matching can reflect the realization degree of the flood regulation service demand of each catchment area,and the source-sink relationship of each catchment area in the river basin can be identified according to the matching of supply and demand.Flood the security pattern and put forward management and control strategies.The research shows that:(1)the actual supply of flood regulation services under the current flood control system generally can not meet the demand of flood regulation services under Extreme Rainstorm scenarios,which is easy to cause loss of life and pro perty.The actual supply surplus is only the catchment area where the two large reservoirs are located,which shows that the large reservoirs have good flood regulation service supply capacity,but the resources of large reservoirs are scarce and the servi ce area is relatively limited;(2)The depression resources in Liuyang River Basin are relatively rich,and the land area is only1.41% of the very important depression subjects in the whole basin.The potential supply provided by the main body can basical ly meet the flood regulation service demand of the basin.On the meso basin scale,depressions have important flood control significance,but in the lower reaches of the basin,the central urban area of Changsha is extremely short of depressions,and there is still a contradiction between supply and demand.Therefore,it is very important to retain some depressions as the main supply body of flood regulation services in urban construction land;(3)The rain and flood safety pattern needs to be managed and controlled in different areas,and the gathering of urban areas in the lower reaches of the Liuyang River has formed a very important source of imbalance between supply and demand.To achieve a balance between supply and demand in the watershed,gray infras tructure needs to be used in the downstream urban areas to make up.According to the quantity matching and spatial matching of supply and demand of flood regulation services in the catchment area,the layout of facilities at the micro level can be guided.