Study On The Flood Carrying Capacity And Flood Risk Zoning Of Small And Medium-sized Watersheds In Xinfeng County

The topography of small and medium-sized river basins in Jiangxi Province is complex,with alternating hilly and plain topography,and flooding occurs frequently,causing great impact on the safety of residents’lives and properties.The changing channel cross-sectional morphology of small and medium-sized rivers,coupled with years of scouring and siltation,often causes uncertainty in the flooding capacity of rivers.It is of great practical significance to study how to scientifically and reasonably assess the flooding capacity of small and medium-sized river basins in Jiangxi Province under the current conditions and to classify the flood risk level of the affected areas,so as to provide a scientific basis for making flood prevention and mitigation decisions.In this paper,three small and medium-sized rivers in Jiangxi Province,including the Xi River,the Dong River and the Anxi River in Xinfeng County,are used as research objects to explore the use of MIKE11 to establish a one-dimensional hydrodynamic model of rivers and to analyze the flooding capacity of small and medium-sized rivers under specific complex river cross-section conditions by simulating the river flood evolution process.Arcgis was used to delineate three zones of flood risk areas in Xinfeng County,where the Xi River,Dong River and Anxi River are located.On this basis,the flood risk levels of rivers with different watershed areas were classified using MIKE11 and FLOODGIS.Among them,taking 200km~2as the boundary,a one-dimensional hydrodynamic model was constructed to calculate the characteristic water level for rivers with watershed area of50-200km~2,and the river risk class range was outlined by combining with DEM data;a two-dimensional hydrodynamic model was constructed using FLOODGIS,a flood analysis software,to calculate the comprehensive risk degree R value for rivers with watershed area of 200km~2or more;the remaining area was analyzed by flow production coefficient The remaining area is analyzed by the flood risk method and classified into risk classes.The main work and conclusions of this paper are as follows:(1)Rainfall data were collected,and the annual rainfall patterns of the Xi River,Dong River and Anxi River were calculated and analyzed and studied by the month-by-month averaging method.The results show that the intra-annual rainfall in Xinfeng County is characterized by a single peak of"high in the first half of the year and low in the second half of the year";the inter-annual rainfall patterns were calculated and analyzed by linear regression,MK test,sliding t-test and wavelet analysis,etc.The results show that from 1981 to 2021,the rainfall in Xinfeng County fluctuates at an average rate of 4.6 mm/a in fluctuating and uniform increase.The years with obvious sudden changes in rainfall are 1987 and 1993.There are two main cycles of rainfall,the first main cycle and the second main cycle are 17a and 7a,respectively,and the corresponding cycle under the 17a main cycle condition is 13a,and the cycle under the 7a main cycle condition is 5a.(2)Using the frequency distribution function to calculate the design storm,the design flood flow and its design flood process were projected for each frequency at the Daa station of the Xi River,the entrance to the study area of the Dong River,the entrance to the study area of the Anxi River and the confluence entrance of their respective tributaries using the hydrological comparison method.The one-dimensional hydrodynamic models of the Xi River,Dong River and Anxi River were constructed by MIKE11 software for the current state of the river network shp data,water level and flow data of the hydrological gauging station cross-sections,and water retention of the river structures.The reasonableness of the constructed one-dimensional hydrodynamic model was verified.Using the constructed model,the along-channel design flood levels of the Xi River,Dong River and Anxi River were derived by combining the measured 15 river cross-sectional dimension data of the Xi River,Dong River and Anxi River in 2019 and the typical flood process of the fifty-year event in 20160617 field.After comparing the model calculated water level and the top elevation of the river embankment section,the weak flooding capacity of the Xi River,Dong River and Anxi River were identified,and suggestions for flood control countermeasures for the weak river sections were proposed.(3)Considering flood,topography,river system,population distribution and other factors,the main river flood control zone,mountain flood threat zone and local flood threat zone in Xinfeng County were divided using GIS,and the three zones of Xinfeng County were mapped.For the 13 rivers with watershed area of 50-200km~2in Xinfeng County,MIKE11 modeling analysis was used to derive each design frequency water level value,combined with the section elevation to classify the flood risk level;for the 6 rivers with watershed area of 200km~2or more,a two-dimensional hydrodynamic model was constructed using FLOODGIS,and the measured flood trace data was used to rate the roughness and verify the reasonableness of the model.The inundation depth data were input into the model to get the comprehensive risk degree R value for six rivers over 200km~2;for mountainous flood threat area and local flood threat area,the flow production coefficient method was used to calculate the R value.Based on the R-value,the flood risk level was determined and the flood risk zoning map of Xinfeng County was drawn.Finally,on the basis of flood risk zoning,measures to reduce flood risk,improve flood control facilities and implement flood avoidance transfer are proposed.