Analysis of Flood Carrying Capacity Change of Small and Medium-sized Rivers in the Upper Reaches of the Zhanghe River in Southern Shanxi

Abstract

Using hydrological data and historical flood survey data of the design rivers, the cross-sections of different reaches are measured, and the hydraulic factors of each cross-section are calculated. HEC-RAS (5.0.7) software is used to analyze and calculate the flood water surface lines of different reaches. Taking the cross-sections measured furthest upstream as the starting points and flood peak discharges of 2% flood frequency and the corresponding water levels as the initial and boundary conditions, the design water surface lines of the design reaches are calculated, And recheck calculation of embankment top elevations is performed. And the results show that: (1) the main channels of the rivers shrink continuously due to the short flood discharge time and the influence of farming and other human activities; (2) the average longitudinal slopes of the Cuiguo Village and Du Village reaches of the Jimingshui River are 9.8 ‰ and 7.2 ‰ respectively, and the average longitudinal slope of the Xixiawang Village reach of the Qinjiagou River is 8.6 ‰; (3) the roughness values of different reaches are analyzed, and the calculated design flood water levels of the Cuiguo Village and Du Village reaches of the Jimingshui River and the Xixiawang Village reach of the Qinjiagou River when a great flood with P=2% occurs are 966.6 m, 938.05 m and 931.16 m, respectively, which are all lower than the embankment top elevations of the left and right banks by more than 2 meters, indicating that the flood in these reaches will not overflow and can pass safely.