Simulation Of Mountain Flood Inundation In Small Watershed Based On HEC-RAS Model And Its Application To The Control Of Qianyou River Reach

In order to improve the efficiency of small watershed governance,this paper uses the HEC-RAS model to carry out two-dimensional simulation of small watershed flood inundation,and then formulates corresponding flood control measures.This article takes the governance section of the Qianyou River as the research object.According to the corresponding provisions of the "Flood Control Standard(GB50201-2014)",the rural protection area has a population of less than 200,000 or arable land area of less than300,000 mu,and the flood control level is IV.The corresponding flood control design standard is once every 20 years.By collecting the basic data of the Qianyou River Basin,using the three methods of hydrological analogy,reasoning formula,and hydrological manual empirical formula,the design flood calculation of the Qianyou River treatment section is carried out,and the design flood calculation results are determined through the rational analysis of the results,to provide basic data for HEC-RAS simulation of flood inundation.The accuracy of the digital elevation topographic map of the treatment section of the Qianyou River selected this time is 12.5m.The specific location of the river channel is not obvious in the topographic map,and the accuracy of flood inundation simulation is relatively low.Therefore,based on the field measurement data and Google Earth map coverage data combined with HEC-RAS and Arc-GIS,this paper reconstructs the channel of the Qianyou River governance section,so that the hydrological information such as the length,depth,and width of the governance channel can be displayed in the topographic map.clearly displayed.On this basis,based on the existing data and design flood calculation results,HEC-RAS is used to carry out two-dimensional unsteady flow flood inundation simulation for the treatment section of Qianyou River.The calculation principle of the unsteady flow module of HEC-RAS is based on the UNET model proposed by Robert L.Barkau,which realizes the two-dimensional effect display of the flood submerged range on the map.The main achievements of the paper are as follows:(1)Floods in the Qianyou River Basin are mainly caused by torrential rains.Floods in the basin occur at the earliest in May and at the latest in October.However,floods with large magnitude and intensity generally occur in July to September,and There is an 80% chance of monthly floods.Most of the floods have the characteristics of high peak,small volume,steep rise and fall during the flood process,and a single peak in the peak shape;due to the small basin area,the duration of a flood process is about 1 day.The HEC-RAS model was used to simulate the one-day flood process of the Qianyou River treatment section once in 20 years.The simulation results of the HEC-RAS model showed that: Five villages and 25 areas in Hecun will be at risk of flooding.(2)According to the flood inundation simulation data of HEC-RAS,the 20-year flood control measures for the treatment section of the Qianyou River were formulated,and finally a flood control wall with a height of 4.16-7.26 m and a width of 3m at the top of the embankment was designed and constructed on the bank of the treatment section;The revetment project is 1m in foot protection and 0.6m in thickness;the anti-seepage wall poured with concrete is 0.4m in thickness,2.2m in average buried depth and 4.16-7.26 m in total height.(3)Based on the HEC-RAS model,the reliability and practicability of the flood control measures for the Qianyou River were carried out.According to the flood control wall with the proposed flood control measures,the HEC-RAS model is used again to carry out the simulation of the inundation of the Qianyou River control section when the 20-year flood comes.The results showed that the average submerged water depth decreased by 89.88%,the submerged area decreased by 96.27%,and the number of economic construction losses decreased by94.29%.It shows that the two-dimensional simulation of flood inundation in small watersheds based on the HEC-RAS model in this paper has a significant effect,which can provide data support for the design of flood control structures,and the results will help improve the efficiency of river management in small watersheds.