Flood Simulation And Early Warning Forecasting In The Suyukou Watershed At East Of Helan Mountain

Flash floods are natural disaster phenomena such as floods,landslides and mudslides caused by heavy precipitation in hilly areas,which often have a great impact on ecological environment,resulting in serious consequences.They also have an impact on the economic development of mountainous areas and the safety of people living in mountainous areas.In recent years,due to climate and subsurface changes and other reasons,flash floods occur frequently in the northwest of China,and there is a trend of increasing extreme rainstorms along the east of Helan Mountains.In the prevention and control of flash floods,in addition to the constructed engineering measures,non-engineering measures are also an important component.The prevention and control of flash floods should establish an effective early warning mechanism for flash floods with the existing engineering measures.In this paper,the geomorphological characteristics of heavy rainfall and flash flood events in the east of Helan Mountains were investigated as the research object.And HEC-HMS(Hydrologic Engineering Center-Hydrologic Modeling System)is used to simulate the historical flash flood events in the area’s Suyukou watershed and explore the rain-flood relationship,and based on the distribution characteristics of rainfall in Suyukou over time,six characteristic rain patterns based on rain pattern characteristic parameters are constructed.Accordingly,the early warning indicators of flash flood occurrence under different conditions are deduced,and the main findings of this paper are:(1)A preliminary survey of the basic geomorphological and hydro-meteorological data of the east of Helan Mountains revealed that flash floods are serious in the Helan Mountains area.In terms of time distribution,flash flood disasters in the area are concentrated in summer.The Suyukou watershed is one of the watersheds where flash floods occur most frequently and on a large scale in the east of Helan Mountains.The occurrence of flash floods in the east of Helan Mountains is consistent with the spatial and temporal variation of the occurrence of heavy precipitation,indicating that the main cause of the occurrence of flash floods in Helan Mountains is the appearance of heavy precipitation.(2)Through ArcGIS and HEC-GeoHMS,the 12.5 m*12.5 m Digital Elevation Model(DEM)of the Suyukou watershed area was used to generate the digital water system map of Suyukou watershed,and a digital watershed model of Suyukou watershed was generated with a typical flood control section of Suyukou watershed as the outlet to provide basic watershed information for the subsequent hydrological simulation.(3)The design flood was deduced and analyzed based on the flow information of Suyukou hydrological station.A combination of automatic rate determination and manual rate determination was used to simulate 5 field floods of the rate period by continuously trial calculation,which stop when the optimized simulation results were close to the actual measurement results.Five field floods in the validation period were selected for simulation,and good simulation results were obtained,which proved that the HEC-HMS hydrological model is suitable for flash flood simulation in the Suyukou basin and can provide good support for flash flood simulation and early warning forecast.(4)By analyzing the characteristics of rainfall time distribution in the Suyukou watershed,six rain patterns were constructed based on the rain pattern characteristic parameters,which can more accurately deduce the early warning indexes in line with the actual local conditions in the Suyukou watershed.The soil water content of the study area is analyzed,and the disaster-causing flow rate of the study object is obtained by actually measuring the location of the typical flood control section and its water level-flow rate relationship curve as well as the disaster-causing water level of the Suyukou watershed.The HECHMS model is used to simulate the flood process lines under different rain types,and the flood flow is compared with the warning critical flow to obtain the critical rainfall under different conditions and to deduce the warning index.