Study On Hydrological Response To Extreme Rainstorm In High Altitude Controlled Watershed In Loess Hilly And Gully Region

Significant progress has been made in the ecological environment control of the Loess Plateau,and vegetation coverage has been significantly increased,but still facing the Yellow River water volume,the amount of sand continuest o decrease.Erosion and sediment transport are serious under extreme rainstorm conditions.In July 2013,July 2017,extreme rainstorms occurred in the Yan'an and Suide regions of the Loess Plateau,respectively.The rainstorm runoff erosion disaster and the threat to people's life and safety caused the country and the industry to question the ecological benefit of the ecological environme nt construction of the Loess Plateau.In view of the weak response of ecologic al function evolution to extreme rainstorm in the small watershed controlled by height on the Loess Plateau,the similarity theory and the basic principle of hydrodynamics are adopted in this study.Based on the further verification of the normal entity model of Yanan Yanergou Kangjia GE Lao small watersh ed with a scale of 100,the response to extreme rainstorm in different stages o f ecological evolution of the basin is studied.The following conclusions are obtained:(1)verify the present situation model of Yanan Yangou watershed in Ka-ngjia Gelao small watershed.Through the topographic restoration of the normalentity model of the constructed small watershed of Yangou Kangjia GE Lao small watershed located at the Institute of soil and Water Conservation Researc h Institute of Northwest Agriculture and Forestry University of Yang Ling,thet errain is verified,and the maximum confluence time,speed and flow rate are verified.For sediment transport gradation and erosion modulus,the terrain verif yication error is 0.5%,the erosion modulus error is 1.9% and the sediment co ntent error is 4.5%.The results show that the hydrological response of the mo del is basically similar to that of the prototype.It can be used to study the hydrological response of watershed to extreme rainstorm.(2)Response to extreme rainstorm caused by high control of runoff in watershed.The experimental results show that the rainstorm occurs once in a hundred years before the control of the small watershed,the confluence time is0.3 h,the current velocity is 0.84 m/s,and the Hong Feng flow rate is 6.39 m/s.Under the condition of 47.6% of terraces,the current concentration time is 0.58 h,the current flow velocity is 0.41 m/s,the Hong Feng flow rate is 2.8 m/s.For each increase of 1 m in the canopy during vegetation restoration,t he catchment time lag 30%-110%,the maximum flow velocity decreases3%~8%,the runoff decreases 5%~25%,and under the condition of strong rain in a hundred years,the maximum flow rate decreases by 3%~8%,and the runoff decreases by 5%~25%.For each increase in rain intensity of 1 mm / min,th ecatchment time increased 3%~4%,the maximum flow rate increased 4%~ 8%,the runoff increased 10%~40%,the Hong Feng flow increased 5%~40%.(3)Response to extreme rainstorm caused by high control of sediment yi-eld in watershed.A rainstorm occurred once in a hundred years before the small watershed was managed,and the erosion modulus was 8529t/(km2·a).Under the condition of 47.6% terrace,the erosion modulus is 4333 t/(km2·a).In the process of vegetation restoration,the sediment content of runoff decreases by 8%~80% and the erosion modulus decreases by 4.9%~10% with each increase of 1 m in the canopy,and the sediment content increases by 13%~40% and erosion modulus increases by 25%~40% when the rainfall intensity increases by 1mm / min when the rainfall intensity is once in a hundred years,and the erosion modulus increases by 25%~40%.(4)The response of carbon,nitrogen and phosphorus loss to extreme torr-ential rain is highly controlled.Under the condition of 47.6% terrace,for ever-y 1 m increase in the canopy during vegetation restoration,the total carbon in the watershed decreased 4.5% ~ 59.8%,the total nitrogen decreased 4.3% ~ 47.6%.the total phosphorus loss decreased by 4.5%~51.8%.The rainfall intensity increases by 1 mm / min under the condition of rainstorm once in 100 years.The amount of carbon loss increased 4.6%~26.7%,the total nitrogen loss incr-eased 4.1%~26.5%,the total phosphorus loss increased 3.5%~34.7%.The simulated experiments of the watershed with high degree of governan-ce indicated that the runoff and sediment yield and the loss of carbon,nitrogen-n and phosphorus gradually decreased with the ecological evolution under theextreme rainstorm conditions.The ecological functions of flood and sediment c-ontrol and carbon,nitrogen and phosphorus loss are greatly improved under extreme rainstorm conditions.