Flood Risk Analysis Of The Downstream Of Large Reservoirs

With the global climate change and La Nina effect,extreme rainy weather occurs frequently in China,which brings great risks and seriously threatens the safety of people’s lives and property.Since 2012,several dozens of heavy rainfall processes have occurred in Beijing,such as"7.21"rainstorm,""6.24"rainstorm,""7.19"rainstorm and"7.20"rainstorm,which bring great risks to Huairou Reservoir and downstream rivers.The watershed of Huairou Reservoir,located on the windward slope of Jundu Mountain,is a rainstorm-prone area with concentrated rainfall,continental monsoon climate and high flood risk.In order to protect people’s lives and property,the downstream rivers and protection areas on both banks of Huairou Reservoir should be analyzed for flood risk.In this paper,a 1D and 2D Coupling hydrodynamic model,DHMUrban（Distributed Urban Hydrodynamic Model）model are used to simulate the downstream of Huairou Reservoir.Flood with different frequencies is set and the inundation of Huairou Reservoir is simulated by calculation.The flooding situation is analyzed to provide reference for flood control decision-making and has certain academic value.The research contents and results of this paper are as follows:（1）Aiming at the problem of flood risk in the lower reaches of the reservoir,this paper conducts risk analysis and assessment on the downstream of Huairou Reservoir and the protection area,uses the finite volume method and finite difference method to solve the equations discretely,and uses DHMUrban tools to build a 1D and 2D Coupling hydrodynamic model.The rationality of the model is verified by the flood discharge data of Huaihe West spillway in 2021.The simulation results verify the reliability and simulation accuracy of the model,which can be used as a tool for the inundation analysis of the protected area and the flood discharge analysis of the river channel.（2）In response to the problem of inundation on both banks under flood,this article takes the flood inundation in the protection area on both banks downstream of Huairou Reservoir as an example to explore the inundation range and other inundation conditions on both banks under design flood.A 1D and 2D Coupling hydrodynamic model is used to calculate the surface inundation situation on both banks under 50-year,200-year,and 2000-year flood conditions.The model calculation results are extracted and based on the result data,the flooded roads,affected populations Evaluate various flood impact indicators such as the affected GDP.Evaluate and determine the disaster impact of floods at different return periods on the protected areas on both sides of the strait through indicator evaluation,and compare the inundation area,arrival time,and various flood impact indicators under three different return periods to observe the different impacts caused by different flood flows.The results indicate that the disaster impact of floods on flooded areas increases with the increase of recurrence period.（3）In response to the issue of flood discharge risk in river channels,this article studies the flood discharge capacity of the Huaihe River and the obstruction of water blocking structures to floods.Based on the the 1D hydrodynamic model of the Huaihe River downstream of the Huairou Reservoir,the river conditions are calculated at constant flows of 320m³/s,500m³/s,600m^3/s,700m³/s,and 800m³/s,and the discharge points of the river model are recorded.The flood discharge capacity of the downstream river channel is analyzed through the location and quantity of the discharge points,And search for the warning water level of key sections.Selecting floods that occur once every 50-year and once every 2000-year,model calculations were conducted under these two design flood conditions.The water level and flood inundation area of the river section were compared with and without water blocking structures.The results showed that the water level was higher and the inundation area was larger with water blocking structures.This proves that water blocking structures are not conducive to flood discharge in the river.In flood control strategies and related research,the impact of water blocking structures such as rubber dams and bridges in the river should be considered.