| In recent years,with the continuous intensification of climate change,the issue of floods and waterlogging disasters has increasingly attracted p eople’s attention.On August 10,2020,Lueyang experienced a heavy rainfall process.At the same time,affected by the rainstorm in seven counties in Gansu Province upstream,the rivers in Jialing River,Badu River and other basins in the teritory rose sharply.The flood caused widespread disaster in Lueyang County.Large area of water inflow in the county seat,serious damage and collapse of road traffic in the county,interruption of most town office roads,extensive damage to crops,and damage to some water conservancy and power facilities.Flood diversion works need to be built.At present,the water flow characteristics of long-distance flood diversion tunnel projects are mostly studied through theoretical analysis and combined with traditional hydraulic model experiments using small-scale models.This article studies the flow capacity and flow field of long-distance flood diversion tunnels through two-dimensional hydrodynamic numerical simulation,which has important practical engineering significance.This paper takes the flood diversion tunnel project of Lueyang reach of Jialing River as the research background,and through the numerical simulation of the two-dimensional flow field of Jialing River and the flood diversion tunnel under different peak flows,studies the tunnel discharge capacity under different peak flows,the rationality of the hydraulic layout at the inlet and outlet of the flood diversion tunnel,and the impact of the flood diversion tunnel project on the flood level in Lueyang County,providing technical support for the planning and design of the flood diversion tunnel project.The main research content and conclusions are as follows:(1)Based on MIKE21 and FLOW-3D,the overall plane 2D numerical model of Lueyang reach of Jialing River and the local 3D flow field numerical model of flood diversion tunnel inlet and outlet are constructed,and the reliability and applicability of the model are verified.Firstly,in response to the particularity of the horseshoe shaped cross-section of the flood diversion tunnel,a cross-section generalization method was proposed,and a reasonable method for terrain processing and grid processing of the straight wall side wall terrain during two-dimensional numerical modeling was summarized;Secondly,an independence test was conducted on the grid;Finally,the roughness of the original channel of the Jialing River was calibrated according to the measured data of flood trace points in Lueyang reach of the Jialing River,and the roughness of the flood diversion tunnel was calibrated using the calculation results of Xie Cai formula,ensuring the accuracy and reliability of the model.Through numerical simulation,the calculated tunnel flow capacity,water surface profile and other results are compared and analyzed.The twodimensional calculation results are basically consistent with the three-dimensional calculation results,which verifies the applicability of the two-dimensional numerical model to the flood diversion tunnel project in Lueyang County,Jialing River.(2)By analyzing the calculation results of water level and velocity field in the tunnel,the tunnel discharge under different peak discharge is obtained,and the relationship curve between the flood level of Jialing River at the entrance of the diversion tunnel and the discharge capacity of the diversion tunnel is constructed.The total discharge capacity of the tunnel with 10-year return period is 656.83m~3/s,and the corresponding flood level of Jialing River at the entrance of the tunnel is 641.93m;The total flow capacity of the 20-year return period tunnel is 944.52m~3/s,with a corresponding flood level of 643.74m;The total flow capacity of the 30-year return period tunnel is 1129.42m~3/s,with a corresponding flood level of 644.78m;The total flow capacity of the 50 year return period tunnel is 1352.25m~3/s,with a corresponding flood level of 645.98m.The designed discharge capacity of the 30-year flood diversion tunnel is 1145m~3/s,which is basically the same as the calculated results.(3)By analyzing the calculation results of urban flood level in Lueyang County of Jialing River before and after the project,the reduction values of urban flood level under different peak flows are obtained.The reduction values of urban flood level are 0.93m,1.10m,1.18m and 1.26m respectively under the peak flows with 10-year,20-year,30-year and 50-year return periods.The design reduction value of flood level in Lueyang County urban area with a 30-year return period of Jialing River flood diversion tunnel project is 1.22m,which is basically the same as the calculation result.(4)Analyze the local flow patterns at the inlet and outlet of the flood diversion tunnel,and evaluate the rationality of the hydraulic layout at the inlet and outlet of the flood diversion tunnel;The flood water surface profile of Jialing River under different peak flows before and after the project implementation is analyzed,and the impact of the project implementation on the flood water level is expounded;After the implementation of the project,the connection between the river channel and the flood water surface line in the tunnel under different flood peak flows was analyzed.From the overall connection of the water surface line,the connection between the river channel and the water surface line in the tunnel under different flood peak flows is good,indicating that the overall layout of the tunnel is relatively reasonable. |
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