Numerical Simulation Of 2-D Flood Evolution In Taiyuan Section Of Fen River

Fen River is the largest river in Shanxi,the total length about 710 km.It flows from north to south through the whole Taiyuan area.In recent years,in order to improve the urban environment and river flood capacity,the Taiyuan municipal government implemented river harnessing and landscaping construction plan.The comprehensive treatment project in Taiyuan area includes water storage project(building 7 rubber dams)and wetland construction.It forms a green corridor in the city center and improves the river ecological environment.Because Fen River is a seasonal river and the rainfall is mainly concentrated in July and August,the flood duration is short and the peak flow is large.According to the flood of different flow,it is a significant problem to ensure the safety that how to manage the rubber dam.Base on river flow characteristics in Taiyuan,the 2-D flood evolution numerical simulation was established.Occurring once-in-five-years and once-in-a-century flood,researched the evolution process through the engineering area including the change of water level,flow and velocity.It has great significance to ensure river safety.The main research contents andconclusions are as follows:(1)By reading the literature of flood evolution at home and abroad,the research status of domestic and foreign has been comprehensively understood,and the numerical simulation method of flood evolution is summarized.(2)Based on the hybrid method of fractional steps,the 2-D mathematical model of flood evolution is established.First of all,after meshed the natural river channel before building engineering,calculated with hydrological data from September 1 to 16,1978,and compared with 1-D results.The results show that the model can better reflect the rule of flood evolution.(3)Using the mathematical model to calculate and analyze the flood evolution after built engineering.Occurring 1% flood,when all rubber dam height is 0,simulated flood evolution;occurring 20% flood,under 5 schemes,simulated flood evolution.In different time,the variation of water level and flow at different positions are analyzed.(4)The results show that the flood propagates in the form of wave and the wave crest is gradually changed in the process of propagation.Occurring 20%flood,from Lancun to 1# dam,flood peak arrivals need about 3.5 hours and peak flow decreases from 1394m3/s to 1262m3/s;occurring 1% flood,from Lancun to 1# dam,flood peak arrivals need about 1 hour and peak flow decreases from 3777m3/s to 3262m3/s.(5)Occurring 1% flood,in the engineering river,the variation range of water depth is 4.2m~4.6m.Maximum flow rate 2.66m/s is appeared in front ofthe left bank of the 5# dam.In all sections,the water level is less than the crest elevation of breakwater and flood can safely pass.(6)The decrease of 1#dam height is a key index to rubber dam management,directly affecting the flood’s flow distribution proportion for storage channel and muddy channel.Meanwhile,if storage channel downstream rubber dam height is the same as 1# dam height,the rubber dam doesn’t have backwater effect.(7)Occurring 20% flood,compared 5 schemes,scheme C(1# ~ 7# dams decreasing height were 0.8m,0.8m,0.8m,0.8m,1.2m,1.45 m,1.6m)is the optimal scheme that can ensure the river safety,protect the platform greening and avoid water waste.In scheme C,the flood flows only in the main channel and doesn’t inundate the embankment.(8)Occurring 20% flood,under the different rubber dam height,the results of water level and flow though the engineering river,can provide important reference value to manage rubber dam for built Fen river beautification project.