Research On The Calculation Method Of Bridge And Culvert Design Flood Flow In Qinba Mountain Area

The Qinba mountains have complicated terrain and abundant rainfall,which make natural disasters occur frequently,and the flood damage in the bridge and culverts along the highway is serious.In order to improve the anti-water damage ability of Qinba mountains highway bridges,and explore the calculation method of design flood flow suitable for the characteristics of Qinba mountains bridge and culverts waterlogging.Based on this,we set Qinba mountains as the research background,through on-site investigation and theoretical analysis,based on the traditional flood flow calculation method,analyzed the sensitivity of the major disaster factors,and the parameters were optimized in a targeted manner.Finally,an optimization algorithm with more characteristics in the Qinba Mountains was proposed.The main contents were as follows:?1?Introducing the natural geography of Qinba mountains from the aspects of climate,geographical conditions,rainfall influence,and the waterlogging mechanism.The Pingkan-Hanzhong section of the Dinghan Line in Shaanxi was selected as the key survey area to explore the factors affecting the damage of highways and bridges in the Qinba Mountains.In combination with the actual water damage status in the Hanzhong,Ankang,and Shangluo,the proportion of water-damage types in different bridges and culverts and their disaster-causing mechanism were analyzed.?2?The concept of sensitivity coefficient is introduced,and sensitivity coefficient is used as the criterion to measure the sensitivity of parameters.The local sensitivity analysis method is used to test the sensitivity of single parameter with different degrees of disturbance,such as±0.5%,±1%,±2%and so on.Finally,judging the effect of each factor on the formula by the sensitivity of single parameter.?3?Introducing several traditional methods for calculating the bridge design flood flow:single factor method,area analogy method,and comprehensive parameter method.Selecting the main factors,sensitivity analysis was conducted on those factors respectively,and the results were as follows:???.It showed that basin area had the greatest impact on the flow of floods,followed by point heavy rainfall,and the impact of river slopes was smallest.Then,modifying the parameters with greater sensitivity and the optimization algorithm was put forward,which was applied to engineering cases.The calculation result of the reasoning formula method was taken as the standard for checking computations.Compared with the traditional calculation method,the optimization algorithm can reduce the error separately:7.76%,3.62%and 13.97%.?4?Introducing several traditional methods for calculating the culvert design flood flow:diameter manifold method,reasoning formula method.Selecting the main factors,sensitivity analysis was conducted on those factors respectively,and the results were as follows:???.It showed that runoff thickness had the greatest impact on the design flood flow rate,followed by the geomorphic coefficient,geomorphic coefficient,the precipitation effect reduction factor,and the flood propagation reduction factor and so on,the influence of plant interception runoff thickness was the smallest.For plant interception runoff thickness,we combined the characteristics of the Qinba mountains and national universal value table,refining the value interval,and the recommended value of the plant interception runoff thickness in Qinba mountain area was given.Assigning parameters such as ?₀,?,?,?,gand so on,so as to simplify the calculation process.The optimization algorithm was put forward,which was applied to engineering cases.The calculation result of the reasoning formula method was taken as the standard for checking computations.Compared with the traditional calculation method,the optimization algorithm can reduce the error:4.25%.