Study On Performance Evaluation And Optimization Method Of Rainwater Drainage System In Old Urban Area

Under the background of accelerating urbanization and frequent urban inundation disasters,the urban rainwater drainage system is under great pressure.Sponge City,as a new way of rainwater management,is widely valued by people.The old urban area has a higher risk of inundation than the newly-urbanized area because of its aged construction,imperfect design.Taking the old urban area of Xiaozhai in Xi’an as the research area,combined with the AHPFEM method,this study explores the background characteristics of the old urban area;Then,this study uses the 2D hydrodynamic rain flood model to analyze and evaluate the performance of rainwater drainage system before and after sponge reconstruction in the study area;Finally,based on the Kriging agent model and the particle swarm optimization algorithm,the pipe network system optimization is carried out in area B,where there still has serious inundation problem.The main conclusions are as follows:(1)When analyzing the background characteristics of the whole Xiaozhai old urban area and the four sub areas a,B,C and D,this study introduces the indicators of rainwater drainage characteristics,and uses the analytic hierarchy process fuzzy comprehensive evaluation method for quantitative evaluation.According to the weight vector of the index layer to the target layer,it can be concluded that the weight proportion of the hardening rate of underlying surface,the drainage capacity of the pipe network,and the regulation and storage capacity is the largest.It shows that them have the greatest impact on the rainwater drainage characteristics;In conducting the fuzzy evaluation,the background characteristics of the old urban area of Xiaozhai before and after sponge construction are quantitatively assessed.It is concluded that the scores of areas A,B,C and D before the sponge construction are low,and there has a large risk of water disaster.After the sponge transformation,the scores of these four areas are significantly improved,of which area A is increased by 21.73 points,the effect is the most significant,however area D only is increased by 7.15 points,the effect is not obvious.The key is that area D is mainly dominated by pipe network transformation,but area A has also carried out large-scale green facility transformation and built large-volume regulation and storage facilities.(2)Based on the 2D hydrodynamic rain flood model,the model of Xiaozhai old urban area is constructed,and the effect of sponge reconstruction on the performance of rainwater drainage system in the old urban area is evaluated from the perspective of numerical simulation.It is concluded that when the return period of design rainfall in the whole area before sponge construction exceeds 10 years,the whole area begins to experience waterlogging,and when the return period is 50 years and 100 years,the number of waterlogging points in the whole area is 29;After the sponge construction,when the return period is 10 years or less,there is basically no waterlogging point.For the working conditions with a return period of 50 years and 100 years,there are only 15 waterlogging points in the whole region,which has been significantly improved compared with that before the sponge construction.(3)For sub area B where inundation still exists after sponge construction,the drainage pipe network in area B is optimized.In this study,the Kriging model is constructed for the sample data through the calculation results of the hydrodynamic model,and is used as an agent model to replace the two-dimensional hydrodynamic calculation process for multi-objective optimization in the particle swarm optimization algorithm.After optimization,the Pareto solution curve is obtained.Under the condition of taking into account the two optimization objectives of total investment of pipe network and total inundation water volume,point P is selected as the optimal scheme after optimization.By comparing and analyzing the surface ponding,pipeline load and outlet flow with the original planning scheme,it is proved that the scheme is reasonable and can significantly improve the drainage capacity of the pipe network system.