Research On Evaluation And Optimisation Of Flood And Overflow Control Capacity Of Urban Drainage System

Constricted by multiple factors in phase of planning,designing,construction and management of operation,urban drainage system in China shows obvious drawbacks relating to waterlog prevention and combined sewer overflow control.How to identify potential threat of system,and to provide decision support for corresponding engineering measures in the target of system performance improving,is still a difficult problem has yet to be solved.To solve these problems,an integrated method for evaluating and optimizing flood and overflow control capacity of urban drainage system is developed to mitigate urban waterlogging and CSO damage,and to support the system operation performance improving in rainy weather.This research sets up a method for efficiently evaluating the flood and overflow control capacity of urban drainage system based on index system.From pipe section,integrated district to the whole system,an index system concludes 4 overflow indexes and 8 flood indexes was formed considering the average performance and high risk period in the system dynamic process.Also,the index system is quantified based on dynamic modelling under uncertainty conditions of rainfall.Corresponding results elaborates the numerical scale,spatial distribution and time characteristics of flood,overflow and potential control capacity.On the basis of which,the system performance could be evaluated.More over,key regions and periods demands control could be identified,thus determining the proper location and placement priority of typical measures such as internal capacity usage,pipe section replacement and storage tanks.To respond the improvement requirements of flood and overflow capacity of urban drainage system,optimal storage facilities designing method is established considering the influence of rainfall uncertainty.And a multi-objective optimal design model is developed to assist the design.The three objective functions include minimizing weighted average spilled volume from CSOs,total volume of urban flooding,and system retrofit cost.The solving strategy combines stepwise optimization and distributed calculation strategy,and based on non-dominated sorting genetic algorithm II(NSGA_II),which can generate Pareto optimal solutions with reconcile of number,location and scale.With the multiformity of variable types,constrictions and nonlinearsystem behaviors,the algorithm is improved to cut down calculation time to fit the design requirements.The evaluation and optimal method and the corresponding tools could support for more scientific and rational decisions.The established method and developed tools are implemented to a representative complicated drainage system in North District of central Kunming City,China.The characteristic of the drainage system's flood and overflow control capacity is recognized.Area critical for flood and overflow control were highlighted.The pipeline replacement control suggestion for different drainage network is proposed,together with the collection of facility storage design proposals.The case study verifies the feasibility and practicability of the proposed flood and overflow control capacity evaluation method of urban drainage system,the effectiveness of the optimal design method of storage facilities,and the reliability of modeling tools.