The Cost-effectiveness Evaluation Of Urban Rainwater Runoff Control Facilities

Initial stormwater from diversionary drainage systems is a major source of pollution in the urban water environment and it has become the focus of water pollution control.Constructing sponge city can effectively solve the problem of urban initial stormwater runoff pollution,but the cost of construction and maintenance of runoff control facilities cannot be ignored.In order to reflect the effectiveness of control facilities for stormwater runoff control more comprehensively and objectively,both effectiveness and cost of the facilities should be taken into account when select control facilities.This study introduces the concept of life cycle cost and uses costeffectiveness to evaluate control facilities.The main studies of this paper are as follows:(1)An independent drainage area in a southern city was used as the study object to analyze its runoff pollution characteristics.The results of the analysis of runoff pollution loads from different types of road(roof)surfaces show that : Pollutant concentrations in the runoff will gradually decrease as the runoff time increases,with higher concentrations in the first 30 min;runoff pollutant concentrations are higher on viaduct pavements and main road pavements than on subdivision pavements and building roofs.(2)The Info Works ICM model is used to construct the hydrological,hydraulic and water quality models and rate the model parameters based on the data of the pipe network,subsurface and rainfall in the study area.Then source low impact development facilities and terminal storage facilities are added into the model to obtain an urban drainage system model for the study area.(3)Permeable pavements,green roofs,bioretention grids and terminal storage tanks are selected as the low impact development facilities,the Info Works ICM-based drainage system model is used to simulate the control rate of each control facility on runoff volume and the reduction rate of runoff pollution,and to examine the effect of rainfall return period on the control effect of various control facilities and to compare and analyze the control effect of low impact development facilities.With the increase of rainfall return period,the reduction rate of SS,COD and TN in runoff of each control facility gradually increases,the control rate of permeable pavement,green roof and storage tank on runoff gradually decreases,and the control rate of bioretention grid on runoff gradually increases.In terms of runoff volume control,permeable pavement has the highest runoff control rate per unit area;in terms of runoff pollution reduction,green roofs have the highest runoff pollution reduction rate per unit area.(4)By introducing the concept of life cycle cost,the cost-effectiveness is defined and its formula is derived.The cost-effectiveness of runoff control,the cost effectiveness of runoff pollution control and the total cost effectiveness of runoff control for each control facility are calculated.The total cost-effectiveness of low impact development facilities at source is ranked from highest to lowest as green roofs,permeable pavement,bioretention grids;the total cost-effectiveness of terminal storage tank is higher than that of the source low impact development facilities.For low impact development facilities at the source,the larger the design size,the less costeffectiveness it is,the terminal storage tank has the highest cost-effectiveness with a storage capacity of 10 mm.