Optimization Technique Of The Low Impact Development Facilities In Shenzhen Qianhai District

This research focuses on exploring the control strategies of reducing the runoff and the non-point source pollution.We use the SWMM software to simulate the runoff,the non-point source pollution,and the water logging points.We deploy the LID facilities in the model to reduce the runoff and the non-point source pollution.To get the best reduction effect,we borrow the optimizing algorithms in computer science to optimize the LID facilities’configuration.Then according to the simulation results,we can provide suitable suggestion for the future urban design in Qianhai.This research investigates the water quality of the two main rivers,along which six monitoring stations are arranged.The concentrations of TSS、BOD₅、COD、NH₃-N、TN in dry season are among 3.5-25.6 m/L、2.2-34.8 mg/L、43.5-116.6 mg/L、2.9-9.8mg/L、9.8-20.6 mg/L、0.4-0.7 mg/L;The concentrations of TSS、BOD₅、COD、NH₃-N、TN in rainy season are among 26.0-62.7 mg/L、7.8-57.2 mg/L、51.5-126.1 mg/L、1.3-14.9 mg/L、8.8-19.5 mg/L、0.3-0.9 mg/L.The authors found that the water quality is lower than the IV surface water quality standard,and need to be improved in urgent.This research uses water environment capacity and class IV water quality standards as the target than getting the reduction demands for specific non-point source pollutants.We get that the reduction percent of COD、NH₃-N、TP、BOD₅、TN、TSS are 76.4%、62.7%、56.7%、61.4%、85.5%、23.5%.The research establishes tree types of LID facilities（permeable pavement、vegetable swale and retention pool）to treat the runoff,and find the best result of the optimization problem which takes the minimization of LID facilities’area as the goal and the control of runoff quantity and non-point source pollution quantity as the constraints.The optimal decision is that three types of LID facilities take 3.3%-19.2%in each sub-catchment,and arrange ecological water tank and constructed wetlandWe apply the above optimization algorithm in designing the LID facility configurations in an example area.We get that the permeable pavement should occupy the 6.9%of the road,30%of the green space should be used to layout the vegetable swale and 5%of the green space should be placed with the bio-retention.We build three rain barrels and 0.8 hectare wetlands at the water logging points.Finally,in a rainstorm lasted for two hours,the annual total runoff reduction rate is 70.7%,the runoff peak quantity reduction rate is 65.3%,and the peak time is delayed by 32 min.As for the pollutants,the reduction rate of the TSS,TP,TN,COD,BOD₅,NH₃-N are 78.0%、64.6%、88.4%、75.3%、80.2%、67.9%.