Research On Water Quality Improvement Technology In Plain River-net Areas Based On LID

Tianjin is a typical plain river network area that located in the Haihe River Basin,where the rivers are characterized by slow flow rate,poor connectivity,insufficient water circulation,low self-purification ability.In recent years,with the rapid development of urbanization,non-point source pollution which caused by rainfall runoff discharged into rivers,resulting in deterioration of river water quality.Therefore,how to recognize and control the pollution of rainfall runoff has become an urgent problem to be solved.As one of the pilot cities in constructing sponge city,Tianjin has successively controlled runoff with low-impact development measures.In this study,SWMM and Mike11 are used to evaluate the control effect of LID measures on rainfall runoff pollution.The main contents and conclusions are as follows:(1)The rainfall runoff model of Tianjin was established by SWMM.Then the runoff and COD,TN and TP loads of each outlet along the river under 2h,3h and 24 h design storm conditions were analyzed.The results show that under the design storm conditions,the runoff and the COD,TN,TP loads gradually increased with the increase of the return period,but the increase rate showed a decreasing trend.The EMC of TP was Level-III water quality standard,the EMC of COD and TN exceeded Level-V water quality standard,which indicated serious pollution of rainfall runoff.(2)LID measures including permeable pavement,concave green space,green roof and biological detention facilities were designed to control the quantity and quality of runoff.The results show that LID measures can effectively reduce the total runoff,peak flow,COD,TN and TP load.However,with the increase of the return period,the control effect declined.(3)The one-dimensional hydrodynamic and water quality model was built by Mike11,and the output of SWMM was input into the model as lateral inflow.Then the influence of LID measures on Haihe River was analysed.The results show that the average concentrations of COD,TN and TP in the Erdaozha sluice under LID measures were lower than the current conditions,which indicated LID measures could improve the water quality of river.