LID Scheme Based On Coupling Simulation Ofurban Water Quantity And Quality

With the pace of urbanization,the primary underlying surface conditions have changed greatly.Pavement hardening makes urban surface runoff confluence faster and urban waterlogging disaster intensifies.Urbanization leads to frequent human activities and a large accumulation of pollutants on the underlying surface.At the same time,the increase of urban flood intensifies the erosion of surface accumulated pollutants by runoff,and pollutants directly enter urban pipe networks and rivers along with surface runoff,causing water pollution and urban water quality deterioration,resulting in serious urban non-point source pollution.In this thesis,Jiefangbei Street in Yuzhong District of Chongqing is selected as the research area.The stormwater management model SWMM was used to simulate the water quantity and quality of the study area after the construction of Low Impact Development(LID)measures.The control effect of different LID measures on water quantity and quality in the study area and the control effect of LID measures combination were explored.The best combination of schemes is expanded,and eight schemes with different construction areas are constructed to compare and select the best scheme of LID renovation in the study area.The cost effect index is calculated by combining the cost index and the effect index.The cost effect index was used to evaluate the scheme,and the best scheme of LID construction measures in the study area was selected.The main achievements are as follows:Firstly,the coupling model of water quantity and water quality in the study area was established.Node and pipe network data in the study area were obtained from relevant departments,and the molecular catchment area was delimited by Tyson polygon method.Nodes,pipe networks and subcatchments are distributed in the model.The rainfall process lines under seven different recurrence periods were set,and the parameters were calibrated according to the continuity error and runoff coefficient of the model.The results show that the coupled model of water quantity and water quality in the study area can simulate the water quantity and water quality in the study area with sufficient accuracy.Second,comparative selection of LID single and combination measures and LID transformation scheme design of Jiefangbei street are carried out.The results showed that,among the single LID measures,the water quantity and water quality of permeable pavement had the best control effect.Among the combined measures,the scheme of permeable pavement,biological retention pool and green roof has the best water quantity and water quality control effect.Therefore,eight LID renovation schemes are proposed,which include three measures:permeable pavement,biological retention pool and green roof,but with different areas.The control effect of each scheme on water quantity and water quality index was explored respectively.Then,the scheme evaluation index based on cost and effect is constructed.Establish the cost effect evaluation index system.The total cost of each programme is calculated using the life cycle cost method,followed by a cost index for each programme through standardization.The analytic hierarchy process was used to construct the subjective weight,and the principal component analysis method was used to construct the objective weight.The weight of the effect index is obtained by combining the two methods,and the effect index is calculated by weighted summation.Combined with the cost index and the effect index,the cost effect index was calculated to evaluate the scheme.Finally,a low impact development recommendation scheme is provided for the study area by comparing the cost effect index.The results show that under different return period,scheme of the highest cost effect index is different.When the return period is 1 year,the cost effect index of option 3 is the largest.Scheme 8 had the highest cost effect index when the return periods were 2,5 and 100 years.When the return period is 10 years,20 years and 50 years,the cost effect index of Scheme 4 is the largest.LID construction scheme can be selected in the study area according to the intensity of rainstorm to be controlled.In Scheme 8,the construction areas of green roof,permeable pavement and biological retention pond are 10.62hm~2,45.15hm~2and 1.14hm~2,respectively.The total cost of construction is 181.54 million yuan.The cost index is0.39,the average effect index is 0.494,and the average effect index is 1.267,which is the highest value among the eight schemes.Therefore,scheme 8 is the recommended scheme for LID renovation in the research area.It is hoped that this study can provide reference for the sponge city construction in Jiefangbei Street and other similar areas.