| With the continuous advance of urbanization in China,the rapid growth of impervious underlying surface has damaged the natural hydrological mechanism,frequent waterlogging,deterioration of water,problems of rainwater resource waste and so on has gradually come out.The traditional rainwater management model based on fast drainage can no longer meet the requirements of sustainable urban development.The Low Impact Development?LID?model,with its source control as the core,has been prevalent in China.However,the existing achievements are mainly focused on single LID technology,and there is still a lack of research on the runoff reduction system and scheme optimization.Therefore,it is very necessary and urgent to construct the system to reduce the runoff by LID technologies and optimize the performance.In this study,the existing LID techniques were classified firstly and the theoretical formulas of runoff reduction for each individual LID technique were summarized,and then a complete set of LID technology runoff reduction system with the parameters of the single LID technology was constructed.Secondly,the field experiment was carried out for the typical LID technology,and the reliability of the system was verified by comparing the actual value with the theoretical value calculated by the formula.Finally,based on Analytic Hierarchy Process?AHP?,the LID combination scheme with the best performance is selected according to the different performance of LID technology.The conclusions are as follows:?1?The LID technique parameters are summed up and the theoretical formulas of 12 LID technologies for runoff reduction are established.Based on the analysis of runoff reduction formula of single LID technology,the parameters range of runoff reduction rate of single LID technique is given,and a complete LID runoff reduction system is established.?2?The results of soil infiltration experiments showed that the permeability of topsoil in most functional areas of Shanghai was very poor,and the infiltration rate was below 10-6 m/s.In the case of sand and soil ratio of 2:3,the permeation rate was 3.5 × 10-6 m/s,which is in line with the requirements of general infiltration facilities.The test results of planting grass ditch,Concave green space,high flower bed showed that: the effect of planting grass ditch on the runoff of small rainfall intensity is good,and the reduction rate was 68.24% under the condition of 1-year rainfall return period and 1% slope.The effect of the concave green space on runoff sedimentation was significant,and when the depth is 15 cm,the runoff was not generated below 5-year rainfall return period.Among the three types of high flower bed,sandy loam substrate has the best effect on rainwater storaging,whit an average reduction rate of 76.77%,followed by 45.31% in loam,silt the worst by 17.88%.?3?The result of calibrating theoretical formula of runoff reduction by using the test parameters of typical LID technologies showed that: the differences between the actual value and the theoretical value of the runoff reduction rate is 14.23% at maximum and 0.73% at the minimum,the difference is not significant.?4?The LID technology efficiency evaluation index system was established by quantifying and normalizing the five performance indexes of runoff control,pollution control,construction cost,management cost and landscape benefit of single LID technology.The weights of the above five kinds of performance were determined by AHP,which were 0.460,0.164,0.286,0.058 and 0.033 respectively.In this study,a complete LID technology runoff reduction system was constructed and the parameters of the pilot test were determined.Based on the LID evaluation index and different performance weight values,the optimal LID combination design scheme was optimized. |
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