Studies And Evaluations On Rainwater Utilization Technology Of Low Impact Development

Water is the origin of life and the source of human civilization.In recent years,due to the rapidly urbanization in China,urban waterlogging occurred more frequently,and urban non-point source pollution was becoming more and more serious.Therefore,China put forward to construct a sponge city,of which the key techonology is low impact development.Studies and evaluations on rainwater utilization technology of low impact development are significant to the construction of the sponge city.This paper takes the typical community in Guangzhou as a study area.Based on the water quality data monitored in study area,the first flush phenomenon is analysed.Meanwhile,the effect of low impact development is evaluated according to the PCSWMM model of study area.The main results are summarized as follows.（1）This paper summarized the notion of low impact development,and introduced the low impact development technology in detail from six aspects: "infiltration","retention","storage","purification","utilization","emission".The results show that low impact development can effectively reduce the runoff volume and peak runoff discharge,purify rain water quality,improve ecological environment.（2）M（Ⅴ）curve,first flush coefficient b and MFF index were used respectively for the qualitative and quantitative analysis of first flush phenomenon and the degree of the first flush based on the monitored water quality data.The results show that the different pollutants of different underlying surfaces have first flush phenomenon at different level.The first flush at greenbelt was more easily occurred,followed by the roofs,and roads.（3）MFF index was used to estimate rainfall runoff pollution load with different index n.The results show that 10% initial runoff carried the pollution load of 1.2%³7% for BOD5,1.2%²5% for CODcr,1.4%²5% for TSS,7%²1% for NH₃-N,10%¹5.7% for TN and 5.3%²3% for TP.20% initial runoff carried the pollution load of 2%⁴8.8% for BOD5,2.2%³6% for CODcr,2.6%³8% for TSS,12.4%⁴0% for NH₃-N,21%²9% for TN and 12%⁴1.2% for TP.（4）PCSWMM model of the study area was constructed.Six different return periods rain data（0.5a,1a,2a,5a,10 a,20a）were inputted respectively to PCSWMM model to evaluate the effect of three low impact development scenarios for water quantity and pollutants.The results show that different combinations of LID measures,such as concave green space,green roof and permeable pavement,have different reduction in runoff and pollutants.The reduction decreases while the increase of rainfall return period.The best results can be achieved by the combination of sunken green space,green roof and permeable pavement at the same time.The maximum reductions rate of runoff,BOD5,CODcr,TSS,NH₃-N,TN and TP were 64.77%,56.93%,57.44%,51.20%,51.91%,55.29% and 71.37%,respectively.