Study On Low Impact Development Stormwater System Model In Green Building And Community

High speed urbanization process resulted in dramatic changes of urabn land surfacecharacteristics. The increase of impervious surface area affected the city’s originalhydrologic cycle and changed the urban area stormwater runoff conditions, which led tothe total runoff volume and peak flow increased significantly, the flow peak arrivedearlier than that of natural area, and the water quality deterioration. In addition to thechange of original structure and function of the underlying surface, urbanization alsohas an influence on the city climate characteristics, which resulted in the increase ofurban rainfall volume and rainfall events occur frequency. Especially in recent years, thefrequent occurrence of city waterlogging disasters has brought serious threat to people’slife and property safety. On the other hand, with the point source pollution graduallybrought under control, non-point source pollution is becoming the most importantproblem facing by urban water environment protection department. Built-up area, whichoccupies nearly70%of the urban area, is the starting point of the urban rainwaterdrainage system. Therefore, it plays an important role in city flood control andutilization. The low impact development technology, based on green building and thecommunity, can effectively reduce the pollutant load of the rainfall runoff, cut down thetotal runoff volume and peak flow rate, and delay the time that peak flow occured fromthe source that runoff generated by the means of rainfall intercepting for infiltration,storage and so on through the combination of a series of different measures. It can be anaviliable way for solving the current issues of urban flood and water qualitydeterioration. Due to the lack of measures to evaluate the effect of this method, theapplication and promotion of the technology was difficult.This article firstly made a comprehensive introduction of several main low impactdevelopment techniques, such as bioretention system, green roofs, permeablepavements, grass swales etc, from the aspects of its structure, function, design methods,application, its economic benefit and existing problems. The effectiveness of runoffreduction and water quality improvement of different techniques were also evaluated.Then a more comprehensive horizontal comparison was made to the low impactdevelopment techniques from the aspects of its hydrological effects, water qualityeffects, applicability, disposition, economy etc, which can provide a reference for theselection of low impact development techniques. On this basis, the low impact development stormwater system model in greenbuilding and community, based on SWMMH model, was built and applied to thedemonstration project in Wanzhangpo, New District of Guangming, Shenzhen. Themain results obtained were shown as following:①Sensitivity analysis of hydrologic and hydraulic parameters and water qualityparameters of the model were carried out using Morris screening method with threeactual monitoring rainfall datum of different rainfall intensity. The results showed thatthe most sensitive parameter in the hydrological and hydraulic module of the modelwas%Imperv. While parameters like pollutant max. buildup and sat. constant, pollutantwashoff coefficient and exponent all have great influence on the water qualitysimulation results. And the influence degree of pollutant washoff exponentwas thehighest. Therefore, a priority should be given to the sensitive parameters during theprocess of parameter identification and calibration.②Researches on the runoff flow changes of the demonstration area rainwaterdrainage system outlet under different rainfall return period were carried out. It wasfound that under the seven different rainfall return period of0.25a,0.5a,1a,2a,3a,5aand10a, the efficiency of low impact development technology for the total runoffvolume reduction of the system were36.82%,34.21%,47.87%,31.03%,30.41%,29.73%and28.97%, respectively.While the peak flow reduction of the system were32.47%,32.33%,27.35%,18.08%,17.74%,18.05%and15.89%, repectively. This revealed thatthe efficiency of low impact development technology for the total runoff volume andpeak flow reduction tended to decrease gradually with the increase of rainfall intensity.Besides, it also can be obtained from the modelling results that by using low impactdevelopment technology the moment that peak flow appeared was relatively laggingbehind no matter what rainfall return period was, compared with the system without lowimpact development technology. This result showed that low impact developmenttechnology not only can reduce the total runoff volume and peak flow of the system, butalso has a certain retention effect for the moment that peak flow appeared.③Researches on the water quality changes of the demonstration area rainwaterdrainage system outlet under different rainfall return period were also carried out. It wasfound that under the seven different rainfall return period of0.25a,0.5a,1a,2a,3a,5aand10a, the efficiency of low impact development technology for the reduction of thetotal load of COD of the system were25.98%,17.81%,15.68%,14.94%,14.7%,14.36%and14.14%, respectively. The efficiency of low impact development technology for the reduction of the total load of SS of the system were24.10%,17%,14.68%,13.97%,13.65%,13.45%and13.3%, respectively. The efficiency of low impact developmenttechnology for the reduction of the total load of TN of the system were37.04%,23.6%,15.37%,13.83%,11.34%,10.44%and9.19%, respectively. While the efficiency of lowimpact development technology for the reduction of the total load of TP of the systemwere43.57%,32.06%,21.49%,14.45%,11.96%,11.7%and10.51%, respectively.Soconclusion that low impact development technology has a favorable removal efficiencyof pollutant and can improve the runoff quality efficiently can be made from themodeling result. It also can be found out that a certain similarity was presented betweenthe different pollutant concentration change process curves, although the total loadreduction degree of the different pollutant were different. Besides, with the increase ofrainfall return period, the reduction rate tended to decrease.The researchs on low impact development stormwater system model in greenbuilding and community have important meanings for solving the issues of urbanstormwater disasters in China. It can offer an effective way for the evaluation of lowimpact development techniques, and provide data support for the application andpromotion of the low impact development technology.