Study On Stepped Greenland Retarding Runoff Technologyin Green Building Community

With the rapid development of urbanization and increase of human activities, theoriginal hydrological cycle has been severely damaged. Green land is replaced byimpervious surfaces like roads, squares and roofs, etc., which triggers a series ofecological problems, such as flood, runoff pollution, ecological damage, urban heatisland effect and falling of water table and so on. Rainwater is an important part ofwater circulation system，playing a key role in the regulation and supplement of waterresource and change of environment.The proper treatment of the rainwater has becomea common concern of all countries. Low impact development (LID) is anurbanstormwater management concept emphasizing the maintaince and protectionof thehydrological features of the site, effectively alleviating the increase of peak flow, runoffcoefficient and non-point source pollution caused by increased of impervious area viasource dispersed small control facilities. LIDmaintains the original hydrologicalconditions before development, control runoff pollution, reduce pollution emissions andachieve sustainable development of regional water cycle via bioretenion, roof greening,grass ditch, permeable pavement, etc.Based on the ultimate principle of LID, a two-stage stepped greenland retardingrunoff experiment device taking low potential of green space and rain garden forprototype was designed. And experiments were taken in a green building community inShenzhen City. The control effectiveness of runoff water equality, water amount andtotal amount of pollutant by the device under the condition of different combination ofthree kind of underlying surfces, namely, road, square and roof in six rainfall eventswere studied, and themain results were as following：①Study on underlying runoff water equality showed that: As rain continued, theconcentrations of the underlying surface runoff pollutions were on declining curves anddropped quickly early and smoothly later,which met the Level Ⅴ of the Surface WaterQuality Standards (GB3838-2002). The correlations of TP, TN, NH3-N and NO3-N withSS and COD, and SS with COD were significant, and correlations of TP, TN, NH3-Nand NO3-N with COD were also obvious.In the three kinds of underlying surface, SS, asone of the main pollutants, significantly affected the content of other pollutants in therunoff, and there were similar erosion properties between the other pollutants and COD.②Study on control of event mean concentrationof runoff pollution by the device showed that: removal rates of all pollutants were negative, may because the goodinfluent quality led to the release of the pollutants by the grass and surface soil. Whilecompared to influent，infiltration effluent was purified. Nevertheless，the removal ratesof NH3-N and NO3-N were low，may because there were no conditions for nitrificationand denitrification in the device, and unstable device stable led to the leaching effect.③Study on the rain flood control device for the rainfall events showed that:Thedelay time of the peak flow was10to50min, reduction rate of peak flow were7.93%to73.79%, and volume reductions rate of runoff were23.31%to93.55%. As for rain oflarge intensity and long duration, control effct of water amount was not significant. Asfor bimodal type rainfall, the dely effect of peak flow was obvious. For different typesof rain, when the total runoffs were equal, the earlier came the rainpeak; the betterwasrain peak control effect.Although theremoval rates were negative, pollutants wasremoved to some extent，due to volume reduction of runoff influent.④Analysison stepedgreenland retarding ruoff technology showed that: On thecondition of different return periods and different service ratios, reduction of runoffvolume was independent of service area ratio and was decided by the storm intensity. Asfor the same recurrence interval, greater service ratio led to smaller peak flow reductionrate and greater peak flow reduction volume; and as for the same service area ratio,longer recurrence interval led to small peak flow reduction rate.Structure design and design principle were proposed and relative reference designparameters were also provided. The research results would provide an oreticalfoundation for the application of rain flood control technology and lay the foundation ofthe application in appropriate area, which would be of practical significance.