Research On The Characteristics Of Hydrology And Rainwater Quality Of The Green Roof

Green roof serves as an important technical application of low impactdevelopment (LID). It is capable of significantly reducing runoff generation throughrainwater interception and utilization by a vegetation layer and rainwater storage by asubstrate layer. This study quantitatively investigated the runoff retention performanceand a runoff model of green roof systems in Tianjin climate conditions by building apilot scale facility for artificial rainfall.This study determined the structure of the green roof from top to bottom in theorder: vegetation layer, soil layer, substrate layer, filter layer, drainage layer. Thenthis study chose the thickness of the substrate layer, rainfall intensity and the structureof the drainage layer as the main research variables. Artificial rainfall was made bythe raindrops generator which was in the form of nozzle. The rainwater was madeaccording to the Tianjin natural rain water quality. In terms of water quality index,this study selected TN, NO3--N, NH3-N, TP, COD, pH, turbidity as the indicators.In the aspect of hydrology, this study mainly analyzed the ratio of volumeretention, the ratio of flood peak retention and latency, the effluent delay time andeffluent process. The result of the experiment confirmed that: the ratio of volumeretention can reach13.4%-68.9%, the ratio of the runoff retention decreases inaccordance with a power function; for the thicknesses of the substrate layer are5cm,10cm,20cm,30cm, the averages of the flood peak are30.52%,31.24%,71.92%and80.32%.In the aspect of rainwater quality, this study mainly analyzed the relationshipsbetween the seven kinds of water quality indicators and the rainfall intensity and thethicknesses of the substrate layer. The result of the experiment confirmed that:different water quality indicators can present different change trends as the variationof the rainfall intensity and the thicknesses of the substrate layer, the range of qualityretention for the TN was36.78%-80.29%and the range of quality retention for theCOD was27.68%-85.99%; the green roof released a great deal of TP and themultiples could achieve16times of the total quality of TP in the rainfall.