Experimental Study On Grass Swale System For Control Of Urban Storm Runoff

China is a country which is lack of water resource. However, as a precious resource, a large amount of stormwater is drained from the city. In the field of the management of stormwater and flood, on the one hand increasing stormwater runoff is discharged from the city by complicated stormwater drainage system; on the other hand we have to face a serious shortage of groundwater recharge. If the resource utilization of stormwater can be considerd in the design of stormwater discharge system and ground surface mulching, the crisis of water resource, waterlogging disaster and water pollution can be relieved with the improve of urban ecological environment. To solve the problem, grass swale system, which is an ecological system of collection, transport and purification for road stormwater runoff, was used to study its control effect on urban storm runoff.The content of this paper includes:①Water quality monitoring and influencing factors analysis of road runoff in Chongqing, which mainly study the variation of water quality and quantity of road runoff and its influencing factors. It will support the decision-making process for effective utilization of urban stormwater and control of non-point source pollution.②Experimental study on grass swale system for control of urban storm runoff. The research contents include the design and construction of the system; start-up of grass swale system; purification capacity of storm runoff pollutants; surface removal effect of SS along the grass swale and the storm runoff storage effect.③Economy performance evaluation,design and management for grass swale system, which can provide reference for engineering application.The research results mainly include:①The results of water quality monitoring and influencing factors analysis of road runoff in Chongqing indicates: COD and SS are major objects to be controlled and their concentration of road runoff are high; the order of runoff water quality form different underlying surfaces is roof runoff>road runoff inside the school> road runoff outside the school> freeway runoff; road runoff pollution of initial phase is worst and the concentration of pollutants will decline and tend to stabilize finally during the rainfall process; road runoff contaminations are insoluble mostly, so the research on non-point source pollution control should emphasis on the removal of SS.②Start-up experiment indicates: the start-up process of grass swale system can be well achieved by the adoption of plant transplanting, natural bio-film and low influent load under 18℃~23℃. In the late phase of start-up, vegetations grow well, the removal rate of COD and turbidity stabilized around 50%~60%and 75%~85% respectively.③The results of purification capacity experiment shows: for simulated stormwater pollutants, removal rate of turbidity keeps above 70%, while that of COD and TP are during 47%~82%; the removal effect of NH3-N ranges between 25%~73% and the removal rate of Pb achieves at 80%~90%. The distance of horizontal seepage affects runoff contamination removal effect markedly.④The surface removal experiment of SS along grass swale indicates that the removal rate of turbidity ranges between 32% and 90%, and the rate tends to decline obviously with the increase of hydraulic load.⑤The stimulated stormwater experiment shows that the grass swale system has good anti-fluctuation capacity of water quantity and quality. The removal rate of COD, TP and NH3-N can reach 51.44%, 58.6% and 46.28% respectively. The amount of contaminations removal by infiltration mechanism accounts for 83%~92% of the total.⑥The storm runoff storage effect indicates: The system has marked function of delaying and storage the flood runoff, with 30%~50% cut of runoff quantity and 15~40min delay of flood peak. The grass swale system can accept 3.42 times runoff from hard pressing surface area as its own area. It can also increase the storm rainfall return period of downstream storm sewer system from 0.5 to 2 years and extend the flow time t2 obviously. So it can decrease the engineering cost of downstream storm sewer effectively.⑦The recommended design parameters of grass swale system were proposed such as soil infiltration rate, service area, maximum of slope, the allowed velocity maximum and so on.⑧The grass swale has good function of pollution interception and storage, which also has advantages of low capital expenditure, easy operation management and so on. It is believed that the grass swale system has wide application foreground on the decentralized treatment and reuse of road runoff to establish an ecological urban stormwater management system.