Study On Stormwater Runoff And Pollutants Reduction Of Urban Green Space

With urbanization deepened, the rapid growth of urban impervious areas, thewaterlog disaster caused by urban runoff has become a critical issue hindering urbaneconomic and social development in China. Besides, the non-point source pollutioncaused by urban stormwater runoff has become an important factor of urban waterenvironment pollution and ecological degradation. It is the third pollution source ofrivers and lakes. The urban green space is a major method to reduce stormwaterrunoff and pollutants, which is paid extensive attention and an important researchsubject of urban construction.On the basis of widely consulting domestic and overseas relevant study results,The simulated soil-column experiment and field experiment were used to explore thereduction of urban green space on stormwater runoff and pollutants. The migrationmodel of rainwater and pollutants in the greenbelt was established based onHYDRUS-1D. The main conclusions are as the follows:First, according to the range analysis and variance analysis of the L9(34)orthogonal experiment data, the impacts of factors such as rainfall intensity, grasstype, rainfall duration and vegetation coverage on the stormwater runoff are extremelysignificant. The sequence of four factors on the produce of stormwater runoff israinfall intensity> grass type> rainfall duration> vegetation coverage. Theprediction equation of stormwater runoff was established by the quantitative theorywith the L9(34) orthogonal experiment data. It was validated by the level effect,engineering average estimation and field experiments.Second, the standard particle swarm optimization was improved and used toevaluate the model of soil moisture characteristic curve and soil infiltration model.The Van Genuchten model is the best model described the soil water characteristiccurve of urban green space of Tianjin. The Horton model is an optimum modeldescribed the soil infiltration characteristics of greenbelt in the center of Tianjin. TheHYDRUS-1D can better describe the vertical infiltration process of rainwater in thebare land and green land, and predict the runoff volume accurately. The reduction rateof stormwater runoff by green space and rainfall intensity are significant relation ofpower function. With the sunken depth deepened, the rainwater detention storage ofgreen belt is enhanced.Third, the green land has a good and stable ability to reduce three stormwater runoff pollution concentrations, which CODcrare68,137and550mg/L, TN are3.01,7.51and30.06mg/L, TP are0.29,0.69and2.73mg/L, and NH4+are0.44,1.61and2.19mg/L respectively, with3.5,3.0and2.5cm/h hydraulic loading rate respectivelyand continuous inflow1h. The pollution reduction rates of CODcr, TN, TP and NH4+by green space reach to41.52%,78.96%and84.68%,50.21%,70.23%and60.91%,73.18%,95.88%and94.99%, and62.72%,55.16%and69.98%respectively.Finally, the migration model of pollutants was established and the simulated testof soil column was utilized to verify the model, the root mean square error is less than9.50mg/L. In the range of soil capacity, the CODcrreduction rate of green space isindependent on the rainfall-runoff pollution concentration. With the hydraulic loadingincreased, the CODcrreduction rate of green space decreases, however, it shows agradually increasing trend with the time interval increased. The effect of concavedepth on the CODcrreduction rate of green space is highly depended on the hydraulicloading. With the hydraulic loading increased, the CODcrreduction rate of greenspace decreases with the concave depth deepened.