Urban stormwater treatment by artificial wetlands

This thesis examines the feasibility of using artificial wetlands to improve the quality of urban stormwater. The extensive literature on the quality of urban runoff is reviewed, together with that concerning methods of improving urban stormwater quality. The potential treatment function which wetlands could provide is also examined. A case study of an artificial wetland, which receives only urban stormwater, is presented. This year-long study, and the preceding pilot study, was undertaken at a site located in the London Borough of Sutton. The site was constructed as a detention basin and subsequently planted with Typha latifolia. The wetland covered an area of 13,125 m2 with a detention capacity of 10,000 m 3. During 1991 an estimated 60412.97 m3 of urban stormwater flowed into the site. The quality of the stormwater was monitored, weekly, at the inlet and outlet ends of the wetland, and at four intermediate sites. In addition to the stormwater samples, sediment cores and vegetation samples were taken quarterly from each site. The stormwater samples were analysed for fifteen pollutant parameters including nitrate, phosphorus, dissolved oxygen content, heavy metals and total coliforms. There was evidence of statistically significant reductions in the concentrations of many of these pollutants. The overall average reduction in the concentration of nitrate, for example, was 68.9%, and of total coliforms was 77.5%. The greatest reductions occurred in the late spring and early summer, when the vegetation was growing most rapidly. The results of the analysis of the stormwater, sediment and plant samples are discussed and the efficiency of the wetland is compared with that of other methods of stormwater treatment. Finally conclusions are drawn, based on the literature review and the case study, on the feasibility of using artificial wetlands for urban stormwater treatment