THE DESIGN OF WETLAND SYSTEMS FOR THE TREATMENT OF URBAN RUN-OFF

The results of studies of the pollution removal performance of constru cted wetlands for urban runoff treatment are discussed. The design of urban runoff wetlands including primary treatment components, substrat e composition and flow rate regulation are considered. The use of fron t-end treatment systems such as oil interceptors, spillage containment facilities and wetland forebays or lagoons are recommended to provide an initial pollutant removal capacity as well as attenuating the impa ct of high discharges. Design criteria which will ensure inlet flow ve locities do not exceed 0.7m/s and which will achieve optimum retention times (10-15 hours) for maximum pollutant removal are described. The relative advantages of different soil types are discussed and an overa ll minimum substrate depth of 0.6m is recommended for sub-surface syst ems. Two case studies of urban runoff wetlands in the UK which are cur rently being monitored are described. (C) 1997 IAWQ.