ABSTRACT
A large part of the design of event-driven treatment wetlands is the determination of the flows and loads to be treated. Compared to continuous or pumped treatment marshes, event-driven systems do not have easily characterized source waters. The wetland–watershed area ratio (WWAR) is an often-used descriptor of event-driven treatment marshes. The effect WWAR on performance is not well quantified or predictable, but can provide a high level understanding of an approximate size of wetland. In many instances, rain events are separated by inter-event periods of no inflow to the treatment wetland. In some watersheds, the chemograph is not synchronized with the hydrograph, but instead provides higher concentrations early in the inflow event. This phenomenon is termed “first flush” behavior, referring to the surge of pollutants contained in the first water to leave the contributing basin. Stormwater wetlands experience event flows and concentrations, followed by periods of batch operation.
