Constructed wetlands to support urban waterway protection from stormwater pollutants

Stormwater runoff, predominantly over impervious surfaces, is an important source of pollutants (nutrients and metals) from point and non-point sources within the catchment. Furthermore, due to the rapid expansion of impervious areas in cities around the globe, the magnitude of pollutant loads associated with untreated stormwater are increasing, and subsequently creating significant challenges for the downstream urban waterway. Therefore, stormwater quality needs to be monitored and managed to safeguard and restore urban watercourses. Constructed wetlands (CWs) are potential water sensitive urban design option for stormwater management. In this study, we investigated
stormwater pollutants attenuation in the Anvil Way Compensation Basin (AWCB) and the Wharf Street Constructed Wetland (WSCW) in Western Australia by assessing data spanning for decadal, seasonal and diurnal time-scales. These CWs were built to protect the downstream Swan-Canning estuary/river from being discharge of stormwater pollutants and to maintain ecological sensitivity. The AWCB is a meandering surface flow (SF) system with possible groundwater connectivity, while the WSCW is a multi-compartment i.e., multiple SF and subsurface flow (SSF) compartments without any groundwater inputs. These CWs experience with prolonged low flows and macrophytes senescence during the
summer periods, and episodic stormwater pulses during the winter periods. Therefore, stormwater pollutants attenuation optimization within such CWs during different flow regimes and season is challenging. Both CWs were found effective for the attenuation of nutrients such as nitrogen (N), phosphorus (P) and metals from being discharged to the downstream Swan-Caning River system.