The impact of water reuse on the hydrology and ecology of a constructed stormwater wetland and its catchment

Constructed stormwater treatment wetlands are essential components in many existing stormwater management strategies. As part of an integrated stormwater treatment system, they can be highly effective in the removal of fine pollutants from catchment runoff. Although the vegetation within constructed stormwater wetlands plays an important role in the treatment processes taking place, its density and distribution depends on the wetland bathymetry and the imposed hydrological regime. This paper describes an ecological and hydrological assessment of a constructed stormwater treatment wetland. A continuous simulation hydrological model of the urban catchment and the wetland system is combined with the results from previous a site monitoring program of vegetation and ecosystem characteristics within both the wetland and the upstream and downstream sections of the urban stream system. The hydrological analysis of the system has been used to investigate the impact of the hydrological regime on the ecosystem. The model is also used to investigate the reuse of rainwater from household rainwater tanks within the catchment and stormwater harvesting from the wetland. The study has shown that the wetland provides significant interception of rainfall, which is linked to the improved ecosystem characteristics observed in the stream system downstream of the wetland. Reuse of rainwater and stormwater harvesting is shown to provide potable water savings of up to 36% of the annual average household potable water demand. Harvesting stormwater from the wetland can also be used to modify the inundation frequency characteristics, which should lead to a significant improvement in the survival of vegetation throughout the wetland.

► Urbanisation has a significant increase in runoff due to a reduction in interception of runoff within the catchment.
► The wetland system reduces runoff from the catchment to pre-urbanised conditions but has little impact on flood mitigation.
► The wetland improves stream ecological health by intercepting and reducing runoff and modifying the hydrological regime.
► Rainwater reuse and harvesting stormwater from the wetland can significantly reduce potable water demand in the catchment.