Opportunities at the End of the Pipe - A Reconfiguration of the TP10 Constructed Wetland

A reconfiguration of the TP10 constructed wetland design has been undertaken to extend detention to 10 days while still maintaining extreme event stormwater attenuation. The reconfigured design was developed during appeal mediation of a granted consent for combined treated wastewater and stormwater disposal. Located in Ruakaka the 6ha wetland, when fully developed, will receive stormwater runoff from up to 180ha mixed land use and 3000m³/day dry weather treated wastewater flows. The wetland discharges to Ruakaka Estuary with wildlife sanctuary, which in turn drains into Bream Bay with seawater takes for the Bream Bay Aquaculture Park. Appellants’ concerns provided much of the design brief and included long detentions times, mixing of waste water and stormwater, containment of accumulated contaminants during extreme events, containment of wetland water in event of spills and early warning systems; meanwhile the stormwater attenuation requirements were achieved within the same footprint. The reconfiguration includes a wetland partition, drop weirs and bypass flume. Investigation was undertaken with MIKE Urban by DHI with UHM and Kinematic Wave + Infiltration models for design events and four year rainfall record respectively. Analysis included flows, effect on upstream ponding, detention times, and exacerbation of wetland water levels for plant health.