Lake Horowhenua (Punahau) is a 3.9-square-kilometre shallow coastal dune lake, situated just west of Levin on New Zealand’s North Island.
Coastal dune lakes are generally replenished by rainfall and groundwater, creating diverse aquatic environments where freshwater meets saltwater. As well as providing important ecological habitat, Lake Horowhenua holds significant cultural value for the local community.
However, Lake Horowhenua has faced ongoing water quality challenges due to its history of receiving wastewater and runoff from surrounding agricultural and urban catchments. These pressures have contributed to the degradation of the lake and its surrounding wetlands.
As a focus for improving environmental outcomes across the Manawatū-Whanganui region, Lake Horowhenua supports a diverse aquatic ecosystem, with six native fish species inhabiting the lake, including shortfin and longfin eels, smelt and bullies.
Restoration efforts include the development of the Arawhata Constructed Wetland Complex, alongside upgrades to upstream stormwater infrastructure to improve pollution removal across the surrounding catchments. Together, these initiatives are helping to strengthen the conservation of Lake Horowhenua and support improved water quality.
Vortceptor: Retrofitting Our Fibreglass Gross Pollutant Trap
With significant local investment supporting the restoration of Lake Horowhenua, managing nutrient and pollutant loads from surrounding catchments is critical to improving the health of the waterway.
Atlan Stormwater delivered an integrated retrofit solution with the installation of a SQIDEP-verified Vortceptor Gross Pollutant Trap (GPT) alongside a purpose-designed three-metre-wide diversion chamber. This device will support improved water quality outcomes and capture pollutants from Levin’s urban catchments.
As a first line of defence, primary stormwater treatment helps intercept litter, sediment and other urban pollutants before they reach the lake, supporting ongoing restoration efforts and the long-term recovery of Lake Horowhenua.
The Atlan Vortceptor has been independently verified through the Stormwater Australia SQIDEP framework, demonstrating pollution removal efficiencies of 93% Total Suspended Solids (TSS), 86% Total Phosphorus (TP), 49% Total Nitrogen (TN) and 100% Gross Pollutants.
Retrofitted directly into an existing 1650 mm RCP council stormwater pipeline, this strategy enabled the council to improve water quality without extensive reconstruction of the existing drainage network, delivering a practical and cost-effective stormwater management solution.
Challenges on site included the installation’s close proximity to the lake, high groundwater conditions and constraints on site depth due to the shallow stormwater pipe. The Vortceptor’s modular design assisted with the installation, allowing the device to be installed with shorter open excavation time and reduced disruption to the local community.
Engineered for the large catchment and large-diameter pipe network, the overall system was designed to accommodate the 1-in-100-year peak storm flow of 7,400 litres per second, and treatment flowrates of 530 litres per second. Flows above the treatment rate will bypass the treatment unit through the purpose-designed diversion chamber.
Featuring high-performance fibreglass composition and 100-year design life, the Vortceptor provides a resilient, long-term asset capable of supporting the ongoing protection of Lake Horowhenua.
Alternative assets would have required multiple treatment devices to provide the required treatment capacity, while the Vortceptor’s high-capacity design enabled the council to achieve the required hydraulic performance within a single treatment unit. This provided a cost-effective approach that limited installation complexity while streamlining ongoing maintenance.
Working alongside wetland restoration and stormwater management initiatives, this Vortceptor installation will assist the local community in its goals to improve local water quality outcomes. Through innovative, independently verified stormwater quality solutions, Atlan Stormwater will continue to help protect this important local waterway – protecting Joy in Water for future generations.
