32 | GHD - Te Kukuwai o Toa Wetland stores floodwater Kelly Deeks The Elsdon Park wetland in Porirua provides a place to store floodwater and improves the quality of the water entering the harbour. REGIONAL DEVELOPMENT is proud to have completed the Porirua Wetlands project for Wellington Water Ltd and the Porirua City Council. Contact Eddie Carson on 0274 424 343 or eddie@ecarson.co.nz The new Elsdon Park Wetland, Te Kukuwai o Toa, marks the beginning of a brand new future as the land is returned to its previous state as a wetland, as it used to be prior to 1900 and the development of Porirua. The wetland is the final stage of a major Wellington Water project upgrading the stormwater network in Porirua City, to alleviate flooding and improve the health of the harbour. A 1-in-100-year storm event in Porirua in 2015, which at its peak saw 33.6mm of rainfall in 30 minutes, caused millions of dollars of flood related damage. While it was a severe weather event, it was not the only flood in recent times. Parts of this catchment are regularly flooded, Porirua School for example has flooded 10 times in the past six years. Flooding is not the only challenge in this urban environment and every time it rains, contaminants are washed from the road, industrial sites, and homes, making their way into the stormwater network and out into Te Awarua-o-Porirua Harbour. The low-lying Elsdon Park area is the ideal place to address these issues, providing a place to store floodwater and at the same time, improving the quality of the water entering the harbour. GHD and Morphum Environmental were engaged by Wellington Water in 2017 to deliver the Porirua City Council Central Stormwater Upgrades project suite of works. In collaboration with Porirua City Council and Te Rūnunga o Toa Rangatirai, GHD and Morphum developed a plan to provide additional flood resilience for Porirua CBD and stormwater treatment for the Semple Street outfall, which included the construction of a new wetland area, a high capacity wetland bypass pipeline, and flood barriers to protect Porirua School, and properties on Ngatitoa Street. Large scale civil infrastructure combined with the water sensitive urban design practices of the wetland provide a holistic stormwater management solution which reduces the risk of flooding, reduces contaminant loading, and provides an asset of value to the community. “This is a unique, major, and multidisciplinary project for Wellington Water, and it wouldn’t have happened without the collaborative approach across the whole team and a can-do approach from the construction contractor, E Carson and Sons,” says GHD water lead Callum Allison. “We all need to work together the right way through these major projects, and that is one of the most enjoyable aspects of working on them with our partners.” With iwi consultation and the project providing work for local trades and suppliers, Te Kukuwai o Toa is truly a community project. Not only is the harbour and the people who interact with it set to benefit from the improvement in water quality, but the wider community now has an attractive green space for recreation and education, and the extensive planting of about 38,000 native trees and plants provides an urban habitat for native wildlife. Callum says one of the most exciting aspects of the success of this project is its demonstration of how environmentally aware, sustainable, and cost-effective stormwater design can connect a CBD to a green space. “This is a unique, major, and multidisciplinary project for Wellington Water, and it wouldn’t have happened without the collaborative approach across the whole team ...”
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