POLITICS, THE POND AND THE PARK - THE STORMWATER JOURNEY OF TE PĀ HARAKEKE

A. Halder (Stantec)

ABSTRACT

The Modellers Pond project has been a political hot potato for the Nelson City Council for well over 20 years. Set within the coastal area of Tahunanui, the Pond, once regularly used by model boat enthusiasts and surrounded by a miniature railway is a popular attraction for both locals and visitors.

However, over time the ponds use had become restricted as it silted up, choked by thick weed, and partly coated with a scum of odorous algae. Many believed that the root cause of the problem was a decision in 1998 to use the pond to receive pumped stormwater flow from the surrounding catchment. The pond now an algae infested eye sore was regularly in the media spotlight and despite several attempts by council to clean it up and treat the algae and weeds the problem remained. This paper presents the journey of how the final solution resulted in a new unique recreational asset for the community as well as improving the quality of stormwater discharge to the coastal environment.

In 2017 a design to concrete line the pond and install a mechanical scrapper had been completed and consented. However, this was not the preferred option by many within Council who felt that the additional land which would be gained by filling in the pond would provide a much greater recreational use. A Council resolution to consult local iwi on the concrete lined option left the door open for an alternative solution. Stantec were initially approached to assist with costing of an alternative option and subsequently presented a concept option at a full Council meeting. The concept involved filling in the pond and discharging the stormwater through a separate planted swale following upstream treatment. After much debate Councillors voted to overturn the concrete lined option and proceed with Stantec’s concept of filling in the pond and separating the treated stormwater discharge.

During the design Stantec worked closely with landscape architects Botha Miskell with a vision of providing a recreational asset that embraced its coastal location. The new park is designed to be partially inundated during high tides and considers both future coastal erosion and sea level rise. Stantec also worked with Hynds to retrofit a vortex stormwater treatment device to provide treatment at the upstream pump station which would discharge treated flows to the same location within the former pond but out to the estuary through a bunded planted swale. The new design essentially both separates and integrates the recreational asset and the stormwater asset.

The new park, named Te Pā Harakeke (which is a Māori whakatauki, or saying, about the importance of whanau) in recognition of its family-friendly use, opened in November last year and provides a unique recreational asset for the community as well as improving the quality of stormwater discharge to the coastal environment.

This paper describes how the concept was developed and presented to Council, the vision for the outcome, the technical challenges throughout both design and construction, and the key learnings on this stormwater journey.