Alongside a pedestrian path in Bayfield Reserve, Herne Bay, several sinkholes had begun to form in the ground. These tomos (sinkholes) were forming due to the collapse of an old, unmarked earthenware stormwater pipe that ran adjacent to the path. Naturally, this presented a significant health and safety risk to pedestrians and detracted from the appeal of the environment, with safety fencing and neon hazard mesh across the park for several years.

Auckland Council’s Community Facilities department engaged Morphum to assess the site, undertake investigations and prepare an options assessment for how best to resolve this issue in the park. This began a journey that would lead to the beautification and naturalisation of a failing asset that adds to the local community to this day.

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Following investigations into the site, multiple options were considered for the park. One solution was to just replace the failed pipe with a new stormwater pipe that would carry stormwater flows under the park to release into the stream that would flow into Cox’s Bay. After some internal deliberation the option to do more than just repair was identified, given the opportunity to improve the local environment and community amenity.

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The Morphum team presented multiple options to the Community Facilities and Local Board, with the option to replace the unmarked broken pipe with a naturalised stream as the preferred solution.

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Redirecting stormwater flow via overland channel was selected by the assessors as the option to proceed to preliminary design. This process, known as daylighting, was intended to add a new feature to the park that many could enjoy, and add to the local environment.

The initial preliminary design was prepared after Morphum’s science team undertook an Assessment of Environmental Effects, or AEE, and identified some opportunities and challenges of the site.

Unexpectedly, native Kauri Trees were present on the site. Kauri are Aotearoa’s largest trees and are commonly found in the dense bush of the Waitākere Ranges and Te Tai Tokerau (Northland), but not often found in urban parks. Because of this, protecting these individuals was important to achieving the goal of ecological improvements for the area, and working around them was a part of the design.

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The preliminary design mimicked a natural hillside cascading stream, with added obstacles for the stormwater flow to reduce its speed. It incorporated rocky formations and purposeful woody debris that would be supported in place by adjacent rock to prevent potential damage from the wood dislodging, while creating habitat for invertebrates and the foundation of a natural waterway. The sides were to be planted with native flora, inviting wildlife to the area and helping stabilise the bank.

With the preliminary design approved, the detailed design went on to add a timber boardwalk structure that crossed the stream itself, improving pedestrian access and adding to the amenity of the site.

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At the time, Community Facilities at Auckland Council were also working on a cycle path that ran through the park below where the naturalisation was taking place. To make the most of the projects and their concurrent timing, the walkway design connected to the ongoing construction of the cycle path. Our team opted to use the same contractor that was working on the cycle path in the construction of this project as well, in order to reduce costs to the council and the public.

Morphum went on to support Auckland Council with the physical works procurement and undertook the works supervision in accordance with NZS3910, acting as the Engineer-To-Contract and assuming all responsibility on behalf of the council.

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The physical works were completed on time and under budget, and the naturalised stormwater system was opened to the public with great feedback from both clients and the community.

With the newly reinstated stormwater network in the area, this project has opened up the opportunity to separate approximately 20 dwellings from the combined network. This would reduce demand on the combined network and reduce the combined stormwater and sewage overflows into nearby Cox’s Creek as a result.

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In all, approximately 100m of failed stormwater infrastructure was naturalised, improving the park amenity to the local community, protecting the pathways and visitors, and improving the native habitat in the area for both flora and fauna.

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