Mangaonua Gully Stream Restoration

Strengthening Kirikiriroa/Hamilton’s waterways as part of the city’s erosion control programme.

As part of Hamilton City Council’s 2018-28 Long Term Plan, a number of city waterways were identified as candidates for erosion control works, weeding, pest control, and native plantings. Mangaonua Gully Stream was one such waterway in need, and a plan was drawn up to strengthen its banks and restore the gully to a more natural state, while increasing accessibility to the area.

HEB Construction was brought in to undertake the works, with Ngāti Haua Mahi Trust scheduled to supply and plant over 40,000 native plants (while also removing pest species).

A highly sustainable, collaborative approach was chosen by the HEB team, with a priority on reusing on-site debris to shrink the project’s carbon footprint, save time and money, and leave the area looking as natural as possible. Unusual for a project of this type, the team mainly designed and built the required new road, tracks and weirs using waste organic materials.

Overall, HEB and partners addressed 1.6 km (20 hectares) of gully and waterway, armouring and excavating to improve erosion control, installing a new access road for both maintenance vehicles and walkers/cyclers, and installing new timber boardwalks and bridges. After putting in such a significant effort to reduce costs and improve sustainability, the project was crowned the overall winner at the 2023 HEB Environmental Awards.

Our work

• Excavation of the streambed to prepare for installation of new protection measures.
• Construction of up to 20 log weirs and up to 10 rock rifles for gradient control.
• Construction of log groynes, partial rock armouring and bush layering for erosion protection.
• Creation of an access track to provide side-by-side vehicle and pedestrian access to the gully, involving 2,500 cubic-metres of earthworks.
• Construction of timber boardwalks and three timber bridges across the Mangaonua Stream.
• Sustainable approach involving recycling of local materials, bat monitoring and complying with restrictions on vegetation removal.