RED ZONE RENAISSANCE: ŌTĀKARO/AVON RIVER CORRIDOR REGENERATION AND LEARNINGS FROM THE WAITAKI STREET STORMWATER PROJECT

Z. Evans & A. Guidon (GHD Ltd), M. Penrice (Christchurch City Council)

ABSTRACT

Resilient, biodiverse, and full of life are terms once used to describe the now empty, flood-prone land within the earthquake damaged corridor of the Ōtākaro/ Avon River. Poor water quality has made the river no longer suitable as a source of food and water, with recreational activities like swimming now a thing of the past. In an effort to change this, work has begun on the Waitaki Street Stormwater Project (“Waitaki Street”), the first of many stormwater projects aimed at improving the biodiversity and landscape of the red zone and the health of the Ōtākaro/Avon River, a waterbody of great significance to mana whenua and its residents.

The 2010 and 2011 Canterbury earthquakes caused significant damage to 602 hectares of land alongside the Ōtākaro Avon River Corridor ("ŌARC"). After the earthquakes, the government classified this area as a "residential red zone" and Regenerate Christchurch developed a plan for the ŌARC with four objectives focused on restoring habitat, supporting communities, and creating opportunities for recreation, leisure and future prosperity.

In addition, treatment of stormwater discharge into the river is required to improve water quality and meet Christchurch City Council’s (Council's) obligations for 2043 under their Comprehensive Stormwater Network Discharge Consent. The Waitaki Street project aims to assist in achieving these obligations while also aligning with the objectives of the ŌARC and Council’s vision of providing multi-value benefits with the six values of ecology, drainage, culture, heritage, landscape and recreation.

The Waitaki Street project applies nature-based solutions to enhance water quality, community resilience and improve the red zone landscape. The project scope includes: flood protection in the form of a new seismic resilient stopbank, stormwater treatment with a constructed wetland, and a tidal wetland to promote native habitat and reconnect the area to the river. A designated bird viewing area, and future plans for walking and cycle paths will provide a recreational space for the community to reconnect with the area.

The Waitaki Street design aims to integrate Council’s six values while negotiating the many unique challenges of the red zone landscape. These challenges have included achieving a seismic resilient design in liquefiable ground conditions, minimizing interaction with a high groundwater table, enabling drainage over a flat gradient, re-using existing infrastructure, working in a previously urbanised area, and designing a stormwater treatment facility that will not only treat our runoff to an acceptable level, but will adapt to a rising sea level and provide flood attenuation in larger rainfall events, adding protection to the surrounding community.

In January 2022, construction began at Waitaki Street and Council was faced with a new set of challenges. As the ŌARC programme progresses with the design and construction of additional stormwater projects, it is important that we learn from the challenges encountered in this flagship project. This paper discusses the significance of the ŌARC stormwater projects, the challenges of designing and constructing in the red zone, and the importance of collaboration and learning from past experiences as we dive into future ŌARC projects.