Client: Environment Canterbury & Selwyn District Council
New Wetland Design To Revitalise Fresh Water Taonga
Many Kiwis have fond memories of family holidays at Coes Ford campground, on the banks of the Waikirikiri (Selwyn) River south of Christchurch. Unfortunately, water quality has progressively declined over the years as agriculture continues to expand in the region. This is especially apparent during summer and has made swimming at this popular spot unsafe for much of the year.
Just downstream of this location is also Te Waihora (Lake Ellesmere), a nationally significant freshwater ecosystem whose water quality has declined significantly since European settlement. To address these concerns, Environment Canterbury (ECan) is exploring and implementing a range of projects throughout the catchment. A constructed wetland at Coes Ford is an important step on a long journey to restoring the fresh water of Canterbury to its former mauri.
The Challenge
A catchment-wide approach with multiple interventions is needed to address the declining water quality and habitat loss in the Selwyn District. The constructed wetland project at Coes Ford is one such intervention.
Site of proposed wetland
Morphum was engaged to design a system that will provide optimal water treatment of flows from two tributaries (Snake Creek and Silverstream) before they enter the Waikirikiri (Selwyn) River. These tributaries are fed by numerous springs and farm drains.
The wetland must also be constructed within the constraints of a flood-prone section of marginal pasture which is directly upstream of the campground. This land is part-owned by both ECan and Selwyn District Council (SDC).
The Approach
Morphum was first engaged in 2019 to carry out a feasibility study. This assessed whether the site is suitable for a constructed wetland and could provide the desired outcome of improving water quality in the Silverstream tributary before it enters the main river.
After confirming the effectiveness of the idea, Morphum began designing an integrated wetland system that improved water quality and enhanced the recreation values and biodiversity of the site. This concept development process was done in collaboration with ECan, SDC, Te Taumutu Rūnanga, members of the public such as local farmers and representatives from Fish & Game, and our project partner - RMM landscape architects. Together we crafted a design for the site that responded to a variety of economic, cultural, and environmental drivers.
The design features two parallel flow-through treatment wetlands that divert a portion of flow from their respective streams. The two wetland cells are separated by a raised bund with a walking track that loops around the site and connects to the Coes Ford Reserve. Both streams have existing habitat values and as such, base flow will always be maintained in the streams and the channels enhanced with planting. A visitor engagement zone is proposed at one of the wetland outlets which will connect people with flowing water and the importance of wetlands to the local ecosystem.
Once this concept was approved by the client, Morphum undertook detailed design and prepared the necessary documentation, ready for funding and resource consent applications.
The Result
ECan is very pleased with Morphum’s final design and is currently seeking resource consent and funding from the Ministry for the Environment for the construction phase of this project.
We are proud to have delivered this wetland design on budget, and our client was impressed with our social and technical skills.
“Very happy working with Morphum Environmental - good people, intel, products, and communication. We always receive a response,” – Sylvia McAslan, ECan Project Coordinator
Morphum’s collaborative approach and ability to balance the project’s objectives, improving water quality, while also providing additional biodiversity and recreation outcomes, will ultimately help restore the natural habitat around Te Waihora (Lake Ellesmere) and contribute to the revitalisation of a taonga of national significance.