Environment Canterbury

RIV_2600497 Asburton River North Branch Stopbank

Canterbury Regional Council (Environment Canterbury) (the Council) (the Principal) has a statutory function under the Soil Conservation and Rivers Control Act 1941 to manage land use within the region to prevent and mitigate damage caused by floods and erosion (see s126 of the Act). In the 2021 Ashburton Floods, a breakout flood at this location caused extensive damage and risk to life. A ~4 km stretch of the river around Shearers and Walkhams Road, where this breakout occurred, has been identified as an ongoing major flood risk. This reach is significantly narrower than the general stopbank-to-stopbank width in the North Branch of the Ashburton River (NBAR), increasing the likelihood of a breakout. Severe aggradation through this reach has also caused the river to be perched well above the surrounding land, decreasing the capacity of the river and increasing the out-of-river flow risk. Modelling conducted of the whole NBAR identified an opportunity to address some of this risk, through relocation of the stopbank and widening of the river.

The Council is proposing to construct a new stopbank starting in November/December 2026 located at about 1 km downstream of Shearers Road. The Council wishes to engage a suitably experienced contractor who will work collaboratively with the Council and its professional advisors to deliver an outcome which fully meets all time, stakeholder requirements, cost and quality objectives.

This contract involves the extraction of approximately 35,000 to 40,000 cubic metres of gravel from the reach, construction of approximately 770 metres of stopbank and deconstruction of the existing stopbank. The first phase is the construction of the new stopbank which involves site preparation, gravel extraction to supply stopbank construction material, stripping/stockpiling of topsoil, and placement/compaction of the gravels to form a stopbank. The second phase is the deconstruction of the existing stopbank and placement of this material to form groyne bunds to protect the new stopbank. The gravel will be extracted from the river under the Council’s resource consent to undertake works in the river, and the Council’s gravel authorisation.

Department/Business Unit: Field Services