A major flood event in December 2019 affected several alpine rivers in Canterbury. The Rangitata River broke out of the main channel at three key locations, causing a significant amount of damage to flood protection, roading, rail, farm, electricity supply and other assets.
New flood protection and erosion control infrastructure and tree planting are required to protect communities and critical lifelines such as road, rail and communication networks.
Immediately following the flooding of 2019/20, our priority was to stop the outflow of floodwaters from the river onto the adjacent floodplain and over key roads. Emergency works were undertaken to retain ongoing and future flood flows within the main channel. Bulldozers were used to construct three temporary gravel bunds, one across each of the breakout flow paths, and other river works to divert active braids away from the breakout locations.
This project for the Rangitata comprises of several workstreams. Workstream one addresses the immediate flood risk to the community with ‘Make it Safe’ flood recovery works commencing in the Rangitata River mid-April 2021. Works include extension of the emergency embankments, construction of stopbanks and gravel groynes at the three breakout locations and strengthening of existing rock stub groynes and construction of additional groynes adjacent to the Rangitata South Irrigation Ltd (RSIL) ponds.
Workstream two of this project involves remediation to 12 critical sites on the lower Waitaki River caused by the same weather event that caused breakouts on the Rangitata River.
A number of science investigations are planned for the river as well as a substantive natural infrastructure programme focusing on planting, weed control, wetland enhancement and mahinga kai enhancement opportunities.