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, along with additional tree planting were required to protect the communities and critical infrastructure.
The Rangitata project was delivered in several workstreams. Initial phases addressed flood risk to the community with ‘Make it Safe’ flood recovery works commencing in mid-April 2021 to repair the flood protection infrastructure to the pre-2019 flood level. Works included 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. Further work was aimed at the additional enhancement of the flood protection assets across four more sites where further rock work and pole planting were completed in May 2023 to strengthen the existing flood protection infrastructure.
A number of science investigations have also been underway on the river, along with a substantive natural infrastructure programme focusing on planting, weed control, wetland enhancement and mahinga kai enhancement opportunities. Significant vegetation clearance work was delivered on the two islands on the true left bank of the Rangitata River below SH1 that have been overgrown with exotic weeds.
One of the workstreams focused on repair of 2019 flood damage to various sites on the lower Waitaki River and included installing rock and gravel groynes and anchored tree protection (ATP) to prevent rapid bank erosion.
