Rangitata 2019 flood recovery

In December 2019, the Rangitata River broke out of the main channel at three key locations causing major damage to flood protection, roading, rail, farm, electricity supply and other assets.

Access across the river was cut at SH1 and SH79, the rail corridor was cut off, telecommunications and power were cut, and goods couldn’t get through to the lower South Island.

Our initial priorities

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.

New flood protection and erosion control infrastructure and tree planting were then needed to protect communities and critical lifelines such as road, rail and communication networks.

Works completed

This project comprises several workstreams:

‘Make It Safe’ flood recovery works at the Rangitata River

We have completed the pole planting season in the last quarter of 2023 with over 10,000 plants now in the ground, supporting reinforced hard infrastructure and rock work completed earlier in the project. This workstream is now complete.

Lower Waitaki remediation

We experienced some delays due to unfavourable weather conditions but were able to resume the works in the last quarter of 2023. The work completed in this workstream included rock placement and anchored tree protection (ATP) across three remaining sites, all of which was completed by the end of December.

Natural infrastructure enhancement

The scope of work for this workstream comprised of targeted weeding, vegetation removal, and native sub-canopy planting across various sites along the Rangitata River.

The large-scale clearance of choked channels on two large islands on the north branch of the Rangitata River (Withell’s and Stoddard’s Islands) to reduce flooding risk was finalised in quarter 3 of 2023 and we have already seen a few freshes come through the cleared area. Innovative new clearance methods have enabled good efficiency across these sites, resulting in lowered herbicide use and additional removal of all pampas grass, a tussock-like pest plant, across the area. The total area to receive weed control as part of this project is 395 ha. The works on these sites have now been wrapped up.

Cleared area to the right vs. uncleared area to the left

Native trees discovered during vegetation clearance

Drill and fill example post vegetation clearance

Map of 5 restoration sites on Rangitata River

Te Kete Tipuranga o Huirapa who delivered the on-the-ground work across five restoration sites have completed the final pass of spraying in the last quarter of 2023. The maintenance plan for these sites developed as part of this workstream has been finalised and will be delivered internally. We have received positive feedback on this workstream both externally and internally and, thanks to this shovel-ready funding, have been able to complete work that otherwise would have taken significantly longer to fund and undertake.

Science investigations

This workstream was focused on delivering science reports on the current state of the south branch of the Rangitata River, to initiate a conversation about the future of the south branch. A community workshop took place in November 2023 which marked the final activity for this workstream. Further community engagement will continue under the Rakitata Revival Programme.

Infrastructure enhancement post investigation

Building on the success of workstream 1, this workstream was focused on delivering additional infrastructure work to strengthen the repaired flood protection assets and increase the levels of flood resilience of the Rangitata scheme. We rounded off all the physical works that came into this workstream earlier in 2023, marking the completion of the infrastructure enhancement works.