River projects

Rangitata River during 2019 flooding

We’re continuing and expanding our successful programme of work on the Rangitata River. This project will improve flood resilience across the catchment and includes investigations, construction, and enhancement work.

We’ve completed flood protection planting at the railway breakout above SH1 and are monitoring the results regularly. Vegetation clearance to improve channel capacity is underway. The modelling and design for the new stopbank alignment are complete, and we’re now drafting consent documents.

Project description: This project will upgrade and expand flood warning systems (telemetry) to provide reliable, real-time data. The goal is to improve forecasting and reduce the impacts of severe weather before, during, and after flood events.

Work completed: July 2023

The Ashley Rakahuri River is a key feature of the North Canterbury landscape that poses a significant flood risk to the communities living on its floodplain. This project involved removing exotic vegetation (willow and brush weeds) choking a 15km section of the Ashley River from the Ashley Gorge (about 536ha), an 8km section of the Ashley River to the Ōkuku River confluence and an approximately 7.5km section of the Ōkuku River upstream to the west of the Grey River confluence (about 140ha).

The clearance work gave the rivers significantly more room to move naturally and reoccupy the cleared fairway, with properties affected by the 2021 floods now better protected.

Complementary works have included:

• Removal and cutting through islands to improve flow paths.
• Construction of a two-metre–high gravel bank to provide additional flood protection at a localised breakout site.
• Anchored tree protection (ATP) at a localised site. (This involves securing cut willows to the riverbank with wire rope and concrete blocks. The trees continue to grow, forming a stable mass of plant material, which helps to stabilise the bank and prevent further erosion.
• Strategic planting of willow trees to improve resilience for adjacent properties.

Find out more about the transformation of the Ashley River/Rakahuri.

Work completed: December 2023

We own and maintain many valuable instream flood protection structures like flood gates, culverts and weirs across Waitaha, and some can make it difficult for ika/fish, including native taonga species tuna (long and shortfin eel) and īnanga/īnaka (common galaxias), to move through waterways. While these structures often provide essential protection and cannot be removed, they can be made easier for fish to navigate through.

Throughout this project:

• 44 structures within awa/river and drainage rating districts were assessed and ranked according to the risk to successful fish passage, with 14 chosen to remediate as part of this project.
• Remediation works included:
  • the placement of 60 tonnes of rock across 5 sites
  • 7 new fish-friendly floodgates installed
  • 15 2.4m long concrete pipes installed.
• 21 types of migratory and non-migratory fish were captured during pre- and post-remediation works as part of this project.

The fish surveys undertaken before and after the works were completed showed a positive trend in fish passage at most sites.

Learn more about fish passage improvement through flood protection structures.

Culvert before installation

Culvert during installation

Culvert after installation

Work completed: September 2024

The Halswell Huritini weed barrier project aimed at replacing a piece of aged infrastructure in the Halswell Canal used to capture cut river weed.

Weed is cut from the riverbed to manage water levels (both ground and surface water) in the Halswell/Huritini catchment.

If weed were to enter Te Waihora/Lake Ellesmere, it would severely degrade water quality through the release of stored nutrients during decomposition. The purpose of this infrastructure is to reduce the potential environmental impacts in this nationally important wetland of huge cultural importance.

New solution boosts safety

The design for the new structure was agreed through a detailed optioneering process and consultation with key stakeholders and mana whenua partners. The new screen installed on site is much safer as it is now controlled by a winch and is anchored by several piles installed into the riverbed, providing additional structure reinforcement. The new solution will ensure efficiency in the weed capture process and future-proof the weed cutting operation.

The old weed barrier looking upstream

The new weed barrier looking downstream

Work completed: December 2023

In December 2019, the Rangitata River broke out of the main channel at five key locations, causing major damage to flood protection, roading, rail, farmland, 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.

Emergency works were undertaken to retain ongoing and future flood flows within the main channel; however, further infrastructure resilience works were required to protect communities and critical lifelines.

The project included five workstreams and key works included:

1. Infrastructure repair and enhancement – initial works to return the flood protection to the level that existed before the flood event via rock and gravel bunds construction, pole planting, aerial spraying to target invasive weeds along the river, temporary repair works at the Peel Forest Landfill, and clearance of the tree debris at the Rangitata Huts post 2021 floods, as well as further strengthening of the repaired flood protection assets to increase the levels of flood resilience;
2. Natural infrastructure enhancement - vegetation clearance of the two overgrown islands on the true left bank of the Rangitata River below SH1 (Whittell’s and Stoddard’s Islands), to a total of 395ha; planting of native species across 5 restoration sites in the lower reach of the Rangitata River, in collaboration with the Department of Conservation and the delivery arm of Arowhenua Rūnanga (Te Kete Tipuranga o Huirapa);
3. Science investigations - 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. This work feeds into the Rakitata Revival Programme, a multi-agency partnership to revive the mauri of the Rakitata awa;
4. Lower Waitaki remediation - Remediation to 12 sites, including various flood protection and erosion works. The work included the construction of rock and gravel groynes, gravel beaching, layering, anchored tree protection (ATP), and various channel works.

Rangitata river works at Ferry Rd

Rangitata river works Stoddards Island cleared

Work completed: December 2023

River berms and margins are the strips of land next to the active part of the riverbed where there are areas of unstable gravel and flowing channels. Many river berms have become choked with weed growth, and this is expected to accelerate with the effects of climate change.

This comprehensive project used natural infrastructure to increase the flood resilience of river berms, which also supported the regeneration of habitat for native animals and plants over 60 sites across 22 awa/rivers throughout Canterbury.

More than 250,000 trees were planted along the river margins to buffer critical structures from flood waters and slow flows to prevent bank erosion. The enhanced environmental and biodiversity outcomes, as well as clearer braid plains to allow uninhibited room for flood flow, were achieved through the control of 1,200 ha of listed weed species.

We worked collaboratively with ngā Papatipu Rūnanga as well as the community to choose the locations based on a broad range of values, and which can achieve multi-benefit outcomes reflecting the primary goal of enhancing flood protection while achieving progress in other areas such as biodiversity, kaitiakitanga/stewardship, and community.

The project consisted of:

1. Strategic flood protection planting (natural infrastructure) - in and around river margins to increase the flood resilience of river berms (with trees providing a buffer that slows floodwaters and prevents erosion) as well as under-canopy native planting.
2. Targeted invasive weed control - to allow water to flow more freely through existing channels and to stop the smothering of flood protection vegetation in river berms.
3. Erosion protection - for existing engineered flood protection infrastructure, and wetland enhancement to build on the potential of moist ground spaces as holding areas for excess water in flood conditions.

This project is a great example of how a holistic awa management strategy can provide both environmental and flood management benefits.

Berm Transition Opihi River Te Ana o Wai after

Berm Transition Opihi River Te Ana o Wai before

 Progress map: See planting and berm changes across the region.

 Download berm transition project reports

Work completed: December 2023

New inlet grate

The Waitarakao Washdyke pipes are an outlet for adjacent flood and drainage schemes that we manage. The ageing structure posed a risk to the community in case of an adverse weather event and needed future proofing, especially with the coast’s gradual move landward because of climate change.

The project involved:

• Securing the pipes in place to prevent them from floating if water overtops the current bank in the case of a high tide or a significant weather event.
• Enhancement planting of two sites was completed, with the design developed in collaboration with Te Rūnanga o Arowhenua and delivered by their delivery entity, Te Kete Tipuranga o Huirapa Ltd.

Our Waitarakao 

Waitarakao Washdyke Lagoon is a special place for wildlife and mahika kai food gathering, but now it's in decline, and the habitat for plants and animals has degraded. Department of Conservation, Environment Canterbury, Te Rūnanga o Arowhenua and Timaru District Council have joined together to make a plan to restore the health of the lagoon and its wider catchment.

Our Waitarakao: Learn about actions and projects underway and how you can get involved.

Work completed: February 2022 

Waiau stopbank during construction

Waiau township in North Canterbury has in the past been subject to many flood events from both the Mason and Waiau Uwha Rivers. Numerous ad-hoc stopbanks were constructed over the past century, the earliest dating between 1907 and 1922 by the Waiau Riverside Protection Board. Some of these were damaged by the 2016 Kaikōura earthquake.

This project included:

• remediation and strengthening of two existing stopbanks on Inland Road
• construction of a new stopbank, including topsoiling and fencing, which borders the eastern side of the town.

Through the upgrades and linking of existing banks, these works have majorly improved the resilience of the Waiau community to flood events, which are predicted to become more frequent and of greater magnitude with climate change.

Work completed: October 2021

Waimakariri River Flood Protection at McIntoshs Bend

The Waimakariri and Kaiapoi River stopbanks protect Kaiapoi township as well as the Greater Christchurch area from flooding. In the 1960s, riverbank rock armour was installed to prevent erosion and stopbank breach on this very sharp bend (McIntoshs Bend). Over the years, the river narrowed, and a deep scour hole developed, increasing erosion vulnerability to the nearby communities and critical infrastructure such as the Waimakariri District oxidation ponds. McIntoshs Bend is a highly valued salmon fishing area, with substantial wetland and recreational values.

The works were built on the completed Waimakariri Flood Protection Project and included:

• large-scale rock work to strengthen existing rock protection around McIntoshs Bend and add additional rock protection along the lower Kaiapoi River and adjacent stopbank
• native planting to enhance existing biodiversity values in the area
• upgrade of the the nearby public amenities (carpark and recreational area).

Find out more about the Kaiapoi flood protection project:

• Kaiapoi flood protection - $24 million three-year programme of flood protection works kicks off with Kaiapoi rock works