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Canterbury Waterway Rehabilitation Experiment (CAREX)

14 December 2023

The Canterbury Waterway Rehabilitation Experiment (CAREX) is a stakeholder-driven stream restoration experiment. We work with farmers, councils, iwi, and the public to co-develop, co-design, and trial solutions to rehabilitate the health of freshwater ecosystems. Learn more about CAREX.

Carex 2
CAREX river study
Carex 3

We focus on solutions that have the potential to scale and be applied across waterways in Canterbury, Aotearoa New Zealand and beyond.

CAREX is testing practical tools to address aquatic weed, sediment, and nutrient management issues in lowland Canterbury and to improve agricultural waterway health. We have developed demonstration sites to showcase our rehabilitation tools and best practice in riparian management.

The information provided on our website are based on preliminary findings and will be subject to revision and peer-review. Materials cannot be reproduced without our express permission.

For enquiries please contact:
Team Leads - Professor Jon Harding or Angus McIntosh

The Sediment Story

In partnership with Living Water, we investigated the water quality issues of the Ararira/LII catchment near Lincoln, and advised on potential rehabilitation tools. We identified localised cases of elevated nitrate, phosphate and E.coli. However, excessive sediment was a widespread issue in this catchment and we believe that this impacts both the ecological communities as well as the drainage functioning of the network.

Firstly, to understand how and when sediment moves through the system, we used a combination of stage height loggers to continuously record water levels, and sampled sediment during floods and sediment transported along the bed of the waterway. Most of the sediment was silt and fine sand (<0.25 mm), which means that these particles will take a long time to fall out of suspension and be deposited on the streambed.

From left: downloading a stage height logger which continuously records water height; carpeted tiles installed to measure sediment transport along the bed of the waterway; pottles attached to a waratah at various heights to measure sediment transport in the water column during flood events.

In order to reduce sediment being transported out of the system and into Te Waihora/Lake Ellesmere we have been working on the installation of sediment traps. A sediment trap provides a simple, effective and potentially money-saving way to deal with excessive sedimentation in affected waterways.

To enable more sediment traps to be constructed, we set out to create a simplified table using easily-obtained measurements (water velocity and waterway width) to guide the design. This table provides a guideline for anyone to build a sediment trap to capture approximately 50-60% of the transported load. This design focused on fitting within the current waterway dimensions, to limit the effect on the surrounding land and facilitating the use of sediment traps in space-limited catchments.

CAREX Trap Table

Suggested sediment trap dimensions based on the width and water velocity of the waterway.

Watch our video Sediment traps - a simple and effective solution to sediment in waterways to learn more about why sediment traps are effective, how they work and how they can have ecological and financial benefits.

The CAREX Toolbox

What are the best tools for improving the health of local waterways? We are developing a toolbox of different tools that can be used individually, or in combination, to address macrophyte, sediment, and nutrient management issues and are testing their effectiveness in rehabilitation trials.

CAREX Toolbox

The Freshwater Biodiversity Box - A Teaching Resource

School Students using Biodiversity Teaching Resource.

The Freshwater Biodiversity Box is a dedicated set of freshwater sampling gear and activities available for schools.

It includes the tools to sample freshwater invertebrates, information on sampling methods, invertebrate identification guides and activities based on three key concepts:
1) healthy freshwater habitats;
2) invertebrates as biomonitoring tools; and
3) food webs.

The Freshwater Biodiversity Box was developed by the CAREX team with the $2000 prize from the Canterbury Aoraki Conservation Board Award & Trophy received in 2017. This award recognises the efforts of local groups and individuals supporting conservation within the wider Canterbury region and is supported by the Isaac Conservation and Wildlife Trust. CAREX was recognised with the prestigious award for their efforts in improving freshwater biodiversity and ecosystem healthy in agricultural waterways.

Head over to the UC Biology Science Outreach website for other printable resources and to make a reservation.

Contents of the Freshwater Biodiversity Box

2x waders (size 7 and 10)
2x surber samplers - for taking quantitative samples of organisms
4x kicknets - for taking qualitative samples of organisms
1x dissolved oxygen meter

5x clipboards
2x one metre rulers
1x 30m tape measure
12x white invertebrate sorting trays
1x detergent spray
30x forceps

15x freshwater invertebrate id guides
15x macroinvertebrate guides
15x fish guides

Resources for junior students:
1x Up the River book 
1x Tuna and Patiki book
4x foodweb game 
Printed resources 
- Observe like a scientist
- Water quality monitoring
- Waterway scavenger hunt

Rehabilitation Trials 2013-2018

We conducted in-stream and laboratory trials to evaluate rehabilitation tools designed to manage macrophytes, reduce and remove sediment inputs, reduce nutrient levels in waterways, and improve in-stream habitat and biodiversity in agricultural waterways.


Macrophytes can fill waterways, raise water levels, and accumulate sediment. We investigated practical alternative management tools that can be used to eradicate or control the growth and spread of macrophytes. We also conducted trials to help us understand the importance of timing and placement of macrophyte control activities.


Excessive fine sediment can clog stream beds, reduce habitat for aquatic biota, and enable macrophytes to grow more easily. We trialled ways to reduce “hot spots” where sediments may enter waterways and remove sediment legacies that have accumulated over decades.


Establishing riparian buffers and adopting nutrient limits are commonly used tools to reduce nitrate levels in agricultural waterways. We experimented with denitrifying bioreactors to remove nitrates from tile drain outflows, which can be highly-localised point sources of nitrates, in our experimental waterways. We also trialled in-stream organic matter additions to help stimulate nitrogen removal.


Most agricultural waterways lack important habitat for freshwater biota. We added in-stream habitat, including boulders and wood, to one of our waterways to demonstrate the value of habitat for fish and invertebrates. We also monitored the effectiveness of native riparian plants for providing shade and improved habitat.

Read and watch more

  • Collins, K.E., Febria, C.M., Devlin, H.S., Hogsden, K.L., Warburton, H.J., Goeller, B.C., McIntosh, A.R. and J. S. Harding. (2020). Trialling tools using hand-weeding, weed mat and artificial shading to control nuisance macrophyte growth at multiple scales in small agricultural waterways. New Zealand Journal of Marine and Freshwater Research.
  • Goeller, B.C., Febria, C.M., McKergow, L.A., Harding, J.S., Matheson, F.E., Tanner, C.C. and McIntosh A.R. (2020). Combining tools from edge-of-field to in-stream to attenuate reactive nitrogen along small agricultural waterways. Water. 12(383). doi.10.3390/w12020383.
  • Goeller, B.C., Burberry, L.F., Febria, C.M., Collins, K.E., Burrows, N.J., Simon, K.S., Harding, J.S and McIntosh, A.M. (2019). Capacity for bioreactors and riparian rehabilitation to enhance nitrate attenuation in agricultural streams. Ecological Engineering. 134: 65-77.
  • Goeller, B.C., Febria, C.M., Warburton, H.J., Hogsden, K.L., Collins, K.E., Devlin, H.S., Harding, J.S. and McIntosh, A.M. (2019). Springs drive downstream nitrate export from artificially-drained agricultural headwater catchments. Science of The Total Environment. 671: 119-128.
  • Collins, K.E., Febria, C.M., Warburton, H.J., Devlin, H.S., Hogsden, K.L., Goeller, B.C., McIntosh, A.M. and Harding, J.S. (2018). Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury, New Zealand. New Zealand Journal of Marine and Freshwater Research. 53(2): 182-200.
  • O'Brien, J.M., Warburton, H.J., Graham, E.S., Franklin, H.M., Febria, C.M., Hogsden, K.L., Harding, J.S. and McIntosh, A.M. (2017). Leaf litter additions enhance stream metabolism, denitrification and restoration prospects for agricultural catchments. Ecosphere.  8(11).
  • Goeller, B.C., Febria, C.M., Harding, J.S. and McIntosh, A.R. (2016). Thinking beyond the bioreactor box: Incorporating stream ecology into edge-of-field nitrate management. Journal of Environmental Quality. 45(3): 866-872. doi.10.2134/jeq2015.06.0325.

  • WATCH: Healthy Headwaters - Catherine Febria, gives an overview seminar on concepts and applications related to small streams and their protection. Here she connects narratives from around the globe - Great Lakes in Canada, Chesapeake Bay in mid-Atlantic USA and Canterbury, New Zealand - to illustrate the vital importance of small streams and the complex dimensions associated with their protection and restoration (22 November 2018).
  • WATCH: Highlights and lessons learned - Angus McIntosh, Jon Harding and Catherine Febria present lessons learned after a five-year agricultural stream restoration experiment. Tailored for a wide range of end-users in Environment Canterbury, this seminar describes main findings and associated public resources for use and application across the region (19 November 2018).
  • WATCH: Part One and Part Two of Catherine Febria's talk from the AGRI Innovation Mid Canterbury Seminar 2018. The seminar was about sharing knowledge and advancements with science and technology in agri-innovation. Catherine gave a talk about bioreactors and the CAREX project (2 May 2018).
  • WATCH: Katie Collins' talk from Crazy and Ambitious 2017. This was the first national meeting of the New Zealand’s Biological Heritage Ngā Koiora Tuku Iho National Science Challenge. The talk is titled “Moving beyond riparian fencing: partnering ecosystem scaling, services and society to achieve stream restoration” (14 June 2017).
  • WATCH: Professor Angus McIntosh's talk on the problems facing Canterbury's fresh waterways and some of the CAREX findings so far. This talk was part of the UC Connect public lecture series (5 July 2016).

  • Ashburton Guardian Article (PDF 828KB). "A simple nitrogen reduction tool" - Mary Ralston from Forest and Bird wrote a piece on how woodchip bioreactors can be a simple tool for nitrate reduction using a CAREX trial site as an example (28 January 2020).
  • Latitudes Article (PDF 461KB) "Clean Up Our Waterways" - Latitudes magazine recently did a piece on CAREX. Read about how bioreactors and riparian planting are effective tools at reducing nitrates in a waterway on a lowland, mid-Canterbury farm (15 August 2018).
  • UC Chronicle (PDF 1.0MB) - The CAREX team won the 2017 Canterbury Aoraki Conservation Board award for improving freshwater biodiversity and ecosystem health (18 July 2018).
  • NZ Farmer Article "Scientists work on simple ways to clean streams" - Read about how sediment traps are a simple method for reducing fine sediment load in waterways (23 April 2018).
  • Fonterra Article "Stirling Silverstream Effort" -  The journey of a wetland at one of our CAREX sites (27 October 2017).
  • WATCH: Fish&GameNZ "Snake Creek Restoration Baseline Sampling" - Catherine and Hayley helped set up a sampling regime for the data collection of the three year project to restore Snake Creek, a tributary of the Selwyn River (16 October 2017).
  • RadioNZ Interview: "Rebuilding healthy rivers" - Dr. Catherine Febria spoke with Kathryn Ryan on Radio NZ's Nine to Noon on rebuilding healthy resilience in streams and rivers (26 January 2017).
  • Ashburton Courier Article (PDF 303 KB) "Into the trenches with pine chips" - Read about what Brandon Goeller is doing with untreated pine woodchips as part of his PhD research (26 January 2017).
  • Central Rural Life Article (PDF 377KB) "Restored drains better every way" - Dr. Kristy Hogsden talks about the importance of rebattering before riparian planting to reduce slumping and sediment erosion (21 December 2016).
  • UC Chronicle (PDF 919KB) "Can we rehabilitate our problem waterways?" - Professor Angus McIntosh talks about the CAREX research objectives (20 September 2016). 
  • WATCH: MPI's "Growing our future" interview - We chatted with Ministry for Primary Industries (MPI) about the work CAREX is doing on a Canterbury arable farm as part of Katie Collins PhD research. The interview is part of MPI's "Growing our future" initiative showcasing local champions in the primary industry (9 September 2016).
  • NZ Farmer Article - Read about the transformation of a boggy piece of land into a thriving wetland and how CAREX is involved along with DOC and Fonterra as part of the Living Water partnership (24 June 2016).
  • Central Rural Life Article (PDF 682KB) "Boots on for planting" - Read about the community planting day CAREX held down in Hinds (25 May 2016).
  • Country Life on RadioNZ - Listen and read about the collaboration of CAREX with the DOC-Fonterra Living Water project and ESR at one of our sites near Lincoln (20 May 2016).
  • Ashburton Guardian Article (PDF 513KB) - Professor Jon Harding meets with the Hinds Drains Working Party to discuss weed management (14 April 2016).
  • WtW Article "starting at the top" - Whakaora te Waihora (WtW) spoke to Professor Jon Harding about the work that the CAREX team are doing. Two of the ten research sites from this project are in the Te Waihora/Lake Ellesmere catchment. Read what Professor Harding says about how "starting at the top" is critical for restoration of the lake (18 November 2014).

Our Funding Partners

Living Water
Living Water is a 10 year partnership between Department of Conservation and Fonterra, 2013-2023. Their focus is "finding game-changing and scalable solutions that will enable farming, freshwater and healthy ecosystems to thrive side-by-side". Living Water helped to fund our demonstration site in Springston between 2014-2018 and now we have partnered with them for 2019-2020 to provide advice and trial rehabilitation tools in one of their five catchments across New Zealand, the Ararira/LII, Canterbury. 

Mackenzie Charitable Foundation
The Ashburton-based Mackenzie Charitable Foundation was formed in 1976 by brothers Alan and Don Mackenzie, who were both successful farmers in mid-Canterbury. A key purpose of the foundation is to focus on development of the science and practice of agriculture. The Mackenzie Charitable Foundation funded the Freshwater Ecology Research Group for 10 years to research the effectiveness of riparian management (2008 – 2013) and to trial management tools and strategies to improve ecosystem health in agricultural waterways (2013 – 2018).

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