Rakaia River
The Rakaia River is one of New Zealand's largest braided rivers, and an outstanding feature of the Waitaha/Canterbury landscape.
It is a vital habitat for indigenous birds and aquatic species, and a recreation hotspot for walkers, anglers, campers and boaters. Water drawn from the Rakaia is vital to the local economy, as a major source of hydroelectricity generation and irrigation water for hundreds of farms.
Managing water use
Hundreds of water users rely on water taken from the Rakaia for irrigation, stock water or other use.
We manage this water use through consenting. Each water take consent contains conditions designed to ensure that water taken is documented, excess water is not taken, and water is not taken when river flow is low.
Each consent contains a minimum flow condition – that is, a level at which water cannot be abstracted. These restrictions are also updated daily on our irrigation restriction data page.
The Rakaia Water Conservation Order (RWCO)
In 1988, the Rakaia became New Zealand's second waterway – and the first in Canterbury – to be subject to a water conservation order.
Read the full text of the National Water Conservation (Rakaia River) 1988 Order
The RWCO identified four outstanding natural characteristics of the Rakaia River:
- An outstanding natural characteristic in the form of a braided river.
- An outstanding wildlife habitat above and below the Rakaia River Gorge.
- Outstanding fisheries.
- Outstanding recreational, angling, and jet boating features.
Rakaia River flow has a large natural variation, and dry summers in Canterbury are becoming more common. The river flows seen in dry times can affect the Rakaia's outstanding characteristics.
Among other details, the RWCO sets a minimum flow regime for the river. Any consent to take water from the Rakaia has this minimum flow condition – or one more restrictive – attached to it.
We issue consents with these minimum flow conditions and monitor compliance with them.
The 2013 amendment to the RWCO allowed water to be stored in Lake Coleridge for the purposes of irrigation, not just hydroelectric power generation. This did not increase water allocation, but it increased the frequency at which already-consented water could be taken.
Our role in enforcing the RWCO
We've been hearing from anglers and environmental groups about reduced river flows and ecological values at the Rakaia River mouth. We take these observations seriously.
In response to questions over whether we are correctly enforcing the WCO, in early 2023, we filed for an Environment Court declaration to confirm our role in the RWCO.
We applied for four declarations that established:
- Our duty to enforce the RWCO is limited to ensuring our regional plans are not inconsistent with the RWCO and not granting resource consents that are inconsistent with any part of the RWCO.
- Our duty to enforce the observance of the Canterbury Land Water Regional Plan does not extend to a duty to enforce the observance of the RWCO.
- Our role in monitoring compliance with the resource consents we issue does not extend to a role in monitoring and gathering information on the RWCO itself.
- The RWCO does not limit the volume of water that can be stored in Lake Coleridge.
During conferencing with interested parties, all agreed we were at least responsible for that role as we defined it. So with no points of declaration left for the Environment Court to decide upon, we withdrew our application.
Environmental Defence Society and North Canterbury Fish & Game sought further declarations from the Environment Court on our role in upholding the RWCO, including clarification on whether the we as the Regional Council are responsible for monitoring and assessing whether the natural characteristics of the RWCO are being maintained.
We submitted to the Court that our role is to monitor the state of the environment to enable us to effectively carry out our functions under section 32 of the RMA, which includes monitoring compliance with resource consents that are issued in accordance with the RWCO – not that our role extends to monitoring the RWCO in the way the submitters described.
The Environment Court found in our favour, stating: "The Council’s obligation to monitor and enforce compliance with resource consents affected by the RWCO will focus on the terms and conditions of the relevant resource consent and not (alternatively or additionally) on the RWCO in and of itself."
Download the full Environment Court decision on the RWCO (PDF; 540KB)
The Rakaia water balance model
We've built a water balance model that simulates flow in the Rakaia River and explains the observed differences between river flow at the gorge and river mouth.
Download the Rakaia Water Balance Model Report (PDF file, 13.8MB)
Download the Methods report for the live model (PDF file, 1.8MB)
There are three factors that significantly affect river flow between the gorge and the mouth. Discharge from Highbank Power Station adds to the flow, while water abstraction and loss to groundwater reduce the flow. Our model calculates flow at the river mouth by adding and subtracting these factors from the flow observed at Fighting Hill.
We receive certain data at 24-hour intervals, so our model calculates the average flows, discharge and losses in cubic metres per second (cumecs) over those 24 hours. The model operates with a two-day time lag, so the most recent available data will be 48 hours old.
How to interact with this graph
- Click or tap on the legend labels to turn the data off and on.
- With a mouse pointer, zooming is performed by dragging out a rectangle in the graph. On touch devices, zoom by pinching in the graph and move the zoomed area by panning with one finger across the graph.
About the data points
Rakaia River at Fighting Hill: Earth Sciences New Zealand operates a river flow recorder near Fighting Hill in the Rakaia Gorge. Flow is recorded at five-minute intervals and can be viewed on our website.
Highbank discharge: The Highbank hydroelectric power station lies the end of the Rangitata Diversion Race. When operating, it discharges water into the Rakaia, adding to river flow. Manawa Energy operates a flow recorder on the discharge race, which records water flow at five-minute intervals and sends data to us once per day. Highbank Power Station began a refurbishment process in October 2024, expected to last around 18 months. During this time, discharge to the Rakaia River will be reduced.
Total abstraction: There are 120 consumptive consented water takes on the Rakaia. All consented water users who take water from the Rakaia must have a water meter installed at each point of take. These water meters measure water abstraction at 15-minute intervals and report use to us daily. These data are summed to give a total daily volume for abstraction. This volume is then converted to cumecs for use in the water balance equation.
Surface water losses: The Rakaia's gravel riverbed is a naturally leaky surface. Surface water losses represent how much water is lost into the ground between the Fighting Hill recorder site and the river mouth. The average loss is 21.4 cumecs, and we use this figure as a constant in our model.
Rakaia River at mouth: Our model takes the above data points and uses a simple formula to calculate flow at the river mouth where: Flow at the river mouth = flow at Fighting Hill − abstractions + discharges − river losses.
More detail about our water balance model
Our water balance model operates within defined limits and is based on specific assumptions.
Here you can find detailed information about irrigation restriction exceptions, how we calculate abstractions, missing data and background information about the development of the model.
Why irrigators can sometimes take water when levels are low
Manawa Energy operates a hydroelectric power scheme at Lake Coleridge with an outflow into the Rakaia River. It also uses the lake to “store” water for irrigation.
Some irrigators with water abstraction points below the Rakaia Gorge can “order” stored water a day in advance when they are on restriction. Manawa will spill this water from Lake Coleridge into the Rakaia to allow them to take water they otherwise would not be able to access.
Because the Lake Coleridge outflow is above the Fighting Hill flow measurement point and abstraction points are below, this means that sometimes water abstraction is permitted even when the river is on full restriction.
The daily release flow from Lake Coleridge is listed on our irrigation restrictions webpage
Factors affecting river flow above Fighting Hill
Rainfall and snow accumulation and melt control much of the timing of flows in the upper Rakaia. The main outflows from the upper catchment are the inflows to Lake Coleridge and the flow in the Rakaia River at Fighting Hill.
Upstream of Fighting Hill there is currently 0.686 cumecs of consumptive allocation affecting flow at the recorder. The operation of Lake Coleridge has various diversions to the lake and discharges from the lake are occurring.
Measuring river flow at the Rakaia Gorge
Earth Sciences New Zealand operate a water level recorder at Fighting Hill. This recorder measures water level at five-minute intervals and the data is graphed on our data page. Find out more about how we collect river flow data.
Development of river flow model
Measuring how much water is entering and leaving the Rakaia River is extremely complex, and requires us to receive and analyse many data points each day.
Flow is continuously monitored at Fighting Hill in the Rakaia Gorge, but due to the mobile braided nature of the river, it's not possible to continuously monitor flow in the lower river.
Our community has expressed interest in flows reaching the mouth and why these differ from those reported at Fighting Hill, and asked for clearer information about abstraction from the river.
We've been working to build a model that can account for river flow in the Rakaia from the flow recording station at Fighting Hill to the river mouth.
Early drafts of the water balance model contained errors in data, which produced results indicating possible significant non-compliance by water users.
We are now using updated data that gives us a clearer understanding of the operation of the hydropower and irrigation schemes.
These have been integrated into the model, which has been peer reviewed and tested against observed flows near the river mouth.
Data reliability and issues
The data used in this model comes from recorders found on waterways in remote areas operated by Earth Sciences New Zealand, Manawa Energy and consent holders. They are subject to interruptions due to weather or telecommunications issues. If this happens, we will work to restore data as soon as safely possible.
Limits and assumptions in the model
- The model inputs used to calculate flow at the Rakaia River Mouth are all required for the model to successfully run. If a single input is missing the model run will fail.
- This model relies on raw telemetered flow data available for each day’s model run. This data has not been quality assured or verified due to being near real-time. The archived (quality assured) data may be different to that used for the model due to updates of rating curves or data audits etc. Stability of underlying database may impact the ability for a model run to occur.
- Highbank Power Station discharge data is received by Environment Canterbury from Manawa Energy daily via telemetry. If the process that transfers the data from Manawa Energy to Environment Canterbury fails, then the model run will fail. Manawa Energy are only required to provide discharge data for the Highbank Power Station on request (not specifically required to telemeter the data).
- The water abstraction data used by the model has also not been quality assured. The model has some quality checks it undertakes (e.g. filtering out data spikes, duplicate days, negative values etc.), however this is unlikely to identify all potential data issues. Stability of underlying databases may impact the ability for a model run to occur.
- Our current method for estimating abstraction where metered data are not available, does not explicitly account for low flow restriction of takes when estimating abstraction. Metered water abstraction data should reflect low flow restriction requirements of the day, and this should therefore be translated to any estimated water abstraction.
- Model simulated flows are at an average daily resolution. We acknowledge that there can be changes in the river at a sub-daily scale. This includes the impacts of hydropeaking as the discharges from hydroelectricity generation fluctuate to meet demands. The impacts of sub daily impacts of changing abstraction and discharges are not captured and there will likely be occasions where flows dropped lower that those simulated for short periods of time.
- This model is not a compliance tool for assessing individual consent holders’ activities.
- The model assumes there is no lag time between flow, discharges and abstractions within the Rakaia River catchment.
Get in touch
For more information about the RWCO and water use on the Rakaia, contact our Customer Advisory team by email or by calling 0800 324 636 and we can put you in touch with the water and land science team.
For any media enquiries please email us.