High flows expected in lower Waitaki River as storage lakes are spilled 

Page last updated: Friday 2 September 9am

Flows in the lower Waitaki River are expected to run significantly higher than normal from late Thursday 1 September, while spill flows from the storage lakes in Lake Pūkaki and Lake Takapō/Tekapō are released.

Releasing this water is necessary to manage high lake levels and will increase the storage capacity for upcoming forecasted rain, but the rainfall is still expected to increase levels in the lower Waitaki River in the coming days. Any such increase (if it is expected to exceed 850 cumecs) will be communicated by us.   

Adjacent landowners to the lower Waitaki River should prepare and act accordingly. A text alert may be sent once significant rain begins to fall in the catchment and more information about expected peak flows is known. 

Wet winter sees saturated catchments  

The MetService has issued an orange warning for rain in the headwaters of alpine rivers with some spillover – we are expecting alpine rivers south of Arthurs Pass to be impacted by this event. 

“This is the seventh rain warning that has been issued for Canterbury in the last two months. It’s been an unusual winter and catchments are completely saturated, so when it rains again there is little capacity for water to be absorbed and it runs off faster,” rivers manager Leigh Griffiths said.  

“People should expect rivers to rise faster and behave differently than with smaller amounts of rain.

“On top of this, we are observing more flood damage and erosion than usual at the moment due to these saturated conditions. Breakouts are possible at lower flows than normal.”

More information on the forecasted weather can be found on the MetService website.

Flows likely to remain varied 

Varying high flows and lake levels can be expected to persist for a period of several weeks depending on how much spring rainfall occurs in the area.

“Lake Pūkaki is at 180% of average storage for this time of the year. With more rain forecasted over the next few days, we need to release water to maintain a safe lake level and reduce pressure on our hydro structures,” Meridian Energy general manager wholesale Chris Ewers said.  

“All the upper Waitaki lakes are high, and we’re focussed on generating as much as we can and moving water through the system. Based on the current forecast, we would expect the flow to be up to 800 cumecs on Saturday,” he said.   

River flow levels can be seen at on our river data page.

Affected areas 

“The largest affected area will be the lower Waitaki River (downstream from the Waitaki Dam), which has the potential to see flood conditions, possibly starting to increase on Thursday evening or Friday and peaking sometime on Saturday. Flows will continue to be monitored and modelled based on weather and spill data, and further updates to these will be provided throughout the event,” Ewers said.  

Pūkaki, Ōhau, and Takapō/Tekapō Rivers will also have increased flows. 

“The unprecedented rain levels over the last couple of months has altered the rivers’ carrying capacity for high flows. Varying high flows also have the potential to create new or accelerate existing erosion damage along the river margins, but we would expect the flooding to be confined to the immediate area of the lower Waitaki riverbed and its margins,” Griffiths said. 

“It’s important for landowners adjacent to the lower Waitaki River to be aware and be prepared,” she said.

Supporting information  

When will high flows begin?

Increased flows in the rivers connecting the upper Waitaki Lakes have started in some areas. Increases in lower Waitaki River flow may start late Thursday 1 September or Friday 2 September. Varying high flows and lake levels can be expected to persist for a period of several weeks depending on how much spring rainfall occurs in the area.

Why are Meridian spilling the water?

Typically, the Waitaki Power Scheme (WPS) acts to reduce floods in the lower Waitaki River by using storage lakes in Lake Pūkaki and Lake Takapō/Tekapō.

As a result of high rainfall over the last couple of months, combined with very high snowpack, the lake levels are significantly higher than usual for this time of year.

High lake levels need to be managed and dropped to provide flood protection to downstream landowners. This is done by spilling water from the lakes through the dams.

What's been done to manage the flows?

Meridian Energy, Genesis Energy, and Environment Canterbury are in regular communication and sharing information to understand when and what peak flows will look like.

How will I stay up to date?

Environment Canterbury and Meridian Energy will continue to post any updates on their channels – website and Facebook – and for elevated flood flows in the lower Waitaki River by text alert to subscribers.

Who manages the hydro infrastructure in this area?

From Lake Takapō/Tekapō, water travels through the Takapō/Tekapō Power Scheme, which is managed by Genesis Energy. All the other hydro lakes in the area are managed by Meridian Energy with the final discharge point being from the Waitaki Dam into the lower Waitaki River.

During high lake level/flood events, Meridian and Genesis have agreements to work together to manage flows through the entirety of the system.

Who can I contact if I'm concerned?

If you’re a landowner adjacent to the lower Waitaki River and you are concerned, please contact the Environment Canterbury flood controller at 03 687 7893 or your local District Council Civil Defence Emergency Management Officer.