Trustpower's application to vary the Rakaia River Water Conservation Order

December 2012


The ability to ensure consistent supply of water from source waterways is critical to the viability of any irrigation scheme. This is particularly relevant to the Central Plains Water Scheme, which requires water to be diverted from the Rakaia River and is subject to the Rakaia Water Conservation Order.

This article looks at what the Rakaia Water Conservation Order does, and what TrustPower is seeking through its request for a variation to the Order. The article also looks at the benefits TrustPower’s proposal will have for irrigators using water from the Rakaia River and, in particular, the Central Plains Water Scheme.

What does the Rakaia Water Conservation Order do?

The Rakaia River Water Conservation Order (RWCO) recognises the outstanding natural character, wildlife, and fish habitats of the Rakaia River (the Rakaia) and related tributaries; and requires the natural rate and flow of water in the Rakaia and related tributaries are retained in their natural state.

The RWCO sets minimum gorge flows that are considered appropriate to ensure the outstanding features can be maintained. The RWCO also provides that when the gorge flows are below the minimum flow set by the RWCO, no water can be taken or diverted from the Rakaia. When minimum flows are exceeded, the RWCO allows up to 70 m3/s to be abstracted from the Rakaia when gorge flows permit. However, gorge flows never get high enough to allow for this amount to be taken.

TrustPower applied to the Minister for the Environment to vary the RWCO, and this was referred to ECan for determination as required under the Environment Canterbury (Temporary Commissioners and Improved Water Management) Act 2012.

What does TrustPower want to do?

Currently, TrustPower operates the Lake Coleridge Hydro-Electric Power Scheme. Water is diverted from a number of water bodies into Lake Coleridge and is used to generate power via the current Coleridge and Highbank Power Stations. It is proposed that an additional canal will be constructed along the true left bank of the River incorporating four to six new power generation stations.

TrustPower’s application seeks to amend the RWCO to allow for construction of the new scheme, and also broaden the use of the scheme to allow for both power generation and to allow for water stored in Lake Coleridge to be used to supplement irrigation of the Canterbury Plains.

The variation to the RWCO will see some water in Lake Coleridge classified as “stored water” once gorge flows exceed a certain limit. The variation to the RWCO will mean that this “stored water” will not be subject to the provisions of the RWCO.

It is intended that “stored water” will be released from Lake Coleridge at times when flows in the Rakaia prevent water permits held by irrigators to be exercised. As this water is not subject to the RWCO, irrigators will be able to extract water under from the Rakaia under their permits even if the Rakaia is below the minimum flows required by the RWCO.

In addition to releasing stored water through the tail race of the existing Coleridge Power Station, it is proposed that water will be conveyed along the new canal that will be constructed.

The recommendation of ECan is that the RWCO be granted as per the terms set out in the decision. It is now with the Minister for the Environment awaiting approval.

What is the effect on the Central Plains Water Scheme (CPWS)?

There are obvious benefits to the CPWS. Water storage in Lake Coleridge provides certainty of supply, as water can be held and released to match irrigation demand. In addition, reliability of supply means that efficient use of irrigation water can be increased, as water will be available to irrigate at optimum times. TrustPower is now in discussions with Central Plains Water, as well as other entities, around what infrastructure will be required and whether infrastructure between various users could be shared. In addition, TrustPower will likely be looking to approach Central Plains Water with a view to securing investment, and ensuring that any additional infrastructure will be economically viable. At this stage, TrustPower intends to start development of the new canal by 2015; having already invested in a new pumping plant that it hopes will be able to supplement the Barhill Chertsey Irrigation scheme in the coming irrigation season.


The need for consistent supply of water for irrigation schemes is critical to both the scheme viability and the efficient use of irrigation water. TrustPower’s request to vary the Rakaia WCO, if approved, will have a positive effect on the viability of the CPWS and other irrigation schemes utilising water from the Rakaia River.



Disclaimer: This is a brief sumamry for information purposes only and is not legal advice.

Posted on Friday 25th January, 2013 at 02:13 pm