Making Money out of nothing at All

Trustpower’s unlawful budgeting of Lake Coleridge’s “stored water”

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Canterbury anglers have seen a collapse of both the recreational and native fisheries in the lower Rakaia River since the Rakaia River National Water Conservation Order 1988 (RWCO) was amended in 2013.

The 2013 RWCO amendment proscribes a complex set of conditions for the “storage” of irrigation water in Lake Coleridge during periods when natural river flows exceed the RWCO monthly minimum flows.

Anglers’ fears that the consented water storage regime have not been complied with by Trustpower has been confirmed in a recently released partial Environment Canterbury Report;

The Rakaia Water Balance – catchment overview and model development September 2021 Report No. R21/11 (in draft). Environment Canterbury

The Rakaia water balance _model development report V4 Draft 051021.pdf


“The “Lake Coleridge Project” is defined in the RWCO Amendment Order 2013. This amendment specifies additional rules to the RWCO 1988 about damming, diversion, takes, and discharge of water, as well as rules about “Stored Water” for irrigation use. Prior to the amendment, Lake Coleridge storage was only used for hydro-electricity generation purposes, without the ability to store water for irrigation.

The “Lake Coleridge Project” was originally anticipated to include major changes to physical infrastructure (new canals and powerhouse); however, the current approach is to use existing infrastructure. With the amendment, “Stored Water” can be released upon request, to meet downstream irrigation demand during times of low river flow. Only users who have a contract with Trustpower can order this “Stored Water”.

In February 2015, Trustpower implemented another change to how “Stored Water” is managed. The change involves utilising the entire lake when accounting for stored water for irrigation, rather than only water that can be physically accessed within the operating range. This occurred without an amendment to the RWCO 1988”.


Without changes to the original RWCO there would be insufficient natural flows in the Rakaia River to give certainty of supply to approximately 100,000 ha of planned new irrigation under the Barrhill Chertsey and Central Plains Water enhancement irrigation schemes.

An additional 50 m3/sec abstraction was required – 17 m3/s allocated to the BCI scheme and 33 m3/s allocated to CPW Ltd.

The solution was to “store” water in Lake Coleridge where Trustpower could both generate electricity and then sell the water to contracted irrigation schemes.

The 2012 Ecan managed Lake Coleridge Project consent Hearing recommended the necessary consents based on Trustpower’s application that outlined a three stage plan with stage III involving raising the level of Lake Coleridge for increased water storage and the construction of a canal with a capacity of 25 m3/s to carry water directly from Lake Coleridge to the Central Canterbury Plains. Between 4 and 6 small hydroelectric power stations were to be built along the proposed canal.

Since the 2012 Hearing only Stage I and Stage II have been implemented. This gives Trustpower the windfall of being able to sell Rakaia River water to irrigators without having to spend a cent on infrastructure other than the pumping station at Highbank to supply the BCI scheme.

The “water storage” in Lake Coleridge is in essence virtual water storage where Trustpower had a degree of control over when the outflow water is released.

This is limited by the inflows into Lake Coleridge and restrictions on the operating levels of the lake.

There is insufficient accessible storage to hold enough “stored water” within these levels to meet the needs of irrigators and comply with the original RWCO 1988.

Trustpower’s cunning plan

Appendix 2 Description of Trustpower’s implementation of the Warehouse Stored Water concept The text below describes Trustpower’s implementation of the Warehouse Stored Water concept and is largely quoted from a letter from Russell McVeagh (26 March 2014). Quoted sections are shown in italic font.

Introduction Within the usual operating range (509.4 m – 506.4 m, which is slightly less than the operating range provided for under the consents), Lake Coleridge holds approximately 100 MCM of water. This volume is a mere fraction of Lake Coleridge’s total volume of approximately 4 BCM. Trustpower’s modelling has indicated that about 800 MCM of water flows through Lake Coleridge in a normal hydrological year, and of this about 450 MCM would qualify as “Stored Water”. The total volume of water that flows down the Rakaia River in a normal year is approximately 6.7 BCM. The issue and the opportunity In any given year, approximately 450 MCM of water enters Lake Coleridge that would qualify as “Stored Water”. At noted earlier, there is only approximately 100 MCM of capacity available within the normal operating range of Lake Coleridge, and so the productive use of up to 350 MCM of “Stored Water” would potentially be forgone in any year. Trustpower has developed a solution that would allow significant additional storage (in excess of 200 MCM) within Lake Coleridge, with no additional environmental effects, and with the operation of Lake Coleridge remaining within the currently consented operating range. Trustpower describes this solution below, followed by their analysis demonstrating that this can be implemented without any variations to either the resources consents for the Coleridge HEPS or the Rakaia WCO. Description of Trustpower’s solution In essence, Trustpower’s proposed approach would enable it to store “Stored Water” anywhere within Lake Coleridge, and not just in the top 3 to 4 meters. This expands the theoretical storage capacity for “Stored Water” within Lake Coleridge from approximately 100 MCM up to over 300 MCM. While water can only be taken from within the top 3-4 meters, assuming there is enough “Stored Water” elsewhere within Lake Coleridge, Trustpower can continuously classify and reclassify water within the top 3-4 meters as either “Normal Water” or “Stored Water”, depending on what type of water is required. An example best illustrates the benefits of this concept. For the purpose of this example, the term “top storage” refers to a situation where “Stored Water” can only be stored in the top 3-4 meters (Lake Coleridge is effectively treated as if it were only 3-4 meters deep, with any water of whatever type below the operating range being disregarded), whereas the term “whole lake storage” refers to the storage of “Stored Water” anywhere within Lake Coleridge.

Environment Canterbury’s (lack of) Response

Perhaps unsurprisingly Ecan’s Government appointed Commissioners appear to have accepted this blatant non-compliance in 2014. The Commissioners were after all appointed to greatly expand irrigation within the Canterbury region and by becoming complicit in Trustpower’s unconsented (altered) water balance method, irrigation was allowed to take precedence over the Rakaia Water Conservation Order, (Amended 2013).

With the return to a democratically elected Canterbury Regional Council anglers would have hoped for a council with more integrity.

Sadly it seems Ecan finds itself unable to end this unconsented non-compliance. The September 21 partial Ecan report appears to be an attempt dodge the compliance question by purporting to be a scientific study into the generalities of water budgeting. Typical of the “issue avoidance” we have come to expect from one of New Zealand’s largest business friendly Regional Councils.

Ecan is a council of “Ecan’ts”;

  • It can’t manage the over allocation of the region’s water
  • It can’t manage the rising levels of nitrate and pathogens in the region’s aquifers and lowland streams
  • It can find ways of deferring and delaying taking necessary action against non-compliance
  • It can always have another meeting. New Yorker Cartoons

Opinion piece by

Dr Peter Trolove



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1 Response to Making Money out of nothing at All

  1. Peter Trolove says:

    As a postscript to this article, Trustpower sells “stored water” to contracted irrigation schemes for $900 per 250 m3.
    This a clear economic driver for Trustpower to employ “creative accounting” in its water budgeting.
    The issue for anglers is that every m3 purported to be stored water is one m3 of river flow that is removed from the lower river. This is the section of the Rakaia River experiencing massive declines in native and recreational fish since the Rakaia NWCO was amended in 2013.

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