Mataura River water takes

The Mataura River – the challenge of water allocation

The 190km long Mataura River is renowned as a source of brown trout and is a legendary dry fly river, drawing national and international fishers. The Mataura River catchment also has significant cultural values, with a freshwater mātaitai reserve on the Mataura River recognising the importance of the river for customary food gathering.

Water Conservation Order

In 1984, four organisations applied for a national water conservation order in respect of the Mataura River and its tributaries, in order to protect trout and the trout fishery. It was a long process to get the order, going through a series of public consultation, hearings and appeals, before the Water Conservation (Mataura River) Order 1997 (WCO) was made on 7 July 1997.

Although the WCO’s primary goal was to protect the trout fishery, other values such as native fish, wading birds and gulls are protected as a consequence.

The WCO stipulates that at any point, 95% of the natural flow in the Mataura River must remain and as a regional council, we are required to adhere to the order when issuing consents for water takes. The WCO prohibits us from issuing any new or replacement resource consents if more than 95% of the flow is allocated for abstraction.

How is water allocated?

Water takes are allocated in accordance with the WCO, which allows for 5% of the instantaneous flow to be allocated. For pragmatic management this has been divided up to allow for 5% of the flow below 9 cubic meters per second (cumecs) at Gore. Minimum flow cut-offs are then progressively increased at two cumec blocks at Gore e.g. 9, 11, 13, 15, 17, 19, 21, 23 cumecs. The over-allocation is occurring in the lower blocks, with the higher blocks being within the allocation limits.

Abstractions that impact flow in the Mataura River fall into two broad categories:

Direct abstractions from rivers and streams; and
Abstractions from groundwater that has a good hydraulic connection to surface flows in streams and rivers. This groundwater pumping effect on surface waterways is referred to as “stream depletion”. This is indicated in the schematic diagram below for a bore pumping groundwater near a stream.

The issue

We’ve identified an issue with our consent allocations for water takes in the Mataura catchment, specifically affecting those above Gore.

The river above Gore has been over-allocated, which means that more water is allocated to abstractors than is allowed by the WCO.

Environment Southland have conducted an independent review (carried out by Pattle Delamore Partners Ltd) as to how this over-allocation situation occurred. The review did not find any errors in the decisions on previous consent applications based on the information that was provided to decision makers at the time. The over-allocation has occurred because:

Some consents, that affect the flow in the river, had been omitted from previous allocation totals;
The effect of some groundwater takes on the river flow had not been properly assessed;
Implementation of the stream depletion calculation methods in the proposed Southland Water and Land Plan have increased the overall quantity that needs to be included in the surface water allocation bands.

The WCO precludes the granting of new or replacement consents while the catchment is over allocated. There are several replacement consent applications in process which are ‘on hold’ until the over-allocation is resolved.

You can find out more about our methods of estimating stream depletion in the proposed Southland Water and Land Plan.

What happens next?

We intend to work with all affected consent holders in the catchment to determine the most equitable way to reduce the volume of water allocated to consents to the level set out in the WCO.

Further work is being done in collaboration with consent holders, iwi and key stakeholders to finalise the extent of the over-allocation. Among other things, we have completed additional field work to get more robust data on the hydraulic connection between groundwater takes and nearby rivers or streams. We are also working to ensure that there is a common interpretation of key aspects of the regional plan and WCO.

We want to look at a number of options and also consider alternatives which may come about as a result of our discussions with consent holders. There are several different ways this situation can be resolved, each with its own benefits and challenges.

There’s not a one size fits all rule to deal with the over-allocation. Together, we can find the best fit for our own community, while meeting the legislative requirements of the WCO.

Note: The PDP report is partly redacted under Section 7(2)(a) of the Local Government Official Information and Meetings Act 1987 to protect the privacy of natural persons. Below is some further information.

For context, the memos prepared by PDP which are included below, do provide some early potential numbers regarding the size of the over-allocation and potential solutions to ensure compliance with the Water Conservation Order. The memos were drafted in the early stages of our understanding of the nature of the over-allocation and investigations into possible solutions. The information in these, while correct at the time, has been superseded by the finalised PDP report.