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.
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.