Clutha Mata-au main stem 

This summary paper provides an overview of the environmental flows and take limits relating to the main stem of the Clutha Mata-au, Kawarau River and Hawea River main stems.  

Definition/map of main stem

Setting take limits and environmental flows

Draft proposed environmental flows

Draft proposed take limits

Definition/map of main stem 

The “Cutha Mata-au main stem” includes the  

  • Hawea River from Lake Hawea Dam Outlet to the Confluence with Clutha Mata-au
  • Kawarau River from outlet of Lake Whakatipu to the Confluence with Clutha Mata-au arm of Lake Dunstan 

 

A map of the Cutha Mata-au main stem is shown below.

map of the Clutha Mata-au main stem fmu showing boundaries

Setting take limits and environmental flows

The Clutha Mata-Au main stem is a high valued and unique water body. There are many values present and other matters that will inform the setting of take limits and environmental flows, these include:

  • High natural character and unique river form
  • The Kawarau River and parts of the Clutha Mata-Au main stem have been identified as a potential Outstanding Water Body
  • Water Conservation Order on the Kawarau River
  • High recreational values
  • Ecological habitat/flow relationship is in reverse and not the key driver for setting EFL and take limit (less water means more habitat)
  • Renewable electricity generation 
  • Water quality and the requirement to maintain or improve where degraded

 

Draft proposed environmental flows

It is proposed to retain existing environmental flow regime as established by the conditions of the resource consents held by Contact Energy Limited for operating hydro-electricity generation infrastructure at the Lake Hawea outlet and the Clyde and Roxburgh dams.

The draft proposed environmental flows for the Clutha Mata-au, Kawarau River and Hawea River main stems are shown in Table 1 below.

Draft proposed take limits

Two options have been developed for setting take limits for the Clutha Mata-au main stem, the Kawarau River and the Hawea River. These options are shown in table 1 below.

 

Option A:

This option proposes a take limit of 5 % of the Clutha Mata-au’s 7dMALF for different sections of the Clutha Mata-au main stem, the Kawarau River and Hawea River. This option reflects a more precautionary approach to limit setting that seeks to provide for the river’s environmental, recreational and cultural values while still providing for future water demand.

Under this option more water it is likely that more water can be allocated from the Clutha Mata-Au main stem, Kawarua and Hawea Rivers.

 

Option B:

This option proposes a take limit at 10 % of the Clutha Mata-au’s 7dMALF for different sections of the Clutha Mata-au main stem, the Kawarau River and Hawea River. This approach is consistent with the approach applied by ORC for developing default take limits for rivers in other parts of the Otago region.

Table 1 Draft proposed environmental flows and take limits for the Clutha Mata-au main stem, the Kawarau River and the Hawea River.

Name Environmental flow(s) (l/s) Take limit (l/s) Further allocation available (estimate based on best available information)
Option A Option B
10 % of 7dMALF
Upper Clutha
  • Clutha Mata-au main stem from outlet of Lake Wanaka to Clyde Dam; 
  • Hawea River from Lake Hawea outlet to Clyde Dam
Minimum flow of 10,000 l/s for the Hawea River 5,500 l/s* 11,000 l/s* Likely
Kawarau river from outlet of Lake Whakatipu outlet to confluence with Clutha arm of Lake Dunstan at Cromwell 120,000 l/s below Clyde Dam  4,650 l/s** 9,300 l/s **  Yes
Clyde dam to Roxburgh Dam 250,000 l/s below Clyde Dam 4,850 l/s*** 9,700 l/s*** Yes
Lower Clutha from below Roxburgh dam to mouth 250,000 l/s below Roxburgh Dam

* Based on estimated 7dMALF of upper Clutha Mata-au at confluence with Cardona (111, 000 l/s)
** Based on estimated 7dMALF of MALF of Kawarau River at chards (93,000 l/s)
** Based on estimated 7dMALF of MALF of Clutha Mata-au at mouth (298,000 l/s)

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