Planning for Increased Flows and Snowy Cultural Water

Water planning

Annual water allocations to the water entitlements recovered from water savings and purchases in the western rivers determine the total volume of water available for the Snowy, Snowy Montane and Murray River Increased Flows programs each year.

The amount of water available influences the release strategy for the following year. Environmental flows to the Snowy River are set in February for a 12 month period and implemented from May to April.

The NSW Government considers advice on the appropriate release strategy from a number of sources including Victorian and Commonwealth Government agencies. The release strategy for the Snowy River and the Snowy Montane Rivers for the following year is included in Snowy Hydro Limited's annual water operations.

Previous water years

To date four flow strategies have been implemented in the Snowy River (SRIF) between 2002 and present.

Stage one: 2002-2006

Tributary releases - low allocation

To provide flushing flows to improve habitat quality the outlet works at Jindabyne Dam were required to be upgraded. Construction occurred between 2003 and 2006. While this work was occurring, the initial three years of releases from 2002 to 2006 were made via a tributary release at the Mowamba Weir on the Mowamba River.

During the initial stages of the increased flows to the Snowy River, water was borrowed from the Snowy Scheme as the water savings had not yet been achieved. These releases from the Mowamba River occurred prior to the recovery of significant amounts of water entitlements. In effect, the water was borrowed in order to make the initial releases - see case study in stage two. This stage occurred during a period of drought and low allocations. The water borrowed at the end of this stage was 32.1 GL and for pay-back accounting purposes, was maintained in a ‘Mowamba Borrowings Account’.

Stage two: 2006 -2010

Jindabyne releases - low allocation

The second stage involved making releases from the new outlet works from Jindabyne Dam, again during a period of historic drought conditions across south-east Australia.

During this stage, the overall volume was comparatively similar to stage 1, but the flow regime differed from the first stage, in that there was a reduction in daily flow variability.

Case study: Mowamba Borrowings Account

In the years following Corporatisation, the release of SRIF was restricted by physical limitations of Jindabyne Dam and the volume of environmental water recovery. In response, governments agreed to release up to a maximum of 38 gigalitres per year of SRIF down the Snowy River via the Mowamba River and Cobbon Creek, with the water borrowed from water held in the Snowy Scheme. This was to occur until new outlet works were constructed at Jindabyne Dam.

The volume of water borrowed was recorded in the Mowamba Borrowings Account.  In total, 64.9 gigalitres of SRIF was borrowed and debited from the account between 2002/03 and 2005/06.

Under the SWIOID, the Mowamba Borrowings Account must be repaid from water apportioned to the Snowy River (SRIF). Each year the first 38 GL of water was to be made available for environmental flows, and any additional water was to be used to repay the Mowamba Borrowings Account, up to a yearly re-pay limit of 38 GL. Any further water apportioned to SRIF beyond these amounts was also available for environmental flows.

During the height of the drought, water allocations were only sufficient to provide the first 38 GL of environmental flows and did not allow repayments to the Mowamba Borrowings Account (which accumulated 64.9 GL). Therefore on 11 August 2010, the NSW, Australian and Victorian Governments agreed to provide an additional 56.3 GL in 2010-11 for higher environmental flows in the Snowy River. This agreement allowed the Mowamba Borrowings Account to be fully repaid (32.1 GL), as well as an additional 24.2 GL of environmental flows to be released from Jindabyne Dam to the Snowy River. As a result, the total environmental flows to the Snowy River in 2010-11 exceeded 62 GL.

Stage three: 2010-2013

Jindabyne releases - single large spring pulse

The third stage of releases occurred as more entitlements were generated from water savings projects, and the drought across south eastern Australia gave way to wetter conditions. This provided sufficient water savings for flushing flows to be made to the Snowy River.

A significant change in the operation of Jindabyne Dam occurred during this period, as the higher water allocations allowed the first large flushing flows to be released and the lake water level is now required to be held at higher levels to allow for the flushing flows. These flushing flows were designed to address the initial objective of the Snowy River recovery, which was to improve the in-stream habitat quality by re-introducing an annual spring flood.

These flows initiated the start of the physical recovery of the Snowy River habitat by scouring the riverbed of the stored sediment in the river channel, and improving habitat condition. These high flows were a significant event for the local community and landholders. An additional large release occurred in March 2012 (i.e. similar to the 2011 spring event) as a flood mitigation measure, because Lake Jindabyne was at full supply level.

However, the flushing flows typically consumed about 60 per cent of the annual water allocation and resulted in limited daily flow variability for the remainder of the year. Many of the other hydro-ecological targets could not be met during the remainder of the year.

Stage four: 2013-2017

Jindabyne releases - multiple spring events

The fourth stage of the environmental water releases commenced during the 2013-14 water year. This stage of the program is attempting to build on the previous release program by including high flows, but also increasing the daily flow variability for the entire water year.

The stage four strategy has the following broad objectives:

  • To better reflect the hydrology of a Snowy montane river, including increasing the daily, seasonal and annual flow variability.
  • To provide multiple high flow events to meet the primary ecological objective of habitat improvement.
  • To fully utilise the infrastructure capability of Jindabyne Dam to provide variable flow rates.
  • To provide complementary tributary releases in Autumn to provide basal resources to stimulate the aquatic foodweb.

The flow pattern during this stage differs from previous years, as it better reflects the hydrological characteristics of a Snowy Montane River. The SRIF strategy includes higher flows over winter and spring, with five high flow events occurring in a water year. These events will have an eight hour pulse of high flow water to promote scour of the river bed which improves habitat. These five events include one primary event (the flushing flow) and four secondary high flow events.

Previous Snowy River Increased Flows strategies

An overview of environmental water flows for the 2013-14, 2014-15 and 2015-16 years is available.

Previous Snowy Montane Rivers Increased Flows strategies

Snowy Cultural Water