Environmental issues

Water

Murrumbidgee Valley environmental watering updates

Murrumbidgee River 2014 ‘piggyback’ flow        

The Office of Environment and Heritage (OEH) is currently working with partner water management agencies to plan for an environmental water release in the Murrumbidgee River during late winter to early spring 2014. The objective for this water flow is to reach many nationally significant mid-Murrumbidgee wetlands and other low-lying wetlands along the Yanco Creek system.

What is the ‘piggyback’ flow?

OEH is planning an environmental water release in the Murrumbidgee River in late Winter/Spring 2014 to achieve a number of environmental outcomes.

The intent is to release environmental water into the Murrumbidgee River from the two major water storages, Burrinjuck and Blowering Dams, to allow water to reach low-lying wetlands right along the river and along the Yanco Creek system.

Releases would be made when there are significant unregulated inflows from tributary streams, downstream of the major water storages. By ‘piggybacking’ onto these natural inflows, the storage release requirements can be reduced and this can make the limited environmental water allocation last longer and create a more effective watering event.

 If necessary, additional minor piggyback releases may potentially be made from the Tombullen off-river Storage (near Darlington Point).

What level will the flow reach?

The environmental water releases are targeted to reach a river level of 4.9m (or 27,500 ML/d) at Wagga Wagga. The predicted river heights for the release are shown at Table 1. This is well below the minor flood level of 7.3m and 1m lower than previous environmental water release levels in 2011.

By setting the target of 4.9m, it is hoped that inconvenience to stakeholders is minimised. However, the possibility of exceeding or falling short of this target due to unforeseen circumstances, such as heavy local rainfall, needs to be recognised.

If heavy rainfall is predicted during or shortly after the planned release of environmental water, the event will be managed accordingly, postponed or immediately ceased, to achieve river levels of 4.9m at Wagga.

Table 1. Predicted river heights for proposed Murrumbidgee Piggyback event.

Location

Height (m)

Discharge (ML)

Duration

(days)

Travel time from Burrinjuck

Gundagai

4.0 to 4.41

20,900 to 24,800

3-4

1.5 days

Wagga

Up to 4.92

Up to 27,500

3-4

2 days

Narrandera

5.0 to 5.4

21,500 to 25,200

4-5

5 days

Yanco Creek Offtake

3.4 to 3.8

1,700 to 2,200*

4-5

6 days

Darlington Point

4.4 to 5.0

16,100 to 20,900

5-6

7 days

Carrathool

4.5 to 5.0

13,300 to 15,800

5-6

10 days

D/S Hay Weir

5.0 to 5.5

12,000 to 14,000

6-7

12 days

D/S Maude Weir

5.0 to 5.6

11,000 to 13,000

8-9

13 days

D/S Redbank Weir

5.7 to 5.9

9,280 to 10,100

10-12

15 days

D/S Balranald Weir

5.3 to 5.8

7,900 to 9,700

12-14

18 days

1 similar to max irrigation flow levels in full allocation years

2 lower than any previous piggyback flow event

How much environmental water will be released?

The volume of environmental water released over the duration of the event could range from 40,000 megalitres (ML) up to a maximum of 220,000 ML, depending on allocation availability and the size of the base flow. Water will primarily come from NSW environmental water allowances and also from Commonwealth environmental water holdings.

Why is it being done?

During the drought years (2002-2010), hundreds of wetlands along the Murrumbidgee River that connect to the river during high river flows remained dry. The lack of return flows to these wetlands has resulted in severe impacts on their aquatic vegetation and ecology. The planned environmental water releases will be designed to inundate a large number of the lower lying wetlands and greatly assist in their recovery.

Well-functioning wetlands provide critical breeding and foraging habitat for native fish, waterbirds, and frogs. They support a wide range of native plant species, help in improving water quality, and feed the river with insects and crustaceans, juvenile fish, nutrients and carbon – supporting its productivity.

When will it happen?

The decision to release water is dependent on sufficient rainfall to initiate tributary flows that will reach a minimum river level of approximately 3.0 m at Wagga. Environmental water releases would then piggyback on these flows to target a combined river level of up to 4.9 m at Wagga.

These environmental water releases are being planned for some time before the end of September 2014. The actual commencement date and duration for the event will be dependent on rainfall and irrigation use. High rainfall and low rates of irrigation water extraction are required to maximise the efficiency of the proposed piggyback flow. Irrigation water use increases through September and peaks in October and November significantly reducing the effectiveness on any piggyback flow.

Bureau of Meteorology rainfall forecasts and State Water operational limitations indicate that the likely timing for an event currently is:

1-15 September – Possible. Currently watching the forecast rainfall for the 9-10th which may provide sufficient rainfall to trigger the proposed e flow. Daily stakeholder communications occurring from Monday the 8th September.

16-30 September – Less likely. Increasing irrigation demand will reduce the effectiveness of the proposed piggyback flow (the flow will be more successful with low rates of extraction)

1-15 October Unlikely. Generally a higher irrigation demand at this time of year means a very significant rainfall event is required.

16-31 October – Highly unlikely. Typically, peak irrigation occurs at this time. A very significant rainfall event is required to provide sufficient runoff to trigger the event, while also temporarily reducing irrigation demand.

The above event timing indications will be reviewed by OEH and provided to stakeholders weekly and when a potentially suitable rainfall event is forecast these updates will be provided to stakeholders daily.

Stakeholders will be notified once a commencement window has been confirmed and prior to releases of environmental water.

If environmental releases are not required, or if the piggyback flow is abandoned, stakeholders will be notified as soon as this decision is made.

Will it impact me?

If you have property that is normally affected by rising Murrumbidgee River levels, there is a possibility that you could be affected. However, as the proposed release is well below the minor flood level, impacts are expected to be minimal.

OEH has consulted with a number of landholders who could be affected with a view to identifying risks that may be associated with this environmental flow and to inform the development of strategies to deal with these risks should they arise.

Who is responsible for the event?

OEH manages environmental water allocations in NSW and is the lead agency for the environmental flow event. State Water manages water orders and deliveries.

Partnering agencies include State Water, NSW Office of Water, Riverina Local Lands Services and the Commonwealth Environmental Water Office. 

How will I know if the flow is occurring?

Landholders/managers - who may be impacted by rising river levels will be contacted and notified through either face-to-face meetings, phone or email.

Communication will continue for the duration of the event through the provision of regular event updates to website, local media and contact lists, or via direct calls to OEH. 

OEH staff will manage the pre-event communications and State Water will take over during the release phase; together they will provide regular communication updates to:

Local councils – contact with the relevant councils will be made to ensure infrastructure such as roads or drainage systems are not unexpectedly inundated by released environmental water.

Project partners – to ensure project partners are aware of the details of the proposed event and that potential risks are identified and managed within a risk management strategy.

SES – will be notified by OEH prior to any releases as a courtesy and preventative measure. However, as the proposed flow (4.9m) is below the minor flood level (7.3 m) at Wagga, it is not anticipated that the SES will be involved in flow-related operations. 

Public information – OEH media releases will be issued to local newspapers and radio stations to inform the wider Murrumbidgee community of the environmental water release and the objectives of the flow. Regular event updates will be posted on this web page.

Where do I get more information?

For further information contact:

NSW Office of Environment and Heritage
Main switchboard: (02) 9995 5000
Environment Line: 131 555

Page last updated: 08 September 2014