The South Esk Great Lake Water Management Review

The South Esk Great Lake Water Management Review was initiated in 1999 with the publication of the Environmental Review report (PDF 7.2 MB) >

In 2000, the Community Consultation Report consolidated issues raised by stakeholders and lead to twelve technical studies (which can be downloaded via links on the right) download the Community Consultation Report (PDF 1 MB) >

In 2003, the South Esk – Great Lake Aquatic Environment Management Program (PDF 673 kB) consolidated the outcomes of the SEGL review and provided a Package of Commitments for South Esk – Great Lake Aquatic Environment Management Program (PDF 218 kB).

1. Brumbys and Westons Weirs Pump Maintenance

Issue: The main issue of concern was the flooding along Westons Rivulet when pumps in Weston Weir have insufficient capacity or fail to pump all the water diverted from Upper Brumbys Creek and Westons Rivulet into Great Lake.

Our commitment: Hydro Tasmania commits to ensure reliability of the pumps at Westons Weir through a scheduled program of maintenance, and will review it procedures accordingly.

Outcome:  Hydro Tasmania has installed remote monitoring of the pumps which enable operational issues to be identified sooner.  The pumps are part of Hydro Tasmania’s scheduled maintenance program.

2. Spills at Trevallyn Dam

Issue: The main issue of concern was access by irrigators in the South Esk and Macquarie catchments to floodwaters for the purpose of filling on-farm storages, rather than see this water spill over Trevallyn Dam.  Hydro Tasmania undertook extensive hydrological analyses and identified the flow conditions that can be used as triggers to allow DPIWE to grant temporary licences to extract water during periods of high flow.

Our commitment: Hydro Tasmania commits to make timely and appropriate hydrological data available to Tasmania’s Department of Primary Industries, Parks, Water and Environment in order to enable them to issue temporary water licences when the Trevallyn Dam is spilling.

Outcome: Hydro Tasmania provides data to DPIPWE which is updated at least twice a day.

3. Arthurs Lake

Issues: The key issues focussed on in the investigations were threatened native fish populations and fishing amenity, as this is by far the most popular recreational trout fishery in the State.  Native fish studies undertaken during this study found that fish populations in Arthurs Lake are currently healthy and are not threatened by the present lake level management regime.

Our commitment: Hydro Tasmania will endeavour to maintain Arthurs Lake levels above a minimum of 949 metres above sea level (mASL) particularly during the fishing season subject to Great Lake being above 1029.8 mASL.  At all other times the system will be operated to avoid, where possible, the lake going below this level.

Outcome: Since 2001 lake levels in Great Lake have been below 1029.8 mASL. It was acknowledged that lake level in Great Lake rarely will exceed 1029.8 mASL which makes the commitment inefficient in protecting native fish populations and fishing amenity.  To better accommodate the multiple demands on water from Arthurs Lake, including electricity generation, fishing, irrigation, and ecosystem health, new operating rules and an updated Memorandum of Understanding (MoU) between Hydro Tasmania and Inland Fisheries Service have superseded this commitment.

The new commitment is that Hydro Tasmania will make reasonable endeavours to operate Arthurs Lake so that the lake level is at, or above, 950.00 mASL on 1 November each year and at, or above, 949.00 mASL on 1 June each year subject to the water level in Great Lake being above 1023.00 mASL and the Midlands Irrigation Scheme being in operation.

If Great Lake is below 1023.00 mASL, or if the Midlands Irrigation Scheme is not operating, then Hydro Tasmania will make reasonable endeavours to operate Arthurs Lake so that the water level is at, or above, 949.00 mASL on 1 November each year and at, or above, 948.00 mASL on 1 June each year.
This will ensure that Arthurs Lake is at, or above, 949.00 mASL during general Brown Trout angling season (1 August to 30 April in the following year)
Environmental and Social Risk Bands have been developed for this lake (see Low Lake Level Management Program).

4. Woods Lake

Issues: The key issues focussed on wind-generated sediment re-suspension causing poor water quality, native galaxiid fish species, recreational angling and downstream irrigators.  Aim to avoid the lake level being drawn down to depths where turbidity levels have been shown to increase.

Our commitments: Hydro Tasmania commits to maintain the minimum operating level for Woods Lake at 735.4 metres above sea level (mASL).  Hydro Tasmania will also support further research into native fish species through the provision of data and field assistance.  Hydro Tasmania, as part of this commitment, will review its alarm systems for the lake to ensure that system operators are aware when lake levels are approaching this minimum and adjust system operation accordingly.

Outcome: Hydro Tasmania has maintained its commitment to a minimum operating level of 735.4 mASL, although incursions below this occurred in 2007 during the prolonged dry period when water was required to meet irrigation requirements along the Lake River.

In a Memorandum of Understanding (MoU), on Water Level Management, established between Hydro Tasmania and Inland Fisheries Service, Hydro Tasmania agreed to make reasonable endeavours to maintain a water level in Woods Lake at, or above, 736.20 mASL.

In addition, Hydro Tasmania has reviewed its alarm systems for the lake, to ensure that system operators are aware when lake levels are approaching this minimum and adjust system operation accordingly.  Environmental and Social Risk Bands have been developed for this lake.

Hydro Tasmania funded research, completed in 2004, on the distribution, reproductive and dietary habits of the Saddled Galaxias (Galaxias tanycephalus) in Woods Lake.

5. Downstream Poatina Power Station Re-Regulation Pond

Issues: Key issues of concern were the impacts of normal power station operations on water levels in Brumbys Creek and the lower Macquarie River – specifically the impacts on riparian land use and water extraction, erosion of riverbanks, and poor water quality and power station flood rules. The majority of these issues were investigated in depth as part of studies for the Basslink Integrated Impact Assessment Statement.  Basslink was shown to be likely to exacerbate many of the concerns downstream of Poatina, and a re-regulation storage was identified as the best option to mitigate these issues.

Our commitment: Hydro Tasmania is committed to construction of a re-regulation storage downstream of Poatina Power Station.

Outcome: Hydro Tasmania completed development of a re-regulation storage downstream of Poatina Power Station in 2006 – read the press release.  A ramp rule is also in place which means flows do not fluctuate as frequently as previously and at a much reduced magnitude.

6. Great Lake

Issue: The key issue raised was movement of algal beds in response to water level fluctuations.  These beds are habitat to a number of endemic fauna species listed under the Tasmanian Threatened Species Protection Act 1995, and the concern was that the beds are unable to migrate up and down at a sufficient rate to ensure habitat protection.  Investigations showed that not only lake level variations but other factors such as water clarity (affected by turbidity due to long-shore erosion and wind-induced sediment suspension) had an influence on algal bed movement, and these factors were not well enough understood at this stage to define management responses.  Faunal relationships also needed further understanding.

Our commitment: Hydro Tasmania is committed to support a further five years of research into the Great Lake algal beds and associated faunal relationships.

Outcome: Hydro Tasmania conducted five years of research into the Great Lake algal beds.  The research showed that there is a high degree of variability in the charophyte beds themselves and the interactions with the threatened species.  The charophyte flora of Great Lake has been found to be diverse and inherently resilient to changes based on a high species richness and widespread seed bank of oospores in sediments.

7. Lake Augusta

Issue: The key issue for the investigations was dune erosion in relation to lake level fluctuations.  The study was unfortunately inconclusive due to an absence of long-term data.

Our commitments: Hydro Tasmania will install instrumentation at Lake Augusta to monitor groundwater movement in relation to lake levels for a three year period, and commits to supporting further investigation of the dune system.

Outcome: Monitoring equipment was installed for groundwater movement in relation to lake levels and a Masters study was completed on the erosion of the dune system.

8. Environmental Flow at Cataract Gorge

Issues: Key issues in Cataract Gorge were whether the existing environmental flow was sufficient to meet ecological requirements of aquatic fauna, water quality deterioration during the summer months, and implications of summer minimum flows for public use, amenity and aesthetics.

Our commitment: Hydro Tasmania commits to a year-round environmental flow of 1.5 m3/sec and seasonal monitoring of effectiveness at three sites in the river for five years.

Outcome: The flow was increased from 0.43 m3/sec to 1.5 m3/sec.  Monitoring and a number of scientific studies have been conducted in the Gorge.  The flow was reviewed five years after of implementation.

The outcome of this review was to increase the flow to 2.5 m3/sec, you can read all the detail here >

9. Eel Passage at Trevallyn Power Scheme

Issue: The main issue of concern is that the Trevallyn Dam blocks upstream migration of juvenile eels (elvers) from the sea, and adult eels enter the power station on their downstream migration toward the sea to breed.  The investigations looked at a wide range of options, but were unable in the time frame of these investigations to finalise a preferred option to facilitate eel migration.

Our commitment: Hydro Tasmania is committed to further research into eel movements, fate and options at the Trevallyn Power Scheme, to the feasibility of eel deterrent at the Trevallyn Power Station intake, and to continue work towards facilitating eel migration at the Trevallyn Dam.

Outcome: Hydro Tasmania has installed an elver ladder in the dam wall – find out more.  The effectiveness of the ladder is being monitored each year during the elver migration season.

Deterrent options are currently being investigated to prevent mature eels going into the power station.