Managing low lake levels
We manage environmental risk in lakes where water levels are low to minimise impact on threatened species and water quality. Our approach is to identify water levels where environmental or social risks may arise, establish risk bands to address the risks, and initiate a monitoring and reporting program of key water quality variables before a lake enters its risk band.
We monitored five lakes under the program throughout the year - Arthurs, Woods, Echo, King William and Great lakes. Water levels and associated environmental risk bands for three lakes are shown in figures 24, 25 and 26.
Arthurs Lake water level remained within its medium risk band from February 2008 until early July 2009, raising concern for water quality conditions and threatened fish species. Woods Lake lowered to its medium risk band in April 2009 and rose above it as a result of rains in June.
The storage rebuild strategy contributed substantially to raising the level of Great Lake from a low of 16.7 per cent full in energy terms9 in July 2008 to 24.7 per cent by 30 June 2009.
We are currently undertaking a research program at Great Lake and Arthurs Lake which aims to develop scientifically-based strategies for sustainable management of threatened fish species.
In response to stakeholder concerns, we monitored and reported on algal blooms at three highland lakes and identified these blooms as non-toxic. In April 2009, the Trevallyn Lake algal monitoring group, in which Hydro Tasmania participates, identified an algal bloom which was short-lived.
We continued to monitor blooms at the Lagoon of Islands where very poor water quality conditions remained.
Hydro Tasmania takes the risk of oil spills seriously and is investing in preventative measures, as oil spills are a significant threat to the health of waterways. Nevertheless, a number of relatively small spills occurred during the year.
The largest spill involved 1000 litres of oil at Devils Gate Power Station which is on the Forth River. It was classified as a moderate incident and reported accordingly. It was estimated that approximately 100 litres of oil was lost to the waterway. With the assistance of the Environment Protection Authority (EPA), the spill was cleaned up with minimal impact and a low risk of ongoing environmental concern. Another oil spill involved approximately 92 litres at Poatina, with up to 82 litres lost to the waterway and cleaned up with the help of the EPA. Water samples taken downstream showed no detectable oil contamination.
As a result of the spills we reviewed, and where necessary modified, the oil containment capacities within power stations across the system. We are also investigating permanent and temporary deployable oil boom systems for use in areas that are susceptible to oil loss. We reviewed our oil handling and spill procedures during the year, and provided further training for employees where required.
Hydro Tasmania manages the waterways under its stewardship to promote sustainable development and to maintain the ecology and genetic diversity of these waterways in accordance with the Water Management Act 1999. This Act includes (among other things) that we release specified environmental flows.
In 2008/09, we initiated a review of environmental flows for the Cataract Gorge, which is situated downstream of the Trevallyn Dam. In 2003, we voluntarily increased the environmental flow to the gorge from 0.43 cumecs to 1.5 cumecs, and made a commitment to review the environmental values of the gorge and adequacy of the flow in five years time. This year’s review, which will continue into 2009/10, fulfils this commitment. As part of this review we will be consulting widely with the community.
The environmental flows into the Gordon River were initiated to mitigate the impact of expected changes to the river due to the operation of Basslink. During the year we made significant progress in ensuring that operations could conform to these requirements, following a number of non-conformances with requirements reported last year for changing water discharge rates at the Gordon Power Station.