Monitoring the Gordon River

Joining the National Electricity Market via the Basslink interconnector was expected to alter some of our hydropower operations, particularly changing the pattern of water flow down the Gordon River below the Gordon Power Station. To minimise our environmental impacts, we assessed the state of the river from 2001 and monitored the changes since Basslink was commissioned in an intensive monitoring program from 2006 to 2012. We carefully assessed the effectiveness of two mitigation measures: maintaining enough continuous flow in the river to provide suitable conditions for fish and macroinvertebrates, and limiting the rate of changes in water flow to protect riverbanks from erosion. 

Impact of Hydropower on the Gordon River

Our long-term monitoring of the Gordon River has provided valuable information on the impact of hydropower operations on the river’s riparian vegetation, fish, macroinvertebrates and riverbanks. Specialists across many scientific disciplines have monitored water quality and levels, riparian vegetation, fish, macroinvertebrates, algae, riverbanks and karst caves across 35 km of the river.

Through the monitoring program, we have learned a great deal about the ecosystem of the Gordon River and how different hydropower operating scenarios affect the river. We’ve been able to translate this wealth of knowledge into a set of models that help us better understand how the ecosystem responds to different conditions. 

We started monitoring the Gordon River in the late 1990s, first to establish baseline conditions and understand how the river was responding to the existing operation of the Gordon Power Station, commissioned in 1978. From 2006, when we joined the National Electricity Market via the Basslink interconnector, we monitored and assessed the impacts on the ecosystem of changes in our hydropower operations. Connection of Tasmania’s energy network to the NEM was expected to increase ‘hydro-peaking’, which involves frequent variations in water flows.


To minimise the expected impacts of hydro-peaking, we put two specific management measures in place: 

•  maintaining a minimum flow of water in the river of 10 cumecs in summer–autumn and 20 cumecs in winter–spring to provide suitable conditions for macroinvertebrates and to increase habitat and food for fish by keeping important habitat under water, even when the power station is not operating and less water flows down the river

• limiting the rate of change in water flow (a ‘ramp-down rule’) to reduce the erosion of riverbanks.
  
  

Monitoring of the minimum environmental flow indicates that it has brought positive environmental results, particularly for macroinvertebrates and fish.

We assessed the suitability of our ‘ramp-down rule’ over four years, finding evidence that seepage erosion still occurred when water levels decreased rapidly at times when riverbanks were heavily saturated. The rule had been expected to allow riverbanks to drain gradually as water levels fell, reducing erosion and the potential for riverbank collapse but this was not the case when banks were saturated.

In response to this evidence, we revised the ramp-down rule in 2012, determining the rate of change of water flow depending on the level of saturation of the riverbanks.

We continued our monitoring program to determine the effectiveness of this change and the revised rule has been effective in reducing seepage erosion. 

For more information about the condition and responses of all aspects of the Gordon River ecosystem to the operations of the Gordon Power Station, download the Summary Gordon River Basslink Monitoring Program Report 2001-2012.

The full reports produced as part of the Integrated Impacts Assessment Statement (IIAS), the baseline (pre-Basslink) monitoring, the impact and assessment (post-Basslink) monitoring and review reports can be found here.