These are some photos of Ardnacrusha hydroelectric station taken on the morning of the 24th November 2014. In addition to the four turbines being on full load, water was also being released from the spillway at the time of taking these photographs. Overall it is estimated that 500 cubic meters of water per second (cumecs) were being released at Ardnacrusha. Meanwhile flows in the Old River Shannon were being reduced back to the compensation flow of 10 cumecs.
Instead of spilling water though the spillway here we would argue that any ‘excess’ water like this should be released though Parteen weir, as this would help maintain the old river channel. A higher and more variable compensation flow is required for the old River Shannon to restore its good physical and ecological status. At the time of taking the photos below there was approximately 10 times more water going though the Ardnacrusha spillway alone than is normally released down the old River Shannon. For more about compensation flows on the Old River Shannon please see this post.
It is noted that it would also probably be better for silver eel escapement to spill water through Parteen weir as the pressure changes etc. would be less due to the lower head at Parteen weir. It is clear that any silver eels using the spillway at Ardnacrusha could also be damaged or killed.
We are now at the peak of the silver eel run on the River Shannon and most of the eels migrating downstream have to pass though the turbines, and suffer high rates of damage and mortality. We tried to collect some dead silver eels but the flows in the tailrace were too high at the time of our visit.
There were over 120 cormorants foraging in the tailrace of Ardnacrusha during our visit this week, and they were apparently feeding on silver eels killed or damaged after passing downstream. The cormorants make the most of this situation, but the abundance of dead and dying eels probably keeps the local cormorant population artificially high.
The ESB operate a ‘trap and transport’ programme for silver eels. The silver eels are captured in coghill nets at Killaloe and transported downstream around the turbines. However, this programme is not operated every day, and is thought to capture only about 30% of the downstream migrating eels when it is being operated. The nets only cover approximately half the width of the river, and any eels captured in the nets are held overnight against the full flow of the river and handled a number of times before their ultimate release. We believe that this ‘trap and transport’ programme is not a suitable mitigation response for the endangered European eel, and only serves to allow the ESB to continue hydroelectric generation operations without compromise. We believe that water should be spilled though Parteen weir and hydroelectric generation suspended during the peak of the silver eel runs, to allow silver eels to safely migrate down the Old River Shannon channel. An increased and variable flow in the old river would also bring significant hydro-ecological benefits.
For further information please see the following posts:
- A sustainable compensation flow is needed for the Old River Shannon
- Inadequate silver eel mitigation on the Shannon
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