Calls for ESB to drop Carrigadrohid Reservoir water levels

It is not just the River Shannon which has been severely damaged by the development of hydroelectricity schemes in Ireland. The River Lee has also been severely affected; both as a result of the original impacts of the scheme and also as a result of ongoing management protocols.   The River Lee hydroelectric scheme has recently been featured in a film documentary highlighting the damage of the scheme to salmon and the Gearagh alluvial forest, and there is increasing awareness about the environmental (and social) impact of this scheme

Construction of Carrigadrohid reservoir and hydroelectric scheme – the upper of two schemes in the Lee valley – commenced 1953 and required the logging and subsequent flooding of approximately 60% of the great alluvial forest of the Gearagh. The tree trunks of this great forest can still be seen in the reservoir. This was the largest alluvial forest in Western Europe. The alluvial woodland which remains today in the Gearagh today is still of unique scientific interest, and is a designated Special Area of Conservation, a Ramsar site and a Biogenetic Reserve. Despite the fact that most of original ancient forest was destroyed by the ESB, the remnants still actually represent the only extensive alluvial forest west of the Rhine. Alluvial forest with Alnus glutinosa and Fraxinus excelsior (Alno-padnion, Alnion incanae, Salicion albae (91E0) is a priority Annex I habitat of the Habitats Directive 92/43/EEC. 

As well as the loss of this great forest, the flooding of the Gearagh also resulted in the release of massive volumes of greenhouse gasses and the de-oxygenation of the River Lee due to the presence of large quantities of decomposing vegetation in the reservoirs during the filling of these reservoirs. This wiped out the salmon stocks of the river and runs have never recovered as the fish passes provided did not work effectively.  Hundreds of thousands of Freshwater Pearl Mussels Margaritifera margaritifera were also though to have been lost. And for what? The Lee Hydroelectric scheme produces a negligible amount of electricity and it is clear that the environmental costs of the River Lee Hydroelectric schemes were far too high.

Upper River Lee (3)
Carrigadrohid Reservoir, February 2016
Upper River Lee (6)
Carrigadrohid Reservoir, February 2016, with tree trunks of the former Gearagh alluvial forest visible.

However if the ESB would agree to modestly drop the water levels in this reservoir much of this forest could regenerate. The Carrigadrohid hydroelectric station only generates 8MW while even the remnants of the Gearagh alluvial forest is still the largest habitat of this type west of the Rhine. Reducing the operational head of this hydroelectric scheme by just 1m – from 13m to 12m – would allow much of the former forest to regenerate.

In 2008, Inland Fisheries Ireland’s predecessors set themselves an “ambitious” 50-year target to restore salmon to the River Lee (see 50-year plan to restore Lee salmon). This was of course a ridiculous proposal and simply aimed to defer the issue of addressing environmental problems in the River Lee catchment well down the road. There will be no salmon in the upper Lee in 2058 either if the current management regime continues. However, we can start managing the River Lee sustainably next summer by modestly reducing the operational head of Carrigadrohid reservoir. New fish passes will also be required, but it would cost practically nothing to lower summer water levels in this reservoir, could be done immediately, and this would be the first steps to restoring the Lee valley and An Ghaoraidh’ – the “wooded river”.

For more see here : Also see this PhD thesis by Aileen Cudmore from the University College Cork entitled ‘The impacts of past land-use on the ecology of an ancient woodland in south-west Ireland‘. Other relevant posts are as follows:-

If the ESB lowered the operational water levels of Carrigadrohid dam, much of the alluvial forest could be expected to regenerate and options like this need to be explored though a sustainable management plan for this unique site. During low water levels many of the stumps of the old forest are visible at the eastern end of the reservoir, and by balancing biodiversity interests with hydroelectric generation water levels could be kept like this to allow the restoration of much of this unique site. It is clear that there is much scope for sustainable management of Ireland’s hydro rivers.

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