Aerial Surveys of the Lower River Shannon

We have been undertaking aerial surveys of the Lower River Shannon over the past month using a Phantom 3 drone. The study is being undertaken to assess the ongoing impacts of the reduced post-Shannon scheme flows on this Natura 2000 river. During June/July 2015 we surveyed a number of sections of the corridor of the old River Shannon between Parteen Regulating Weir and Limerick City, collecting extensive video footage and photography. The output of this and other surveys we are completing will be used to inform a management plan for the Lower River Shannon Special Area of Conservation.

Here is a selection of aerial photos we took along this river corridor in June/July 2015. Click on any of the photos to activate the galley. We have also provided some selected videos further below.

Parteen Regulating Weir

The video below is of Parteen Regulating Weir which controls the flow of water to Ardnacrusha Hydroelectric Station and to the Old River Shannon. The compensation flow provided to the old river is just 10 cubic meters per second (cumecs), which is equivalent to the 95%ile flow in the river prior to the Shannon Scheme. The rest of the water from the River Shannon is diverted at Parteen Regulating Weir down the headrace canal to Ardnacrusha Hydroelectric Station. The compensation flow is also an unvaried flow, and is only increased when Ardnacrusha Hydroelectric Station can no longer output the flows into Lough Derg while operating at full capacity  – 400 cumecs (e.g. extreme floods). In this situation ‘excess’ water is spilled though Parteen Regulating Weir and this can result in flows in the river abruptly increasing from 10 cumecs up to a few hundred cumecs – sometimes in a matter of hours – and reducing again in a relatively short time-scale. This can cause significant impacts on river – for example these major changes in discharge can occur during sensitive periods, such as when Atlantic salmon (a key conservation interest of the SAC) are spawning in the river.

In addition to issues associated with the reduced and unvaried flows on the old river, the Shannon Scheme has also resulted in severe impacts on migratory fish populations on the River Shannon, such as Atlantic salmon, European eel and Sea lamprey due to inadequate fish passage provisions. The conservation escapement target for Atlantic salmon through the Shannon Dams is 45,000 adult salmon per year. However, only a few hundred adult salmon now now pass upstream annually at Parteen Regulating Weir and Ardnacrusha Hydroelectric Station combined.  It is noted that this scheme can no longer be considered to be source of sustainable renewable energy when it is responsible for the collapse of salmon and eel populations on this river and decisions about its day-to-day management are causing significant hydroecological impacts on the Lower River Shannon cSAC. For more information and discussion see here. It is also noted that less than 20 sea lampreys  – a species at unfavourable conservation status in Ireland and a key conservation interest of the Lower River Shannon SAC – manage to make it past these dams each year.

See more about the compensation flow to the old River Shannon in this post entitled ‘A sustainable compensation flow is needed for the old River Shannon‘.

Old River Shannon at Hermitage, Castleconnell

This video was taken on the Old River Shannon at Hermitage, which is located downstream of Castleconnell, Co Limerick. This section of the river was perhaps the most important salmon fishery on the River Shannon prior to the Shannon scheme.  Today, it is no longer known as a significant salmon fishery. The reduced post-Shannon scheme flows are apparent in the video, along with the instream physical modifications which have been installed in the river to compensate for this. A combination of fish passage issues and reduced flows to the old river channel has severely impacted on the Lower River Shannon – now a Natura 2000 river. The work we are completing will be used to formulate a plan to manage the river sustainably.

Old River Shannon, Castleconnel Fishery, Beat 6

This is the Old River Shannon further downstream at the end of the Castleconnell fishery beats.  The impact of the reduced post Shannon scheme flows is again very apparent, along with the ESB’s instream modifications. Clearly this has had a significant morphological impact on this river corridor; both as a consequence of the reduction in flow and due to the instream physical modifications which have been used to date. This has had significant consequences for both the ecology and amenity value of the river.

For further information please see the following posts from the Old River Shannon Research Group:-

It is clear that there needs to be increased and variable flows in the Old River Shannon to be delivered within the context of a sustainable management plan for the river and cSAC.  Spillages of water duing flood events should also be tapered up and down slowly mimicking a natural hydrograph. International experience has shown that by utilising a good process of establishing environmental flow objectives, it can be possible to find ways to address these objectives without significant loss of hydroelectric generating potential. A sustainable compensation flow, involving increased and variable flows, can be introduced on the Old River Shannon while not significantly affecting generation capacity at Ardnacrusha hydroelectric station. We also of course need new fish passes, including diversion systems for downstream migrants (e.g. salmon smolts and silver eels) to keep them away from the turbines. The instream physical modification along the river would also need to be removed to restore the river back to a more natural state.

It is clear that there needs to be a change in the way this Natura 2000 river is managed to balance the requirements for hydroelectricity generation with the interests of ecology, fisheries and of course the catchment residents and varied user groups on the river. The current management regime was set in the 1920’s; the scientific knowledge to manage things better is there now and needs to be acted on. The work we are undertaking at present will used to draw up a sustainable management plan for this Natura 2000 river

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