Dredging the Shannon is not the solution to Shannon Floods
The recent flooding which has devastated so many communities around the country was record breaking for many reasons. The flooding came at the end of the warmest year globally on record. A very strong El Nino super charged by climate change [Note 1] has pummelled Ireland with six storms resulting in an entire winter's worth of rainfall falling during December alone.
These conditions are unprecedented with many weather stations around the country recording their highest levels of rainfall on record according to Met Eireann.
Even with a reprieve in storms Ireland’s swollen rivers and flooded towns and countryside will continue to receive normal levels of winter rainfall. These kinds of extreme flooding events are to be expected according to climate change scientists and indeed they will only increase in frequency in line with increasing global greenhouse gas emissions.
What steps should be taken to alleviate the problem?
A number of ‘self-styled’ experts are appearing on the media telling us how to control the flooding on the River Shannon. An Taisce is not claiming such expertise but the answer must be based on the entire Shannon Catchment and must allow for the fact that climate change will increase the problems over coming years. The best answers will come from the Shannon CFRAM (Catchment Flood Risk Assessment and Management Study) being undertaken by the OPW although as yet climate risk is not included.
The CFRAM assessment treats the Shannon on a River Basin basis and will ‘Identify measures and options for managing flood risks, both in local high-risk areas and across the whole study area’.
Today’s Press Release from the European Commission [Note 2] explains the actual wording of Nature Directives and Natura Sites, and the limited usefulness of of dredging. It states:
" EU Nature Directives (Birds and Habitats) do not prevent measures being taken to protect lives and property. In particular they provide for situations of 'over-riding public interest' to permit activities that might damage a Natura 2000 site but which are necessary for human welfare. The Directives do however require an assessment of the options available before a conclusion is reached that such damage is unavoidable.
Dredging is not always the solution for flooding. It may help to sort out a local problem but it may also transport the problem downstream, sometimes from rural to urban areas where the damage on properties and economic activities can be much higher. Therefore the basin-wide approach included in EU policies is essential to find effective and long-term solutions."
An Taisce first called for a single authority for the Shannon river basin over 30 years ago, it is the basic step required for coherent flood management and now, with climate change, it is even more urgently required. Any Task Force or Single Authority that is formed must also allow for proper Public Participation in the form of Social, Community and Environmental groups.
One of the first reports of the Shannon CFRAMs is a Jacobs report [Note 3] that summarises the current knowledge and references the many previous reports.
The important points of those reports are:
- There is no single, simple solution to prevent flooding along the River Shannon, and a combination of works would be required to reduce flood levels by a significant degree.
- The ESB Regulations for managing Loughs Derg, Ree and Allen provide, on balance, optimum management of floods within existing storage and land control capabilities.
- The effects of high Lough Derg levels do not extend upstream above Meelick Weir.
- Localised dredging upstream of Meelick Weir was not found to have a significant impact on flood levels.
- The extent of aquatic and riverside vegetation has increased over the last 50 years, and at constricted locations such growth will have some affect on flood levels.
- The River Shannon and its callows are, over much of their length, considered to have environmental significance on an international scale.
- There is a case for one organisation being responsible for overseeing all flood management operations on the River Shannon prior to, during and after a flood event.
- The principal cause of flooding between Meelick and Athlone is the shallow gradient of the river and the limited channel capacity along this reach. Channel works along this reach would be critical to the success of any general scheme.
- The issue of siltation has repeatedly been identified as a potential problem, but has never been quantified or proven as a problem.
- Enhanced management of storage in Loughs Derg and Ree (and possibly Lough Allen) could form part of a scheme for relieving flooding from short duration floods, but would not eliminate major winter flooding as a standalone option.
- The use of embankments as a general flood relief option is not likely to be viable due to local soil types, but may have localised applications.
- The use of river diversions for flood relief would either be entirely uneconomical or offer no significant benefit.
- The development of an effective storage area above Roosky Weir would be uneconomical due to significant inundation of infrastructure, properties, etc.
- The impacts of any scheme would need to be assessed in relation to the economic benefit, environment, navigation, fisheries, tourism, etc.
Given the nature of the Shannon basin and the languid flow along the majority of its length, increasing the speed with which water enters the river through drainage works will only exacerbate flooding along the main river and in the Shannon’s lower stretches.
We need to slow down the speed with which water is moving into the Shannon and that will require change on a landscape/catchment basis. The drainage of our bogs and wetlands by Bord na Mona and through the arterial drainage scheme and various forestry programmes over the preceding decades have unquestionably exacerbated this winter’s floods.
The restoration of dredged and canalised tributaries can help to slow down flood waters and reduce the Impact of flooding by reducing peak flows within the main river.
Natural flood plains will need to be restored. Agri-environment schemes may need to be tailored to help farmers reduce surface run-off by blocking drains, planting native woodlands and reducing over grazing and burning in our uplands.
We will also need to improve the accuracy with which we can predict the approach of storms and pre-emptively increase flow through Ardnacrusha and Parteen Weir ahead of their arrival.
Apparently simple quick-fix flood protection measures such as dredging and 'hard engineering often have short-lived usefulness or unintended negative consequences . As communities in the UK are finding out, 'soft engineering', working with nature is often far more effective and, in the long-run, far less costly. [Note 4]
For further information, please call:
Charles Stanley-Smith, Communications, An Taisce. Tel: +353 87 241 1995
An Taisce The National Trust for Ireland
Extreme weather linked to El Niño and climate change – Irish floods from Storm Desmond rendered 40% more likely by global warming http://www.irishtimes.com/news/environment/extreme-weather-linked-to-el-ni%C3%B1o-and-climate-change-1.2477954
Risk of extreme storms on west coast up 25% due to climate change - study http://www.rte.ie/news/2015/0311/686391-extreme-storms/ Prof. Conor Murphy, NUIM giving details of forthcoming, accepted journal paper: doubling in likelihood of these sort of winters over past 100 years; over past 140 years, precipitation intensity has increased markedly in more recent years; flood events are likely to become up to 8x more frequent with continued high emissions; 1 in 100 year events can become 1 in 30 or 1 in 40 years. Interviewed on RTE News, 04/01/2015. video starts at 23m:20s. http://www.rte.ie/player/ie/show/six-one-news-30003249/10512472/?ap=1