National Barriers Programme
River fragmentation is the breaking up of a river’s continual flow from source to the sea. It is one of the greatest global threats to freshwater ecosystems because it interrupts fish migration, blocks the movement of fish and other animals within the channel, alters the flow of sediment throughout the channel, affects habitat diversity and impacts overall biodiversity.
Irish rivers are heavily fragmented by weirs, dams, sluices, culverts, bridges and other artificial barriers. The impact of these structures can be broken down into two broad categories:
- Obstructing to fish migration
- Habitat damage
The National Barriers Programme deals with issues related to barriers and works to reduce their impact, within the context of the Water Framework Directive. There are five main aims of this programme:
- Developing a barriers assessment tool
- Barrier surveys and risk assessment
- Creating a national barriers database
- Focusing our efforts
- Guidance for planning and construction
Diagram of the effects of barriers on rivers and fish movements.
Developing a barriers assessment tool
For primary assessment, Inland Fisheries Ireland has developed the I-BAST (IFI Barrier Assessment and Screening Tool) application as an initial screening and barriers assessment tool. This portable data collection application captures information such as barrier location, barrier type, structural dimensions and images. This assessment has been developed to assist in the assessment of instream structures, with the aim of improving fish passage on the island of Ireland. A secondary, more intensive survey may be done subsequently to advise on potential mitigation measures.
Example of a culvert.
A structure that allows a river to flow through or under an obstruction, such as bridges.
Example of a dam.
A barrier that blocks the flow of a river and raises the water level, forming a reservoir.
Example of a ford.
A structure that creates a shallow place for crossing a river by vehicle or on foot.
Example of a sluice.
A movable barrier that can be opened or closed to regulate the flow and water level of a river.
Example of a weir.
An instream structure to regulate flow and water levels, to trap sediment or to reduce the slope of the river channel. Weirs usually allow water to flow freely over the top.
Barrier surveys and risk assessment
To date, we have surveyed almost 22,600 structures using the I-BAST assessment and a further 175 structures using the secondary assessment. Inland Fisheries Ireland has also been joined by colleagues in the Local Authority Waters Programme (LAWPRO), a number of whom we have trained to help record barriers, which further adds information to our national database.
Surveying Askeaton Weir on the River Deel.
Barrier survey of weir at St. Mullins on the River Barrow.
Barrier survey of an impassable bridge apron.
Barrier survey of Athlone Weir on the River Shannon.
Survey drone used for aerial imagery in the National Barriers Programme.
Creating a national barriers database
Thanks to other national organisations, who have given us lots of data, we have been able to use desk-based techniques to add to our list of potential barriers around Ireland. This supplements our on-the-ground surveys and has increased our total to 73,376 potential barriers on the Irish river network.
Focusing our efforts
Identifying barriers is only the first step, after which mitigation measures may be necessary. Naturally, this can be an expensive endeavour, and some should take priority over others. Prioritisation incorporates many factors, such as amenity value, requirements for compliance with EU Directives, cost-benefit analysis and fish migration benefits.
Guidance for planning and construction
The National Barriers Programme will produce guidance documents that may be used by various stages of the planning, construction and mitigation processes to advise them on best practices and help them comply with legislation.
This project is being done by Inland Fisheries Ireland under the direction of the Department of Housing, Planning, Community and Local Government, with assistance from colleagues in various Catchment Flood Risk Assessment & Management (CFRAM) groups, Irish Rail, Local Authorities Waters Programme (LAWPRO), Office of Public Works (OPW), Ordnance Survey Ireland (OSI), Transport Infrastructure Ireland (TII) and Waterways Ireland.
