Annual Exceedance Probability Or AEP

The probability, typically expressed as a percentage, of a flood event of a given magnitude being equalled or exceeded in any given year. For example, a 1% AEP flood event has a 1%, or 1 in a 100, chance of occurring or being exceeded in any given year.

Appropriate Assessment

An assessment of the potential impacts of a plan or project on the integrity of a site designated as a Natura 2000 Site, as required under the Habitats Directive.

Area for Further Assessment Or AFA

Areas where, based on the Preliminary Flood Risk Assessment, the risks associated with flooding are considered to be potentially significant. For these areas further, more detailed assessment was required to determine the degree of flood risk, and develop measures to manage and reduce the flood risk. The AFAs were the focus of the CFRAM Studies.

Arterial Drainage Scheme

Works undertaken under the Arterial Drainage Act (1945) to improve the drainage of land. Such works were undertaken, and are maintained on an ongoing basis, by the OPW.

Benefiting Lands

Lands benefiting from an Arterial Drainage Scheme


The area of land draining to a particular point on a river or drainage system, such as an Area for Further Assessment (AFA) or the outfall of a river to the sea.

Catchment Flood Risk Assessment and Management Study Or CFRAM Study

A study to assess and map the existing and potential future flood hazard and risk from fluvial and coastal waters, and to define objectives for the management of the identified risks and prepare a Plan setting out a prioritised set of measures aimed at meeting the defined objectives.


Cities, towns, villages or townlands where there are a collection of homes, businesses and other properties.


The impacts of flooding, which may be direct (e.g., physical injury or damage to a property or monument), a disruption (e.g., loss of electricity supply or blockage of a road) or indirect (e.g., stress for affected people or loss of business for affected commerce)


Works to remove or facilitate the removal of surface or sub-surface water, e.g., from roads and urban areas through urban storm-water drainage systems, or from land through drainage channels or watercourses that have been deepened or increased in capacity.

Drainage District

Works across a specified area undertaken under the Drainage Acts to facilitate land drainage.


The  temporary covering by water of land that is not normally covered by water. 

Flood Extent

The extent of land that has been, or might be, flooded. Flood extent is often represented on a flood map.

Flood Hazard Map

A map indicating areas of land that may be prone to flooding, referred to as a flood extent map, or a map indicating the depth, velocity or other aspect of flooding or flood waters for a given flood event. Flood hazard maps are typically prepared for either a past event or for (a) potential future flood event(s) of a given probability. 

Flood Risk Management Plan 

A Plan setting out a prioritised set of measures within a long-term sustainable strategy aimed at achieving defined flood risk management objectives. The Plan is developed at a River Basin (Unit of Management) scale, but it is focused on managing risk within the AFA’s.

Flood Risk Map

A map showing potential risks associated with flooding. These maps may indicate a particular aspect of risk, taking into account the probability of flooding (e.g., annual average economic damages), but can also show the various receptors that could be affected by floods of different probabilities. 


The area of land adjacent to a river or coastal reach that is prone to periodic flooding from that river or the sea.

Floods Directive

The EU ‘Floods’ Directive [2007/60/EC] is the Directive that came into force in November 2007 requiring Member States to undertake a PFRA to identify Areas for Further Assessment (AFA’s), and then to prepare flood maps and Plans for these areas.


Riverine, often used in the context of fluvial flooding, e.g., flooding from rivers, streams, etc. 

Habitats Directive

The Habitats Directive [92/43/EEC] aims at securing biodiversity through the provision of protection for animal and plant species and habitat types of European importance.


Something that can cause harm or detrimental consequences. In this context, the hazard referred to is flooding. 


The science of the behaviour of fluids, often used in this context in relation to estimating the conveyance of flood water in river channels or structures (such as culverts) or overland to determine flood levels or extents. 


The science of the natural water cycle, often used in this context in relation to estimating the rate and volume of rainfall flowing off the land and of flood flows in rivers. 

Hydrometric Area

Hydrological divisions of land, generally large catchments or a conglomeration of small catchments, and associated coastal area. There are 40 Hydrometric Areas in the island of Ireland.


This term is typically used to refer to the flood maps developed under the PFRA. The maps developed are approximate, rather than highly detailed, with some local anomalies. 

Individual Risk Receptor Or IRR

A single receptor (see below) that has been determined to represent a potentially significant flood risk (as opposed to a community or other area at potentially significant flood risk, known as Areas for Further Assessment, or ‘AFAs’). 


Another word for flooding or a flood (see ‘Flood’).


A measure (when used in the context of a flood risk management measure) is a set of works, structural and / or non-structural, aimed at reducing or managing flood risk. 

National CFRAM Programme

The programme developed by the OPW to implement key aspects of the EU ‘Floods’ Directive in Ireland, which included the CFRAM Studies, and built on the findings of the PFRA.


Refers to rainfall, often used in the context of pluvial flooding, i.e., flooding caused directly from heavy rainfall events (rather than over-flowing rivers).

Point Receptor

Something that might suffer harm or damage as a result of a flood, that is at a particular location that does not cover a large area, such as a house, office, monument, hospital, etc.

Preliminary Flood Risk Assessment or PFRA

An initial, high-level screening of flood risk at the national level to determine where the risks associated with flooding are potentially significant, to identify the AFAs. The PFRA was the first step required under the EU ‘Floods’ Directive. 

Public Consultation Day or PCD

A public and stakeholder consultation and engagement event advertised in advance, where the project team displayed and presented material (e.g., flood maps, flood risk management options) at a venue within a community, with staff available to explain and discuss the material, and where members of the community and other interested parties could provide local information and put forward their views.


Something that might suffer harm or damage as a result of a flood, such as a house, office, monument, hospital, agricultural land or environmentally designated sites.

Return Period

A term that was used to describe the probability of a flood event, expressed as the interval in the number of years, that, on average over a long period of time, a certain magnitude of flood would be expected to occur. This term has been replaced by ‘Annual Exceedance Probability’ as Return Period can be misleading. 


River bank. Often used to describe the area on or near a river bank that support certain vegetation suited to that environment (Riparian Zone). 


The combination of the probability of flooding, and the consequences of a flood.

River Basin

An area of land (catchment) draining to a particular estuary or reach of coastline. 

River Basin District or RBD

A regional hydrological division of land defined for the purposes of the Water Framework Directive. There are eight RBDs in the island of Ireland; each comprising a group of River Basins.


Related to a river.


The flow of water over or through the land to a waterbody (e.g., stream, river or lake) resulting from rainfall events. This may be overland, or through the soil where water infiltrates into the ground.


The accumulation of particles (of soil, sand, clay, peat, etc.) in the river channel. 

Significant Risk

Flood risk that is of particular concern nationally. The PFRA Main Report sets out how significant risk was determined for the PFRA, and hence how Areas for Further Assessment have been identified.

Standard of Protection or SOP

The magnitude of flood, often defined by the annual probability of that flood occurring being exceeded (the Annual Exceedance Probability, or ‘AEP’), that a measure / works is designed to protect that area at risk against.

Strategic Environmental Assessment or SEA

An SEA is an environmental assessment of plans (such as the Plans) and programmes to ensure a high level consideration of environmental issues in the plan preparation and adoption, and is a requirement provided for under the SEA directive [2001/42/EC].

Surface Water

Water on the surface of the land. Often used to refer to ponding of rainfall unable to drain away or infiltrate into the soil.


The phenomenon of high sea levels due to meterological conditions, such as low pressure or high winds, as opposed to the normal tidal cycles.

Survey Management Project

A project commissioned by the OPW in advance of the CFRAM Studies to specify and manage a large proportion of the survey work.


The capacity to endure. Often used in an environmental context or in relation to climate change, but with reference to actions people and society may take.


Related to the tides of the sea / oceans, often used in the context of tidal flooding, i.e., flooding caused from high sea or estuarine levels.


The shape of the land, e.g., where land rises or is flat.

Transitional Water

The estuarine or inter-tidal reach of a river, where the water is influenced by both freshwater river flow and saltwater from the sea.

Unit of Management or UOM

A hydrological division of land defined for the purposes of the Floods Directive. One Plan has been prepared for each Unit of Management, which is referred to within the Plan as a River Basin.


The potential degree of damage to a receptor (see above), and/or the degree of consequences, that could arise in the event of a flood.

Water Framework Directive or WFD

The Water Framework Directive [2000/60/EC] aims to protect surface, transitional, coastal and ground waters to protect and enhance the aquatic environment and ecosystems and promote sustainable used of water resources.


A term used in the Water Framework Directive (see below) to describe discrete section of rivers, lakes, estuaries, the sea, groundwater and other bodies of water.