Glossary
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.
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.
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.
Catchment:
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.
Communities:
Cities, towns, villages or townlands where there are a collection of homes, businesses and other properties.
Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms.
Design Life:
The design life of a component or product is the period of time during which the item is expected by its designers to work within its specified parameters; in other words, the life expectancy of the item.
Consequences:
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).
Drainage:
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.
Flood:
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 is focused on managing risk within the AFAs.
Floodplain:
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 (AFAs), and then to prepare flood maps and Plans for these areas.
Fluvial:
Riverine, often used in the context of fluvial flooding, i.e., 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.
Hazard:
Something that can cause harm or detrimental consequences. In this context, the hazard referred to is flooding.
Hydraulics:
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.
Hydrology:
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 areas. There are 40 Hydrometric Areas in the island of Ireland.
Indicative:
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’).
Measure:
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.
Mitigation:
The term is used to describe an action that helps to lessen the impacts of a process or development on the receiving environment. It is used most often in association with measures that would seek to reduce negative impacts of a process or development.
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.
Ordnance Datum (or OD) Malin:
A vertical datum used by an ordnance survey as the basis for deriving altitudes on maps. A spot height may be expressed as AOD for "above ordnance datum". Usually meansea level (MSL) is used for the datum. In the Republic of Ireland, OD for the Ordnance Survey of Ireland is Malin Ordnance Datum: the MSL at Portmoor Pier, Malin Head, County Donegal, between 1960 and 1969. Prior to 1970, Poolbeg Ordnance Datum was used: the low water of spring tide at Poolbeg lighthouse, Dublin, on 8 April 1837. Poolbeg OD was about 2.7 metres lower than Malin OD.
Overtopping of Defences:
Failure of a flood defence when flood water reaches levels that are higher than the flood defence level and flows over the top of the structure. While the structure may remain stable, erosion of the landward face of the defence could cause the defence to collapse.
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.
Resilience:
Sometimes known as “wet-proofing”, resilience relates to how a building is constructed in such a way that, although flood water may enter the building, its impact is minimised, structural integrity is maintained, and repair, drying & cleaning and subsequent reoccupation are facilitated. Resistance, sometimes known as “dry-proofing”, this relates to how a building is constructed to prevent flood water entering the building or damaging its fabric. Receptors Things that may be harmed by flooding (e.g. people, houses, buildings or the environment).
Riparian:
River bank. Often used to describe the area on or near a river bank that supports certain vegetation suited to that environment (Riparian Zone).
Risk:
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.
Riverine:
Related to a river.
Pluvial:
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.
Precautionary Approach:
The approach to be used in the assessment of flood risk which requires that lack of full scientific certainty, shall not be used to assume flood hazard or risk does not exist, or as a reason for postponing cost-effective measures to avoid or manage flood risk.
Public Engagement Event:
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.
Residual Risk:
The risk which remains after all risk avoidance, substitution and mitigation measures have been implemented, on the basis that such measures can only reduce risk, not eliminate it.
Resitance:
Sometimes known as “dry-proofing”, this relates to how a building is constructed to prevent flood water entering the building or damaging its fabric.
Run-off:
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.
Sedimentation:
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.
Source:
A source of hazard (e.g. the sea, heavy rainfall).
Source-Pathway-Receptor Model:
For there to be flood risk, the three components of flood risk - the source of the hazard, the receptors affects by the hazard and the mechanism of transfer between the two - must all exist.
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 the 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.
Sustainability:
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.
Regularly used definitions:
"Meeting the needs of today without comprimising the ability of future generations to meet their own needs. Sustainability has three pillars; social, economic and environmental."
Topography:
The shape of the land, e.g., where land rises or is flat.
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.
Vulnerability:
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.
Waterbody:
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.
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 use of water resources.
