Term
Definition
Overtopping of defences
When water exceeds defence height and flows over structures.
Run-off
Water flow from rainfall across land surfaces.
Appropriate Assessment
An assessment based on best scientific knowledge, by a person with ecological expertise, of the potential impacts of the plan on the conservation objectives of any Natura 2000 Environmentally Protected sites and the development of mitigation or avoidance measures to preclude negative effects.
Arterial Drainage Scheme
Works undertaken under the Arterial Drainage Act (1945) to improve the drainage of land, maintained by the OPW.
Breach of defences
A structural failure at a flood defence allowing water to flow through.
Catchment
The area that is drained by a river or artificial drainage system.
Consequences of flooding
Health, social, economic and environmental effects of flooding.
Conveyance function
The ability of a river and floodplain to transport water downstream during flooding.
Detailed flood risk assessment
A quantitative assessment of flood hazard, risk and effectiveness of mitigation measures.
Drainage
Works to remove or manage surface or subsurface water.
Flash flood
Rapid flooding due to intense rainfall or infrastructure failure.
Flood defence
A man-made structure designed to prevent flooding.
Flood extent
The area of land that is or may be flooded.
Flood hazard
Characteristics of flooding such as depth, velocity and duration that cause harm.
Flood plain
Low-lying land adjacent to rivers susceptible to flooding.
Flood Relief Scheme (FRS)
A scheme designed to reduce flood risk in a specific area.
Flood risk
Combination of flood probability and consequences.
Flood Risk Management
Activities to manage and reduce flood risks before, during and after events.
Flood Risk Management Plan
Strategic plans developed under EU policy to manage flood risks.
Flood storage
Temporary storage of excess water in basins, reservoirs or floodplains.
Flooding (or inundation)
Overflow of water onto normally dry land.
Flooding Directive
EU Directive 2007/60/EC on flood risk assessment and management.
Fluvial flooding
Flooding from rivers or watercourses.
Freeboard
Safety margin between water level and top of a structure.
Groundwater flooding
Flooding caused by rising groundwater levels.
Habitat
Natural environment where plants and animals live.
Habitats Directive
EU Directive protecting habitats and species of European importance.
Hydraulics
Study of fluid behaviour, particularly water movement in channels and structures.
Hydrology
Study of the water cycle and flow processes.
Hydrometric Area
Large hydrological divisions used for water management.
Likelihood (probability) of flooding
Probability of a flood event occurring within a given timeframe.
Measure
Hydrological division or grouping of catchments and coastal areas.
Mitigation
Actions taken to reduce negative environmental impacts.
Natura 2000
EU network of protected ecological sites (SACs and SPAs).
Option
A combination of measures used to manage flood risk.
Ordnance Datum (OD) Malin
Standard reference level for elevations in Ireland.
Pathways
Routes through which flood water reaches receptors.
Pluvial flooding
Flooding caused by rainfall exceeding drainage capacity.
Precautionary approach
Principle of managing risk despite uncertainty.
Receptors
People, property or environment affected by flooding.
Residual risk
Remaining risk after mitigation measures are applied.
Resilience
Ability of structures to withstand and recover from flooding.
Resistance
Measures to prevent water entering buildings.
Return Period
Average interval between flood events (now replaced by AEP).
Risk
Combination of probability and consequences of flooding.
River Basin Management Plans (RBMP)
Strategic plans for managing water bodies under EU WFD.
Source
Origin of flood hazard (e.g. rainfall, sea).
Source-pathway-receptor model
Framework describing how flooding occurs.
Standard of Protection (SoP)
Level of flood protection provided by a scheme.
Strategic Environmental Assessment (SEA)
Process integrating environmental considerations into planning.
Strategic Flood Risk Assessment (SFRA)
Large-scale assessment of flood risk for planning purposes.
Surface water management
Management of rainfall runoff in urban areas.
Sustainability
Ability to maintain environmental and societal systems long-term.
Sustainable Drainage Systems (SuDS)
Drainage systems that mimic natural processes to manage runoff.
Vulnerability
Susceptibility of people, property or environment to flood damage.
Water Framework Directive (WFD)
EU Directive for integrated water resource management.