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 (including Natura 200 sites not situated in an area encompassed by the plan or scheme) and the development, where necessary 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. Such works were undertaken, and are maintained on an ongoing basis, by the OPW.


The area that is drained by a river or artificial drainage system.

Climate Change

Long-term variations in global temperature and weather patterns, which occur both naturally and as a result of human activity, primarily through greenhouse gas emissions.

Detailed Flood Risk Assessment 

A methodology to assess flood risk issues in sufficient detail and to provide a quantitative appraisal of flood hazard and potential risk to an existing or proposed development, of its potential impact on flood elsewhere and of the effectiveness of any proposed measures.

Flood Defence

Flood Extent

Flooding Directive


Fluvial Flooding


Habitats Directive







Natura 2000


Pluvial Flooding



Standard of Protection (SoP)


Water Framework Directive

A man-made structure (e.g. embankment, bund, sluice gate, reservoir or barrier) designed to prevent flooding of areas adjacent to the defence. 

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

The EU Directive 2007/ 60/ EC of 23 October 2007 on the assessment and management of flood risks which is aimed at integrating the way flood risk is managed throughout the European Union transposed into Irish Law under SI122/2010. 

Flooding from a river, stream or other watercourse. 

A factor of safety applied for water surfaces. Defines the distance between normal water level and the top of a structure, such as a wall or embankment. 

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.

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.

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. 

The EU-wide network of protected areas, recognised as ‘sites of Community importance’ under the EC Habitats Directive (Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora). They comprise “Special Areas of Conservation” (SACs) under the Habitats Directive and “Special Protection Areas” (SPAs) under the Birds Directive (Council Directive 79/409/EC on the conservation of wild birds). 

Usually associated with convective summer thunderstorms or high intensity rainfall cells within longer duration events, pluvial flooding is a result of rainfall-generated overland flows which arise before run-off enters any watercourse or sewer. The intensity of rainfall can be such that the run-off totally overwhelms surface water and underground drainage systems. 


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.

A European Community Directive (2000/ 60/ EC) designed to integrate the way we manage water bodies across Europe. It requires all inland and coastal waters to reach “good status” or “good ecological potential” in the case of heavily modified water bodies by 2015 through a catchment-based system of River Basin Management Plans (RBMP), incorporating a programme of measures to improve the status of all natural water bodies.


Postal address: Crossmolina Flood Relief Scheme Project Manager, Office of Public Works, 52 St. Stephen's Green, Dublin 2, D02 DR67.

Telephone: 01 647 6000


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