Planning guidelines for local authorities
There are many areas in Ireland, including towns and cities that are already at risk from periodic flooding. The flood risk management programme of the OPW, including the construction of flood relief schemes, will help to reduce this existing risk. It is however critical to avoid ever increasing risks to people, property and the environment that we do not inadvertently create new risks or exacerbate existing risks.
Development in flood plains can itself be at risk from flooding, as well as creating or increasing risks up and downstream, while development anywhere within a catchment can increase the rainfall runoff rates and volumes through paving over of previously permeable surfaces and accelerating drainage. The role that good planning has in avoiding and reducing such risk was recognised in the Report of the Flood Policy Review Group, which was approved by the Government in 2004.
The OPW, in partnership with the Department of Environment, Heritage and Local Government, have produced Planning guidelines for local authorities, that set out a transparent and robust framework for the consideration of flood risk at all stages within the planning process, including the preparation of plans and the preparation and assessment of planning applications.
These guidelines require the planning system at national, regional and local levels to:
- Avoid development in areas at risk of flooding, particularly floodplains, unless there are proven wider sustainability grounds that justify appropriate development and where the flood risk can be reduced or managed to an acceptable level without increasing flood risk elsewhere;
- Adopt a sequential approach to flood risk management when assessing the location for new development based on avoidance, reduction and mitigation of flood risk; and
- Incorporate flood risk assessment into the process of making decisions on planning applications and planning appeals.
The new Guidelines were issued to planning authorities and An Bord Pleanála under Section 28 of the 2000 Planning and Development Act, which requires them to have proper regard to the principles and procedures of these guidelines in carrying out their functions.
Guidelines on the Planning System and Flood Risk Management
Technical Appendices to the Guidelines
The underlying causes of flooding, heavy rain and high sea levels, are, essentially, uncontrollable. However, the factors affecting the extent and severity of the flood can be addressed. The most influential of these factors is development, in particular development in flood plains i.e. areas adjacent to rivers that tend to become flooded following periods of heavy rain. Historic records will help to indicate which areas might be prone to flooding, although it is always possible that areas not known to have flooded in the past or for which no records of flooding are available, might flood in the future due to changes in upstream or downstream conditions or the occurrence of a more extreme rainfall event.
The risk of flooding should be taken into account in all cases where development is being considered. This is in the interests of individuals proposing the development and of the public in general.
Impact of flood risk on development
Locating development in an area at risk from flooding can lead to property damage, human stress and hardship, problems obtaining property insurance and consequential demands for the expenditure of local authority or central government resources on flood protection works. The construction of protection works either at the time of the development, or at a later date, will incur additional costs, may not provide absolute immunity from the risk of flooding and can, if not appropriately designed, have detrimental effects on flood risk elsewhere.
Impact of development on flood risk upstream
In times of flood, the river flows not only through its normal channel but also along the flood plains. Any constriction of the natural flow path can ‘back-up’ the river and lead to increased flood levels upstream. The construction of buildings or houses, and particularly embankments for infrastructure or protection, in or across a floodplain can therefore not only put the development itself at risk of flooding, but can also increase the flood risk for land and properties upstream. The same is obviously true of any construction in, or encroachment into, the normal river channel.
Impact of development of flood risk downstream
Natural or agricultural land, such as forests, woodland, pastures or crop fields, is normally able to absorb a considerable proportion of any rain that falls onto it. Covering such land with buildings, tarmac (such as for parking areas or roads), or other impermeable materials significantly reduces this ability to absorb rainfall, and will lead to increased land runoff. As a result, large developments, including those away from major rivers, can increase river flows and the risk of flooding to land and property downstream. A number of smaller developments built up over a period of time can have the same effect.
Impact of tidal flood risk on development
A combination of high tides, waves, high winds and surges developed from low-pressure systems can lead to extensive flooding. Current predictions of climate change indicate that the risk of flooding from the sea will increase in the future. Any area below current or predicted future peak sea levels, including areas behind existing defences that offer only a certain level of protection, are at risk from flooding in the future.
Impact of possible climate change
Current predictions of climate change in Ireland indicate that winters will become wetter and the rainfall distribution ‘stormier’, and that sea levels will rise. This would mean that areas not currently prone to flooding may be at risk from flooding in the future.
The contents of these pages are provided as an information guide only. They are intended to enhance public access to information about flooding. While every effort is made in preparing material for publication no responsibility is accepted by or on behalf of the Office of Public Works for any errors, omissions or misleading statements on these pages or any site to which these pages connect.