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PPS 15: Planning and Flood Risk
Policy FLD 3: Development beyond Flood Plains

Policy FLD 3 Development beyond Flood Plains
Beyond coastal flood plains and the flood plains of rivers the Department will not permit development which is known to be at risk from flooding, or which would be likely to increase the risk of flooding elsewhere.
An exception to this policy will only be permitted where an application is accompanied by measures to mitigate the risk of direct flooding and it is demonstrated that such measures:
  • will not increase flood risk elsewhere;
  • will not result in an adverse impact on visual amenity or the character of the local landscape; and
  • will not result in an adverse impact on features of importance to nature conservation, archaeology or the built heritage.
As part of the precautionary approach to dealing with flood risk the Department will, where appropriate, require a drainage assessment to accompany planning applications (see Annex D).

Justification and Amplification

8.23 Flood risk can arise from sources other than natural drainage systems (watercourses) and the sea, for example, from overland flow, which occurs when rainwater flows over saturated ground. Flood events can also arise when modified or artificial drainage systems cease to function. This may occur where they are overwhelmed by an extreme weather event or where they are blocked by debris.
8.24 Although generally localised, these types of flooding can cause significant damage. Where drainage infrastructure fails inundation may be rapid. A flood event caused by an artificial drainage system surcharge can pose public health risks from foul water contamination. Overland flow floods may be extended in duration causing more damage to property and greater hardship to the people affected, than a short duration event.
8.25 The Department will therefore operate a presumption against development in areas known to be directly at risk from flooding or where it would increase the risk of flooding elsewhere unless acceptable flood mitigation measures accompany the proposals.
8.26 Appropriate flood mitigation measures may enable a development to take place that would otherwise be unacceptable. Where such measures are proposed, the applicant must demonstrate that they will prevent any increase in direct and indirect flood risk over the lifetime of the proposed development. Accordingly their design will need to address the impact of the more frequent or extreme weather events likely to arise from climate change.
8.27 Where planning permission is granted subject to the undertaking of mitigation measures8, a planning agreement to facilitate their long-term management may be required.
8.28 Where a drainage assessment is required it should evaluate the impact of the proposal on the drainage regime in the locality and identify any measures necessary to ensure that the development does not add to the risk of flooding at the site or elsewhere.
8 Flood mitigation measures accompanying applications for built development should also make provision for the protection of proposed parking areas, garaging and bin and fuel storage areas.
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