FRD1 Development within Floodplains

Closeddate_range16 Oct, 2019, 9:30am - 11 Dec, 2019, 5:00pm

Policy FRD1 Development within Floodplains

A proposal for development within a floodplain of a river or the sea will not be permitted unless the applicant can demonstrate that the proposal constitutes an exception to the policy.

Where the principle of development is accepted by the Council through being an exception to policy (as set out below), applicants are required to submit a Flood Risk Assessment (FRA) which demonstrates that:

  1. all sources of flood risk to and from the proposed development have been identified; and
  2. there are adequate measures to manage and mitigate any increase in flood risk arising from the development throughout its operational life.


Defended Areas:
  1. A proposal on previously developed land protected by flood defences (confirmed by DfI Rivers as being structurally adequate), provided it does not fall into any of the following categories:
    1. essential infrastructure, such as power supply and emergency services;
    2. development for the storage of hazardous substances;
    3. bespoke accommodation for vulnerable groups, such as schools, residential/nursing homes, sheltered housing; or
    4. any development located close to flood defences.

A proposal involving significant intensification of use will be considered on its individual merits and will be informed by the FRA.

Undefended Areas:
  1. New development within settlements in the coastal floodplain where the land is raised (through infilling), to an acceptable level above the floodplain and subject to meeting all of the following criteria:
    1. the proposal is not dependent on the provision of new coastal flood defences or likely to require such protection as a result of anticipated climate change;
    2. the site is not in an area likely to be at risk from coastal erosion or land instability and the proposed development will not significantly increase such risks in the locality; and
    3. the elevation of development above the floodplain will not unduly disrupt the provision and ongoing delivery of essential services, including access, power, water and wastewater.
  2. Replacement of an existing building, provided it does not include essential infrastructure or bespoke accommodation for vulnerable groups, or involves significant intensification of use.
  3. Development for agricultural use, transport and utilities infrastructure, which for operational reasons has to be located within the floodplain.
  4. Water compatible development such as for boating purposes mooring, navigation and water based recreational use, which for operational reasons has to be located within the floodplain.
  5. The use of land for sport and outdoor recreation, amenity open space or for nature conservation purposes, including ancillary buildings. This exception does not include playgrounds for children.
  6. The extraction of mineral deposits and necessary ancillary development.
Development Proposals of Overriding Regional or Sub-Regional Economic Importance

A proposal within the floodplain that does not constitute an exception to the policy may be permitted where it is deemed to be of overriding regional or sub regional economic importance and meets both of the following criteria:

  1. demonstration of exceptional benefit to the regional or sub-regional economy;
  2. demonstration that the proposal requires a location within the floodplain and justification of why possible alternative sites outside the floodplain are unsuitable.

The applicant is required to submit a FRA for all proposals. Where the principle of development is established through meeting the above criteria, the Council will steer the development to those sites at lowest flood risk.

Minor Development39

Minor development will be acceptable within defended and undefended floodplains subject to a satisfactory FRA.

Flood Protection / Management Measures

The following flood protection and management measures proposed as part of the planning application, in order to facilitate development within floodplains, will not be acceptable:

  1. new hard engineered or earthen bank flood defences;
  2. flood compensation storage works;
  3. land raising (infilling) to elevate a site above the flood level within the undefended fluvial floodplain, where displacement of flood water would be likely to cause flooding elsewhere.

Justification and Amplification

As floodplains40 store and convey water during periods of flood, they are of vital importance in the wider flood management system. Any built development will cause piecemeal reduction of the floodplain and potentially remove valuable flood storage area, which may cause or exacerbate flooding elsewhere. Development also has the potential to impair the conveyance function of the floodplain and its ecological integrity. For these reasons, and also the need to limit exposure of people and property to flood risk, built development and infrastructure works, particularly on green field sites, will normally not be permitted.

This policy seeks to ensure that development within the floodplains of rivers or the sea is permitted only in exceptional circumstances. The Council will adopt a precautionary approach in assessing proposals in areas that may be subject to flood risk presently or in the future as a result of climate change predictions.

DfI Rivers advise Council on the extent of river and coastal floodplains in Mid and East Antrim. Current information on flooded areas, including the spatial definition of present day river and coastal floodplains and those which take account of future climate change predictions, is available on the Strategic Flood Maps NI website at These maps are regularly updated as more detailed information becomes available, so the extent of floodplains will therefore change over time.

The policy for development in floodplains distinguishes between defended areas and undefended areas.

Defended Areas

A ‘Defended Area’ is that part of the floodplain where flooding would normally occur except for the presence of flood defences. Previously developed land protected by existing flood defences, confirmed by DfI Rivers, as being structurally adequate and providing a minimum standard of 1 in 100 year Fluvial, or 1 in 200 year Coastal flood protection, will generally be considered acceptable for development.

The flood risk within a defended area cannot be entirely eliminated as the possibility of a flood event exceeding the design limit of the defence and overtopping them (the residual flood risk) will always remain. Another risk arises through the potential for structural collapse and breeching of the defences which could result in sudden and rapid inundation of flood water. Because of these flood risks the policy places restrictions on the location and type of development permissible in defended areas.

Development close to flood defences will be resisted as such land will often be low lying and therefore the most susceptible to flooding. Also, it may need to be available for temporary flood storage in a flood event. Before progressing proposals in proximity to flood defences, developers are advised to seek guidance from DfI Rivers on acceptable separation distances.

Due to the residual flood risk, the policy operates a presumption against permission being granted for development associated with vulnerable groups. This includes facilities such as children’s nurseries, schools, residential care/nursing homes, sheltered housing and hospitals. This list is not exhaustive.

Development proposals for essential infrastructure, such as for emergency services/emergency depots, power supply and telecommunications will be resisted because access and uninterrupted operation cannot be guaranteed in locations where there is a residual flood risk.

Development likely to give rise to significant levels of environmental pollution in the event of damage caused by flooding will also be resisted. Therefore proposals for development associated with the storage of hazardous substances, fuel storage depots, sewage treatment works or other development likely to give rise to environmental pollution in the event of flooding will only be granted planning permission where it is demonstrated that an alternative lower risk location is not available and that adequate provision is made for pollution containment so as to prevent a pollution incident in the event of flooding.

Development involving a significant intensification of use, such as the conversion of a single dwelling unit to a number of apartments, would be liable to expose more people to the residual flood risk in defended areas. However, this risk must be balanced against other material considerations, for example relating to existing density in the locality or that considered appropriate from a broader planning perspective. Accordingly, Council will determine each application on its individual merits taking account of the scope for mitigation of the residual flood risk.

There will be a presumption against development of green field sites in defended areas. As well as exposing more people and property to the residual flood risk, this form of development could remove valuable flood storage should the defences overtop or breach.

Undefended Areas

An ‘Undefended Area’ is an area within the floodplain that is not protected by flood defences. This applies to the vast majority of fluvial and coastal floodplains. Undefended areas are at much higher flood risk than defended areas, although the flooded areas are usually more predictable and flood water usually recedes more quickly. There is also the added potential impact of coastal flooding on coastal change.

Whilst there is a general presumption against development, it is recognised that in certain cases, particular development or infrastructure has to be in such locations, as alternative lower flood risk sites may be neither feasible nor available. Exceptions to the policy are therefore set out for a range of development types, including for example, agricultural development, minerals development and transport or utilities infrastructure. In regard to agricultural and minerals development, this exception will only apply where the existing unit is located wholly in the floodplain or where the use of other land outside the floodplain would not be feasible and available.

The policy provides opportunity for new development in the undefended coastal floodplain on the basis that infilling and land raising to an appropriate level above the floodplain will have a negligible effect on its extent and therefore will not result in additional flood risk elsewhere in the coastal floodplain. Importantly, such development should not generate a present or future need for flood defences nor should it cause or escalate coastal erosion in susceptible areas. As part of the precautionary approach, this exception will be restricted to settlements.

Replacement of an existing building may be considered on the basis that this should not normally result in any material increase in the flood risk to the development or elsewhere. The adoption of suitable flood proofing measures through resistance and resilience construction will normally be expected. However the replacement of a building to provide bespoke accommodation allowing for the introduction of vulnerable groups to the flood risk area is unacceptable. Similarly, replacement of a building to accommodate essential infrastructure will be unacceptable as continual access and egress for operational activities will no longer be possible when the area has been cut off during a flood event. Finally, a replacement proposal which involves significant intensification of use, for example through increasing the existing footprint or change of use, will be resisted if this would have the effect of introducing more people to a high flood risk area.

The policy allows for the provision of areas for amenity open space, sports, outdoor recreation and nature conservation purposes on the basis that such areas are not generally occupied and are unlikely to incur major damage as a result of flood inundation. Children’s playgrounds are not included in this exception to the policy as such proposals would have the effect of exposing a vulnerable group to flood risk. Ancillary development such as changing facilities, clubhouses, social facilities, 3-G pitches, as well as job-related accommodation for caretakers and staff may be acceptable where justified by the flood risk assessment. Even though these areas are intermittently occupied, proposals will be required to demonstrate mitigation in regard to minimising flood impacts as well as providing for adequate flood warning procedures and safe means of evacuation from the site.

Development Proposals of Overriding Regional or Sub-Regional Economic Importance

While most economic development is best located outside of floodplains, it is accepted that certain projects because of their nature, size or site specific requirements, may require a site that happens to fall within a floodplain. In such circumstances the policy allows for development that is demonstrated to be of significant regional or sub-regional economic importance. Normally, such a proposal will be expected to demonstrate its particular contribution to the regional economy. However, a proposal may also be considered acceptable if it provides employment for a substantial number of people living in Mid and East Antrim and potentially adjoining council areas.

In regard to such proposals, the applicant must justify the need for a location within the floodplain and also demonstrate why other potential sites outside of the floodplain are not suitable. Subject to the principle of development in the floodplain being accepted by the Council, the applicant will be expected to identify a suitable site in the least vulnerable parts of the floodplain in consultation with DfI Rivers and other statutory consultees as required. The development of greenfield sites in the undefended fluvial floodplain will rarely be acceptable as these areas pose the greatest flood risk.

Flood Management and Mitigation Measures

Where Council determines that development is acceptable in principle in the floodplain, then the onus is on the applicant to submit a Flood Risk Assessment (FRA). This must demonstrate measures to be taken to manage and mitigate the identified risks to the proposed development and elsewhere as a result of the development. These measures will be proportionate to the flood risk and generally will be more rigorous in undefended areas than in defended areas where the flood risk (residual) is lesser. Technical details and methodology relating to flood risk assessments and drainage assessments can be found in Appendix I.

  • 39 - Non-residential extensions with a footprint less than 150 sq. metres. Alterations - development that does not increase the size of buildings, e.g. alterations to external finishes. Householder development - e.g. sheds, garages, games rooms etc. within the curtilage of the existing dwelling in addition to extensions to the existing dwelling. This excludes any proposed development that would create a separate dwelling within the curtilage of the existing dwelling e.g. subdivision of a dwelling house into flats.
  • 40 - The generally flat areas adjacent to a watercourse or the sea where water flows in a flood, or would flow, but for the presence of flood defences. The limits of the floodplain are defined by the peak water level of an appropriate return period event (currently defined as 1 in 100 year or AEP (Annual Exceedance Probability) of 1%for the river or fluvial floodplain and 1in 200 year or AEP 0f 0.5% for the coastal floodplain, incorporating climate change prediction). Floodplains as so defined aredepicted on the Strategic Flood map on the DfI Rivers website.