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Flood Risk Assessment NI

Flood Risk Assessment NI – O’Sullivan Macfarlane regularly undertake various types of Flood Risk Assessment (FRA) in Northern Ireland (NI) for a range of hydrological settings. We have successfully assessed a wide range of Flood Risk Assessment NI, to include: –

  • Developments in or near river floodplains (Fluvial Flood Risk Assessment);
  • Developments in close proximity to reservoirs or dams;
  • Developments at risk of costal flooding (Coastal FRA); and
  • Developments at risk of surface water flooding (Drainage Assessments).

Flood Risk Assessments (FRA) in Northern Ireland (NI) are now commonplace, and are often required by the Planning Service for a large number of planning applications, with the Flood Risk Assessment requiring River Agency’s approval (in line with Revised Planning Policy 15 – Planning and Flood Risk), before the development can proceed. Our staff at O’Sullivan Macfarlane have successfully worked on Flood Risk Assessments for a range of developments types throughout Northern Ireland (NI), including:-

  • Single dwellings;
  • Large scale housing projects;
  • Hydro-electric schemes;
  • Commercial / industrial developments; and
  • Commercial sports grounds.

Modelling for Flood Risk Assessments (FRA)

Should modelling be required as part of a Flood Risk Assessment (FRA), this work is carried out in-house using Rivers Agency recognised software, and modelling techniques which represent industrial best practice.

Our staff have extensive experience in modelling a range of scenarios and hydrological settings, including culverts, bridges, weirs and engineered watercourses. Over the past number of years, our staff have built up a good working relationship with the Rivers Agency, and continue to use industry recognised best practice for water course modelling.

With a combined experience of over 20 years in the environmental sector, drawing on expericance from both the private sector and the Northern Ireland Evironment Agency (NIEA), we have a significant expertise in the fields of Flood Risk Assessment and brownfield redevelopments.

All works are undertaken on a strictly confidential basis. If you would like any further information on our Flood Risk Assessment services, please do not hesitate to contact us.

Flood Risk Assessment Belfast

Almost all rivers in the greater Belfast area have been ‘Modelled in Detail’ by Rivers Agency, which means modelling of watercourses is unlikely as part of any assessment. Therefore, should a Flood Risk Assessment be required in the greater Belfast area, these would typically be desktop assessments.

Flood Risk Assessment NI

Across Northern Ireland, the majority of all major watercourses have been ‘Modelled in Detail’ by Rivers Agency in urban areas. Outside these areas, modelled Flood Risk Assessments are often required. O’Sullivan Macfarlane use globally recognised modelling software and analytical tools to model the extents of flood plains in a wide range of scenarios and developments in order to ensure that development can take place where it is safe to do so.

Primary Sources of Flooding In Northern Ireland


The four main types of Flood Risk Assessment in Northern Ireland (NI) are Fluvial Flood Risk Assessments (river flooding), Pluvial Flood Risk Assessments (surface water flooding), Impounded Waterbodies FRA (reservoirs) and Coastal Flood Risk Assessments. Each of these scenarios are detailed below.

Fluvial Flood Risk Assessment NI

Fluvial flooding occurs when a river bursts its banks, resulting in flood waters flowing across what would normally be dry land. A correctly modelled watercourse allows the hydrologist to assess whether this is likely to occur, as assess the level of flood risk during this event. Typically a Flood Risk Assessment undertaken for watercourse will accompany a new planning application the planning service.

Pluvial Flood Risk Assessment (FRA)

A Pluvial Flood Risk Assessment (FRA) will review the level of risk posed to site, or land downstream of a site, during a high intensity rainfall event. During an event of high intensity rainfall, pluvial or surface water flooding occurs overwhelming natural or man-made drainage systems resulting in water flowing overland and ponding in depression in the ground. Pluvial flooding is a particular problem in urban areas which are often dominated by non-permeable surfaces such as roofs, roads and carparks. This hardstanding inhibits the natural ability for infiltration of water into the ground.

As part of a pluvial FRA, modelling is undertaken to assess the extent of infiltration within a site, and the level of attenuation required to ensure either the greenfield run-off is met, or that worsening does not occur.

Impounded Water Body Flood Risk Assessment (Reservoir Flood Risk Assessment NI)

A flood risk assessment will be required for an new development located within or near the potential flood inundation area of a ‘controlled reservoir’. There are over 100 ‘controlled reservoirs’ in Northern Ireland, which typically serve urban areas across the country. Given the volume of reservoirs, the requirements for a flood risk assess for new developments has steadily increased over the past decade.

In line with Planning Policy PPS15  (FLD5) planning permission can be granted so long as a planning application is accompanied with a FRA which can demonstrate that there is no material increase in the flood risk to the development or elsewhere.

Coastal Flood Risk Assessment NI

A coastal flood risk assessment is typically untaken in low lying land adjacent to the shore line around Northern Ireland which is at risk from flooding during what is called a Q200 coastal flood event. A Flood Risk Assessment will assess a number of contributing factors during a coastal flood event such as storm surge, wave height and climate change to ascertain the extents and depth of flooding on the proposed development site and general area.

Whilst it is recognised that there is a lower annual probability of flooding within coastal floodplains compared with river floodplains, a Flood Risk Assessment should consider the effects of rapid inundation by fast flowing sea water which can result in a greater risk to human health.