1st Cycle - Preliminary Flood Risk Assessment

We completed a Preliminary Flood Risk Assessment (PFRA) for Northern Ireland in December 2011, which identified areas where flood risk is most significant. These areas are referred to as Significant Flood Risk Areas (SFRAs) and they are the focus for flood mapping and planning under the legislation. The focus of the Directive is to identify and manage the risk of flooding where it is considered to be significant at a national level.

To identify SFRAs, the assessment took account of historical flood events and the potential for future flooding from all significant sources of flooding which for Northern Ireland are, rivers, the sea, surface water and impoundments (reservoirs, dams and large ponds). The assessment also addressed the potential effects of climate change on flood risk.

It examined the adverse consequences that flooding has on four flood risk classifications defined within the Floods Directive:

• human health
• the environment
• cultural heritage
• economic activity

Why is a flood risk assessment important?

The assessment ensures that we have the information to identify the areas where flood risk is most significant. This enables us and others to target valuable resources in a coordinated manner to manage flood risk effectively.

How we undertook the assessment?

We have mapped where previous floods have occurred and using computer models, we can predict the potential extent and impact of future floods. Using a Geographical Information System (GIS) applications we determined the adverse impacts on human health and economic activity. We also consulted with the Northern Ireland Environment Agency (NIEA) on the impacts flooding may have on the environment and cultural heritage. The flood risk to key elements of NI’s infrastructure was also considered.

This methodology allowed us to rank areas at flood risk in Northern Ireland according to the significance of flood risk.

What did the assessment show?

Areas with the potential to flood have been mapped which informs us about how many people and properties could be affected and the economic value of potential property damage. Through our own research and consultation with others, further information has been gathered on these areas in relation to demographics, business activity, infrastructure, land use, sites of cultural heritage and environmental importance. By using all of this information, we have determined the areas that we consider to be at significant flood risk in Northern Ireland (SFRAs).

With regard to reservoirs, when the PFRA was prepared in 2011, Northern Ireland did not have legislation in place to manage reservoir safety. Detailed structural assessments were not available or readily derivable and while the consequences of dam failure for certain impounding reservoirs (over 10,000 cu m capacity) was estimated, it was not possible to estimate the likelihood of failure of the dams or determine the actual “significance” of the risk from these reservoirs. Given this background it was decided that the risk from reservoirs would be most effectively managed through reservoir safety legislation similar to that in the reminder of the UK and flood risk from reservoirs was not used in the determination of SFRAs.

Subsequently, The Reservoirs Act (Northern Ireland) was introduced in 2015 which makes provision about the regulation of the management, construction and alteration of certain reservoirs, in particular in relation to their safety to collect and store water; and for connected purposes.