Expert Consultancy – Flood Risk Assessments

Flooding is a natural process. It occurs when a combination of events, including overflow of riverbanks, coastal storms, and deluges on inadequate drainage systems. A flood presents a risk when the potential to damage people, property or the environment arises. Due to the growing consequences of climate change, the frequency and severity of flooding have increased dramatically. We have witnessed the effects of flooding globally with the recent devastating flash floods in Belgium and Western Germany in July 2021, New York in September 2021, Australia in February 2022, and almost on a scheduled annual basis across Ireland and the UK over the last decade.

On a European level, the EU Floods Directive 2007/60/EC was introduced in October 2007, requiring member states to identify all areas that pose a significant flood risk and prepare flood hazard and flood risk maps and flood risk management plans (FRMPs). AS AMENDED, the EU Floods Directive is transposed into Irish law by SI No. 122 of 2010 – European Communities (Assessment and Management of Flood Risk) regulations 2010. The Office of Public Works (OPW) are the lead agency in Ireland in meeting the objectives set out by the Flood Directive 2007/60/EC, along with the Environmental Protection Agency (EPA), local authorities and other relevant stakeholders.

The impacts of flooding can be reduced by preparing in advance and implementing flood management into the initial stages of a development. In 2009, under section 28 of the Planning Act, the (then) Department of Environment, Heritage and Local Government produced “The Guidelines on the Planning System and Flood Risk Management“. These Guidelines set out a transparent and robust framework for the consideration of flood risk in planning and development management. In Ireland, it is now a common requirement for planning authorities to request a site-specific flood risk assessment before being permitted onto the next stage of the planning process. There are three stages of flood risk assessment required depending on the Flood Zone a development falls within; these stages are discussed in more detail below.

Flooded River Boyne – County Meath, Ireland

Flood Risk Assessment 

Flood risk assessments (FRAs) are now a design and planning consideration for Ireland’s small- and large-scale developments. A sequential approach should be adopted when carrying out FRAs to limit or avoid development in areas with potential flood risk.

Flood planning policy is set out in “The Planning System and Flood Risk Management – Guidelines for Planning Authorities 2009”. The policy aims to incorporate flood risk identification, assessment and management into the planning process, thus avoiding unsuitable development in flood zones.

Flood zones and flood compatibility are used to describe the flood vulnerability of a development. The vulnerability of a site increases once the compatibility decreases (i.e., residential developments for instance, would possess higher levels of risk than a water-compatible development and therefore may not receive planning permission unless flood mitigation measures can be provided). There are 3 Flood Zones used within an FRA. These are Flood Zones A, B or C, with A being the highest risk and C the lowest. A justification test needs to be passed on developments with low flood compatibility in areas with a high probability of flooding.

The predicted impacts of flooding were initially illustrated in Preliminary Flood Risk Assessment (PFRA) maps, but these maps are beginning to be phased out for the more accurate Catchment Flood Risk Assessment and Management (CFRAM) maps. Three hundred locations across Ireland were selected for Catchment Flood Risk Assessment and Management (CFRAM) studies, and detailed flood maps have been developed for these locations. Flood risk assessments (FRA) can vary in complexity and scale depending on the Flood Zone a development is determined to fall within and are divided into three stages.

Stage 1 – Flood Risk Identification 

To identify whether there may be any flooding or surface water management issues related to the site and to give an early assessment to base further recommendations.

Stage 2 – Initial Flood Risk Assessment 

A Phase 2 assessment expands on the stage 1 assessment and includes:

• Appraisal of existing flood risk information.
• Qualitative review of flood risk posed to the site.
• Examination of the potential impacts the development will have on flooding elsewhere.
• Production of a Flood Risk Assessment Report including possible flood risk mitigation measures which would reduce flood risk to acceptable levels.

Stage 3 – Detailed Flood Risk Assessment

A Level 3 assessment is a quantitative assessment of potential flood events. It is undertaken if the previous stages determine the need for quantitative analysis to assess flood risk issues relating to the development site and may include:

• Topographic survey of the river channel and surrounding ground levels/floodplains.
• Hydrological assessment of the subject catchment.
• Hydraulic calculations and modelling to quantify the flood risk to the site.
• Assessment of flood risk upstream and downstream.
• Review of existing and proposed surface water drainage.
• Recommend appropriate flood risk mitigation measures.

ORS environmental consultants provide specialist flood risk assessments, site surveys and flood modelling. If you require a design phase FRA or need to respond to a ‘Further Information’ request from a planning authority, speak to a member of our team today. For further resources on the benefits of incorporating Flood Risk Assessments into your building process, click here.