A new national flood policy has redefined the approach to flood risk management in Ireland, promoting a pro-active and catchment-based approach to the assessment and management of national flood risk, says COLIN BRAY.
For decades, flood management in Ireland focused primarily on drainage and rural embankment schemes for the purpose of land improvement for agricultural production. In 1945, the Arterial Drainage Act empowered the Office of Public Works (OPW) to undertake catchment-wide drainage schemes. Following increasing urbanisation and a series of significant urban flood events in the early 1990s, the 1945 Act was amended in 1995 to empower the OPW to undertake localised flood relief schemes, primarily in urbanised areas.
New flood risk management policy
Major flooding in 2000 and 2002, along with changing international perspectives on living and dealing with floods, led to a complete review of the Irish national flood policy. This review, carried out by an interdepartmental group, included an assessment of the flood issues in Ireland, the roles and responsibilities of relevant bodies, and an approach for the future. The review led to the publication of the Report of the Flood Policy Review Group (OPW, 2004). In September 2004, the Irish Government adopted the report, its recommendations and policies.
This new Irish flood policy has the aim of minimising the national level of flood risk to people, businesses, infrastructure and the environment, through the identification and management of existing and potential future flood risks, in an integrated, proactive and catchment-based manner.
Under the new policy, the OPW was assigned the role of the national lead agency for flood risk management, and in 2005 developed an outline implementation plan for the policy. This plan set out a co-ordinated management structure involving relevant Government departments, national agencies and other key stakeholders, and a number of thematic work programmes focusing on the development and/or enhancement of:
- the national strategic information base;
- capacity and implementation of non-structural flood risk management measures; and,
- process and programme management and delivery.
Flood hazard mapping
In October 2006, the Minister of State at the Department of Finance with special responsibility for the OPW officially launched the flood hazard mapping website – www.floodmaps.ie.
The OPW commenced work on the National Flood Hazard Mapping Programme in 2003, collecting and developing a comprehensive database of historic flood information for Ireland. www.floodmaps.ie contains information on over 5,000 historic flood events, and a large amount of spatial/polygon data, as well as supplementary datasets from the OPW, Environmental Protection Agency and other Government bodies. Over 3,000 flood-related documents (reports, maps, photographs and videos) were collected, reviewed, validated and quality controlled in order to ensure the correctness of the flood event information presented. Flood event information was collected and collated from a wide range of organisations, including local authorities and national organisations.
The available maps and data provide information that is useful for purposes of land-use zoning, development control, planning of infrastructure, identification of properties at risk, and raising the general awareness of flood risk among the public.
Predictive flood mapping (mapping indicating the estimated area of inundation for flood events of given frequencies) will also be made available to the public through this website once they have been developed through the catchment flood risk assessment and management (CFRAM) studies.
Catchment flood risk assessment and management studies
Central to the implementation of the new flood policy in Ireland is the pro-active and catchment-based assessment and management of flood risk. CFRAM studies have been developed to meet this objective. These comprehensive studies, undertaken at a catchment level, identify and map existing and potential future flood risk areas through detailed hydrological/hydraulic modelling and flood mapping. This flood risk assessment accounts for the likely impacts of land use change, urban development and climate change on flood risk.
The studies will deliver predictive flood maps of catchments, indicating areas that are likely to be flooded for flood events of a range of magnitudes/frequencies. These maps will then be made available through www.floodmaps.ie.
Once the flood risk has been mapped throughout the catchment (with particular focus on developed areas, or areas under potential development pressure), catchment flood risk management plans (CFRMPs) will be developed, which will include a prioritised strategic programme of future actions, measures and works to manage the flood risk in the catchment.
What needs to be surveyed?
A key component of the CFRAM studies is the development of the strategic information base necessary for making informed decisions in relation to managing flood risk. This includes detailed information about the catchment, its hydrology, the river system, flood defence assets and flood risk receptors. The following are some of the data required for creating these databases and models:
- macro-scale digital terrain data;
- channel and structure cross-section data;
- high-resolution digital elevation and terrain models; and,
European Directive and OPW programme
The national flood risk management programme led by the OPW is in line with the programme as defined in the European Directive “on the Assessment & Management of Flood Risks” – Directive 2007/60/EC of the European Parliament and The Council of October 23, 2007. The Directive sets out the following programme delivery for the Member States:
- national preliminary flood risk assessments to be completed by December 22, 2011;
- flood hazard maps and flood risk maps to be completed by December 22, 2013; and,
- CFRMPs to be completed and published by December 22, 2015.
The stated purpose of this European Directive is to establish a framework for the assessment and management of flood risks, aiming at the reduction of the adverse consequences for human health, the environment, cultural heritage and economic activity associated with floods in the community.