COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF LUCAN/PALMERSTOWN/FONTHILL AREA COMMITTEE

Tuesday, January 28, 2020

QUESTION NO. 24

QUESTION: Councillor G. O'Connell

To ask the Chief Executive for a report on areas of the LAC that are (“officially” and/or by Insurance Companies) described as “areas in Danger of Flooding” and to include in his report the basis for such a description, what actions this Council had taken over the past 20 years to alleviate or eliminate such risks, with what success and what support can be given to residents who have been refused a quote by an Insurance Company “because they are located on a flood risk”

REPLY:

Flood risk areas have been identified by the OPW Catchment Flood Risk Assessment and Management (CFRAM) Programme using weather data, hydraulic modelling and topographic modelling. The purpose of these studies is to identify areas that are at risk of flooding in order to support planning decisions, emergency response, and flood scheme design. The detail of this work and the mapping is available at https://www.floodinfo.ie/ There is a scheme proposed for the area for the liffey from Lucan to Chapolizod and we will work with the OPW when funding is approved for this.

Flood risk is typically described in terms of  Annual Exceedance Probability (AEP) which refers to the probability of a flood event occurring in any year. The probability is expressed as a percentage. For example, a large flood which may be calculated to have a 1% chance to occur in any one year, is described as 1% AEP. (0.1% and 10% AEP are the other two bands of “risk “or likelihood typically referred to). The November 2000 flood event in Lucan Village had a 1% AEP, or a 1 in 100 year probability.

The last 20 years has seen a major growth in development throughout the Lucan Area, the result of which is a significant increase in surface water runoff into our watercourses; from roads, footpaths, roofs and other hard standing areas. The impact of development has been reduced in recent times with the mandatory implementation of Sustainable Drainage Systems (SuDS) at the design stage of new developments which limit the surface water runoff  to pre development volumes, using various measures including on-site surface water attenuation and flow restriction devices.

The Griffeen River Flood Alleviation Scheme was a major project along the Griffeen Catchment area which was completed in 2004. Works included additional walls, attenuation ponds and increasing the capacity of the river bed. These works were designed to give protection to a 1% AEP event.

Regular monitoring of river levels and debris screens at culverts, particularly following a Met Éireann weather alert, in addition to the routine clearing of vegetation from the banks of waterways in the summer are the primary methods of reducing the risk of fluvial flooding. To mitigate pluvial flooding, road gullies are routinely checked and cleared, especially in the autumn months where fallen leaves could cause a blockage. Severe Weather Assesment Team (SWAT) Team meeting take place ahead of and in responce to severe weather events.

Other recent works carried out or in progress on the Surface Water Network in the Lucan Area include:

Celbridge Road- Culvert restoration- Complete 2018

Ballyowen Lane- Surface water pipeline- Complete 2019

Old Lucan Road- New surface water pipeline for road drainage- 2020 programme

Palmerstown Woods- New surface water pipeline- 2020 programme

SDCC adopted a Flood Emergency Plan in 2018 to assist in the multi-agency response to flood events when they arise. This plan details the responsibilities for each Principal Response Agency (PRA), of which the Local Authority is one of three (the HSE and Gardai are the others).

South Dublin County Council also hosted and participated in a regional Major Emergency exercise last year that consisted of a tabletop exercise simulating a 1 in 1000 year event on the River Liffey catchment caused by a discharge of water from Poulaphouca Reservoir. Many different agencies and other Local Authorities were represented. This was extremely positive for inter-agency communication and highlighted areas where additional planning and resources may be required in the region.