COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

south dublin county council crest

MEETING OF SOUTH DUBLIN COUNTY COUNCIL

Monday, December 14, 2009

MOTION NO. 16

MOTION: Councillor S. Crowe

This Council calls on the manager in view of the widespread flooding throughout the State,the poor planning, the lack of flood warning,preparedness and overall preventative systems,  to immediately carry out with staff and other agencies where nescessary, a review of structures, the training of personnel,  the ability of this local Authority to respond to emergency situations, and including in that review the present and real and possible dangers of rivers bursting their banks , the condition of water storage facilities and other areas of large volumes of water, and agrees to draw up  plans, possible scenarios and  preventative measures for this county in light of the present crisis and the clear dangers facing many families now and in the near future.

REPORT:

In spite of the heavy and consistent recent rainfall there were no flooding events located in South Dublin.  The Council engages with other agencies, uses its emergency plan, has in place strong attenuation measures and a proactive maintenace programme which mitigate against such events in the counties and enable good precautionary event planning to be in place.

The Liffey Catchment

Two meetings of the LIFFEY Catchment Flood Risk Assessment and Management (CFRAM) Study Steering Group have been held to date.

The main stakeholders attending the steering group meeting include officials from South Dublin County Council, Fingal County Council, Kildare County Council, Wicklow County Council, Dublin City Council, Office of Public Works and ESB. The OPW are currently carrying out cross sectional surveys of the Liffey and its tributaries.

Summary of Regional Liffey Flood Event of 29/11/09

Most of the Liffey River is controlled by the ESB through its dams at Pollaphuca and Leixlip with the quantity of water per second released through the tailraces regulated by the ESB. The ESB works very closely with Met Eireann and releases extra water in advance of heavy rainfall being forecast so that they have additional storage space at the dams to impound this water and they then release this water after the event thus avoiding property and land downstream of the dams being flooded. There is height storage capacity in the Blessington Lakes and to lesser extent at Leixlip. The ESB also works very closely with Dublin City Council (DCC) as part of the Liffey at its estuary is tidal. DCC had an innovative tidal surge early warning system installed some years ago as part of the Dublin Flood Initiative which was funded by DCC/OPW/EU Interreg. This sophisticated tide surge forecasting is accurate to + or -50mm.

Over the weekend, 21st/22nd November 2009, during the high of the rainfall contolled releases of 70 tonnes per second in pulsed 7 hour bursts were released from Leixlip dam to tie in to the tides in Dublin Bay. Over the weekend, 29th of November 2009, these releases had to be increased to 116 tonnes a second resulting in some flooding of the Strawberry Beds Road near Lucan in the Fingal County Council’s area but no flooding in Lucan Village.

A greater risk of flooding from the Liffey river in Lucan comes from the unregulated Rye Water Stream flowing through Leixlip Village downstream of the dam into the Liffey. During heavy rainfall it is possible to have a greater volume of water coming down the Rye Water than through the regulated dam on the Liffey at Leixlip. It is planned that the OPW will put weirs and gauges on the Rye Water shortly and this information can be relayed back to the ESB so that the Liffey flows can be regulated even more closely.

Since the flooding of Lucan Village and some of its suburbs, Old Forge and Grange Manor Estates, on the 5th and 6th of November 2000 by the Griffeen Stream major flood alleviation works were undertaken by SDCC in Lucan Village and through Griffeen Valley Park right up to the Grand Canal including widening and deepening the river channel, installing new culvert and bridges and lowering weirs and raising walls. This work was completed in 2004 and since then there has been no flooding in the Lucan area from the Griffeen Stream.

All Local Authorities along the Liffey, Kildare, SDCC, Fingal and Dublin City Council plus the Office of PublicWorks (OPW) work closely with the ESB with regard to regulating the flows in the Liffey and if there was a problem which required the deliberate discharge of additional water from either Pollaphuca or Leixlip dams the Local Authorities would be informed in advance so that Public Representatives, residents and businesses could be warned and advised as to the best course of action to undertake and what assistance was available and where. Sandbags would also be issued to potential vulnerable areas.  

During the high rainfall event of 29/11/09, which impacted on the whole of the Liffey Catchment, communication was ongoing throughout the day between South Dublin County Council’s flood management team and the other Liffey CFRAMS stakeholders. The steering group will use the experience gained from this event to inform the ongoing Liffey Study.

Lucan has been identified as an Area of Potential Significant Risk (ASPR) for additional focus. Nearest other ASPRs are Leixlip in Kildare and Chapelizod in Dublin City. Dublin City Council are proposing a new weir at Lucan for flow measurement. The Camac, Poddle and Griffeen are part of this overall study.

The Dodder Catchment

In late 2005/early 2006 the three local authorities in whose functional areas the river Dodder flows i.e. South Dublin County Council (SDCC), Dun Laoghaire Rathdown County Council(DLRCC) and Dublin City Council (DCC) agreed that a study of the river would be commissioned in order to provide a comprehensive report on the Flood Risk Assessment and Management of the river. The Office of Public Works (OPW) is funding the study as it forms part of the national Catchment Flood Risk Assessment and Management Studies (CFRAMS). Dublin City Council is the Contracting Authority on behalf of the three local authorities.  Following the public tendering procedure in early 2006 Dublin City Council appointed consultants/service providers, R.P.S., to carry out the Risk Assessment and Management Report. The major stakeholders, DCC, OPW, SDCC, DLRCC and RPS meet at Steering Group level every three months to review the progress of the contract.  The final plan will require the agreement of all three Councils and the OPW.

The core purpose of this study was to assess the spatial extent and degree of flood hazard and risk within the Dodder catchment, to examine future pressures that could impact on that risk, and to develop a long-term strategy for managing the risk that is economically, socially and environmentally sustainable.

The Report will include measures for the development of a robust model representing the hydrological and hydraulic characteristics of the River Dodder catchment, such a model will provide for the mapping of the flood risk.  Using model output the technical and economic merit of various options for flood management, taking account of current and future land developments, will be presented within the report.

To achieve this aim the following study objectives have been identified:

The main tributaries of the Dodder River are included in the above Risk Assessment and Management Report viz. the Whitechurch, Owendoher and the Tallaght streams.

In June 2008, the consultants issued a strategic environmental assessment (SEA) scoping report on the River Dodder Catchment Flood Risk Management Plan.  This Report is available to download on the Dublin City Council website: www.dublincity.ie/waterwasteenvironment/pages/riverdoddercatchmentfloodriskassessmentmanagementstudy.aspx  Comments can be sent to the above website or doddersea@rpsgroup.com

The final SEA statement will:

Further plans for the Dodder River Risk Assessment and Management Strategy include public information days on the flood risk management, a draft CFRAMS and Environmental Report consultation and a final Strategic Environmental Assessment (SEA) statement.

R.P.S., were also asked to produce an interim modelling report on the Whitechurch River, a tributary of the Dodder, as a result of serious flooding experienced  in the catchment on 22 June 2007. The  Whitechurch River Interim Modelling Report issued from R.P.S. in July, 2008 with recommendations on reducing the flood risks along the Whitechurch River. Following the publication of the report, South Dublin County Council in conjunction with Whitechurch National School completed an emergency culvert upgrade on the Whitechurch Stream at the entrance to the school to prevent further flooding and property damage in the area. The cost of these work was approx. €150,000.

Floods Directive

Directive 2007/60/EC on the assessment and management of flood risks entered into force on 26 November 2007. This Directive now requires Member States to assess if all water courses and coast lines are at risk from flooding, to map the flood extent and assets and humans at risk in these areas and to take adequate and coordinated measures to reduce this flood risk.  This Directive also reinforces the rights of the public to access this information and to have a say in the planning process.

The Directive was proposed by the European Commission on 18/01/2006, and was finally published in the Official Journal on 6 November 2007. Its aim is to reduce and manage the risks that floods pose to human health, the environment, cultural heritage and economic activity. The Directive requires Member States to first carry out a preliminary assessment by 2011 to identify the river basins and associated coastal areas at risk of flooding. For such zones they would then need to draw up flood risk maps by 2013 and establish flood risk management plans focused on prevention, protection and preparedness by 2015. The Directive applies to inland waters as well as all coastal waters across the whole territory of the EU.

The Directive is carried out in coordination with the Water Framework Directive, notably by flood risk management plans and river basin management plans being coordinated, and through coordination of the public participation procedures in the preparation of these plans. All assessments, maps and plans prepared shall be made available to the public.

Member States shall furthermore coordinate their flood risk management practices in shared river basins, including with third counties, and shall in solidarity not undertake measures that would increase the flood risk in neighbouring countries. Member States shall take into consideration long term developments, including climate change, as well as sustainable land use practices in the flood risk management cycle addressed in this Directive.”

Draft Planning System and Flood Risk Management Guidelines

The Ministers published new Draft Planning System and Flood Risk Management Guidelines for Public Consultation in September which are aimed at ensuring a more consistent, rigorous and systematic approach to fully incorporate flood risk assessment and management into the planning system.

The implementation and coordination of WFD policies and Flood Risk policies is ongoing

In relation to more recent events The recent flood events of 29/11/09 and how it impacted on South Dublin was different from normal flooding events. This needs to be understood in the context of the management of the River Liffey.

Heavy rain started to fall on the Liffey Catchment at approximately 8pm on 28/11/09 and continued until 2pm on 29/11/09. The vast majority of this rain fell on the upper and middle Liffey catchment. From approximately midday on 29/11/09 the ESB, through the media started issuing flood alert warnings about the Liffey Catchment, especially through County Kildare. The ESB also contacted officials in South Dublin, Kildare, Fingal and Dublin City at this time to get an understanding of what was happening on the ground. This allowed the ESB to make informed decisions about water releases from the three dams on the catchment. Based on feedback on river levels and monitoring of reservoir levels the ESB ceased releasing water from Poulaphouca and Golden Falls to ensure they did not contribute to already the already rapidly rising Liffey. The middle Liffey through Kildare rose steadily causing flooding but based on discussions with Kildare County Council and the ESB, South Dublin flood management team was able to assess the river at Lucan and make informed decisions. Flooding did not happen simultaneously along the Liffey and Kildare County Council were reporting to South Dublin on locations where water levels had peaked throughout the evening of 29/11/09. The surge was visible moving through Kildare and thus the ESB and South Dublin, Fingal and Dublin City Council could assess and plan for potential river rises.

Due to the amount of water in the Liffey the discharge from the dam in Leixlip was increased steadily throughout the evening. The discharge went steadily from 80 tonnes / per second to 97 to 103 to 106 to 113 to a maximum of 116 tonnes per second. Officials could see what impact this was having through Lucan and inform Dublin City accordingly. Even though rain ceased at approximately 2pm on 29/11/09, peak flow did not arrive in Lucan until 10.30pm that night. At that stage increase discharge could be balanced with a reduction in tributary inflows thus Lucan only experienced road flooding along Strawberry Beds in Fingal. This was relayed to Dublin City and they were in a position to stand down their flood management team at 11pm approximately.

It should be noted that NO flooding occurred as a result of the Liffey in South Dublin

Examples of rainfall rates

Casement Rainfall rate
29/11/09 30.9 mm
28/11/09 4.7 mm
19/11/09 19.2 mm
18/11/09 14.8 mm
4/5 Nov 2000 84 mm
Hurricane Charlie 89.2 mm
   

The return period rainfall for a 12, 24 and 48 hour period are

Duration 2yrs 5yrs 10yrs 20yrs 30yrs 50yrs 75yrs
12hrs 28 35.3 40.3 45.6 48.9 53.3 57.1
24hrs 36.9 45.4 51.2 57.2 61 65.9 70.1
48hrs 45.3 54.7 61.0 676.5 71.5 76.5 81.1

The flood event of 29/11/09 is an example of where rainfall falling some distance from a location can at a later time cause flooding downstream and this is how the Liffey flooding on 29/11/09 occurred through Lucan. This was be managed by way of communication between the ESB and the stakeholder Local Authorities.

(b) The other risk of flooding in South Dublin occurs where heavy rainfall falls directly on a catchment and the flooding happens very quickly through the river and stream or through the drainage systems. This is more difficult to manage.

With regard to future planning – both the Liffey and Dodder studies will produce flood mapping which in turn will become part of the County Development Plan. The GDSDS and the Greater Dublin Regional Drainage Code of practice has recommendations with regard to development buffer distances from rivers and streams.

Severe weather alerts are received by the Council in advance of severe weather, due to the localized nature of some downpours  - a warning does not mean flooding will occur and also a lack of warning does not mean flooding will not occur. The weather alert allows crews to be informed that there is a possibility that an emergency response may be required.

It is impossible to eliminate flooding as there are many variables that cause it.  Pipes / Culverts sized appropriately a decade ago may not be capable of dealing with higher flows being experienced today as a result of more and longer high rainfall events, rainfall events occurring over a longer period with heavy saturation of existing areas also increases the possibility.   Bridges and culverts can be subject to blockages with debris from time to time. Experience has shown that even garden furniture or building material on the banks of a stream can be collected and cause blockages during rises in stream levels.  The drainage crews do carry out a daily screen cleaning rota and the frequency of this is increased during bad weather. SDCC has a programme in place that best manages the risk of flooding and can provide advice with regard to flood prevention and emergency services where flood has occurred.

Bridges in South Dublin are divided into 2 categories, those on National Primary/ National Secondary routes and those on Non National Routes.

There are 62 bridges on NP/NS routes and the NRA is responsible for their maintenance. However SDCC get a yearly allocation to carry out a routine inspection on the bridges and to carry out routine works on them.

‘Principal inspections’ are carried out by NRA itself and any major works needed are carried out by the NRA.

The Non National bridges are maintained by SDCC.

In 2009, SDCC commissioned Roughan O’ Donovan structural engineers

to survey all the Non National road bridges and set up a data base.

89 bridges in total were surveyed and their condition was rated from 0 to 5 (0 being new and 5 being critical.) and in the process rated each of the following components of each bridge.

·        Bridge surface

·        Footway/Median

·        Parapet/Safety Barrier

·        Wing walls/Spandrel walls/Retaining walls.

·        Abutments

·        Deck

·        Riverbed

·        Structure in general

SDCC has no Level 5 rated bridge, one Level 4 rated bridge (which is closed), and four bridges rated at Level 3.

Roads Dept. have carried out a visual inspection on these four Level 3 rated bridges in the last week and have also inspected Lucan, Firhouse, Oldbawn and Rathfarnham Bridges.

Early in 2010, SDCC intends to employ a structural engineer to carry out a ‘Principal inspection’ on all the bridges rated Level 3 and upwards to assess what if any remedial action is needed. As part of the assessment, all bridges carrying a high volume of traffic over large flows of water will be inspected including Lucan, Firhouse, Oldbawn and Rathfarnham Bridges.