Environment and Engineering Department
Block 1, Floor 6, Civic Offices
Christchurch, Dublin 8
An Roinn Comhshaoil agus Innealtóireachta
Bloc 1,Urlár 6 Oifigí na Cathrach
Teampall Chríost, Baile Átha Cliath 8
Progress Report to the North Central Area Committee on the Extreme Pluvial Flooding Event that Occurred on 24th October 2011
The flooding that occurred on the 24th October 2011 was the result of an extreme rainfall event that exceeded the carrying capacity of existing river and drainage systems within Dublin City.
The City Council received over 1300 reports of flooding on roads and properties throughout the City. Investigations by the Drainage Department to determine the full extent of the effects of the flooding and to identify suitable remedial measures are ongoing. The length of time required to complete the investigations will be considerable due to the limited resources, both financial and staffing, that are currently available to the Department.
The following reports which address the nature of the event and the manner in which resources were deployed to handle the emergency have already been presented to the City Council and the Environment & Engineering Strategic Policy Committee.
· Report No. 338/2011 considered by the Council at the Monthly Meeting held on 7th November 2011 on Dublin City Flood Risk and interim report on extreme pluvial flooding event affecting East Coast and Dublin City on 24th November 2011.
· Progress Report on Extreme Event Pluvial Flooding 24th October 2011 considered by the Environment & Engineering Strategic Policy Committee at a meeting on 16th December 2011.
· Progress Report on Extreme Event Pluvial Flooding 24th October 2011 (Incorporating the report from Jacobs titled Interim Review and Recommendations following the Dublin flood event of 24th October 2011) considered by the Environment & Engineering Strategic Policy Committee at a meeting on 15th January 2012.
The purpose of this report is to brief the Area Committee on the specific drainage issues that have arisen in the North Central Area as a result of the rainfall event of 24th October.
Flooding in the North Central Area
Main Flooding Locations
The City Council has received reports of flooding at 112 locations in the North Central Area. The list of these locations is provided in Appendix 1 of the report. These locations were compiled from a number of sources but primarily by complaints from the affected householders, through the Customer Services Centre either on the night itself or subsequently. In addition, flood locations were sourced from the Fire Brigade call out data base for the night. The list of locations is not a definitive list and it should be noted that there may be other locations which were adversely affected by the flood event on the night but have not been, as yet, officially notified to Dublin City Council.
Road Flooding was reported at the following locations:
All Saints Road, Raheny
Ardbeg Road, Artane
Ardlea Road, Artane
Belton Park Avenue
Belton Park Gardens
Carndonagh Park, Donaghmede
Casino Road (Croydon Park end)
Celtic Park Road
Church Avenue/Grace Park Road
Collins Avenue West/Malahide Road Junction
Coolock Village, Main Street
Courtlands, Griffith Avenue
Elm Mount Road
Grace Park Terrace
Grange Park Crescent
Grange Park Rise
Hazelwood Drive, Artane
Kilbarrack Road (Under Bridge)
Marino Mart, Fairview
Maryfield Avenue, Artane
Maypark, Malahide Road
Middle Third, Killester
Mount Prospect Avenue, Clontarf
Newtown Cottages, Malahide Road
Philipsburgh Avenue, Fairview
Saint Aidens Park Avenue
Saint Brendans Avenue, Artane
Saint Davids Wood, Malahide Road
Saint Johns Court, Artane
Saint Lawrence Road, Clontarf
Saint Margarets Avenue
Santry Village (opposite Comet Pub)
Seafield Avenue, Clontarf
Shantalla Road, Beaumont
Slademore Drive, Artane
The Hole in the Wall Road
Victoria Road, Clontarf.
Where road flooding occurred on main roads, significant traffic delays occurred. At the majority of the above locations flooding resulted from surcharged mains. After the amount of rainfall ceased the surface water systems regained capacity, and the flooding quickly subsided.
Property Flooding was reported at the following locations:
Annesley Bridge Road, Fairview
Blackheath Grove/Blackheath Park
Castle Court/Auburn Apartments
Collins Avenue East
Elm Mount Avenue
Grange Park Road
Kincora Road/Kincora Court
Main Street, Raheny
Raheny Village, Howth Road
Swords Road, Santry Village
Saint Kevin’s Soccer Club
Watermill Court Apartments
Proposed Flood Alleviation Measures in the North Central Area
The extreme rainfall event resulted in the carrying capacity of drainage and river systems being exceeded. In particular flooding within the Area emanated from the following rivers:
· The Santry
· The Wad
· The Nanniken
· The Blackbanks Stream
The City Council is progressing a number of flood alleviation measures associated with these within the North Central Area. These measures are listed below.
The Santry River
The OPW has approved an application for a minor works scheme to increase the flood protection of properties along the River Santry in the Raheny area. A brief has been agreed with RPS Consulting Engineers. A topographical survey of the Santry River from 100m downstream of Main Street, Raheny to 200m upstream of Harmonstown Road Bridge is taking place in the week commencing 13/2/2011. The results from this will be incorporated into the upgraded Greater Dublin Strategic Drainage Study (GDSDS) computer model of the Santry river in the following week which will enable various flood alleviation scenarios to be analysed.
The Wad River
A €20m scheme is being developed with the OPW to alleviate flooding related to the Wad. The Clanmoyle portion of this work is due to start construction subject to finance and planning permission.
A meeting was held with residents from 12 different houses in Clanmoyle on 18th November 2011. The residents were generally in agreement with the City Council’s drainage proposal on Clanmoyle Road. It was agreed that the Council will revert back to the residents before the final Part 8 for the scheme is submitted for approval. The City Council purchased No.3 Clanmoyle Road on 5th November 2011. The Flood Defence Unit met with two
representatives from Clontarf Golf club on 25th November 2011. The Golf Club representatives raised a number of items of minor concern. At a subsequent meeting on the 31st January 2012 most of these issues were addressed, however the golf club representatives raised further items which are currently being addressed by the Council and it’s consultants. A drawing of the latest proposal in the golf club is with Irish Rail and a meeting is scheduled for the week commencing 20/2/2012. Further drainage investigations have taken place in the Golf Club and at Castle Court / Auburn where significant flooding occurred on 24th October 2011.
Once agreement with the Golf Club membership and Irish Rail is achieved the City Council will then complete an environmental report and seek planning permission under the Part 8 procedure.
The Naniken River
A CCTV survey of the river Nanniken is currently under way. In addition, some improvement works have been carried out to the Nanniken culvert where it crosses under the railway at Brookwood Rise. These works will increase flood protection to properties at Brookwood Rise and Brookwood Avenue. In order to increase flood protection for the properties at Maryfield Crescent and Ardmore Park a full hydraulic analysis of the culverted river Nanniken will be required. At present the City Council does not have funding to carry out such a study.
The Blackbanks Stream
A CCTV survey of the culverted Blackbanks stream is currently under way. The Drainage Division is at present examining the feasibility of installing additional gullies at No.104/106 Grange Park Road.
The Drainage Network
Flood Resilient City Project (FRCP)
The FRCP currently underway will identify areas that are vulnerable to the threat of pluvial flooding and develop the most appropriate strategies to protect those areas against flooding. A final report will be available by mid 2012.
Gully Management Programme
Dublin City Council radically revised its gully cleaning programme in 2004. A new database was introduced which records the date and location of every single gully cleaning operation. All of the city’s 54,000 gullies are cleaned on average once per annum. Gullies on the main thoroughfares are cleaned more frequently, in some cases once every six to eight weeks. In addition, during adverse weather conditions and in particular on receipt of severe weather forecasts, normal gully cleaning work is suspended and the crews travel to areas which have historically flooded in the past to deal with any visible flooding and also carry out precautionary gully cleaning.
Flood Resilient Communities
The City Council will endeavour to progress alleviation schemes to minimise the adverse effects of flooding within Dublin City. However it is not feasible to afford protection to every location for extreme pluvial events. The City Council’s sandbag policy (Appendix 2) points out that the prime responsibility for the protection of premises at risk of flooding rests with the owners of those properties.
In Scotland a model has been developed by the Scottish Flood Forum that has enabled over 200 Community Flood Groups to plan and prepare for flood events.
Recently the Flood Resilient City Project (FRCP) invited the Scottish Flood Forum to meet with residents in the East Wall area with a view to establishing a Community Resilience Group to deal with floods. This type of model provides individuals and communities with an effective and efficient means of protecting properties from floods by:
- Establishing local area flood watch systems
- Establishing awareness of factors contributing to flood risks.
- Developing local community flood action
- Minimizing the danger of flooding within the local area.
- Assisting at times of flooding and supporting people who have experienced flooding to ensure effective support is available to assist recovery.
- Meeting regularly to ensure that flood preventive methods are being maintained and monitored.
- Monitoring and reporting to the City Council those areas which are at risk of flooding through lack of maintenance or repair.
- Raising the awareness of personal and collective actions to limit the occurrences of flooding.
- Engaging with the City Council and other organisations to reduce the risk of flooding.
- Developing a local community flood awareness training programme
- Promoting flood protection equipment and materials to prevent further flooding to property
- Arranging free surveys of properties and giving specific advice on the most appropriate means of flood protection.
- Providing advice on the type of protection and suitability of products that will minimize the risk of flooding to properties.
- Making recommendations on minor repairs to properties that may prevent entry of water.
- Facilitating substantial reductions in the cost of flood defence products such as flood gates through bulk buying.
The City Council has explored the possibility of establishing Flood Resilience Groups in the recently flooded areas as the most appropriate means of facilitating the protection of homes and businesses from flood events. The FRCP has created a trans-national learning alliance between Dublin City Council and the Scottish Floods Forum (SFF). A workshop between City Council staff and the Director of the SFF was held on Thursday 12th Jan 2012. The purpose of establishing the Alliance is towards developing a Dublin Flood Forum that will encourage and support the establishment of Community Resilience Groups across the Dublin region in areas that are faced with the threat of flooding. This will be advanced through the Area Committees.
Of particular benefit in establishing flood resilience communities in the North Central Area is in combating coastal flooding and the flooding of basements. In the case of the latter a number of the premises that were flooded in the Area were basement properties.
The 2005 Greater Dublin Strategic Drainage Study highlighted a number of issues with regard to basements and the associated flooding risks. Throughout the city many properties have basements with connections to old sewers and culverts. When these sewers become surcharged the flows often enter basements as these basements are built below the surcharge levels. These basements can be protected by backflows from surcharged by the installation of small pumping stations or anti flooding devices.
The City Council has a Basement Policy which advises property owners on all aspects of drainage concerning basements. The policy strongly advises against any basements in new developments as these areas will always be liable to flooding. . The basements in older dwellings in areas like Fairview and Marino are a legacy that will always remain susceptible to flooding. Rooms that may have been once used as storage areas when the buildings were originally constructed have, in many cases, been redeveloped as apartments or other living accommodation.
The Council has produced an advisory leaflet on Basement Flooding (Appendix 3) advising owners of basement properties to install Non-Return Valves or, where possible, a separate drainage system which is then pumped to the public sewer. In both instances the objective is to break the direct connection to the main sewer as in flood conditions the level in the sewer will rise, in many cases to a level above any drain inlets in the particular basement, and the sewer will back-up and flood the basement.
An important measure to reduce flooding within these areas will be the actions taken by property owners themselves, whether in the installation of non-return valves or pumped connections to the main sewer, in many cases it is actions they will undertake themselves that will protect their property from flooding.
Dublin City Council’s Sandbag Policy
The primary role of the City Council during pluvial events is to manage the drainage network in order to minimise the extent of flooding to the general public. The supply and distribution of sandbags would present a considerable impediment to this task. In addition the inevitable increase in telephone requests for sandbags to emergency call centres would seriously interfere with the ability of those centres to cope with major flooding events.
The use of sandbags has become established in the public’s mind as an effective flood protection measure. This is reflected in demands for the City Council to make sandbags available to householders and businesses at risk of flooding.
The Council maintains strategic stocks of sandbags at a small number of locations. These amount to around 9,000 at various locations including Clontarf, Sandymount, Glendhu Park, and the drainage depots at Marrowbone Lane and Bannow Road. The stocks at these sites are maintained for strategic purposes and play a useful role in areas when dealing with flood events which have sufficient advance warning.
General advice to property owners on dealing with floods is provided by the OPW in booklet format and on the website www.flooding.ie. The OPW advice recommends property owners at risk of flooding to have a supply of sandbags close at hand. The advice notes also acknowledge that sandbags can be difficult to deploy during flood events and can also pose health risks if contaminated with sewage.
A major report on of the serious pluvial flooding that occurred in the UK in 2007, known as The Pitt Review, concluded the following with regard to the role of sandbags as a means of protecting individual properties during flood events:
· While it is clear that sandbags have a useful role in certain types of floods when used strategically, their benefits are less clear when they are used by householders to protect individual properties. This weakness is further heightened by their relative inefficiency when compared with alternative dedicated flood defence products that have been developed in recent years, such as floodgates and airbrick covers.
· Extensive evidence of public over-reliance on sandbags which often proved of little value in protecting against flooding.
· Many householders and business owners put time and energy into obtaining and installing sandbags which would have been better spent on other activity such as moving possessions to safety and deploying door boards.
· Sandbags can be effective when it is marginal, as to whether water enters a house or not, but in relation to large volumes of water they are largely ineffective, contrary to public perception.
To supply sandbags to all properties at risk of flood during sudden rainfall events would require a level of resources that is much greater than is currently available to the City Council. Even if such resources were provided the deployment of sandbags in sufficient time to prevent significant flooding of properties, particularly during monster rainfall events would be logistically impossible. During a flood event, invariably the transport network is very busy, which means that DCC crews have great difficulty in reaching certain areas to deploy pumps, close flood gates, or deliver sandbags. If there is little notification that an event will occur, delivering sandbags would not be possible.
The provision of sandbag stores at specific locations around the City that could be accessed locally by residents on foot of flood warnings would require considerable investment by the City Council to manage and maintain. The unpredictable nature of flood warnings which can average 4-5 a year would result in sandbags being deployed more often than required, leading to the unnecessary expense of maintaining the required stock of bags at each location. The transportation and placement of sandbags from local containers would still require a considerable effort by local residents and they would be unlikely to be in position in time to prevent flooding to most properties subject to sudden rainfall events. Furthermore, if sandbags were deployed at certain locations, there is no guarantee that the people who need them will get them. During a flood, panic generally sets in, and those who are not in risk of flood could easily exhaust the supply of bags at the expense of those in need.
Owners of properties that are at risk of flooding are encouraged to keep where possible, their own stock of empty sandbags together with sufficient stocks of sand to fill bags at times of potential flooding. Preferably owners should invest in the provision of suitable proprietary flood gates and covers to protect openings such as doors, windows and vents. Dublin City Council does not have financial provision in the 2012 budget for purchase of any additional sandbags.