OPW Response to Press Queries on Cork City Flood Relief Scheme
2 February 17
Recent newspaper articles on the Office of Public Works' proposals for the Lower Lee flood relief scheme, which is currently at Public Exhibition stage, appear to have been prompted by a campaign being given voice on Facebook and Twitter on accounts called savecorkcity. This campaign is appealing to the public to use the Exhibition process to persuade the OPW to change its mind on certain aspects of the proposals for the flood relief scheme. The OPW welcomes all comments on its proposals as part of the Public Exhibition, which is the final stage of a comprehensive consultative process that included a public awareness event at the inception of the project, a public information day at the stage where an emerging preferred option was identified, briefings for elected representatives and business groups in the city and consultation with a wide range of stakeholders including a large number of personal consultations by members of the Project Team with those who might be affected directly by the project.
The main issue being raised in the savecorkcity campaign is the construction of flood defence walls on the quays in the city and a concern that this will damage the existing historic fabric of the quays, remove vegetation and remove the existing diversity of frontage to the river. As an alternative to flood walls it is being suggested that storage achieved by upstream diversion of open drainage and the utilisation of woodland and wetland buffers or linear parks could reduce the flows sufficiently to avoid the necessity for flood walls on the quays. As an alternative defence to tidal flooding a barrage downstream in Cork harbour is suggested as is a greater use of glass walls. It is also being suggested that there was insufficient study of these and other alternatives and that there was insufficient input from disciplines other than engineering. It is also suggested that there was insufficient consultation on the matter.
The OPW welcomes the opportunity to respond to these comments.
Firstly, in relation to the suggestion of a tidal barrage, it is acknowledged that a barrage downstream could effectively defend against the tidal flooding of Cork. However, at an estimated cost of at least €400 million this proposal is not economically feasible as the cost is far in excess of the value of benefits derived from avoidance of flood damages in Cork city. The proposal would almost certainly have an effect on the Cork Harbour SPA and associated SAC and so would have to overcome considerable environmental hurdles, a factor that would at the very least add further delay to the delivery of the project and, because there is an alternative available, would most likely rule the barrage proposal out entirely. Furthermore, the proposed barrage would not deal at all with the fluvial problems that arise to the West of the city and in the South Channel so further costs would be incurred to alleviate these problems. In view of the above this option was not progressed.
Use of concrete walls and glass walls
The defence wall along the quays when viewed from the land side in the city centre would not exceed 1200 mm, the recommended guarding height for a location of this nature. savecorkcity has focused attention on a location, Grenville Place, where some reclamation and regrading of the land on the dry side is required to achieve the 1200 mm. It is acknowledged that the photomontage view of the proposed post works situation may give the impression that the wall will be very high in this location. This is not the case however, and the wall height will be consistent with other walls in the city and will not dramatically change a pedestrian's view of the river.
The OPW is working in very close collaboration with Cork City Council on the development of the proposals for the flood defence scheme and the Council is a member of the Project Steering Group. The proposed finishes on all of the walls and railings are as suggested by Cork City Council and agreed by the OPW. Cork City Council drew on the services of the City Architect, the Heritage, Parks and Roads Sections in arriving at its position which is that any old stone walls that are being replaced or strengthened will be finished in stone to match the existing situation. Where a new wall is to be erected it will be constructed in fair faced or textured finished concrete, a finish that had already been used a number of years ago in the vicinity of Christy Ring Bridge. The City Council also provided details of the railings to be erected which, with minor modifications, were accepted. There will be five different wall types in use and it is the OPW's and the Council's view that they will not cut the city off from the river and indeed it was very much to the fore of the Design Team to ensure that this did not happen.
The proposed works on the quays will ensure the future stability of the quays, many of which are in a parlous condition. The strengthening of the quays which is to facilitate the installation of the defence walls will ensure the quays are preserved.
There are some short stretches of glass walls where it was deemed for a number of different reasons that other options were not suitable. savecorkcity is suggesting a wider use of glass walls and that cost was the driving factor not to use more of them. Cost is certainly an important factor in considering the use of glass walls. A concrete wall is estimated to cost about €950 per metre and a glass wall is estimated to cost about €2,000 per metre. Cost is not the only consideration however. Glass walls require considerably more maintenance and become shabby looking in a short time if neglected. Though robust, there have been instances where they have been damaged. Where glass walls are expected to defend to their full height they require quite large supports that can be somewhat unsightly even on relatively short stretches.
Embankments at Fitzgerald's Park and use of Green areas for natural storage
A large number of options were considered for defences at Fitzgerald Park and the proposals as exhibited were given very careful consideration. A landscape architect was commissioned to identify the best footprint for the embankment.
The volumes of water to be stored to attenuate the fluvial flood to the point where it will not cause damage to the city are enormous and are not as outlined by savecorkcity. The published technical academic papers that describe the benefits of such “soft or green engineering” proposals acknowledge that little if any benefit is conferred in larger floods - the very floods that cause property damage. No appreciable storage would accrue from the proposal to plant a park/garden along the quays. To illustrate this point, the scheme will have the effect of reducing the peak flood flows through the city in the 100 year flood event by 340 tons per second to 550 tons per second approximately. This is a very significant reduction in flood flows but nevertheless the volume of water still to be conveyed would result in considerable damage in the city without the flood defence walls as proposed. It would not be possible to mitigate the impact of this volume of water through the use of green areas for natural storage as suggested.
The full scheme has a project budget of €140m including construction costs, fees, land acquisition/compensation, construction site supervision, site investigations and future maintenance costs with the cost of the City Quays elements of the project estimated at €48m. approximately. The majority of this will be spent on Quay wall remediation, new parapet walls (including railing and glass) and new Quay walls where required. About 10% of the cost will be spent on road and footpath works while a similar amount will be spent on pumping stations with about €1m to be spent on Bridge works.
The first phase of the Scheme is being advanced by Cork City Council as part of a public realm project for Morrison’s Island. The Council will be submitting the proposals through planning in the coming weeks and, subject to planning approval, expect to appoint a contractor in the second half of the year. The detailed design of the rest of the Scheme will be advanced, following consideration of all submissions made during the Exhibition process, and is expected to be submitted to the Minister for Public Expenditure and Reform for formal approval under the Arterial Drainage Acts before the end of 2017. At the same time, a tender process for a civil works contractor for the next phase of the Scheme will be undertaken with works scheduled to commence in the first half of 2018. The Scheme will most likely be undertaken in six separate phases in order to minimise disruption to the City, with construction likely to take 6-7 years.
The OPW is committed to working closely with all relevant stakeholders in progressing the much needed flood defence scheme for Cork city. The overriding objective for all concerned is to construct a scheme that will protect the businesses and other property owners from the 1 in 100 year fluvial flood event and the 1 in 200 year tidal flood event. The OPW and Cork City Council are fully cognisant, however, of the need to ensure that the design of the scheme is sympathetic to the cultural and heritage aspects of the city and does not fundamentally alter the relationship of the river to the city and its inhabitants and visitors.