Statement of Professor Philip O'Kane
Updated: Feb 9, 2021
I am advised that http://savecorkcity.org/ should build its case in a manner similar to the Irish Georgian Society: unemotional, disinterested, fact-‐based, multi-‐disciplinary, with individual sections by experts in the relevant areas. This protects all the contributors from attack, especially in areas where they are not expert.
The lynch pin of the OPW design is the belief that the dams on the Lee are good for small floods, but not for big ones. Consequently, high walls will alleviate flooding from both the river and the sea. But the premise is false. The dams are good for big floods, so high walls are not required, their construction a significant waste of public funds. Three sites for hydro-‐power reservoirs were examined by the ESB in the 1950s, at Inniscarra, Carrigadrohid and Dromcara on the Lee; the first two were built. The combined storage at these sites is more than adequate to protect Cork from the once-‐in-‐a-‐hundred-‐year design flood of the OPW, which includes a generous allowance for an adverse change in climate. But OPW does not agree. Why? The OPW and its consultants developed a forecasting and control system for the two existing dams that mimic the ESB's "Lee Regulations". Unfortunately, OPW addressed only one of two possible questions. Instead of asking 1. How can the dams best protect the City from floods on the river, while generating hydropower as a secondary activity during the flood?
the OPW asked the question [my words], 2. How can the ESB continue to generate hydropower in accordance with its Lee
Regulations, while providing flood alleviation as a secondary activity?
The answers to these two questions are very different. The OPW's answer to the second question is [my summary]: 2.1 The Lee dams deliver at most a 50%, and on average a 25%, reduction in the flood
peak; consequently high walls are necessary to protect the City from the river.
My answer to the first question is [See audit number 4 for details, referenced at the end of this note]: 1.1 the Lee dams can deliver a 70% reduction in the design-‐flood peak, and
consequently high walls are NOT required to protect Cork from the river. The ESB dams are, de jure, single-‐use dams for hydro-‐power production, which is the reason, I surmise, why the first question was not posed by OPW. But, de facto, the Lee Dams have been multi-‐purpose dams for decades providing water services to Greater Cork: hydro-‐power, flood-‐alleviation, water supply, recreation, and fisheries. The ESB may charge for such services. Consequently, the Electricity (Supply) (Amendment) Act, 1945 should be changed to reflect this reality on the river Lee, and to legitimise the first question and its answer: the Lee dams can protect Cork from the river without high walls on its quays. The money saved by not building the high walls can be used to solve the problem of tidal flooding, to improve the dams, and to pay ESB service charges.
Tidal flooding in the City may be solved with an intermittent tidal barrier at the end of Lough Mahon, with or without a high capacity (250m3/s), low-‐head pump. The uncertainty in sea-‐level rise due to changing climate, up to 0.55m in Cork according to OPW, make a tidal barrier a very flexible solution in the longer term. The Planners in both City and County should imagine and plan the long-‐term future of Lough Mahon incorporating a tidal barrier, creating a body of water with enhanced amenity.
There are many ways to enhance the dams for flood alleviation, in order of increasing cost:
1. A new flood-‐control system, which operates the reservoirs conjunctively, a
significant improvement on the ESB Regulations, where the dams are operated
2. A new hydro-‐meteorological data system; the present system is not fit for
3. A wall of fuse-‐gates [the hydraulic analogue of an ELCB board] replacing the
auxiliary side-‐weir at Carrigadrohid doubling the volume of its flood-‐pool and
restoring its pre-‐1990 value.
4. Improving dam safety at Carrigadrohid. The ESB has said "can't be done for dam
safety reasons" which prompts the question: Is a major safety-‐retro-‐fit required at
Carrigadrohid after 60 years of use, for example, replacing the upstream face of the
dam with a 10m-‐thick frustrum of rolled, compacted, concrete, properly keyed and
founded, delivering more storage capacity?
5. A new dam and reservoir at Dromcara/Allua.
6. A new interceptor aquaduct along the northern side of the N22 picking up streams
such as the Bride and the Curraheen that flow off the southern escarpment of the Lee
valley, and debouching into the Douglas estuary, thereby reducing somewhat the need
for flood storage.
Emeritus Professor UCC. Chair of Civil Engineering (1845). National University of Ireland, Cork. Honorary Fellow UNESCO-‐IHE Institute for Water Education, Delft, NL. Former member of the UNESCO-‐Italian Government Committee for the Safeguard of the Lagoon of Venice.
Four technical audits underpin this note. They were written over the past year gratis pro bono publico for http://savecorkcity.org/ and sent to the Office of the Comptroller and Auditor General, the Chairman of the OPW, the Chief Civil Engineer of the ESB, and the Cork City Architect, with an invitation to discuss anything arising from them under the Chatham House Rule. An email to firstname.lastname@example.org will deliver audit number four.