Home relocations or land-use recategorisation could be utilised in future as part of the OPW's plans to improve flood defences. PJ Rudden reports from the UCD EGA Spring Panel Discussion

Flooding was, yet again, a hot topic for the media and a very real problem for many members of the public last winter, so it was very appropriate that the UCD Engineering Graduates Association (EGA) addressed the issue of flood defences at its 2016 Spring Panel Discussion on 21 April. In recent years, this annual event has focused on other timely subjects such as the banking bailout, water, manufacturing jobs, energy, food, engineering education and the digital future.

The 2016 panel discussion, entitled ‘Tackling Ireland’s Flooding Challenge’, was chaired by Dr Amanda Gibney, senior lecturer in the UCD School of Civil, Structural and Environmental Engineering.

‘The Highs and Lows of Ireland’s Weather’ was addressed by first speaker Evelyn Cusack, deputy head of forecasting at Met Éireann, secretary of the Irish Meteorological Society and RTÉ weather presenter.

Cusack confirmed that the weather during the winter of 2015-16 was the “wettest on record”. She also acknowledged that the “quality of weather forecasting has improved enormously since the 1980s”, due mainly to improved satellite models. Regarding climate change, she stated that “the temperature rise is unequivocal’ and that sea levels are getting higher. She predicted that we will have wetter winters from now on, causing more flooding and more storm damage.

The second speaker at the event was Dr Michael Bruen, professor of hydrology in the UCD Dooge Centre for Water Resources Research. He started by telling us that “floods are natural events and we should not be surprised that they will happen”! Their impacts can, however, be mitigated by a combination of “water storage and conveyance”. He added that a delicate balancing act was required, as flood storage or relief in one area can impact adversely on another area upstream or downstream.

Learning from the Dutch experience of flooding

Flood forecasting specialist Dr Jan Verkade of Deltares and Delft University recounted the severe flooding across the Netherlands in 1953. After levee barriers failed in the south of the country, some 136,500 hectares were inundated – claiming over 1,800 lives and causing 200,000 people to be evacuated from their homes.

In total, some 750,000 people were estimated to have been affected. Ten thousand buildings were lost and another 37,300 buildings were damaged. This happened after a high spring tide coincided with a flood surge and there were no warning systems in place.

The impact was catastrophic and required urgent government action, as much of the country is below sea level and even marginal rises impact on additional and extensive land areas. To make matters worse, most of the country’s highly populated areas and centres of principal economic activity (like the Hague and other major cities, together with the Port of Rotherdam) are sited in the areas most vulnerable to flooding.

In fact, even currently, some 30% of the Netherlands is below sea level and areas supporting some 60% of GDP are vulnerable without very robust engineering defences. Coastal flooding from the North Sea can be severe, but equally problematic is potential fluvial flooding from rivers Rhine and Meuse.

So, what was the Dutch Government’s response to these disasters? Economic factors drove a dramatic response to include shortening of the coastline through new barriers, closing off gaps in the coastline. In addition, a “risk-based approach was adopted to flood protection” in accordance with a new national plan – the Delta Plan – and a new company called Delft Hydraulics (since merged into Deltares) was set up to design the flood defences. These barriers were only completed some 50 years later in 2010 and cost tens of billions of euro to construct.

In the 1960s, a new national risk-based strategy was put in place in the Netherlands where the country was divided into different ‘risk zone’ categories and new flood defences were designed to cater for the designated risk. Areas of high economy activity and areas of high population were prioritised and all dykes and levees raised accordingly.

OPW flood defences

The final speaker was Tony Smyth, chief engineer of the Office of Public Works (OPW), the statutory body charged with implementation of the EU Floods Directive. The OPW has also adopted adopted a risk-management approach following a major National Flood Policy Review in 2004. Thus, it has identified some 300 areas that are “potentially at risk”, according to Smyth.

These projects now all form part of the Catchment Flood Risk Assessment & Management (CFRAM) process, which will be completed during 2016 and implemented thereafter. Parts of Dublin city (in Drumcondra on the Tolka and in Ballsbridge on the Dodder), together with Clonmel, Carlow, Fermoy, Ennis and Waterford city, now have formal flood defences and more are planned.

The country has been divided into six major areas based on the principal river catchments (Shannon, Eastern, South Eastern, South Western, Western and North Western). Some 6,500 km of rivers have been surveyed and 40,000 maps produced based on Lidar surveys. The OPW has sought to ensure that all identified flood-protection works are technically feasible, environmentally acceptable and cost effective. Neither has it ruled out home relocations or land-use recategorisation as a future measure, where justified.

A major capital programme of €430m has been identified to be implemented from 2016 to 2021 for flood-alleviation projects to manage the risk (though it cannot eliminate it entirely) in a whole-of-government holistic approach to the challenge. This will also be a major challenge to the engineering profession in terms of efficiency and innovation, though it was noted that all of the engineered flood barriers and defences recently constructed by OPW held well during the unprecedented floods of last winter.

All of the projects are subject to cost-benefit analysis, strategic environmental assessment and public consultation. The CFRAM maps are based on a comprehensive analysis and best available information. The maps are ‘predictive’ and thus the perception of insurance risk and availability will arise.

For further information, contact PJ Rudden, EGA president, on 087 234 9556.

http://www.engineersjournal.ie/wp-content/uploads/2016/05/irelands-flooding-challenge-1024x580.pnghttp://www.engineersjournal.ie/wp-content/uploads/2016/05/irelands-flooding-challenge-300x300.pngDavid O'RiordanCivilflooding,Netherlands,OPW,UCD
Flooding was, yet again, a hot topic for the media and a very real problem for many members of the public last winter, so it was very appropriate that the UCD Engineering Graduates Association (EGA) addressed the issue of flood defences at its 2016 Spring Panel Discussion on 21...