In thinking about our county, we must think about our coast says Jimmy Murphy
CORK’S coastline forms an intrinsic part of the Wild Atlantic Way and is renowned for its variety and beauty.
From the long sandy beaches in Youghal to the rugged cliffs on Dursey Island, Cork’s 1,118km of coastline is our interface with the ocean and critical for trade, recreation, tourism, fishing and a host of other activities. Our coast is vital for our county.
In terms of its physical classification about 696km is considered to be hard coastline comprising mainly of rocky outcrops while the remaining 422km is soft coastline made up of beaches, dunes, mudflats and soil cliffs.
It is the soft coastlines comprising of relatively small size particles (mainly sand) which can easily be pushed around by waves and currents that are most vulnerable to change.
Such changes that occur along our soft coastline are generally referred to as coastal erosion and accretion. These are respectively the landward recession or the seaward advancement of a designated reference position such as the mean high water line, the vegetation line or the clifftop position.
The movement of the coastline position is a natural phenomenon and can be regarded as necessary to maintain equilibrium at our land/water interface. In an ideal scenario, a coastline should be allowed to evolve as nature dictates but humankind through a desire/necessity to live close to the coast and construct infrastructure (such as roads) next to the coast create an issue in terms of constraining the coastline.
Living on open coastlines poses obvious risks related to higher wind speeds, large wave conditions and elevated water levels during storms that can cause flooding and erosion with consequent property damage.
In addition, with annual mean water level increases of 3.3mm/year attributed to climate change our coastal margin is becoming increasingly squeezed from the landward and the seaward sides.
To combat erosion we must understand nature. When determining the best manner to combat coastal erosion it is critical that there is an understanding of the natural processes that are occurring on the beach.
No two beaches are exactly the same in terms of length, width, profile, orientation, sand size, incident wave conditions and water levels. Such complexity means that it cannot be predicted exactly how a beach will respond to a particular event.
For instance, Storm Ophelia was a major event in 2017 but it did not cause significant coastal erosion or flooding as the peak of the storm did not coincide with the high tides.
Also in 2017, there was great surprise and delight when sand returned to Dooagh beach, in Achill Island, Co Mayo, as it had been sandless for more than 30 years. This delight however, was short-lived as the sand was again pulled offshore by storms in 2019.
Sand may disappear from a beach, particularly during the winter period, but in many cases it is sitting offshore waiting for the right type of conditions to bring it back into the beach again, often during the summer. Unfortunately for Dooagh beach it may be 30 years before sand returns again. To protect against erosion and coastal flooding requires an intervention in terms of a coastal defence solution and in Ireland this normally takes the form of a physical structure placed on the beach.
IN THE past vertical seawalls were common and examples of these can be seen in Garretstown but more recently more flat- sloped revetment using rock or unusual shaped concrete units are used as they have a reduced impact on the beach.
Such a revetment protected by the innovative ECAB units can be seen on Garretstown beach. A different type of approach using rock groynes, extending across the beach was used to protect in The Warren in Rosscarbery as the cause of the erosion merited a different type of solution.
In the US, many beaches disappeared in New Jersey. In many cases when a beach system is constrained by a coastal protection structure the overall impact will be negative as the price of protecting property and roads is the loss of the beach — it often comes to a choice of saving the beach or saving the property.
An important point is that while coastal erosion displaces the beach in a landward direction the beach remains and retains the same overall features. However, with a protection structure in place the beach no longer has material available from the back beach area (dunes/cliffs) so waves remove sand from the beach itself.
This is clearly evident in Lahinch in Co Clare with the rock revetment that protects the town and golf course. This structure fulfils its primarily protective function but does not prevent sand from being taken from the beach.
Falling beach levels means little of no dry beach areas, which decreases the recreational value and ultimately will affect tourism in the town.
In the US, they call this “Newjerseyisation” after many beaches in the state of New Jersey disappeared due to building of coastal protection structures. In Cork, for the most part we have stable beaches such as in Ownahincha, Longstrand and Inchydoney but a few, such as parts of Garretstown and Youghal are showing signs of sediment deficits and a reduction in the dry beach width.
In fact, in the US hard structures such as revetments and groynes are no longer allowed in many states because of potential negative impacts on the beach and coastal protection is provided by nourishing the beach with sand brought in from external sources.
This is called beach nourishment and is now the most common method of coastal protection worldwide but is rarely used in Ireland and it needs to be repeated every three to five years to replenish lost sand. This recurring cost does not fit well with how Irish projects are funded.
Making the correct decisions In MaREI, the SFI Research Centre for Energy, Climate and Marine which is hosted by University College Cork, we have ongoing research that seeks to understand the natural processes that are occurring on beaches.
The primary method of doing this is through continuous monitoring particularly of beach and nearshore bathymetric levels. By tracking sand movement over a period of time and relating it to wave and tidal conditions we can better determine long-term behaviour of a beach.
MaREI is monitoring Longstrand Beach using drones, shallow water survey craft, wave gauges and sand sampling. This type of work is enabling a better quantitative understanding of how beaches behave and with this improved knowledge, we can endeavour to better fit coastal protection.
For instance, we are likely to see more flat-sloped porous revetment structures that can absorb the incident wave energy and thus minimise negative impacts on the beach.
An interesting point on the impacts of climate change on the coastline has been found in an analysis undertaken by MaREI. A scenario for high greenhouse gas emissions, called RCP8.5, indicates wave conditions around the coast will reduce in size and off the Cork coast by up to 7%.
This result is based on numerical modelling and obviously there is associated uncertainty but it does indicate it may not be all bad news for our coastline in the future.
The challenge regarding coastal erosion relates to making the correct decisions in terms of when and how we provide protection.
The coastline is under threat but it is not going to disappear and in particular it is important for the public to be better informed on coastal behaviour as they are now an essential part of the decision-making process.
Jimmy Murphy, funded investigator at MaREI, the SFI Research Centre for Energy, Climate and Marine Innovation