Crumbling Coastal Cliffs

Coastal erosion has been in the news lately (for all the wrong reasons).

  1. Exposing toxic materials:

A site located close to the coastal settlement of Bray, Co. Wicklow has asbestos, rusted metal, plastics and bricks are emerging from a disused landfill.

Recent cliff erosion releases contents of 1980’s landfill (Source: Irish Times 2017)

2. The collapse of homes into the Irish Sea following Storm Emma

The house in Portran had been deemed unsafe by Fingal County Council after Storm Emma hit in March 2018 (Source: RTE news https://www.rte.ie/news/2019/0220/1031821-house-portrane/)

3. Threats to regional infrastructure networks

The steep cliffs adjacent to the bray rail line are subject to landslides.

So what can we do?

In order to develop appropriate coastal management strategies, we need to improve our understanding of the physical response of the coast to current weather and anthropogenic systems. Good management strategies need good data. However, we do not have the appropriate data to make effective management decision. We currently rely on academic studies from too few sites, expert judgement and inferences based on studies undertaken in other jurisdictions.

Rates of coastal erosion:

The predicted rising sea levels and increased storminess poses a significant risk to the soft sediment coastlines. Establishing the response of the coast to is imperative for the effective implementation of long term planning.

The east coastal zone has the highest rates of coastal erosion in Ireland, estimated to be between 0.2-1.6 m/ yr  (Devoy, 2008). In a recent study using a combination of aerial photographs, satellite data and ground truthing of vegetation lines (1952-2017), Caloca-Casado (2018) estimated annual coastal retreat rates 0.65m/yr between Shanganagh and Bray.

These estimates suggests that the hazard of coastal erosion is not new, perhaps exemplified by the history of coastal dwellings at Greystones, Co. Wicklow where coastal erosion caused collapse of houses into the sea.

The aftermath of the 1929 storm at Greystones, Co Wicklow. (Source and historical account at (https://www.greystonesguide.ie/the-north-beach-cottages-a-history/).

Our work:

In 2016 we conducted a baseline aerial survey using a DJI Phantom 3 drone to image a 10 km- long cliff section between Killiney and Greystones. We used Structure from Motion (SfM) to generate Digital elevation models of the cliff (Bourke and Nash, 2016). The aim of the work was to develop baseline data that documented the location, form and rate of retreat of the cliff. Geomorphic processes of erosion and depositional styles are recorded and locations sensitive to higher rates of erosion are identified.  We conducted follow up surveys in 2017 (Bourke and Nash, 2017) and 2018 (Bourke et al., 2018). Two additional surveys were conducted on 6, 200-300 m cliff sections (Bourke and Fay, 2017, Bourke et al., 2018b as part of undergraduate theses (Fay, 2018; Williams, 2019). This approach allowed for comparison of overall cliff retreat rates and specific site detailed responses with centimeter-scale accuracy.

The Study Site:

Map showing the location of the three study sites (Williams, 2019)

The Quaternary Cliffs are composed subglacial tills deposited at the base of an ice sheet on land. There are a number of till units stacked on top of each other. The tills include gravel beds, sand pockets and clay lenses, and are dominated by erratic limestone rocks. Large boulders of Leinster granite are also seen in the section and are strewn across the beach. Small pebbles of a distinctive microgranite from Ailsa Craig in the Firth of Clyde can also be found. The glacial tills overlie slate and mica-schist bedrock of Ordovician age (Gallagher et al., 2014). Within the consolidated muddy till sediment, gravel beds, sand pockets, clay lenses and clastic dykes can be found (Rijsdijk et al., 1999). The cliffs are approximately 16m high and are fronted by a sand and gravel beach.

Shankhill (north) facies (Williams, 2019)

Along the 3 km stretch of coast at Shanganagh provided a heterogeneous stretch of cliff composed of various facies. Sites of differing lithology (clay, gravel and diamict) were selected for detailed study.

Glacigenic sediments at Shanganagh (Photo after Williams, 2019)

Results:

Data shows that rates of retreat were higher in 2017-2018 when compared to 2016-2017 and the average for the two-year period exceeds the upper limits of previous studies. The three facies had differential erosion responses suggesting that lithofacies may be a useful identifier of erosion ‘hotspots’.  

A DEM of Difference (DoD) for Shankhill North site. Note the receding cliff line in one year of data. (Source: Williams, 2019)

A geographer’s perspective:

As geographers we are trained to take a holistic view to the environment. In addition to considering coasts as geological and geomorphological landscapes, they are also dynamic socio-ecological systems. In addition to climate change effects, coasts are subject to increasing anthropogenic pressures. Together these present complex challenges for the design of effective coastal and marine governance systems.

Currently Ireland’s management of its coastal zone is beleaguered by three factors.

1. A reactive approach to coastal management. Protection of property is the most common driving force behind construction of sea defenses and the basis of any associated economic appraisals. This often results in construction of hard engineered sea defenses to protect property.

2. Devolution to local agencies whose potential innovations and progress are constrained by institutional problems.

3 Widespread weak governance (there are at least 34 different government departments, agencies, and bodies with responsibility for estuarine, coastal, and marine management across different territorial scales in Ireland (Kelly, 2017).

These lead to, a currently, unsustainable approach to the management of our coastal marine environment.

There are  four main approaches (Murphy, 2014):

  • Hold the line: this involves maintaining the position of the shoreline primarily through engineering intervention. This approach is expensive and is normally applied when valuable infrastructure is at risk (e.g Lahinch).
  • Managed realignment: this strategy allow for coastal recession on a managed basis with the view that it may be the only financially justifiable option. This often requires  land acquisition.
  • Advance the line:This pushes the coastal seaward and is usually undertaken on a local scale. Beach nourishment or land reclamation are examples of advancing the line.
  • Do nothing: This allows minimal intervention and best defines Ireland’s current approach. It permits the coastline to evolve naturally and requires planning restrictions and/or minimum development setback distances from the shore. In some cases, it can be specified that no development can take place on the seaward side of the road closest to the coastline in others a fixed distance is specified i.e. 100m.

Despite the European mandate to adopt an ecosystem approach to coastal and marine management, it is constrained by legacy effects such as historic management practices and current drivers and pressures (O’Higgins et al., 2019). This is embedded in the legacy exemplified by the dominance of hard engineering solutions for coastal erosion in Ireland.

Examples of Hard engineering structures in Northern Ireland. After Figure 5 in Cooper et al, 2016) (A) Rock armouring at a car park.(B) Railway sleepers used as sea defence, Cushendun.(C) Sloping stone wall, Cushendall. Gabbion baskets, Red Bay.
(E andF) Near vertical, stepped sea wall at Carnlough at low and high tide.

The most common protection measure in Ireland is revetment structures. They represent a ‘Hold the Line’ approach, whereby the large rocks/gabions/concrete armour units placed against a cliff or dune face form a barrier to resist further erosion (Murphy, 2014).

Under the Coastal Protection Act 1963, there is a statutory requirement on the Office of Public Works, to carry out maintenance works on Coastal Protection Schemes that were constructed under this Act. They are to maintain these Schemes in ‘proper repair and effective condition’.

In 2012 the OPW were responsible for the Maintenance of six Coastal Erosion Schemes including The Murrough, Co. Wicklow, Youghal, Co. Cork, Inishcrone, Co. Sligo, Strandhill, Co. Sligo, Rossnowlagh, Co. Donegal and Moville, Co. Donegal (OPW, 2012). 32% of the Northern Irish coast is fronted by hard engineered structures. The extent of defended coastline compares to 44% in England and Wales, and 6% in Scotland (Cooper et al., 2016). There is no figure available for Ireland.

Hard engineered sea defenses are damaging to natural ecosystems (Cooper et al., 2016). In many instances, shoreline armouring is implemented on a case by case basis with little or no regard to the cumulative effects (Cooper et al., 2016).

Lahinch prominade following Storm

Sustainable coastal defenses?

ICPSS

The Irish Coastal Protection Strategy Study (ICPSS) has been ongoing for a number of years and has produced erosion risk maps based on detailed site surveys and numerical modelling.  However, Ireland (and Northern Ireland) does not currently have a coastal erosion management strategy.

 ICZM

Integrated Coastal Zone Management (ICZM) is a process that seeks to bring together all stakeholders with an interest in the coast. Indeed, it is underpinned by a set of principles that espouse stakeholder participation, knowledge exchange, and the need to take a holistic and long-term view. It aims to replace sectoral based planning and management with a more integrated approach towards achieving sustainability.

Although it is not a legal requirement within the EU, ICZM reflects current European coastal and marine policy. While commitments to ICZM are contained within policy and national level statements of strategy, coastal management in Ireland remains sectoral in nature. Experiences with ICZM, although successful, have been limited to pilot, local level, research projects (O’Mahony et al., 2014). An alternative management paradigm is required to deliver an integrated management regime (Kelly et al., 2019).  It is frustrating that and important EU instrument for change, the EU Marine Spatial Planning (MSP) Directive, fails to address the effective integration of the marine with the coastal zone, i.e., land/sea interface. The baseline MSP produced for Ireland (DHPLG, 2018) only consider coastal erosion where it has the potential negatively affect marine and coastal heritage.

Despite the European mandate to adopt an ecosystem approach to management, in Ireland (and elsewhere in Europe) it is constrained by legacy effects such as historic management practices and current drivers and pressures (O’Higgins et al., 2019). While protection of the coastal ecosystem is commonly implied in strategic documents (e.g. Habitats Directive, Water Framework Directive OSPAR Convention), they remain largely aspirational notions that have a low priority in sea defense decision-making. It Is therefore not surprising that defense structures continue to be proposed for the Irish coastline (Cooper et al., 2016).

A final thought for Irish Geomorphologists:

It is worth considering the importance of adopting the approach proposed by Pollard et al (2018) who argue that coastal erosion and flood risk should be considered jointly because of the inherent system feedbacks.

They state that:

  • coastal morphology can modify flood hazard through its interaction with hydrodynamic conditions responsible for flooding (i.e., water level surge and waves, the occurrence of breaching and wave dissipation
  • future flood risk will depend on changing shoreline position as it determines the natural protection provided by coastal landforms and associated ecosystems.
  • erosion and flooding events may occur at the same time, the effects of which drive enhanced sediment transport that may permanently alter erosional susceptibility and natural flood defense capabilities of the coastal zone.

Acknowledgments:

I would like to thank the students who have passed through the Earth and Planetary Surface Processes Group in the Department of Geography who have embraced the challenges of field-based research projects on this topic: Ciaran Nash, Niamh Fay, Nancy Williams, Niamh Cullen, Ankit Verma and Rob Halpin).

The initial phase of this work was funded by a Geological Survey of Ireland Short-Call Griffith Award (2016).

And finally, no thanks, at all, to the amadán santach who stole our UAV following its emergency landing at Shanganagh in 2018. May your picnic sandwiches be forever filled with a thousand sand grains.

References

Bourke, M. C., Fay, N., and Verma, A., 2018, A third Digital Elevation Model (DEM) of Quaternary Cliffs between Killiney and Greystones, East coast of Ireland, Earth and Planetary Surface Process Group. Department of Geography, TCD.

Bourke, M. C., and Nash, C., 2016, A Digital Elevation Model (DEM) of Quaternary Cliffs between Killiney and Greystones, East coast of Ireland, Earth and Planetary Surface Process Group, Department of Geography, Trinity College, Dublin.

Bourke, M. C., and Nash, C., 2017, A second Digital Elevation Model (DEM) of Quaternary Cliffs between Killiney and Greystones, East coast of Ireland in Earth and Planetary Surface Process Group. Department of Geography, Trinity College, Dublin.

Caloca-Casado, S., 2018, Coastal vulnerability assessment of Co. Dublin and Co. Wicklow to impacts of sea-level rise [Ph.D]: NUI Maynooth, 289 p.

Cooper, J. A. G., O’Connor, M. C., and McIvor, S., 2016, Coastal defences versus coastal ecosystems: A regional appraisal: Marine Policy.

Devoy, R. J. N., 2008, Coastal Vulnerability and the Implications of Sea-Level Rise for Ireland: Journal of Coastal Research, v. 24, no. 2, p. 325-443.

D/HPLG, 2018, National marine Planning Framework: Baseline Report.

Fay, N., 2018, The Differential Erosion of Coastal Quaternary Cliff Facies [MSc]: Trinity College, Dublin, 55 p.

Gallagher, V., Meehan, R., Parkes, M., Hennessy, R., and Gatley, S., 2014, The Geological Heritage of Dún Laoghaire-Rathdown. An Audit of County Geological Sites in Dún Laoghaire-Rathdown: Geological Survey of Ireland.

Kandrot, S., Farrell, E., and Devoy, R., 2016, The morphological response of foredunes at a breached barrier system to winter 2013/2014 storms on the southwest coast of Ireland: Earth Surface Processes and Landforms, v. 41, no. 14, p. 2123-2136.

Kelly, C., Ellis, G., and Flannery, W., 2019, Unravelling Persistent Problems to Transformative Marine Governance: Frontiers in Marine Science, v. 6, p. 213.

Matthews, T., Mullan, D., Wilby, R. L., Broderick, C., and Murphy, C., 2016, Past and future climate change in the context of memorable seasonal extremes: Climate Risk Management, v. 11, no. Supplement C, p. 37-52.

Matthews, T., Murphy, C., McCarthy, G., Broderick, C., and Wilby, R. L., 2018, Super Storm Desmond: a process-based assessment: Environmental Research Letters, v. 13, no. 1, p. 014024.

Matthews, T., Murphy, C., Wilby, R. L., and Harrigan, S., 2014, Stormiest winter on record for Ireland and UK: Nature Climate Change, v. 4, p. 738.

Murphy, J., 2014, Coastal erosion around Ireland and engineering solutions, Volume accessed 2015.

O’Higgins, T., O’Higgins, L., O’Hagan, A. M., and Ansong, J. O., 2019, Challenges and Opportunities for Ecosystem-Based Management and Marine Spatial Planning in the Irish Sea, in Zaucha, J., and Gee, K., eds., Maritime Spatial Planning,, p. 47-69.

O’Mahony, C., Kopke, K., Twomey, S., O’Hagan, A. M., Farrell, E. a., and Gault, J., 2014, Integrated Coastal Zone Management in Ireland – Meeting Water Framework Directive and Marine Strategy Framework Directive targets for Ireland’s transitional and coastal waters through implementation of Integrated Coastal Zone Management: Sustainable Water Network (SWAN).

OPW, 2012, Strategic environmental assessment screening statement: maintenance activities of coastal protection schemes under the responsibility of the Office of Public Work.

Pollard, J. A., Spencer, T., and Brooks, S. M., 2018, The interactive relationship between coastal erosion and flood risk: Progress in Physical Geography: Earth and Environment, v. 43, no. 4, p. 574-585.

Rijsdijk, K. F., Owen, G., Warren, W. P., McCarroll, D., and van der Meer, J. J. M., 1999, Clastic dykes in over-consolidated tills: evidence for subglacial hydrofracturing at Killiney Bay, eastern Ireland: Sedimentary Geology, v. 129, no. 1–2, p. 111-126.

Williams, N., 2019, Temporal and Spatial Variations in Recession Rates of Quaternary Soft Rock Cliffs at Shanganagh, SE Ireland [MSc: Trinity College, Dublin, 44 p.

Comments are closed.

Create a website or blog at WordPress.com

Up ↑

%d bloggers like this: