eithne davis - a spatial study of sites susceptible to coastal erosion in county sligo

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Title of Project:

A Spatial Study of Sites Susceptible to Coastal

Erosion in County Sligo.

Author: Eithne Davis

Academic Year: 2014-2015

Supervisor: Mr Declan Feeney

This project is submitted as part fulfilment of the Honours Degree (Level 8) Environmental Science, Institute of Technology, Sligo.

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Abstract

The winter of 2013-2014 brought a series of storms that caused significant damage to coastal

areas all around Ireland. With predictions of more frequent and extreme weather events, it is

important that we understand the dynamics of coastal erosion in order to make informed and

intelligent policy decisions.

A field survey was undertaken to identify damage sustained in the winter of 2013-2014, and

shapefiles of eroded areas created using GIS software. These shapefiles were used as a

baseline to evaluate the quality of the subsequent desktop survey. The desktop survey used

orthophotographs, oblique photographs and maps to gather information on physical

characteristics of the sample sites as well as their socio-economic vulnerability. This

information was then analysed using risk assessment matrices. The resulting data was

processed to produce a series of hazard maps identifying the locations of highest priority for

monitoring and management.

The results showed that the desktop risk assessment methods used are adaptable for various

coasts, and gave a good level of accuracy when compared to the results of the field survey.

Common features such as a sheer cliff-face consisting of unconsolidated material emerged as

high risk factors. Contrary to expectations, direct exposure to prevailing storm fronts did not

automatically increase the risk of erosion. Rather, shorelines lying at a sub-parallel angle to

the prevailing storm fronts showed more damage. Socio-economic features such as

infrastructure and cultural heritage create a priority for attention, but coastal habitats under

protection are dynamic environments, and depend on erosion to maintain their unique fabric.

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Statement of Authenticity

I certify that the content of this project is entirely my own work and is submitted in part

fulfilment of the B.Sc. (Honours) Degree in Environmental Science at the Institute of

Technology, Sligo.

Any material adopted from other sources is duly cited and referenced and acknowledged as

such.

Signed: ______________________________

Eithne Davis (Student)

______________________________

Declan Feeney (Project Supervisor)

Date: 2nd April, 2015

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Acknowledgements

This project grew from small seeds that were planted by many and watered by others. To

each and every one of you who engaged with me, to whatever extent, I want to express my

warmest gratitude. Your questions, your suggestions, your company and your cups of tea all

helped shape this piece of work into what it is, and ultimately made me see the world in a

slightly different way.

First and foremost, I want to express my sincere appreciation to my supervisor, Declan

Feeney: you gave me the space to make it my own, the encouragement to keep going, and just

enough guidance to keep me on track. It was a pleasure to work with you on this project.

The staff and lecturers at IT Sligo; Steve Tonry, Cian Taylor, Sam Moore, James Bonsall,

David Doyle, Fiona Beglane- your support and curiosity made this project take on a life of its

own. The single frames of reference, the fractals..... there were times when I didn't know

whether I was studying science or philosophy, and I am truly indebted.

To my classmates who kept insisting it would be grand - I hate to admit it, but you were right.

Sharing the last four years was fantastic. Thanks for your good spirit, your straight talking,

and when all seemed lost, for the emails of funny cat videos.

To my walking companions; Bridget, Rory, Alan and Sinéad, my trusty proof-readers; Aisling

and Yvette, and my cheerleading squad: my family and friends. You made me take a break

when I would have kept going, and kept me going when I would have given up.

But most of all, my husband, Ciarán - you walked every inch of that coastline with me, and

shared your beautiful photographs. And put up with seeing only the back of my laptop screen

as thanks. I couldn't have done this without you. Thank you.

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Table of Contents

Abstract ................................................................................................................................................... 2

Acknowledgements ................................................................................................................................. 4

Table of Figures ...................................................................................................................................... 7

Introduction ............................................................................................................................................. 8

Context of the study ............................................................................................................................ 8

Aims and Objectives of the study ..................................................................................................... 10

1.0 Literature Review ............................................................................................................................ 12

1.1 What we know about coastal erosion and cliff habitats .............................................................. 12

1.2 The study site chosen - an exposed, dynamic coastline .............................................................. 13

1.3 The influences which lead to erosion on our coasts .................................................................... 18

1.4 Data sources available for desktop surveys ................................................................................. 19

1.5 Limitations - Gaps in the data, and inherent uncertainty in methodology ................................. 23

1.6 International and National Policy on Response to Coastal Erosion ............................................ 24

1.7 Summary of the key points found in the literature. ..................................................................... 25

2.0 Methodology ................................................................................................................................... 26

2.1 Preparatory and planning stage ................................................................................................... 26

2.2 Field survey ................................................................................................................................. 29

2.3 Desktop survey ............................................................................................................................ 31

2.4 Analysis of results using GIS software ....................................................................................... 36

2.5 Return site visits .......................................................................................................................... 37

3.0 Results ............................................................................................................................................. 38

3.1 Field Survey ................................................................................................................................ 39

3.2 Desktop Survey ......................................................................................................................... 400

3.3 Socio-economic vulnerability ................................................................................................... 444

3.4 Analysis of 6 most at-risk, high-value sites, implying high priority locations .......................... 477

3.5 Policy and planning maps ......................................................................................................... 500

4.0 Discussion ..................................................................................................................................... 522

4.1 Main findings from study .......................................................................................................... 522

4.2 Comparison between field survey and desktop survey ............................................................. 533

4.3 Difficulties in geospatial interpretation ..................................................................................... 556

4.4 Use of indices .............................................................................................................................. 58

4.5 Use of OPW Erosion Maps ....................................................................................................... 622

4.6 Limitations on the survey .......................................................................................................... 633

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5 Conclusion ........................................................................................................................................ 667

5.1 Recommendations ....................................................................................................................... 68

References ............................................................................................................................................. 69

Appendices ............................................................................................................................................ 75

Appendix I Boat Survey Photographs ............................................................................................... 75

Appendix II - Raughley Survey Photographs.................................................................................... 77

Appendix III - Lislarry to Streedagh Photographs ............................................................................ 79

Appendix IV - Raughley Survey Field Data Sheets .......................................................................... 83

Appendix V - Attribute Tables from ArcGIS .................................................................................. 105

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Table of Figures Figure 1 - Ireland's coast is exposed to the full extent of weather ........................................................................ 8

Figure 2 - County Sligo, on the North West coast of Ireland ................................................................................ 9

Figure 3 - Section of County Sligo coastline chosen for study............................................................................ 10

Figure 4 - The two lengths of coastline chosen for the study area. ...................................................................... 14

Figure 5 - Exposed soil on eroded cliff-faces ...................................................................................................... 16

Figure 6 - Map illustrating the extent of Natura 2000 site designations in the area ............................................ 18

Figure 7 - Sample image taken from oblique imagery viewer. ............................................................................ 20

Figure 8 - The quality of orthophotographs is improving.................................................................................... 21

Figure 9 - Photograph of shoreline at Lislarry, County Sligo.............................................................................. 26

Figure 10 - A section of the same stretch of coastline as photographed from boat survey .................................... 27

Figure 11 - Orthophotograph of North County Sligo ............................................................................................ 28

Figure 12 - Detailed shapefile of North County Sligo ........................................................................................... 30

Figure 13 - Discrepancies in some GPS recorded positions .................................................................................. 30

Figure 14 - Oblique imagery compared to historic 6' maps .................................................................................. 32

Figure 15 - Hazard index. ...................................................................................................................................... 33

Figure 16 - The aspect of each of the points along the coastline. .......................................................................... 34

Figure 17 - Table showing calculations used to apply hazard ratings. .................................................................. 35

Figure 18 - Resulting table assigning hazard ratings ............................................................................................. 35

Figure 19 - Socio-economic vulnerability index. .................................................................................................. 36

Figure 20 - Map illustrating the areas where erosion was recorded ...................................................................... 39

Figure 21 - Map illustrating the areas where erosion was recorded ...................................................................... 39

Figure 22 - Table quantifying the actual erosion recorded in the field. ................................................................. 39

Figure 23 - During the desktop survey, a total of 47 sites were recorded ............................................................. 40

Figure 24 - Sites surveyed by desktop methods on Raughley peninsula ............................................................... 40

Figure 25 - Locations of recent erosion identified in field survey of Raughley .................................................... 41

Figure 26 - High risk sites identified in desktop survey overlaid with locations of erosion .................................. 41

Figure 27 - Sites surveyed by desktop methods in the Lislarry to Streedagh area ................................................ 42

Figure 28- Locations of recent erosion identified in field survey of Lislarry to Streedagh ................................... 43

Figure 29 - High risk sites identified in desktop survey overlaid with locations of erosion .................................. 43

Figure 30 - Sites with a socio-economic rating higher than the median value ..................................................... 44

Figure 31- Sites with a rating above the median values ........................................................................................ 44

Figure 32 - Sites with a socio-economic rating higher than the median value ...................................................... 45

Figure 33 - Sites with a rating above the median values ....................................................................................... 45

Figure 34 - An analysis of the 3 highest-scoring sites in the Raughley survey ..................................................... 47

Figure 35 - An analysis of the 3 highest-scoring sites in the Lislarry to Streedagh survey ................................... 48

Figure 36 - Table showing occurrence of hazard factors in the 6 most high value, at risk sites............................ 49

Figure 37 - Table showing occurrence of socio-economic factors in the 6 most at risk sites ................................ 49

Figure 38 - Section from the OPW erosion risk map ............................................................................................ 50

Figure 39 - Areas identified as being of high risk and high value from this survey, compared with the areas

identified in the OPW erosion risk map ................................................................................................................ 50

Figure 40 - Section from the OPW erosion risk map ............................................................................................ 50

Figure 41 - Areas identified as being of high risk and high value from this survey, compared with the areas

identified in the OPW erosion risk map ................................................................................................................ 50

Figure 42 - Rock collapse at site R08 on Raughley peninsula. ............................................................................. 54

Figure 43 - Freshly exposed prehistoric midden material behind collapsed cliff face at site R08. ....................... 54

Figure 44 - A map illustrating discrepancies ......................................................................................................... 57

Figure 45 - At larger scales, lack of detail becomes even more evident ................................................................ 57

Figure 47 - Boat survey route ................................................................................................................................ 75

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Introduction

Context of the study County Sligo, where this study is based, is a coastal county in the Northwest of Ireland,

perched on the western edge of Europe, on the North Eastern Atlantic Ocean. This coastline

bears the brunt of the most violent weather systems travelling across the Atlantic from

America, and is subject to prevailing South Westerly winds.

Figure 1 - - Ireland's coast is exposed to the full extent of weather crossing the Atlantic Ocean, with prevailing weather conditions

from the South West

It is here that Atlantic Storms and the tail end of hurricanes first make landfall, dispersing

some of their energy before progressing towards mainland Europe. In this way, Ireland, and

the similar coast that can be found in Scotland, often provide the initial protection to the rest

of Europe in the face of Atlantic storms. With impending acceleration of climate change,

altering weather patterns and predicted sea-level rise, it is highly likely that the dynamics

which have previously affected erosion rates along this coast will alter, perhaps subtly, with

potentially devastating long-term consequences for coastal communities.

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Figure 2 - County Sligo, on the North West coast of Ireland

Understanding coastal processes is the first step in responsible, informed decision-making.

Sustainability Science has a role to play in Integrated Coastal Zone Management, where

scientists, policy-makers and practitioners come together to work with a common purpose.

There is a responsibility on scientists to provide the best information possible. If we want to

establish proactive management practices, it is not good enough to assume that methods

previously employed are still state of the art.

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Figure 3 - Section of County Sligo coastline chosen for study. The coastline is rugged and highly embayed, with a mixture of dune

systems and hard and soft cliffs.

Aims and Objectives of the study

This study aims to review current practices in assessing, monitoring and predicting coastal

erosion. In the context of rapidly changing technology, emerging resources which could raise

the standards of coastal monitoring in the near future are briefly assessed.

The chosen study area is surveyed in order to establish whether or not it is under threat from

coastal erosion. Various methods of monitoring coastal erosion are reviewed to identify an

accurate risk-assessment method.

A brief overview of EU and Irish policies is incorporated into this study to show the context

in which monitoring of specific sites can be a useful tool in decision-making, and to review

the current recommendations and actions being taken with regard to Coastal Zone

Management.

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In order to achieve these aims, an attempt was made to accurately quantify the length of

coastline which was affected by the winter storms of 2013/2014 by ground-truthing the

survey areas. Using GIS software (ESRI), maps were generated to illustrate the extent of

erosion in the area. The physical risk of erosion and the socio-economic vulnerability of the

survey area were assessed in detail using separate matrices. These results were compared

with the results of the field surveys to assess the accuracy level of the desktop methods.

Databases were interrogated to identify areas of high priority, from both a physical risk of

erosion and a socio-economic viewpoint. The results are presented using GIS, in an easily-

interpreted series of maps.

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1.0 Literature Review

1.1 What we know about coastal erosion and cliff habitats

Approximately 70% of coastline globally, and 20% of Ireland's coastline, is identified as

being at risk from erosion. The Coastal Zone Management Review (Cummins et al. 2004,

JNCC 2004) estimates that approximately 60% of the Irish population live in coastal areas.

Sustainable development requires planners to be informed on the long-term effects of

proposed developments, particularly in light of Sea-level Rise predictions. An iterative

approach at coastal management must begin with producing a coastal profile to act as a

baseline for future monitoring.

The Irish Sea Cliff Survey (Barron et al. 2011, JNCC 2004), the first systematic national

survey of sea-cliff habitats and conservation status in Ireland, identified a lack of detailed

information regarding the hard coast of Ireland. The initial preliminary survey assessed 3

sites in County Sligo for the quality of the habitat, biodiversity, with a further, second survey

planned. None of these fall within the survey area. Sea cliffs provide habitat to the Annex I

species chough (pyrrhocorax pyrrhocorax) and peregrine falcon (falco peregrinus), and over

20 species of Red Data Book invertebrates, as well as many salt-tolerant plant species.(Barron

et al. 2011) A provisional list of sites to be surveyed during phase 2 of the national survey is

nominated in the report, but has been postponed indefinitely (O'Connor 2014, Andrady 2011).

Much of the Irish coastline is soft cliff, which consists of unconsolidated material and is

particularly vulnerable to wave action and wash-out from precipitation.

This study was undertaken in order to better understand the state of the knowledge on the

dynamics involved in coastal erosion and the principals being applied to coastal management

at a Regional, National and Local level. To study the effect of erosion on this coast, it is

necessary to investigate the dynamics involved in coastal erosion, and to identify resources

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which may be helpful in surveying this particular stretch of coastline. The literature for this

study was systematically selected using agency reports, their main reference maps and

documents, and predefined database searches.

Erosion is primarily caused by wind action (both through wave generation and direct impact)

and precipitation, and can be exacerbated by land-use practices (Clarke and Rendell 2009).

Significant storms in the winter of 2013/2014 caused extensive coastal damage in Ireland

(met.ie 2014).

The habitat being studied is Vegetated Sea Cliffs of the Atlantic and Baltic Coasts (1230),

which are an Annex I listed habitat under the EU Habitats Directive . The Irish Sea Cliff

Survey was undertaken to inform on the nature of the hard coastline, as part of Ireland's

obligations to monitor and report to the EU (EU 1992). The preliminary stage of this survey

has been completed (Barron et al. 2011). Dune and beach systems are better understood and

are regularly monitored under the Coastal Monitoring Project (Ryle et al. 2009), which is

specifically aimed at these soft shorelines, and thus they are not of a concern for this study.

1.2 The study site chosen - an exposed, dynamic coastline

This project will focus on erosion of hard coastline (hard and soft cliffs and rocky shorelines)

in an area of North County Sligo between Raughley and Streedagh. There is anecdotal

evidence of erosion in this area after every extreme weather event, but this has never been

formally studied.

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Figure 4 - The two lengths of coastline chosen for the study area, highlighted here in red. The sites are primarily cliff habitats, with

anecdotal reports of damage after every storm event.

The Irish Sea Cliff Survey was designed as a preliminary study of the coastline as required by

the Habitats Directive 92/43/EEC (EU 1992). Sample sites were studied from around the

coast, and only 3 sites in Sligo were chosen; Ballincar, Aughris and Streedagh. Of these, only

the Streedagh site is within the study area. While the Sea Cliff Survey produced a large

amount of good data on very specific sites, it was limited in its scope (Barron et al. 2011).

1.2.1 Nature of the shoreline - categorising a complex mosaic.

For this study, hard shoreline is defined as areas which are not made up of mobile sediment

systems, such as sandy beaches and dunes. The Sea Cliff Survey set criteria of a minimum of

5m in height for hard cliffs and 3m for soft cliffs, and a minimum length of 100m. The study

being undertaken here is focussed on observing a continuous length of coastline without

access to extensive technical resources. In contrast, the Sea Cliff Survey was heavily

resourced and studied the finer technical detail of representative sites, so these parameters are

taken as a guideline only for this project, which focuses on using minimal resources to

identify high priority sites for closer examination.

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No site-specific information could be found in the literature that gives a detailed breakdown

of the type of cliff present, and in what proportion. Hard and soft cliffs have very different

characteristics. Hard cliff is inhospitable by its nature, while soft cliff can support a range of

pioneer species (e.g. agrostis stolonifera and tussilago farfara) but these are easily washed

away by extreme weather events. The main objective of soft cliff habitats is that fresh soils

are exposed on a regular basis to maintain the natural conditions, which will struggle to

achieve succession growth (JNCC 2004).

The study area is a macro-tidal, high-energy, embayed coastline, which is likely to have

evolved to a high level of stability. The erosive effect of extreme weather events is known to

have a greater impact in low-energy areas whose soft characteristics have not been tested by

high-energy storm events on a regular basis. It has been demonstrated that locally generated

waves, caused by sudden upwelling of ocean waves when they meet shallower inshore

bathymetry, have a more damaging effect on a coastline than remotely generated ocean

waves. An extreme weather event that coincides with high water spring tides is the most

damaging scenario. (Cooper et al. 2004). Maximum tidal range is approximately 4.5m.

(Marine.ie 2015)

1.2.2 Topography and geology

The bedrock of the study area is limestone (GSI 2015). The foreshore is mainly bare karstic

rock and supports only a very limited range of salt-tolerant plants in the crevices. The nature,

gradient, and direction of slope on these shorelines has a strong influence on the energy

distribution of storm surges reaching the land. Steep terraces tend to dispel the wave energy

before it hits the land. Pebble beaches similarly disperse the ocean's energy, and frequently

create or feed storm beaches on the adjacent land.

The cliffs of the West Coast of Ireland tend to be high and steep, or even sheer. The higher

and steeper the cliff, the greater the influence of gravity on the erosive potential of the site.

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Soft cliffs, consisting mainly of unconsolidated material and limestone are much more

vulnerable to erosion than hard cliffs of metamorphic material (JNCC 2004). The JNCC

document states that soft cliff is generally less steep than hard cliff, but this was challenged by

the Irish Sea Cliff Survey (Barron et al. 2011) which found no difference in gradient between

the two cliff types.

1.2.3 Habitats

The Irish Sea Cliff Survey (Barron et al. 2011) was established to address a gap in the

knowledge of the nature and species of the sea cliff sites of Ireland. Lengths of this coastline

are categorised as . Vegetated Sea Cliffs of the Atlantic and Baltic coasts (1230) which is an

Annex 1 listed habitat, and as such must be monitored and reported on every 6 years. Only 7

sea cliff sites were listed in the survey for County Sligo, and these added up to 17.82km. The

majority of this coastline falls broadly into the category of inshore littoral biotopes. (Connor

et al. 1997b, Connor et al. 1997a) Shoreline habitats are complex to categorise, difficult to

measure, and dangerous to observe during extreme weather events (Williams and Hall 2004,

Hall et al. 2006).

Figure 5 - Exposed soil on eroded cliff-faces is home to Sand Martin (Riparia riparia) burrows, as visible at the top of this cliff.

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Cliff habitats are dependent on the processes of erosion to maintain their nature and specific

biodiversity. Many of the species found there, such as sand martins (riparia riparia), solitary

bees and invertebrates will not be found inhabiting the more stable habitats close by (Barron

et al. 2011, JNCC 2004). Coastal erosion is a natural process. Without it we would not have

cliff habitats. Erosion can only be considered a "risk" for cliff habitats if it is being

exacerbated by anthropogenic factors (JNCC 2004).

The area of the study is rich in high value habitat, and this is evident from the percentage of

Sligo Bay that has been given special designation status under Natura 2000 (see Figure 6).

The study area contains sections of Special Protected Areas (SPA), Special Areas of

Conservation (SAC), Natural Heritage Area (NHA) and proposed Natural Heritage Area

(pNHA) (NPWS 2015, NPWS 2009b). On examination of the Conservation Objectives for

the area, the focus is on mudflats and intertidal areas, and the area of this study is primarily of

concern to the Harbour Seal (phoca vitulina). There are particularly large populations of

barnacle goose (branta leucopsis) and brent Goose (branta bernicla), as well as whooper

swans (cygnus cygnus), ringed plover (charadrius hiaticula), grey plover (pluvialis

squatarola), lapwing (vanellinae), snipe (f. scollopacidea), oystercatcher (f. haematopdidae),

and curlew (g. numenius) in the adjacent areas, and particularly in Ballygilgan Nature

Reserve, which is very close to the study area. The quality of the shoreline enhances the

quality of the overwintering waterfowl habitat in general. (NPWS 2009a, NPWS 2009b)

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Figure 6 - Map illustrating the extent of Natura 2000 site designations in the area, including SPA, SAC and pNHA.

Studies have shown that cliff top habitats can be an important feeding ground for wading

birds when they occur in areas bounded by hard shoreline at high water (Furnell and Hull

2014). This may be of lesser significance in this area due to the topography.

1.3 The influences which lead to erosion on our coasts

1.3.1 Maritime impacts on the land

The west coast of Ireland is directly under the influence of North East Atlantic sea conditions.

In the prevailing south- westerly conditions waves reach here from North America,

unimpeded by any other land mass. Long, rolling ocean waves are first pushed upwards when

they meet the Porcupine Bank, approximately 110nm to the west of the coast. Sea surges are

funnelled into Sligo Bay under this influence.

Studies in the Aran Islands have observed the energy of the North Atlantic by studying the

size and altitude of megaclasts deposited on cliff tops during storm events, as well as the

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distance and direction that existing clasts have been moved during these events. Clasts of 250

tonnes have been carried onto the shore at sea level, 117 tonnes at 12m above sea level, and

2.9 tonne clasts at 50m above sea level, demonstrating the incredible power of these waves.

The presence of plastics trapped under some of these clasts show that they have been

deposited in relatively recent events. (Williams and Hall 2004, Hall et al. 2006)

1.3.2 Meteorological influences - wind and rain.

The weather in the west coast of Ireland is dominated by Gulf Stream influences, making it a

temperate maritime climate. The prevailing wind is from the south west, and rainfall levels

are high, averaging 1000 - 1400mm of rainfall per annum on the west coast (met.ie 2014).

Winds on this coastline are generally unbroken in their crossing of the Atlantic, and the most

severe storms are a result of hurricanes travelling across the Atlantic from North America,

with a fetch of thousands of miles (Lozano et al. 2004). Maximum wind speeds of 98knots in

gusts have been recorded at Belmullet in 1961 (met.ie 2014).

1.3.3 Climate Change as a future threat

As a result of climate change, annual rainfall is predicted to rise by 25% in winter months by

2050 (Sweeney and Fealy 2002, IPCC 2014, Falaleeva et al. 2011, ICCC 2004). Heavy

rainfall can wash out large areas of soft cliff (JNCC 2004). When combined with predictions

of rising sea levels and less frequent but more intense storm activity (Lozano et al. 2004,

Hickey March 2015), this is a significant predictor of increased rates of erosion by the end of

this century.

1.4 Data sources available for desktop surveys

1.4.1 Orthophotographs and oblique imagery as a data source

One of the main data sources for the Sea Cliff Survey is the Coastal Helicopter Survey (OPW

2003), which provides oblique imagery for the entire coastline of Ireland, excluding only

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some of the offshore islands. The imagery is now over 10 years old, but provides good

comparative information. A similar dataset is used in Northern Ireland to study coastal

erosion. (Westley March 2015)

Figure 7 - Sample image taken from oblique imagery viewer. These images were the main source of data for the desktop survey.

(OPW 2003)

Modern orthophotographs are still not accurate enough for measurement of land area, as can

be seen in Figure 8 when attempting to compare the same stretch of coastline using the OSI

Mapviewer (OSI 2014b).

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Figure 8 - The quality of orthophotographs is improving immensely, but is not yet of a high enough quality for comparative

purposes. 1995 orthophotograph (above) compared with 2005 orthophotograph (middle). (OSI 2014b), and 2015 image (below)

(Microsoft 2015b)

Allowances for the curvature of the earth, plus the angle at which the image was captured, and

inconsistent shadows, mean that overlaying orthophotos from different years is difficult.

Since the OPW Helicopter Survey was completed in 2003, rapid developments have been

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made in photogrammetry methods using drone photography. These methods are highly

accurate, allow for 3-dimensional measurements to be recorded, and even have the potential

for the creation of 3-D printed models. Drone photogrammetry is becoming an increasingly

economically viable option , with high quality equipment being developed for the mass

market. (Colomina and Molina 2014, Bemis et al. 2014, Dempsey March 2015)

1.4.2 Maps & Charts - still relevant in a digital age.

Historically, Ireland has some of the world's most sophisticated mapping, undertaken by the

Ordnance Survey in 1846 (6 inch maps) and 1890s (25 inch map) (OSI 2014b). Marine

navigation charts are in the remit of the British Admiralty, and show bathymetry in the study

area (UKHO 1979, UKHO 2006). The accuracy of all maps and charts are somewhat limited

by the methodology of the surveys. Intrinsic errors arise in compensating for the curvature of

the earth when creating a representation of the land in a 2-dimensional format (Lozano et al.

2004, Neilson and Costello 1999, Jenny and Hurni 2011). That said, ground-truthing of the

mapped areas in 1960 by Tellurometer, showed a discrepancy of only an inch in an eight mile

length on the original 6 inch map (OSI 2014a). This is an extraordinary level of accuracy

given the manual nature of the chain-surveying techniques employed at the time.

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1.5 Limitations - Gaps in the data, and inherent uncertainty in methodology

1.5.1 Baseline data

As no baseline data is available for the study area, it is impossible to accurately measure the

volume of land which has been eroded. Many different map projections are used, but each

one is chosen for a specific purpose. At the outer edges of the map, such as at the coastline,

integral inaccuracies in the projection become amplified and area measurements are distorted.

1.5.2 Coastline Paradox

Measuring the shoreline is accepted as being an impossible task, as explained by the concept

of the Coastline Paradox. In 1967, Benoit B. Mandlebrot published his seminal work on

measuring coastlines, in which he explained their fractal nature (Mandlebrot 1967). A large

stretch of coastline observed on a small scale map looks somewhat similar to a cut-out of that

same coastline at a larger scale, and again, repeatedly, at larger and larger scales. Measuring

the same length of coastline on a small scale map will give a much shorter total figure than

measuring the same length of coastline on a large-scale map (see Figure 44, Figure 45). It is

simply not possible to define an exact scale at which to measure, and no two measurements

will be the same. This, coupled with the difficulty in choosing a line to measure at (High

Water/ Low Water/Chart Datum), makes any coastlines' length nothing more than a vague

estimate. This issue has been further described in regard to the fractal nature of the

Connemara Coastline. (Robinson 2003)

1.5.3 Coastal Recession rates

The lack of definitive baseline data means that we do not have any recession rates for the

area. In any case, cliffs do not recede in a uniform, regular fashion. As a general rule, the

rate of recession of cliff-faces will be a very slow process, until such time as a high-energy

storm event causes much larger areas than normal to be torn away. Erosion of hard shoreline

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tends to occur in occasional, unpredictable events, where large chunks of rock, after many

years of being acted upon by waves, will suddenly give way in an extreme event (See Figure

42). Measuring and predicting these events is exceedingly difficult due to their sporadic and

unpredictable nature. (Del Rio and Gracia 2009)

1.6 International and National Policy on Response to Coastal Erosion

Ireland has not taken a strong stance on coastal management, except to monitor development

through planning regulations. General policies from Europe give guidance, but are not really

brought into action (Cooper and Cummins 2009, Cummins et al. 2004, Cummins and

McKenna 2010) . In some areas where houses, roads, or other services are under threat from

erosion, sea-defences have been built as a mitigation measure. It is now accepted that hard

engineering solutions can exacerbate erosion problems by deflecting the wave energy from

the protected area to the adjacent shorelines. These areas, particularly when they consist of

soft cliffs, can deteriorate at a much quicker rate that they would have naturally (Cummins et

al. 2004).

In preference to the development of sea-defences, current policy in coastal zone management

favours retreat in areas where low population density and the inevitability of erosion make

mitigation measures impractical (LIFE et al., Cooper and Cummins 2009, Cummins and

McKenna 2010).

1.6.1 Vulnerability rating as a way of informing policy

Many different indices have been developed to assess the vulnerability of areas of coastline.

Physical indices and socio-economic indices will be blended in a matrix to generate

vulnerability ratings for this study (Del Rio and Gracia 2009, McLaughlin et al. 2002).

Physical indices take into account the topography, geology, aspect in relation to the prevailing

conditions, climate, and exposure. They attempt to make a prediction on the most likely areas

25

to erode. Indices developed in Cadiz, Spain are transferrable to the North Atlantic coastline,

and can be of relevance here. The hazard/impact/risk model used in the Cadiz study (Del Rio

and Gracia 2009) is used as a vulnerability matrix for this project. This takes into account

variables such as cliff lithology, cliff structure, cliff slope, protective beach, rocky shore

platform, engineering structures at cliff foot, tidal range, exposure to storm wave fronts,

difference between storm and modal wave height, relative sea-level trend and rainfall.

Most socio-economic indices are designed around densely populated areas which bear no

resemblance to the study area. The University of Coleraine has produced a socio-economic

index that is designed around a similar coastline type, with culturally similar characteristics

(McLaughlin et al. 2002). This socio-economic vulnerability classification index incorporates

settlement, cultural heritage, roads, railways, land use and designated conservation areas as

variables, and is modified slightly in this study to identify valuable coastal sites.

1.7 Summary of the key points found in the literature.

Coastal erosion is a natural process. It can have serious impacts, which are difficult to

predict. These impacts are predicted to increase with Climate Change. Integrated Coastal

Management Zone policy can only be improved by a greater understanding of the complex

dynamics, and by employing relatively simple models for assessing vulnerability.

In order to assess the vulnerability of the study area, primary data will be collected from a

systematic field study. The data gathered, along with secondary data taken from maps, charts,

oblique imagery and orthophotographs, will be used to generate vulnerability ratings for the

study area. The results will be presented visually using digital mapping techniques and

statistical analysis.

26

2.0 Methodology The survey consisted of several separate stages.

2.1 Preparatory and planning stage Maps (OSI 2012) and charts (UKHO 1979, UKHO 2006) were consulted. These

conventional sources gave a contextual overview of the area, including population density,

infrastructure, topography, nature of the coastline and offshore bathymetry.

2.1.1 Boat survey - 21st September, 2014

A preliminary survey was undertaken by boat. The area between Raughley and Streedagh,

including Innismurray, was photographed. (See Appendix I for map and photographs). The

boat was not exclusively available for survey work, and the speed and exact route of the

passage did not allow for taking detailed photographs. Compounding this, the morning sun in

the east put the shoreline in silhouette, eliminating the required detail from the photographs

(see Figure 9). The resulting photographs did not justify further boat surveys, but were a

helpful familiarisation exercise, gave a unique perspective on the project and informed the

final choice of survey area.

Figure 9 - Photograph of shoreline at Lislarry, County Sligo, taken from boat survey on September 21st, 2014, showing shoreline in

silhouette, without adequate detail for analysis (Photo - Eithne Davis)

27

The advantages of being able to survey from afloat are the speed at which the survey could

potentially be done, and an ability to access sheer sea-cliffs, as practiced in the Irish Sea Cliff

Survey (Barron et al. 2011). However, only very short stretches of the coastline were

inaccessible from a beach, and the vast majority of these were easily photographed from an

adjacent headland. The same information could be garnered from the OPW Oblique Imagery

(OPW 2003), in a process currently being used in other, similar surveys in Northern Ireland

and Newfoundland and Labrador. (Storey et al. March 2015, Ní Cheallacháin March 2015,

Westley March 2015)

Figure 10 - A section of the same stretch of coastline as photographed from boat survey, taken from the Helicopter Survey of

Ireland. (OPW 2003)

2.1.2 Preliminary desktop survey; Choice of study area and scheduling of surveys -

September, October 2014

From a detailed review of maps and charts, and an afloat survey of the entire area, exact

locations for the study were chosen. The criteria used in choosing sites were accessibility,

ability to cover the area on foot in a 6-hour walk (or less), and the presence of interesting

features and/or geology. Two discreet sample sites were chosen, as illustrated in Figure 11

below; the Raughley peninsula and the length of coastline from Lislarry to Streedagh.

28

Figure 11 - Orthophotograph of North County Sligo, showing survey areas highlighted in red.(Google 2015)

This stretch of coastline is particularly varied in its nature and aspect, and no detailed

scientific studies were available on the specifics of the nature and resilience of the coastline,

although there is anecdotal evidence of erosion after every major storm event.

The stretch of coastline is highly embayed, with lengths of coast being exposed from all

points of the compass, and therefore exposed to both the prevailing winds and more

infrequent winds.

As with most of the coast along the North-east Atlantic seaboard, this area is subject to high

energy storms (met.ie 2015a, met.ie 2015b) and a tidal range of up to 4.5metres (Marine.ie

2015).

Land-use in the area is varied. The majority is agricultural, and population density is low.

There are three different designations in effect; SAC, SPA and pNHA (NPWS 2015).

29

2.1.3 Risk assessment and equipment

Before any field work could take place, a risk assessment was completed and a safety plan

written. The remote and unpredictable nature of coastal work necessitated certain precautions

to be put in place, including the provision of a route plan to be left with a responsible person,

no solitary work, a qualified first-aider present, a means of communication in case of

emergencies, and the use of appropriate PPE within 3m of water.

2.1.4 Field data sheets

Field data sheets were designed according to standard guidelines (Fossitt 2007) to record the

physical features of the shoreline, and tested in an unrelated location. Space was left for

comments on features of interest not included in datasheet. (See Appendix IV for completed

data sheets)

2.1.5 Equipment

The entire study was undertaken using minimal resources, primarily a Garmin Etrex GPS,

mobile phone, first aid kit and PPE . An equipment list was incorporated into the field data

sheets.

2.2 Field survey to identify areas of recent erosion - October 2014 The field survey took place over 2 discreet sites, walking the shoreline to identify areas of

recent erosion. Recent erosion was deemed to have taken place where pioneer species had not

yet established themselves, and bare soil was visible. This implied that the area had

experienced erosion during the extreme weather events of 2013/2014 (Met.ie, Gleeson March

2015, Met.ie 2015, Hickey March 2015). The exact location of the eroded areas was recorded

by GPS, and a field data sheet used to record the physical characteristics of the site.

Photographs were taken at each eroded location, using a Nikon D-90 DSLR camera, and the

reference numbers from the camera recorded on the field data sheets. See Appendices II and

III for photographs.

30

2.2.1 Recording the results of the field survey

Using satellite imagery (Microsoft 2015a) in ArcGIS (ESRI), a detailed shapefile of the

vegetation line for the study area was created (Figure 12). To create this vegetation line, points

were taken at <10m intervals along the straighter lengths of coastline, and at 1-3m intervals

along the more embayed, complex stretches of coastline. This vegetation line served as a

basemap for all the subsequent GIS analysis.

Figure 12 - Detailed shapefile of North County Sligo, as

drawn in ArcGIS(ESRI) from the World Imagery basemap

(Microsoft 2015a), with vertices drawn at 1 - 10m intervals

Figure 13 - Discrepancies in some GPS recorded positions

became apparent when digitising data. With reference to

photographs and field data sheets, co-ordinates were

anchored to vegetation line to create accurate records

The results of the field survey were mapped using ArcGIS. Separate shapefiles were created

for each of the survey areas, anchoring the GPS points to the closest corresponding point on

the shapefile of the vegetation line, as illustrated in Figure 13. These field survey shapefiles

were used to indicate eroded and non-eroded areas.

31

2.3 Desktop survey to examine the susceptibility of the coastline to erosion,

and the socio-economic vulnerability of the backshore; January - February

2015

2.3.1 Desktop resources available for interpretation in a risk matrix

The increasing availability of reputable mapping resources online allows the area to be

studied at a level of detail that until recently was not available to the public in one place. This

allows for the study of a detailed geographic area from many different perspectives and

disciplines, facilitating studies which would previously have been impractical in terms of time

and resources.

A preliminary desktop assessment of the coastline informed the choice of study area and gave

a general overview of physical, biological and cultural features.

The main sources of imagery used in the desktop survey were as follows:

1. Maps, both traditional format (OSI 2012) and online (OSI 2014b, GSI 2015, NPWS

2015, NMS 2014)

2. Oblique photographs (OPW 2003)

3. Orthophotographs (Microsoft 2015a, Microsoft 2015b, Google 2015)

4. Nautical charts; both traditional format (UKHO 1979, UKHO 2006) and online

applications (Navionics 2014).

5. Historic maps were consulted to locate specific field boundaries and other features of

reference (OSI 2014b) when further details or clarification were needed to identify

exact locations.

32

Figure 14 - Oblique imagery (OPW 2003) compared to historic 6' maps (OSI 2014b) to identify exact location with reference to field

boundaries, roads, and old buildings

2.3.2 Methods used to record a systematic desktop survey

The chosen study areas were surveyed by desktop methods at 1:250. A "desktop" point

shapefile was created, starting at the southerly most extreme of each area, and points were

recorded at 250m intervals along the vegetation line basemap for both of the survey areas.

Each of these points was then surveyed visually using the methods described below.

These areas were surveyed, and shapefiles incorporating a detailed attribute created. The

attributes were assessed from the oblique imagery of the OPW coastal helicopter survey, the

satellite images, maps and charts.

2.3.3 Cliff Hazard Index

The factors in the following matrix were entered as field headings in an attribute table in each

of the shapefiles, and the appropriate numerical values recorded. (See Appendix V for

attribute tables) A further field was created to record the cumulative total for the hazard

indices at each point. Any location scoring higher than the median value for cumulative total

was deemed to be at high risk of erosion.

33

CLIFF HAZARD INDEX Factor 1 2 3 4

Cliff Lithology Plutonic,

volcanic,

resistant

metamorphics

Limestones,

sandstones,

conglomerates

Non-resistant

metamorphics, fine

consolidated

sediments, coarse

unconsolidated

sediments

Fine unconsolidated

materials

Cliff structure No significant

discontinuities

Alternate sequences

of soft and hard

materials

Isolated gullies

and/or evident

groundwater flow

and/or moderate

cracks/joints/faults

Coastal badlands

and/or dense

cracks/joints/faults

Cliff slope Slope b25° Slope 26°–50° Slope 51°–75° Slope N75°

Protective

beach

Wide/high

beach (waves

reach the cliff

at spring tides

coinciding

with storm

surges)

Intermediate beach

(waves reach the

cliff at spring

tides or during

storm surges)

Narrow/low beach

(waves reach the

cliff during daily

high tide)

No beach

Rocky shore

platform

Wide,

continuous

intertidal

rocky shore

platform

Narrow,

discontinuous

intertidal rocky

shore platform

Submerged rocky

shore platform

No rocky shore

platform

Engineering

structures at

cliff foot

Seawall or

revetment at

the cliff foot

(whole)

Not considered

Seawall or

revetment at the cliff

foot (partial)

No structure at cliff

foot

Tidal range Hypertidal

(MSTR N6

m)

Macrotidal (MSTR

4–6 m)

Mesotidal (MSTR

2–4 m)

Microtidal (MSTR

b2 m)

Exposure to

storm

wave fronts

Roughly

shore-normal

storm wave

fronts (angle

81°–90°)

Angle 46°–80°

Angle 11°–45°

Shoreline subparallel

to main storm wave

fronts

(angle b10°)

Difference

between storm

and modal

wave height

Difference

b0.5 m

Difference 0.5 m–2

m

Difference 2 m–3.5

m

Difference N3.5 m

Relative sea-

level trend

Change b−1

mm/yr (RSL

fall)

Change−1 mm/yr to

+1 mm/yr (RSL

stable)

Change+1 mm/yr to

+2.5 mm/yr (RSL

moderately rising)

Change N+2.5

mm/yr (RSL

strongly rising)

Rainfall Mean annual

precipitation

b500 mm

Mean annual

precipitation 500–

1000 mm

Mean annual

precipitation 1000–

1500 mm

Mean annual

precipitation N1500

mm Figure 15 - Hazard index, developed in Cadiz, Spain, assigning a numerical value to the physical factors that contribute to the

stability of cliffs (Del Rio and Gracia 2009).

34

As the points being recorded were limited to one continuous piece of coastline, the following

factors were left out of the attribute table, as the values were identical at each point.

Tidal range (Macrotidal, MSTR 4-6m)(Marine.ie 2015)

Difference between storm and modal wave height (<3.5m)(Met.ie 2015)

Relative sea-level trend (1mm/yr) (ICCC 2004)

Rainfall (1,000-1,400mm/yr) (met.ie 2014)

Oblique photography (OPW 2003)and orthophotographs (Microsoft 2015a, Microsoft 2015b,

Google 2015) were used to populate the fields in the attribute table according to a visual

examination of each location. See Appendix V for attribute tables..

2.3.4 Interpretation of matrix during the desktop survey

The matrix used (Figure 15) provided very clear parameters for the various hazard indices, and

a significant amount of time was spent on familiarisation and interpretation of the various

factors from the orthophotographs and oblique images.

2.3.5 Calculation of exposure to storm wave fronts

In order to determine exposure to storm wave fronts, the aspect from each point was measured

using the course-plotting tool in the Navionics web app (Navionics 2014)

Figure 16 - The aspect of each of the points along the coastline measured using the Navionics course-plotting tool (Navionics 2014) in

order to calculate the exposure to storm wave fronts.

35

The heading measured was then used in the following calculation (Figure 17), derived directly

from the above Cliff Hazard Index (Figure 15). From consultation with several regular water-

users from different disciplines, local knowledge puts the most common direction of swell to

be 250⁰T. This implies that a shoreline with an aspect of 250⁰ would be at a 90⁰ angle to the

prevailing storm swell, and be considered to be "shore-normal" (SN). Therefore, for this

coastline, SN = 250°. While it is recognised that some of the most damaging storms come

from different directions, the scope of this particular survey only allowed for the prevailing

direction to be taken into account.

Hazard

rating

Min

Angle

SN - Max

extent

SN + Max

extent

1 81° -

90°

241° - 259°

2 46° -

80°

SN +/- 10° -

44°

250° +/- 10° -

44°

206° - 240° 260° -

294°

3 45° -

79°

SN +/- 11° -

45°

250° +/- 11° -

45°

171° - 205° 295°- 329°

4 <10° SN < +/- 80° 250° < +/- 80 >330° <170°

Figure 17 - Table showing calculations used to apply hazard ratings to points on the coastline according to the angle of their

exposure to storm wave fronts coming from 250°.

Aspect from Shoreline Hazard rating

<170° 4

171° - 205° 3

206° - 240° 2

241° - 259° 1

260° - 294° 2

295° - 329° 3

>330° 4

Figure 18 - Resulting table assigning hazard ratings to the "exposure to storm wave fronts" field for each point on the desktop

shapefile according to its aspect. (Assuming the most common storm wave front to come from 250°)

36

2.3.6 Socio-Economic Vulnerability Index

The factors in the following matrix were then entered as field headings in an attribute table

(see Appendix V) in each of the shapefiles, and the appropriate numerical value recorded at

each point. A further field was created to record the cumulative total for the vulnerability

indices at each point. Any location scoring above the median value was deemed to be of high

socio-economic value.

SOCIO-ECONOMIC VULNERABILITY INDEX

Variable 1 2 3 4 5

Settlement No Settlement Village Small Town Large Town City

Cultural

Heritage

Absent Present

Roads Absent R- class Motorway

Railway Absent Present

Landuse Water bodies

Marsh/bog

and moor

Sparsely

vegetated

areas

Bare rocks

Natural

grasslands

Coastal areas

Forest Agriculture Urban and

Industrial

Infrastructure

Designated

conservation

areas

Absent Present

Figure 19 - Socio-economic vulnerability index, chosen because of its relevance to local factors and used to assign a numerical value

to the coastal land. Some features have been modified for local factors, specifically the roads and designated conservation areas

classifications, which were originally designed for UK-specific use. (McLaughlin et al. 2002).

The socio-economic features were directly entered into the attribute table of an ArcGIS

shapefile (ESRI) under their appropriate field headings. The data was interpreted from the

same visual resources as the hazards (OPW 2003, OSI 2014b), as well as the National

Monuments Service (NMS 2014), the National Parks and Wildlife (NPWS 2015) and the

Guide to Habitats (Fossitt 2007).

2.3.7 Review of the OPW Erosion maps

The Erosion Maps as available from the OPW (RPSGroup 2014, OPW 2013) were geo-

referenced against the basemap, and a further shapefile drawn to show the areas considered to

be at risk of erosion according to the policy makers and planners.

37

2.4 Analysis of results using GIS software - completed in stages between

November 2014 and February 2015 Once the data collection was complete, the results were analysed using the attributes functions

in ArcGIS. Exported shapefiles were generated isolating the following:

1. Eroded areas from the field survey

2. High risk areas for erosion from the desktop survey

3. Sites of highest socio-economic value from the desktop survey

4. OPW predictions of future erosion

These shapefiles were used to generate maps comparing the results of the desktop survey with

the actual erosion recorded on the ground. Further maps were then generated identifying the

areas of high socio-economic value which were at the most threat of erosion, and the areas

highlighted by planners as susceptible to erosion.

Length of recorded erosion was generated in GIS field survey shapefile.

2.5 Return site visits - February 2015

Following further storms in December 2014, return visits to 2 specific sites (Stáid Abbey and

Raughley) to observe any further changes. Both sites were again photographed for

comparison. Minor deterioration was observed at Stáid Abbey, and some vegetative growth,

but no further deterioration was noted at Raughley in these quick spot checks.

38

3.0 Results

3.0.1 All sample sites

For the purposes of this survey, two areas were chosen for analysis, as previously illustrated

in Figure 4. The cumulative total area for the survey was measured at 11.5 km from the

vegetation line basemap.

The Raughley field survey covered 3.75km. Of this, 12 different locations showed signs of

erosion, with a cumulative length of 2.59km (Figure 20).

The Lislarry to Streedagh field survey covered 7.75km. Of this, 27 different locations showed

signs of erosion, with a cumulative length of 3.1km (Figure 21).

In the desktop survey, 16 points were analysed in Raughley and 31 in the Lislarry to

Streedagh area, giving a total of 47 data points in an 11.5 km stretch (Figure 23).

39

3.1 Field Survey 3.1.2 Erosion in Raughley

Figure 20 - Map illustrating the areas where erosion was

recorded in ground-surveying the Raughley area

3.1.3 Erosion in Streedagh

Figure 21 - Map illustrating the areas where erosion was

recorded in ground-surveying the Lislarry to Streedagh area

In a visual representation of the eroded areas, it is clear that erosion is present along the entire

coast, and not confined to those stretches of coastline that would be considered to be the most

exposed.

Area Total length (km) Length of erosion*

(km)

% of total

Raughley 3.75 2.59 69%

Lislarry to Streedagh 7.75 3.1 40%

Total survey area 11.5 5.69 49% Figure 22 - Table quantifying the actual erosion recorded in the field. *Because this study was focussing on hard shoreline, dune

systems were not recorded, therefore this result is a conservative estimate.

As can be seen from Figure 22 above, 49% of this coastline has been subject to erosion during

the winter of 2013/14.

40

3.2 Desktop Survey

Figure 23 - During the desktop survey, a total of 47 sites were recorded, 16 in Raughley and 31 between Lislarry and Streedagh

3.2.1 Raughley

Figure 24 - Sites surveyed by desktop methods on Raughley peninsula, taken at 250m intervals

41

Comparison between field and desktop surveys

Figure 25 - Locations of recent erosion identified in field

survey of Raughley

Figure 26 - High risk sites identified in desktop survey

overlaid with locations of erosion identified in field survey of

Raughley

Comparison between the field survey and desktop survey results of Raughley show a high

level of accuracy in predicting areas susceptible to erosion from the hazard indices. Figure 26

above shows all of the predicted high-risk areas except one to be concurrent with recorded

erosion on the ground. Only one site which was predicted to be at high risk showed no

significant proof of erosion.

42

3.2.2 Streedagh

Figure 27 - Sites surveyed by desktop methods in the Lislarry to Streedagh area, taken at 250m intervals

43

Comparison between field and desktop surveys

Figure 28- Locations of recent erosion identified in field

survey of Lislarry to Streedagh

Figure 29 - High risk sites identified in desktop survey

overlaid with locations of erosion identified in field survey of

Lislarry to Streedagh

In Figure 29 above of the Lislarry to Streedagh section, 4 points show high risk of erosion

without any recorded incidents on the ground. These areas are actually dunes, which did not

fall into the survey remit, and being naturally mobile systems were not recorded on the

ground as erosion.

When these points are ignored (most southerly 3 points and the 4th point from the north of the

map), all other predictions are accurate. The desktop survey was inclined to underestimate

the extent of erosion.

44

3.3 Socio-economic vulnerability

3.3.1 Raughley

Figure 30 - Sites with a socio-economic rating higher than

the median value in the Raughley peninsula

Figure 31- Sites with a rating above the median values for

both high risk of erosion and high socio-economic value

Figure 30 above shows 11 sites in Raughley which are considered to have a high socio-

economic value from the desktop survey, identified as priority locations for assessment in any

policy-making decisions.

The next map, Figure 31, shows the 8 sites of high socio-economic value which also coincide

with a high risk of erosion.

The Raughley peninsula is a small area (3.75km in shoreline) with a long history of habitation

and a significant harbour. It also has two sites listed as National Monuments, one of which, a

midden, at site R08 (Figure 43) was discovered and recorded as a result of this survey.

45

3.3.2 Lislarry to Streedagh

Figure 32 - Sites with a socio-economic rating higher than

the median value in the Lislarry to Streedagh area

Figure 33 - Sites with a rating above the median values for

both high risk of erosion and high socio-economic value

By selecting only sites with a socio-economic rating higher than the median value, Figure 32

above identifies 13 locations from the Lislarry to Streedagh survey as priority locations for

assessment in any policy-making decisions.

Figure 33 further narrows down 6 sites of high socio-economic value which also coincide with

a high risk of erosion. These are the sites which this survey would highlight for most urgent

observation. The Lislarry to Streedagh survey area, measuring 7.75km from the vegetation

line shapefile, is more extensive than that at Raughley. It also contains more mobile dune

systems and is not as directly influenced by human activity.

46

Stáid Abbey

Site S02 is the only location along the coast for which we have historic recession rates. The

site is the location of a medieval chapel, Stáid Abbey, which is regularly surveyed to monitor

its distance from the shoreline. The shoreline at Stáid has receded 19m since the 1830s OS

maps were drawn (OSI 2014b), and 19m since total station surveys of the site began in 1994

(Beglane March 2015).

47

3.4 Analysis of 6 most at-risk, high-value sites, implying high priority

locations

3.4.1 Raughley area

Site ref Reasons for high-risk status Reasons for high-vulnerability status

R02

Risk=23

Vuln=16

Lithology: 4

Fine, unconsolidated materials

Settlement: 2

Village

Structure: 1

Continuous

Cultural heritage: 1

Absent

Slope: 2

Moderate slope

Roads: 3

R-class

Protective Beach: 4

No beach

Land use: 5

Infrastructure

Rocky shore platform: 4

No rocky shore platform

Designated conservation area: 5

Natura 2000 site

Engineering structures foot of cliff: 4

No structure at cliff-foot

Exposure to storm wave fronts: 4

Shoreline sub-parallel to storm wave fronts

R06

Risk=23

Vuln=16

Lithology: 4


Settlement: 2

Village

Structure: 1

Continuous


National monument

Slope: 4

Sheer

Roads: 1

None

Protective Beach: 2

Waves reaching cliff during spring tides or

storm surges

Land use: 4


Narrow, discontinuous, intertidal


Natura 2000 site




Shallow angle

R07

Risk=24

Vuln=16

Lithology: 4


Settlement: 2

Village

Structure: 3

Alternate hard and soft materials


National monument

Slope: 4

Sheer

Roads: 1

None

Protective Beach: 2


storm surges

Land use: 4

Infrastructure




Natura 2000 site





Figure 34 - An analysis of the 3 highest-scoring sites in the Raughley survey for combined hazard and vulnerability ratings

48

3.4.2 Lislarry to Streedagh area

Site ref Reasons for high-risk status Reasons for high-vulnerability status

S02

Risk=23

Vuln=13

Lithology: 4


Settlement: 1

No settlement

Structure: 3

Alternate hard and soft materials


National monument

Slope: 4

Sheer

Roads: 1

None

Protective Beach: 2


storm surges

Land use: 4

Agriculture




None

Engineering structures at foot of cliff: 4




S03

Risk=22

Vuln=12

Lithology: 4


Settlement: 1

No settlement

Structure: 2

Fine, consolidated materials


None

Slope: 4

Sheer

Roads: 1

None

Protective Beach: 1

Waves reach cliff only with spring tides

coinciding with storm surges

Land use: 4

Agriculture




Natura 2000 site




Slightly wider angle than shore-normal

S04

Risk=22

Vuln=14

Lithology: 2

Limestone

Settlement: 1

No settlement

Structure: 1

Continuous


National monument

Slope: 4

Sheer

Roads: 1

None

Protective Beach: 3

Waves reach cliff during daily high tide

Land use: 2

Natural grasslands




Natura 2000 site





Figure 35 - An analysis of the 3 highest-scoring sites in the Lislarry to Streedagh survey for combined hazard and vulnerability

ratings

49

3.4.3 Common influencing factors of high priority sites from both locations

Factor Rating No. of sites

Lithology 1 0

2 1

3 0

4 5

Structure 1 3

2 1

3 2

4 0

Slope 1 0

2 1

3 0

4 5

Protective beach 1 1

2 3

3 1

4 1

Rocky shore

platform

1 0

2 0

3 3

4 3

Engineering

structures at cliff

foot

1 0

2 0

3 0

4 6

Exposure to storm

wave fronts

1 0

2 1

3 1

4 4

Figure 36 - Table showing occurrence of hazard factors in

the 6 most high value, at risk sites

Factor Rating No. of sites

Lithology 1 0

2 1

3 0

4 5

Structure 1 3

2 1

3 2

4 0

Slope 1 0

2 1

3 0

4 5

Protective beach 1 1

2 3

3 1

4 1

Rocky shore

platform

1 0

2 0

3 3

4 3

Engineering

structures at cliff

foot

1 0

2 0

3 0

4 6

Exposure to storm

wave fronts

1 0

2 1

3 1

4 4

Figure 37 - Table showing occurrence of socio-economic

factors in the 6 most high value, at risk sites

Figure 36 gives a brief overview of the 6 highest priority sites, the most common physical

characteristics displayed are fine, unconsolidated material, a sheer gradient on the cliff-face,

lack of a protective rocky shore platform, lack of any engineered protection, and a sub-

parallel exposure to storm wave fronts. None of the priority sites have coastal protection

measures.

The most common socio-economic features represented in Figure 37 are cultural heritage (i.e.

the presence of a National Monument), agricultural land-use, and Natura 2000 designated

status. All of the priority sites fall within Natura 2000 areas.

50

3.5 Policy and planning maps

Figure 38 - Section from the OPW erosion risk map,

georeferenced to the vegetation line shapefile, with yellow

polygons illustrating the areas identified to be at risk of

erosion

Figure 39 - Areas identified as being of high risk and high

value from this survey, compared with the areas identified in

the OPW erosion risk map

Figure 40 - Section from the OPW erosion risk map,

georeferenced to the vegetation line shapefile, with yellow

polygons illustrating the areas identified to be at risk of

erosion

Figure 41 - Areas identified as being of high risk and high

value from this survey, compared with the areas identified in

the OPW erosion risk map

51

The areas of interest highlighted in the OPW Erosion maps (RPSGroup 2014), when

compared with the desktop survey, don't show a distinct relation to areas identified in this

study as being of high priority. The exception to this is the harbour at Raughley, shown

between points R04 and R05 in Figure 39.

52

4.0 Discussion

4.1 Main findings from study

The results of the field survey, where the length of eroded coastline was quantified, showed

that 49% of this coastline had proof of erosion in the winter of 2013/2014. Put into the

context of the literature available, 70% of coastlines globally and 20% of the Irish coastline is

considered to be at risk of erosion. Generally, only coast that is being affected by

anthropogenic activity is considered "at risk". It is difficult to extract anthropogenic effects

from natural influences on coastal erosion, as it is accepted that human activity is the main

driver of climate change with its associated implications for more frequent and severe extreme

weather events and rising sea-levels.

Whether or not the results of this study are directly comparable with official research, the

49% figure is significantly higher than the accepted national figure. This is not entirely

surprising, as the area was chosen specifically because of its high-energy, embayed nature and

the complexity of its coastline. It can be expected to be more exposed, and therefore more

vulnerable to erosion in extreme weather events than other coastal areas, such as those on the

eastern seaboard, the lower results of which would have an influence on the national average.

The main findings of interest, (as highlighted in section 3.4.3) from the desktop survey were

the strong influence of lithology, gradient, and the angle of the coastline against approaching

storm wave on the level of damage to the cliff-face. The desktop methods employed

highlighted factors (discussed below) which, when combined, can lead to a much higher risk

of that coastline being damaged by meteorological events.

53

4.2 Comparison between field survey and desktop survey

4.2.1 Raughley

The peninsula of Raughley has a long history of human activity in the form of agricultural and

maritime cultures. The geology of the peninsula includes a tombolo which shows that the

peninsula was once an island, and has therefore been long influenced by erosion and

deposition. The field survey showed that 69% of the coast has been recently eroded (Figure

20). The peninsula supports a small village, an active harbour, and the main land-use is

agricultural. It is therefore not surprising that, overall, this site displayed a higher socio-

economic rating than that of the Lislarry to Streedagh site.

The Raughley site showed very high levels of erosion in proximity to sea-defences; areas

which, by their nature, are of high socio-economic value, such as roads, harbours and

settlements. This evidence of erosion was mainly on the eastern side of the peninsula. While

this area is sheltered from the prevailing marine influences, it is made up of relatively soft,

unconsolidated material, and is at a sub-parallel angle to the prevailing conditions, a factor

which contributes strongly to scouring rates and longshore drift.

The northern side of the peninsula showed definite evidence of sudden, catastrophic collapse

of rocky shoreline, a risk which was anticipated by the desktop survey (see Figure 31). The

evidence of this was the discovery of a prehistoric midden in a section of collapsed cliff. On

the initial survey in September 2014, the midden area was clear of any vegetative growth,

while a return visit the following January showed that vegetation had already begun to

establish itself on the bare rock.

54

Figure 42 - Rock collapse at site R08 on Raughley peninsula.

(Photo by Ciarán Davis)

Figure 43 - Freshly exposed prehistoric midden material

behind collapsed cliff face at site R08. (Photo by Ciarán

Davis)

4.2.2 Lislarry to Streedagh

This more northerly site was more extensive (7.75km in length), and showed frequent

incidents of erosion (40% of site), albeit often in short (<5m) stretches. The high-priority

sites identified from the desktop survey correlated very clearly with those seen in the field

survey, where catastrophic damage was visually evident (see Figure 29). In particular the site

at Stáid Abbey (discussed in separate section below) is a good example of combined high risk

factors along with high socio-economic significance.

Overall, the results of the field and desktop surveys were very compatible in both survey sites,

highlighting the same priority locations.

55

4.2.3 Analysis of the 6 sites of highest priority

The data gathered for the study was collated in spreadsheet format. After some thought and

consultation, it was decided that the scope of the study was adequately served by the outputs

from ArcGIS. The data is available in the appendices of this report should an opportunity

arise for statistical analysis. Logistical regression would be a suitable method of determining

the hazard factors with the greatest influence on erosion, but is beyond the scope of this study.

A brief comparison of the 3 highest priority sites from each area when combined gave a rough

indication of what could be the most influencing factors. (See Figure 36, Figure 37)

Most common influencing physical risk factors

Of the 6 cliff sites, 4 were exposed at a sub-parallel angle to the prevailing storm waves, 5

were made of fine, unconsolidated material and 5 had a sheer gradient. All 6 were without

engineering (sea-defences) in place.

Given current thinking on the damaging influence of hard engineering solution on adjoining

stretches of coastline, it may be appropriate to consider altering the index ratings for this in

the hazard matrix. Particularly on a coastline which has very few sea-defences, the level of

importance attached to this may be skewing the results somewhat.

Most common influencing socio-economic factors

Of the 6 sites, 4 were in proximity to National Monuments, 5 were bordering a road, 4 cited

agriculture as the main land-use, and all 6 were in Natura 2000 sites.

It is debatable whether being part of a designated conservation area should have such a high

influence on the results, given that coastal erosion is a natural geomorphological process and a

characteristic feature of the habitats under protection by these designations.

56

4.3 Difficulties in geospatial interpretation

4.3.1 Inconsistencies in spatial data

The vegetation shapefile that was created in ArcGIS was necessary to give consistency to the

results. Initially it was thought that useful information could be extrapolated from comparing

orthophotographs from different years. The angle from which the image was captured, the

projection of the image into an orthophotograph, and the different light levels and shadows in

the orthophotographs meant that some areas appeared to have extended rather than eroded.

The practicalities of walking the shoreline meant that accurately recording the vegetation line

with a hand-held GPS was not possible. When these points were plotted into ArcGIS there

were natural inconsistencies in the shapefiles. This was overcome by interpreting the data

into a separate shapefile, anchoring the GPS points to the vegetation line (See Figure 44). This

method allowed accurate interpretation of the field data.

The Irish Coastal Helicopter photographs were taken in 2003, their accuracy may be

becoming dated. The increasing availability of drones and the development of

photogrammetry as an environmental monitoring tool should be considered when updating

the current resource.

57

4.3.2 Coastline Paradox

The inherent difficulties in measuring coastlines as explained by the Coastline Paradox

hypothesis (Mandlebrot 1967) was overcome by the choice of the vegetation line as the

consistent baseline for all measurements, as illustrated by figures 45 and 46 below.

Figure 44 - A map illustrating discrepancies between the

shoreline as recorded in the relatively small scale County

Map (OSI 2014b) and the vegetation line drawn from

orthophotographs(Microsoft 2015a)

Figure 45 - At larger scales, lack of detail becomes even more

evident

58

4.4 Use of indices

It is important to remember that these indices were taken from two different sources, one from

Cadiz, Spain, and one from Northern Ireland. They may not be designed to consider the

specific conditions in this region, but it is important to have consistency in assessing

environmental impacts in different regions. While some of the factors may seem redundant in

the context of this study, they may be highly relevant should the same study be repeated in a

different location.

4.4.1 Hazard Indices

Cliff Lithology

Much of the shoreline is made up of glacial till on a limestone bedrock (GSI 2015). Wherever

there has been previous erosion, the unconsolidated soil is exposed and being stripped from

its limestone platform. In this way, the vegetation line is receding, while the remaining

limestone protects the land from inundation.

Cliff Structure

Continuous, un-fragmented cliff-faces allow the energy of the waves to glance off the

shoreline, while in contrast, faults and gullies allow purchase for wind and water, providing a

suitable environment for physical and chemical weathering.

Cliff Slope

The effect of gravity on cliff-fall increases with the height and gradient of the cliff-face, and is

one of the most common features found in the vulnerable sites in this study. A sheer slope

combined with unconsolidated lithology can greatly influence the resilience of the cliff.

59

Protective beach

As waves run up a sandy or pebble beach much of their energy is absorbed by the sediments,

and the impact on the cliff is greatly reduced.

Rocky shore platform

Karstic limestone makes up most of the foreshore in this area. Terracing of the coastal rock

formations helps to absorb wave energy and disperse it before it hits the shore. The impact of

this often causes the familiar spray of seawater rising up on the horizon during storm surges

and heavy sea swells.

Engineering structures at cliff foot

This area does not have a significant number of sea-defences, except in a small section of the

Raughley area. The hazard matrix assigns the highest rating to shore with no engineering

structures. As the matrix was designed in a more densely developed region, this may be more

appropriate in other geographical locations. In the context of this study, the presence of

engineering structures greatly increases the susceptibility of the nearby, undefended coastline,

speeding up erosion in adjacent sites. This is a factor that should be reviewed for further

studies.

Tidal range

Not taken into account for this study, as all sites were under the same influence.

Exposure to storm wave fronts

This factor was quantified according to Figure 17 in the Methodology section, and was an

influencing factor in 4/6 of the vulnerable sites.

Although this study was observing the effects of the 2013/2014 winter storms, the scope only

allowed the prevailing wave direction to be taken into account. This may have strongly

influenced the cumulative hazard rating in various areas. As the coastline tends to be attuned

60

to its prevailing conditions, it is likely that significant weather events that come from

directions other than the prevailing one have a far greater impact.

The calculations used to assess this in the methodology section were deliberately designed to

be easily recalibrated for different conditions. A predicted sea swell from an extreme weather

event can be easily incorporated into the ratings to interpret the potential effect on all the

sample locations. This could have significant implications for coastal management in a

scenario for sea-level rise.

Difference between storm and modal wave height


Relative sea-level trend


Rainfall


61

4.4.2 Socio-economic Indices

Settlement

This parameter takes on a greater significance in urban areas. The rural nature of this area

minimises the effect of settlement on the cumulative ratings for this study.

Cultural heritage

The west coast of Ireland has a very high incidence of archaeological features (NMS 2014),

which is why this parameter had a significant influence on the ratings. In a scenario where

active infrastructure is at risk, it may be difficult to prioritise cultural heritage in a

management plan, but its importance must be acknowledged.

The case study of Stáid Abbey in section 4.6.1 below illustrates this.

Roads

Roads are frequently found hugging coastlines, and are critical to society. Re-alignment

schemes, inconvenience to commuters and road repairs are all very costly. Roads are often

the first place to be defended by engineering, leading to complications in adjacent areas.

Railway

Not taken into account for this study, as none present.

Land use

The majority of this area is under agricultural use. With a rising global population and

Harvest 2020 targets to meet, this makes it high-value land use. Where infrastructure is

present, in the case of harbours, buildings, bridges etc., there is a high value put on land.

Scrubland and coastal badlands are obviously of lesser priority for attention, even though the

ecosystem services they provide may not be wholly recognised.

62

Designated conservation areas

All of the sites that rated in the top 6 priority list were in a Natura 2000 area, which falls into

the highest rating on this matrix. This adjustment was made from the original matrix,

designed for UK use, which allows for a national designation which doesn't exist in Ireland.

The effect of erosion, being a natural process, should have a minimal impact on these sites,

many of which are designated because of their location in the first place. It is highly unlikely

that any action will ever be taken to control erosion in these areas as a result of their

designation.

4.5 Use of OPW Erosion Maps

The results of this study showed very little consistency with the priority areas highlighted in

the OPW Erosion Maps. (Figure 39, Figure 41) This raises concerns for the accuracy of

methods employed, in both this study and the OPW report.

4.5.1 Differing methodologies

The methodology in the OPW study involved taking 25km stretches of coastline and

comparing the orthophotographs from the 1970s with those from 2010 (Casey 2014), a

method which was dismissed at the early stages of this study because of inherent inaccuracies.

Shapefiles were drawn of each, and a probabilistic projection drawn, assuming the same areas

would recede at the same rate. This reactionary method ignores the changing rates of erosion

at play once the existing geology and soil-cover has been compromised by an erosion event or

engineering. Any inaccuracies in this report, which is an advisory document for planning

decisions, could have serious implications for misinformed decisions in the future,

particularly in more densely populated or at-risk areas.

This method ignores the level of detail and the dynamic nature of coastal environments that

was taken into account in this risk-assessment based study. It also raises the question as to

63

why no use was made of the resource that the OPW own in the helicopter survey, which was

publically available at the time that the erosion report was commissioned.

The risk-assessment methods used for this survey gave an extremely high level of detail, with

locations assessed at 250m intervals. This method may or may not be practical for the entire

coastline of Ireland. Only a skill level in human resources would be required, as no

specialised equipment is needed. Individual Local Authorities could benefit from assessing

their coastline at this level. If the OPW revise this report (which is set to predict erosion to

2050), a risk-assessment approach should be considered.

4.6 Limitations on the survey

There is an increasingly regular update of orthophotographs, but it will take time to

build a historical database of high resolution images suitable for comparative analysis.

This type of information would allow monitoring and appropriate adjustment of

indices.

Georeferencing on orthophotographs should improve as the technology becomes more

commonplace. There is still a certain amount of distortion obvious on coastlines in

different orthophotographs, limiting their usefulness for analytical purposes.

The scope of this study didn't allow for in-depth analysis of the cumulative effect of

significant factors in coastal erosion. The data gathered could provide for further

analysis.

Neither does the scope of this study allow for the analysis of storm events driving

waves from directions other than the prevailing directions. Individual storm cells

increasingly come from other directions. Climate change is altering Jet Stream

activity and has moved the mean storm track northwards by 200km. We cannot

currently accurately predict the cluster of elements that will create future extraordinary

storm events (Hickey March 2015). This limits the results of this study.

64

New information about the impacts of hard-engineering solutions in coastal defences

has not been taken into account. This could affect the hazard ratings of any areas

protected by engineering, and the adjacent areas.

65

4.6.1 The case study of Stáid Abbey

Stáid Abbey is an ecclesiastical site which has links with the monastic settlement on

Innismurray island. It has an implied connection, through the letters of Captain Francisco De

Cuellar (De Cuellar 1592), with the Spanish Armada ships which were lost off this coast in

1588. The site holds large midden deposits, which are being further washed away with every

storm. A souterrain on the site has already been destroyed, and holds historic graves. As

such it a National Monument with a high level of historic significance.

Stáid Abbey is a unique site in this survey , as it has been monitored for coastal recession

since 1994. This makes it the only site for which recession rates are available. These

recession rates show that the location is subject to catastrophic damage in major storms rather

than continuous linear regression. Recession rates have accelerated dramatically in the last 20

years as storms compromise the vegetative protection and the integrity of the ground, and the

cliff-face is overhung and collapsing. The church is currently (February 2015) 3.8 metres

from the shoreline. The 1830 maps show it at 19 metres from the shoreline (Beglane March

2015).

66

Figure 46 - Eroded shoreline, showing exposed midden material, at Stáid Abbey. The structure dates from the Early Medieval

period, is now 3.8 metres from the shoreline, and is expected to be destroyed by erosion in the next 10 - 20 years. (Photo by Ciarán

Davis)

Despite the significance of this structure, the only plans in place are to monitor and record any

materials exposed by erosion. Sea-defences are inappropriate, and would more than likely be

ineffective in protecting the site. Restoration or relocation of the structure is impractical. It is

expected that this site will be completely lost to erosion in the next 10-20 years.

This scenario will be repeated at many similar locations around the country in the coming

years. Indeed, a recent International conference held highlighted the similarity in issues being

addressed in France, Iceland, Newfoundland, Scotland and England. (Benlloch March 2015,

Pálsdóttir March 2015, Storey et al. March 2015, Dawson March 2015, Timpany March 2015,

Daly March 2015)

It seems little has changed since the 12th Century legend of King Canute and his attempt to

hold back the tide.

67

5.0 Conclusion

The area surveyed for this study shows extensive evidence of recent erosion. With 49% of the

shoreline damaged, the incidence of erosion here is higher than the national recorded average.

This is a natural process, part of the dynamic of the coastal landscape, and a key feature of

this habitat. Indeed, it is erosion that gives the coastline of Ireland it's dramatic landscape

which is considered such an asset. It is only in locations where key socio-economic features

are under threat, or where man-made structures are contributing to the problem that

intervention should be considered.

The methods used here to gather and analyse data appear to have been effective at identifying

key areas which are at risk. An understanding of the individual factors involved can also help

to inform future intervention methods. Mimicking the features that lend a natural resilience to

the shoreline is the most likely approach to give successful results in such a hostile

environment.

Increasing concern and an inherent uncertainty around how climate change will manifest itself

makes it all the more urgent to carefully monitor the effects of extreme weather around our

coasts. Ideally we should put ourselves in a position to take proactive measures to mitigate

against its influence on our infrastructure, settlements and heritage. Difficult decisions will

have to be made in the face of environmental damage, and it is inevitable that we will watch

parts of our cultural heritage which have been a feature of the landscape for hundreds, or even

thousands of years crumble into the sea.

There is a responsibility on the scientific community to provide accurate and timely data and

information on the state of our coastlines, just as there is an onus on policy-makers and

practitioners to act in an informed and responsible, proactive fashion to mitigate against the

68

societal impacts of erosion. A successful Integrated Coastal Zone Management Plan should

be an iterative process, under constant review while maintaining focus on a core aim. ICZM

plans should, at the very least, identify highly vulnerable locations and have intelligently

designed procedures in place for managed retreat.

5.1 Recommendations

It is not enough to trial these methods in a single area. Further research is recommended,

particularly investigating the accuracy under different environmental contexts, such as urban

areas. The oblique images provided by the helicopter survey are very useful, but becoming

dated. The increasing accessibility of drone photogrammetry would appear to make it a very

viable option for updating these images, with the added advantage of allowing for

measurement of recession. Over time, a catalogue of 3D data in this form would provide us

with a level of information that has never before been available on the dynamics of coastlines.

69

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Appendices

Appendix I Boat Survey Photographs The following photographs were not considered to show adequate detail to be used as a survey

method.

Figure 47 - Boat survey route

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Appendix II - Raughley Survey Photographs (Photos by Ciarán Davis)

Figure 48 - photo no. 8575



Figure 51 - photo no 8605





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Appendix III - Lislarry to Streedagh Photographs . (Photos by Ciarán Davis)









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81








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Appendix IV - Raughley Survey Field Data Sheets

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Appendix V - Attribute Tables from ArcGIS

Raughley

Lislarry to Streedagh

eithne davis - a spatial study of sites susceptible to coastal erosion in county sligo

Documents