Journal
Journalof
ofCoastal
CoastalResearch
Research
SI 64
pg -- pg
1316
1319
ICS2011
ICS2011 (Proceedings)
Poland
ISSN 0749-0208
Erosion of a depositional coast in NE Rhodos island (SE Greece) and
assessment of the best available measures for coast protection
C. Anagnostou†, P. F. Antoniou† and G. A. Hatiris∞
†Institute of Oceanography
Hellenic Centre for Marine Research, Athens
19013, Greece
[email protected];
[email protected]
∞Hydrobiological Station of Rhodos
Hellenic Centre for Marine Research, Rhodos
85100, Greece
[email protected]
ABSTRACT
Anagnostou, C., Antoniou, P.F. and Hatiris, G.A., 2011. Erosion of a depositional coast in NE Rhodos island (SE
Greece) and assessment of the best available measures for coast protection. Journal of Coastal Research, SI 64
(Proceedings of the 11th International Coastal Symposium), 1316 – 1319. Szczecin, Poland, ISSN 0749-0208
The mixed material beach at the north eastern tip of the island of Rhodos in south eastern Greece has
experienced strong erosion during the last few decades due to a progressive decrease in sediment feed, resulting
from human induced activities in the hinterland and local annual and seasonal wind-wave variations. The eroding
beach threatens valuable public infrastructure as well as safe recreational use. The local government and other
involved decision makers are particularly interested in the protection of the coastal infrastructure from damage,
as well as the preservation of the beach, which has attracted great touristic interest over the years, and protection
of its users. A thorough coastal geomorphological survey of the area coupled with an assessment of the local
wind and wave climate was conducted in an attempt to determine the drivers of erosion and propose potential
methods of coast protection to involved authorities. The results of the analysis helped to critically assess the
available solutions and their impacts; it was revealed that the optimal method for beach protection should involve
a periodic artificial nourishment scheme, supported by a monitoring program, with the aim to restore gradually
all the material lost since the early 20th century.
ADDITIONAL INDEX WORDS: Sediment Starvation, Coastline Change, Beach Nourishment
INTRODUCTION
The main goal of this paper is to propose optimal methods for
beach protection for an eroding beach in Greece. Coastal erosion
is a very well known phenomenon in Greece, currently affecting
various coastal areas and populations (Xeidakis et al., 2006).
The dynamics of a coastal area are mainly driven by two
mechanisms: that of sediment feed and that of deposition
(Kombiadou et al., 2009). The first depends on the geological
substratum of the greater region, the geomorphology, the local
hydrology and land coverage; while deposition greatly relies on
the wind/wave regime (tides in Greece do not play a remarkable
role in coastal dynamics). Seasonal variations of meteorological
phenomena drive sediment transport dynamics and seasonal
coastline changes and, in turn, determine erosion and accretion
patterns. On the other hand, various human activities influence
coastal processes. The EU Recommendation on Coastal Zone
Management (McKenna et al., 2008) recommends that authorities
attempt to work with natural processes. This presents several
challenges (Cooper & McKenna, 2008).
The problem of erosion has become particularly intense during
the last 30 years at the NE coasts of the island of Rhodos in SE
Greece. This disturbance has been expressed by a progressive
deficit in sediments, which has led to significant coastline retreat
with significant environmental and socioeconomic impacts given
the area is also a major tourist attraction.
In this work, an attempt was made to combine
geomorphological information and wind/wave data which were
either directly available or collected in the field, in order to define
which processes drive erosion locally and propose feasible
remedial and protection measures.
DESCRIPTION OF STUDY SITE
The eroding coast of concern is located at the NE tip of the
island of Rhodos in the SE Aegean Sea in Greece (Figure 1). It is
a mixed material depositional coast, characterized by a natural spit
of reversed U-shape, approximately 500 m long. The shoreline
comprises a beach with tourist facilities (sun chairs, umbrellas,
etc.), a lighthouse which is operated by the local Port Authorities
and the facilities of the Hydrobiological Station of Rhodos. The
area is also very densely populated; the city of Rhodos has grown
towards the north and over the years has seen major development,
with large hotel complexes and other infrastructure to the NW as
well as port and tourist facilities (including a casino) to the east.
The area of study is the only uncovered area, with sand and gravel
beaches on both sides. The Hydrobiological Station of Rhodos
which is located at the tip is a research unit of the Hellenic Centre
for Marine Research (HCMR), dedicated to aquatic research,
conservation of the marine environment and environmental
awareness. It hosts an aquarium museum which attracts more than
200,000 visitors annually. Besides the main building of the
Station, there are also underwater pumping facilities extending 30
m deep to the west, which provide seawater to the aquarium tanks.
The geological substratum of the NE tip of Rhodos is made up
of coherent Plio-Pleistocene formations of marl, sandstone and
conglomerates (Kombiadou et al., 2009). These formations have
been the main source of sediment of the area during the recent
Journal of Coastal Research, Special Issue 64, 2011
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Erosion and coast protection methods
Figure 1. Study site, Rhodos island, SE Aegean Sea, Greece (Photo of April 22nd, 2009, adapted from Google Earth).
Holocene. The geomorphological relief is generally low and mild.
The seabed is also dominated by hard bottom formations of PlioPleistocene origin.
The area is frequented by W and NW winds which generate
waves that cause a clockwise sediment displacement from west to
east. At the same time, stronger, sometimes extreme, but less
frequent E and SE winds relocate the sediment counterclockwise
from the east back to the west. This seasonal variation induced by
dominant westerly winds and strong easterly winds causes
significant changes in coastline configuration which are further
translated to local coastal erosion.
At the same time, the great urban development of the area
especially during the last few decades, as well as uncontrolled
anthropogenic activities of the hinterland, such as removal of
sediment from local rivers (the main sediment source of the study
area) for construction purposes, have led to sediment starvation
and amplified coastal erosion.
This erosion induced by natural processes and human activity
has not only impacted on the beach but on the local coastal
infrastructure as well: the lighthouse which is located at the tip has
suffered considerable damage during major storm events, whereas
Figure 2. The lighthouse after a major storm event in March 2003.
wave action has also damaged part of the underwater foundation
of the Hydrobiological Station and tourism facilities (Figure 2).
The significant environmental and socioeconomic implications of
these phenomena have alerted the local government, the
administration of the Station and the Port Authorities which are
particularly concerned about the protection of the infrastructure
from erosion and damage, as well as for the preservation of the
coastal area, which has attracted great touristic interest over the
years.
METHODS
In the present work the problem of erosion is investigated with
the aim to establish a clear picture about the mechanisms that
shape the coast of concern and those driving erosion which both
have triggered a considerable loss of beach material since the mid
20th century. A thorough geomorphological survey of the area
included coastal and bathymetric surveying and profiling using
GPS and portable echosounding equipment. The mechanisms that
shape the beach, the local morphodynamics and the geological
background of the area were defined and a detailed sediment
Figure 3. Historical coastline changes between 1997 and 2005
(after Kombiadou et al., 2009).
Journal of Coastal Research, Special Issue 64, 2011
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Anagnostou et al.
investigation at certain beach locations was performed. Recent
changes in coastline configuration between 1997 and 2005 (Figure
3) were also analysed.
This was combined with a study of the local wind and wave
climate. Available historical wind data from the meteorological
station of the International Airport of Rhodos covering the time
frame between 1955 and 1986 was utilized to acquire an image of
the wind climate in mid 20th century. High resolution hindcast
wind and wave results produced during the operational phase of
the POSEIDON system (Soukissian et al., 2000) operated by
HCMR, covering the period between 1999 and 2005, were also
used. The results refer to an unobstructed offshore location 25 km
NE of the concerned site (28ο30"Ε, 36ο30"Ν) at 900 m deep.
Once the wind and wave regime was established and the
morphodynamics (sediment type, paths etc.) were clarified, the
next step was to assess the potential solutions for coast protection.
These were first categorized according to their type and position
on the coast and each solution was then evaluated based on its
characteristics, possible impacts on the coast of concern and long
term effectiveness.
RESULTS
Seabed morphology
Figure 4 shows the locations where beach profiling and
bathymetric surveys were performed. The profiles extended to a
distance offshore where the first Posidonia oceanica meadows
were witnessed (at 10 m deep). No profiling was conducted west
of the study site, since this is the less impacted part of the site.
The eastern part of the study site is characterized by slopes of
the order of 10-12%, for depths ranging between 0 to 5 m. Further
deep the slopes become milder (3%). To the north, the relief
becomes smoother and the slope is uniform, at 6%, between 0 and
10 m deep. Greater slopes (of the order of 20%) are encountered
further deep (below 10 m deep).
The seabed at the eastern part of the site (which is strongly
influenced by severe wave action during winter) exhibits a very
characteristic zoning, which is summarized as follows:
i. Between 0 and 4.8 m: a hard substrate zone with
conglomerate formations parallel to the coastline.
ii. Between 4.8 and 7.0 m: sand and gravel formations and sand
bars.
iii. Between 7.0 and 8.0 m: hard bottom substrate –
conglomerate formations.
iv. Between 8.0 and 10.0 m: zone with fine sand to gravely sand
formations and bars.
v. Below 10 m: scarce rocky formations and Posidonia beds –
morphology is considered as non-changing.
Wind and Wave Climate Analysis
Analysis of the historical wind data from the meteorological
station of the airport of Rhodos for the years 1955-1986 as well as
wind/wave analysis of the hindcast data (1999-2005) showed that
winds of westerly directions (SW, W and NW) dominate the area
and the frequency of their occurrence is of the order of 60%. On
the other hand, winds of easterly directions (NE, E and SE) are
remarkably less frequent (11% frequency of occurrence). Winds
directly blowing from North are less experienced.
The western part of the study area is directly exposed to the
dominant westerly winds which may reach in intensity the order of
6 on the Beaufort scale. These winds occur during spring and
summer. The eastern part is dominated by SE winds, usually
blowing in the area during winter; although less frequented these
winds are much stronger (8 on the Beaufort scale) and create
waves of relative intensity which can relocate large amounts of
sediment.
Sediment transport patterns
Due to the configuration of the coastline and angle of incident
waves there is significant sediment move around the tip and
therefore seasonal coastline changes. During spring and summer,
the western and north western winds are dominant and create
waves of relevant direction and intensity. These waves move
sediments in a clockwise manner towards the north; sediment is
deposited on the northeastern side of the tip. Due to wave
diffraction, a sand spit is formed towards the east. Keeping in
mind this material originated from the western part of the tip,
during summer months the width of the western side becomes
significantly smaller.
On the other hand, during winter months, the eastern part of the
tip is dominated by easterly and south easterly winds which
generate waves of same directions. In a similar manner to that
described before, wave action during winter forces sediments to
move counterclockwise back to the west. In other words, the
material which was once forced away from the west now returns
where it came from. If winter events are intense and durable, then
there is relocation of significant sediment amounts to the west and
this has threatened the coastal infrastructure.
The seasonal variation described above and the sediment loss
which has been identified over the years are expressed through
seasonal change in coastline configuration. This is illustrated in
Figure 3.
DISCUSSION
Figure 4. Bathymetry and beach profile locations.
When it comes to protecting an eroding beach the available
coastal engineering solutions include beach structures parallel to
the shore, structures normal to the shore, stabilization works (such
as sea walls) and beach nourishment (Anagnostou et al., 2002;
Simm et al., 1996). Selecting the most suitable method depends on
environmental, technical, economical, political, social and visual
limitations. Any decision as to whether structures are needed and
where should be seen as part of an integrated approach for beach
management (Antoniou et al., 2009).
Journal of Coastal Research, Special Issue 64, 2011
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Erosion and coast protection methods
From the analysis presented it is clearly established that there is
a periodic movement of sediments around the tip which is
attributed to seasonal wind variations. This is exemplified also by
the many changes experienced by the coastline, as shown in
Figure 3.
Another important aspect that needs to be taken into
consideration is the recreational (touristic) use of the beach. This
is a rather limiting factor during the design of coastal measures.
Combined with various environmental criteria, the attention is
placed on maintaining the beach in its natural form. These pose
limitations to construction of coastal works directly on the coast or
parallel to it, as this would aesthetically deteriorate the site, with
negative consequences on the marine environment as well.
Construction of groynes or breakwaters would also entail
placement of large amounts of blocks on the beach or within very
few meters from the coastline, which is again not an effective
solution given the recreational use of the site. What is more,
construction of a groyne field to the west would require
foundations being placed in very deep water, which is very
expensive.
A feasible and rather environmental friendly solution would be
the artificial nourishment of the area. This method, if carefully
designed, has smaller environmental impacts than engineering
works discussed so far, it is less expensive, and, except during
construction phase, there is no visual impact. However, for a
sustainable design of this scheme, simulation of sediment patterns
would be appropriate and is strongly recommended. Also, a
monitoring scheme should support all stages of the nourishment
project and advise accordingly. Monitoring of the first stage would
determine the execution or not of successive stages ensuring
viability of the method.
Kombiadou, K.; Chatiris, G.A; Androulidakis, G.; Sioulas, A;
Krestenitis, G.; Anagnostou, Ch. and Issaris, G., 2009.
Investigation of erosion at the cape of Rhodos and defence
measures. 9th Symposium on Oceanography & Fisheries, Vol.
1. In Greek.
McKenna, J.; Cooper, J.A.G. and O’Hagan, A.M., 2008.
Managing by principle: a critical assessment of the EU
principles of ICZM. Marine Policy, 32, 941-955.
Simm, J.D.; Brampton, A.H.; Beech, N.W. and Brooke, J.S., 1996.
Beach management manual. London: Construction Industry
Research and Information Association (CIRIA), Report 153,
448p.
Soukissian, T.H.; Chronis, G.T. and Nittis, K., 2000. POSEIDON:
Operational Marine Monitoring System for Greek Seas. Sea
Technology, 40(7), 32-37.
Xeidakis, G.S.; Delimani, P.K. and Skias, S.G., 2006. Sea Cliff
Erosion in the Eastern Part of the North Aegean Coastline,
Northern Greece. Journal of Environmental Science and
Health, Part A, 41(9), 1989 – 2011.
ACKNOWLEDGEMENT
Special thanks are extended to the research team of the
Laboratory of Maritime Engineering and Maritime Works,
Department of Civil Engineering, Aristotle University of
Thessaloniki and to Yannis Issaris for their enormous support
during this study. The authors are also thankful for the help of the
research staff at the Hydrobiological Station of Rhodos.
CONCLUSION
Several types of beach protection measures may be applied to
prevent or battle erosion. The available coastal engineering
solutions for restoring an eroding beach in Rhodos island (SE
Aegean Sea, Greece) were critically assessed and compared.
Given the specific geomorphological characteristics of the area,
the local wind/wave climate patterns which generate a local
seasonal climatic variation and various environmental, social and
technical limitations, the optimal solution proposed is that of
periodic beach nourishment at certain beach locations. However,
this remains one yet human intervention and several
environmental impacts should be anticipated. As such, it should be
seen as part of an integrated coastal strategy involving a good
understanding of beach and coastal dynamics of the wider coastal
system (contrast to common localized approaches applied so far),
which would assist in sustainable management of this valuable
resource.
LITERATURE CITED
Anagnostou, Ch.; Drakopoulou, P. and Soukissian, T., 2002. The
morphodynamics of the west coast of Messiniakos Gulf and
the role of the Agios Andreas marina. Proceedings of the 2nd
Pan-Hellenic Conference on Management and Development
of Coastal Zones (Athens, Greece), pp. 249-252. In Greek.
Antoniou, P.F.; Kyriakidou, H. and Anagnostou, Ch., 2009.
Cement filled geo-textile groynes as a means of beach
protection against erosion: a critique of applications in Greece.
Journal of Coastal Research, Special Issue No. 56, pp. 463366.
Cooper, J.A.G. and McKenna, J., 2008. Working with natural
processes: the challenge for Coastal Protection Strategies.
Geographical Journal, 174, 315-331.
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