Journal
Journalof
ofCoastal
CoastalResearch
Research
SI 64
pg -- pg
875
879
ICS2011
ICS2011 (Proceedings)
Poland
ISSN 0749-0208
Environmental Sensitivity Maps: the northern coast of Gibraltar Strait
example
A. Bello Smith†, G. Cerasuolo†, J.A. Perales†† and G. Anfuso†
† Dep. Ciencias de la Tierra, Facultad de Ciencias del
Mar, Universidad de Cádiz, Polígono Río San Pedro
s/n, 11510 Puerto Real, Spain.
E-mail: [email protected];
‡ Dep. Tecnología del Medio Ambiente,
Centro Andaluz de Ciencia y Tecnologías Marinas
(CACYTMAR), Universidad de Cádiz,
Polígono Río San Pedro s/n, 11510 Puerto Real, Spain.
E-mail: [email protected];
ABSTRACT
Bello Smith, A., Cerasuolo, G., Perales, J.A. and Anfuso, G., 2011. Environmental Sensitivity Maps: the north
coast of Gibraltar Strait example. Journal of Coastal Research, SI 64 (Proceedings of the 11th International
Coastal Symposium), – . Szczecin, Poland, ISSN 0749-0208
In order to create Environmental Sensitivity Maps for the northern coast of the Gibraltar Strait (Spain), UHOHYDQW
information has been collected in three different layers (“Geomorphologic characteristics”, “Biologic” and
“Socio-economic” resources) by means of field observations and measurements of beach morphology, personal
interviews with professionals of different areas and the collection of bibliographic information. The collected
data have been represented in Environmental Sensitivity Maps developed in a GIS environment and best
cleaning techniques to be adopted in each zone have also been proposed according their effectiveness and
environmental impact. Most common techniques included natural long-term restoration (principally), aspiration,
absorption, manual removal, flushing and bioremediation.
ADDITIONAL INDEX WORDS: oil pollution, beach changes, oil burial, cleaning techniques.
INTRODUCTION
Petroleum is the most important energy source in actual society
and it’s importance in global economy has not stopped growing
since the 19th century. Tankers move approximately 2·109 metric
tons of oil every year (UNCTAD, 2006) in the world with an
associated high risk of oil spill which is extremely harmful to
coastal environments and socio-economic activities. Impacts of an
oil spill depend on a set of factors such as the amount of oil
spilled, oil physical-chemical properties and environmental
conditions, essentially wind, waves and currents at the moment
and after the accident. Other important aspects are the presence of
sensitive biological and/or human-use resources and the lapsed
time between the spill and the activation of response and
restoration actions, e.g., shorter it is better it is (Jensen et al.,
1998, Dicks, 1999, NOAA, 2002).
In order to have a well organized and fast response to such kind of
accidents, the knowledge of coastal environments and human
activities and the existence of management and prevention tools
are crucial factors. In this sense, Contingency Plans (or
Emergency Plans) can be developed for very specific areas that
present a high level of risk. Environmental Sensitivity Maps
represent a key tool within the Contingency Plans, and contain
basic information on coastal geomorphology, biology and socioeconomic activities in different geo-referenced layers which are
overlapped by GIS tools to obtain a vulnerability map for a
specific area. The assessment of coastal sensitivity to oil spill
events started in the 1970s in the U.S.A. (Gundlach and Hayes,
1978) and rapidly evolved in past decades because of the
development of Geographical Information System (GIS),
Multivariate Analysis, Remote Sensing techniques, etc. (Jensen et
al., 1990, NOAA, 2002, Santos, 2009, Lorenzo et al., 2009,
Azevedo et al., 2009).
Many oil spill accidents affected coastal areas around the world in
past decades, in Spain most important have been accidents in
which these vessels were involved: “Polycommander” (1974),
“Urquiola” (1976), “Mar Egeo” (1992) and “Pestige”, in
November 2002, which released 40,000 tons of oil that affected
more than 1,000 km of littoral in Galicia (northwest Spain),
Portugal and France.
In Spain, despite all aforementioned accidents which affect the
very energetic coast of Galicia, one of the most problematic and
risky area that, fortunately, until present days only recorded minor
accidents, is the Gibraltar Strait which communicates the
Mediterranean Sea and the Atlantic Ocean and Europe with
Africa. In this specific zone, the major risk of oil spill is due to
ship collision: c. 100,000 vessels cross it every year including c.
18,000 vessels with dangerous shipments and a high flow of
ferries transporting passengers between Spain and Morocco
(Walliser and Piniella, 2000). The aim of this work is the
realization of an Environmental Sensitivity Maps for the northern
coast of the Gibraltar Strait taking into account the guidelines
proposed by NOAA (2002).
STUDY AREA
The studied area, which presents a length of c. 130 km, extends
from Trafalgar Cape to Chullera Point, along the Atlantic Ocean,
the Gibraltar Strait, and the Mediterranean Sea, and
administratively included in Cadiz Province, in Andalusia Region
(SW Spain, Fig. 1).
The Atlantic sector presents micro (< 2 m) and mesotidal (> 2
m) environments exposed to wind and waves approaching from
the west and, secondarily from the southeast. In detail, the
investigated area is composed by cliffs and quartz-rich sandy
sectors and generally presents a low level of urbanization with
several isolated coastal villages and tourist beaches.
Journal of Coastal Research, Special Issue 64, 2011
875
Environmental Sensitivity Maps for Gibraltar Strait
Figure 1. Location map of the investigated area (source: Google Map).
The Gibraltar Strait is microtidal environment exposed to winds
and waves approaching from the east and, secondarily, from the
west. Coastline is composed by high cliffs, bluffs and rocky shore
platforms. Within this zone, Algeciras Bay presents several small
quartz-rich beaches and it is the most populated area (around
250,000 inhabitants) with coastal towns, port activities,
petrochemical industry and fishing activities.
The Mediterranean littoral is a microtidal environment
particularly exposed to wind and waves approaching from the east
and southeast. Elongated and rectilinear beaches and (secondarily)
pocket beaches are observed and composed by fine and medium
dark litarenitic sands. Littoral area is generally urbanized because
summer houses and coastal villages and beaches present an
important tourist use.
METHODS
In order to create Environmental Sensitivity Maps for the
selected area, several information has been collected and
organized in different layers: i) the “Geomorphologic” layer,
where the different geomorphologic environments have been
described; ii) the “Biological resources” layer, where different
biological resources have been represented from a oil vulnerability
point of view, and iii) the “Socio-economic activities” layer.
Information concerning the different layers has been obtained by
means of field observations, personal interviews with
professionals of different areas, as well as the collection of
bibliographic data from governmental, technical and no
governmental institutions. Special attention has been devoted to
beach characteristics, e.g., beach slope, morphodynamic behavior,
vertical beach changes and sediment grain size. All previous
aspects are key factors for the establishment of cleaning
techniques because control oil percolation in sediments, burial risk
and viability of people and machinery to operate during cleanup
activities (NOAA, 2002). In this sense, four beach surveys have
been carried out in May, June, August and September 2010 at 12
beach locations (Fig. 1). A total station has been used to carry out
beach proofing from the backshore to a depth equivalent to the
mean spring tide low water level. Beach width, beachface slope
and vertical beach changes (i.e., erosion/accretion processes) have
been afterwards quantified (Table 1). Foreshore slope has been
classified following the NOAA (2002) guidelines which
differentiate among steep slopes (e.g., presenting values greater
than 30º), moderate (between 30º and 5º, indicated in Table 1 with
the letter ”M”), and flat slopes (“F”, less than 5º). Each beach
profile has been considered as broadly representative of a coastal
sector according to detailed field observations. Samples of beach
sediment have been collected and sieved in laboratory with a Rotap machine using a nest of sieves at 1 phi intervals.
Granulometric parameters have been calculated according to Folk
and Ward (1957) and used to classify investigated beaches within
the substrate type classes of NOAA (2002). In detail,
aforementioned classification distinguishes among fine- to
medium-grained sand (ranging in size from 0.06 to 1 mm and
indicated as “F-M” in Table 1), coarse-grained sand (“C”, 1-2
mm), granule (“G”, 2-4 mm), etc.
The collected data have been represented in Environmental
Sensitivity Maps developed in a Geographic Information System
(GIS) with the ArcGIS©9, ESRI® ArcMap™ 9.2 and the ESRI®
ArcCatalog™ 9.2 software. The orthophotographs of the
Andalusia coastline at 1:10,000 scale, based on a Quickbird
satellite image with a geometric resolution of 0.7 m, have been
used as basic cartography.
RESULTS AND DISCUSSION
Geomorphologic characteristics, biological resources and human
activities and uses have been investigated along the studied littoral
(Fig. 2). Special attention has been devoted to geomorphologic
characteristics and especially to sandy littoral sectors in order to
characterize beach behavior, morphological changes and beach
grain size. Previous factors are extremely important in
Journal of Coastal Research, Special Issue 64, 2011
876
Bello Smith et al. (2011)
Geomorphologic characteristics
The “Geomorphologic” layer (Fig. 2) contained information about
main geological features, e.g., cliffs, rock shore platforms, dunes,
estuaries, lagoons and freshwater wetlands, dry and intertidal
beach areas and riverside zones.
Atlantic
Ocean
Table 1. Morphological changes, slope and grain size at
the investigated beaches.
Changes (m)
Slope Gr. Size
Location
Berm Foreshore (º) Ber./For.
+0.15
M
F-M/C
Cape Trafalgar +0.41
Gibraltar
Strait
determining most appropriate cleaning techniques and in
establishing priorities in cleaning activities.
Potential burial of oil in beaches is in fact an important issue that
must be kept into account in Environmental Sensitivity Maps and
Emergency Plans (NOAA, 2002). As exempla, Gonzalez et al.
(2009) stated that cleaning activities in Galicia, after the Prestige
accident continued during several years because of the sporadic
appearance of reduced quantities of fuel. In the beaches
investigated by previous authors, more than 10,000 tons of
residual materials were removed from the berm and intertidal zone
in the period between winter 2002 and summer 2006 because the
intermediate-reflective beach state and great morphological
variability which favored the oil to become partly buried. Similar
processes were recorded in near beaches by Lorenzo et al. (2009)
which used ground-based radar to investigate the depth of oil
burial that ranged from few centimeters to 1-2 meters.
Med.
Sea
Figure 2. Geomorphologic characteristics, Biological and
Anthropic resources for the investigated area.
Cliffed sectors and rock shore platforms especially prevail in the
Gibraltar Strait and within Algeciras Bay. Beaches and dunes are
observed, on the Atlantic side, at Trafalgar Cape, Barbate, Zahara
de los Atunes, Bolonia, Valdevaqueros and Los Lances and on the
Mediterranean side, at Sotogrande, Torreguadiario, Guadalquiton,
La Atunara and La Alcaidesa. Small pocket beaches (e.g., Getares,
Rinconcillo, Espigon, etc.) are observed within Algeciras bay.
Most important estuaries, lagoons and freshwater wetlands are
observed at Palmones and Guadiaro river mouths and Barbate.
The beach monitoring program allowed the reconstruction of
beach characteristics, behaviour and seasonal variability, in fact, it
was carried out during spring-autumn period when, after winter
storm season, natural beach recovery and berm formation take
place (Anfuso et al., 2002). Maximum morphological changes
recorded during the study period at berm location and in foreshore
zone of investigated beaches have been presented in Table 1.
Foreshore slope values and grain size have also been reported
following the terminology explained in methods. Beach sediments
ranged from fine sand to gravel with sorting values ranging from
the “moderately well sorted” to the “poorly sorted” intervals (Folk
and Ward, 1957).
On the Atlantic side, beaches at Trafalgar, Hierbabuena and
Cañillo recorded important morphological changes due to berm or
beach cusps formation. Mentioned beaches presented an
intermediate state between the “dissipative” and “reflective” states
described by Wright and Short (1984) and Masselink and Short
(1993) and showed the prevalence of plunging/spilling breakers
and medium to coarse sediments. Zahara de los Atunes and
Bolonia were similar to the “Low tide terrace” beach state
described by Masselink and Short (1993), characterised by
spilling/plunging breakers. Valdevaqueros and Los Lances
presented fine to medium sediments, moderate beach slopes and
small-intermediate changes in the foreshore, berm being a
common figure in August and September. Within Algeciras bay,
Getares, Rinconcillo (partially) and Espigon (Table 1), showed
relatively steep and narrow foreshore areas and very small
morphological changes because located in sheltered microtidal
environment. They are visually similar to the “reflective” beach
state described by Wright and Short (1984) and Masselink and
Short (1993) and are composed by fine to medium sand and
granule (terminology according to NOAA, 2002).
Last, Mediterranean beaches presented moderate slope and
significant changes in the upper foreshore because the formation
Hierbabuena
+0.35
-0.75
F
F-M
Cañillo
-0.18
0.01
M
C/G
-0.25
+0.98
F
F-M
+0.45
Bolonia
Valdevaqueros -0.20
+0.24
Los Lances
+0.30
F
F-M
+0.38
M
F-M
+0.55
F
F-M
Getares
+0.25
+0.15
M
F-M/G
Rinconcillo
+0.12
+0.15
F
F-M
Z. los Atunes
Espigon
-0.13
0.01
M
G/F-M
Castillo
+0.65
+0.20
M
F-M
Torrenueva
+0.22
+0.15
M
F-M/G
Journal of Coastal Research, Special Issue 64, 2011
877
Environmental Sensitivity Maps for Gibraltar Strait
of cusps or berm, they being close to the “reflective” beach state.
Overall, concerning beach change modalities, investigated beaches
principally recorded parallel accretion or retreat more than beach
pivoting which was observed in very few beach surveys.
Biological characteristics
The “Biological” layer (Fig. 2) contained different categories
according to their level of protection, which has been strictly
related to their ecological interest (NOAA, 2002): i) Natural parks,
i.e. “La Breña and Marismas de Barbate” and “Estrecho de
Gibraltar”; ii) Natural Spots, i.e. “Los Lances” Beach, “Río
Palmones” Marshes and “Guadiaro River” Estuary, and iii)
Natural Monuments, i.e. the “Trafalgar” Isthmus and “Bolonia”
Dune. Further, it has been mapped the location of organisms of
special interest such as several species of protected marine and
other birds (feeding and resting areas), of Orange corals (Astroides
calycularis) and Kelp fields (Laminarias ochroleuca), these two
last essentially localized close to Tarifa.
Socio-economic characteristics
The “Socio-economic” layer (Fig. 2) contained information
concerning land uses and human activities developed on the
coastal zone and sites of historical and cultural heritage. In detail,
coastal uses have been divided into “Ports and industries” and
“Urban Areas” categories. The most industrialised and urbanized
area is Algeciras bay with thermal power industries, a refinery,
water intake points, etc. Other urbanized areas are Barbate, Zahara
de los Atunes, Tarifa and Sotogrande. Anthropogenic structures,
generally associated with ports or industries, i.e., breakwaters,
groins, seawalls, riprap revetments and dikes, have been
recognized and mapped too. Three principal socioeconomic
activities have been also differentiated: i) “Aquaculture”, mainly
developed in Barbate, ii) “Tuna fishing”, in Barbate, Z. de los
Atunes and Tarifa and iii) “Shellfish farming”, in Barbate and
Palmones rivers, and between Gibraltar and Torrenueva.
Within the cultural and historic patrimony, they have been
identified: i) the “Terrestrial Historic Heritage” areas, which
included Watching Towers distributed along the whole
investigated littoral, Roman and Phoenician archaeological
remains (i.e., the villages of Carteia, in Algeciras bay, and Baelo
Claudia, on the Atlantic littoral), Civil War Bunkers and the
remains of the Getares Whale Factory and ii) the “Subaquatic
Archaeological” Heritage, which included areas containing
archaeological vestiges essentially linked to the presence of
sunken vessels.
Littoral operational ranking
Coastal sectors have been classified according to the ranking
presented in NOAA (2002), which is essentially based on
geomorphologic characteristics and ranges from 1 (for low
sensitive) to 10 (for high sensitive) environments. In a further step,
considering
information
contained
within
the
three
aforementioned investigated layers, the study area has been
divided into 58 zones according to their geomorphology. For each
section of littoral best cleaning techniques (effectiveness and
environmental impact) has been proposed.
Cliffed sectors and rock shore platforms at Gibraltar Strait area
have been respectively ranked as 1 A and 2 A, in fact these kinds
of shorelines are exposed to energetic conditions which tend to
keep oil offshore by reflecting waves. The substrate is
impermeable so oil remains on the surface where natural processes
quickly will remove it within a few weeks. No cleanup is
generally required, except for removing oiled debris and oil
deposits at the high-tide line in rock shore platforms when access
is safe.
Investigated sandy sectors have been classified taking into account
grain size, beach slope and morphological changes. Grain size was
the most important factor because control the depth of penetration
which is also linked to sediment sorting (range of grain sizes in the
sediment). Deepest penetration is expected for coarse sediments
(gravel) that are most uniform in grain size (well-sorted). Beach
slope and grain size also control the ability for people and
machinery to operate during cleanup activities. At places, beach
slope values are affected by the presence of contouring conditions
such as rock shore platforms in nearshore area, human structures,
etc. (Anfuso et al., 2002). The application of the NOAA (2002)
criteria designed for tidal environments does not take into account
tidal range for beach classification. In the study area all beaches
(but Trafalgar, Hierbabuena, Cañillo and Z. de los Atunes) are
microtidal environments and their foreshore slope is probably
overestimated when compared with the values presented in the
NOAA (2002) classification, in fact exists a well recognized
indirect proportionality between foreshore slope and tidal range.
All the Atlantic beaches (but Trafalgar and Cañillo) and the
Rinconcillo and Espigon (in Algeciras bay) belong to the category
3 A, within rank 3 “Semi-Permeable Substrate, Low Potential for
Oil Penetration and Burial” (NOAA, 2002). These characteristics
are attributed to beaches with fine- to medium-grained sediments
typically well compacted and generally flat slope values and oil
penetration values usually less than 10 cm. Despite the moderate
slope of Espigon beach, it has been classified within this category
because in sheltered habitats slope is a less important
distinguishing factor and, further, its slope is partially artificial
because affected by the presence of a groin on the southern beach
edge and a promenade on the back beach. Following NOAA
(2002), the rate of sediment mobility is low, so the potential for
rapid burial is low; this is certainly applicable to studied beaches
classified within this category but exceptions can be observed at
Hierbabuena and Z. de los Atunes because the presence of beach
cusps that can generate important morphological changes in a tidal
cycle. Smooth slopes observed in beaches belonging to this
category, promote dissipation of wave energy further offshore and
oil remains longer in the intertidal zone. Best cleaning techniques
consist in the construction of artificial berm, use of artificial
barriers, absorbents, manual removal of oiled debris and flushing
with sea water. Cleanup is simplified by the relatively firm
substrate that can support vehicular and foot traffic.
Trafalgar, Cañillo, Getares and the Mediterranean beaches belong
to the rank 4, “Medium Permeability, Moderate Potential for Oil
Penetration and Burial”.
Substrate is permeable with sediments from coarse-grained sand to
granule, with oil penetration up to 25 cm is possible. Following
NOAA (2002), beaches within this category present a relatively
high variability with accumulation of up to 20 cm of sediments
within a single tidal cycle and have great potential for burial,
particularly if the oil is stranded at the beginning of the
depositional period. Previous assumptions are partially applicable
to beaches classified in this study within this category but beach
changes are probably less important and related to the presence of
beach cusps. Their steep intertidal areas are usually subject to
abrupt wave run-up and breaking, and even reflection in places,
which enhances natural cleanup of the shoreline. Cleaning
techniques consist in the construction of artificial berm, use of
artificial barriers, absorbents, manual removal of oiled debris and
flushing with sea water and high pressure and finally
bioremediation when polishing techniques are needed.
Journal of Coastal Research, Special Issue 64, 2011
878
Bello Smith et al. (2011)
Exposed breakwaters and docks at Tarifa, Algeciras and
Sotogrande port structures belong to the rank 6 “High
Permeability, High Potential for Oil Penetration and Burial”.
These kind of human-made structures have added problems
because they are usually placed at the high-tide line where the
highest oil concentrations are found and the breakwaters and
docks boulders are sized so that they are not reworked by storm
waves. Flushing can be effective for removing mobile oil, but
large amounts of residue can remain after flushing, particularly for
heavy oils.
Sheltered breakwaters, seawalls, docks, riprap revetments
(essentially located in Algeciras bay) are ranked 8 “Sheltered
Impermeable Substrate, Hard; epibiota usually abundant”. Oil
tends to coat rough block surfaces persists long-term because in
sheltered settings. Oil natural removal rates are slow and cleanup
is often required and often difficult and intrusive. For these areas,
flushing is the most appropriate technique.
Salt marshes and estuarine environments at Barbate, Palmones and
Guadiario rivers have been ranked 10, “Vegetated Emergent
Wetlands”. Marshes and other vegetated wetlands are the most
sensitive habitats because of their high biological use and value,
difficulty of cleanup, and potential for long-term impacts to many
organisms depending on the season of the year when the spill
happens and the species. It is important to protect aforementioned
environments by the use of floating barriers and construction of
artificial berm. Most common cleaning techniques are manual and
mechanic removal, use of absorbents and aspiration.
Overall, the technique that prevails is the natural long-term
restoration, although aspiration, use of absorbents, manual
removal, flushing with sea water and bioremediation have to be
used too at several coastal sectors.
CONCLUSIONS
Investigated area presents a length of c. 130 km and extends
along the Atlantic Ocean, the Gibraltar Strait, and the
Mediterranean Sea, in SW Spain. In order to create Environmental
Sensitivity Maps for the investigated area, which is a very
problematic and risky area to oil spill accidents because the high
possibility of ship collision, several information has been collected
and organized in different layers.
Regarding to the geomorphologic aspects, Gibraltar Strait is
essentially characterized by cliffed sectors and rock shore
platforms and Atlantic and Mediterranean zones present a
predominance of sandy beaches which have been further divided
in smooth, fine to medium sand beaches and relatively steep and
coarse grained beaches according to the NOAA (2002)
classification. Further studies are needed to full understand
morphodynamics behavior of investigated beaches that at places
recorded beach slope values, morphological changes and grain
size characteristics linked to contouring, specific conditions, this
way making difficult their classification according to the NOAA
(2002) guidelines.
Concerning the biological resources, there is a predominance of
Natural Parks in the Atlantic and Gibraltar Strait areas and of
Natural Spots in the Atlantic and Mediterranean zones.
Regarding to the anthropogenic resources, large industrial and
urban areas are observed within Algeciras bay; fish farms,
aquaculture activities and tuna fishing are concentrated in Barbate
area and shellfish farms are found on the Mediterranean littoral.
Cleaning techniques that prevail are natural restoration, followed
by mechanical and manual elimination of oiled debris, flushing
and finally when polishing is required, bioremediation techniques
could be a possible solution.
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ACKNOWLEDGEMENTS
This work is a contribution to the Andalusia Research Groups PAI
RNM-328 and TEP 181 and was partially developed at the Centro
Andaluz de Ciencia y Tecnología Marinas (CACYTMAR), Puerto
Real (Cadiz, Spain).
Journal of Coastal Research, Special Issue 64, 2011
879