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The Nazaré coast, the submarine canyon and the giant waves - a synthesis

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The topic of this work is the coastal zone of Nazaré (located in central western mainland Portugal) and adjacent offshore, in particular the submarine canyon, summarizing and organizing available information in order to be used by a wide public. The physical characterization, mainly focused on the geomorphology and coastal dynamics, is based on previously published works but also on new data. The information here provided aims to help tourists not familiar with the region, namely those involved in surfing practices, in order to understand the peculiar setting and the expected waves. An explanation for the genesis of the Nazaré giant waves is also provided.
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1
THE NAZARÉ COAST,
THE SUBMARINE CANYONand
THE GIANT WAVES - a synthesis
Pedro Proença Cunha and Margarida Porto Gouveia
MARE – Marine and Environmental Sciences Centre
University of Coimbra, Faculty of Sciences and Technology
Department of Earth Sciences
Coimbra, Portugal
Coimbra, February 2015
CHAPTER 1.
INTRODUCTION - 2
Abstract
1.1 Objectives - 3
1.2 Geographical setting - 3
1.3 Climate - 5
1.4 Geological setting - 5
1.5 Geomorphological setting - 7
1.6 Anthropic interventions in the vicinity of Nazaré - 10
1.7 The picturesque village of Nazaré - 11
CHAPTER 2.
LITTORAL MORPHODYNAMIC AGENTS - 15
2.1 Winds - 15
2.2 Tides - 15
2.3 Waves - 15
CHAPTER 3.
THE EVOLUTION OF THE NAZARÉ COAST - 18
3.1 Evolution during the last 18 kyrs - 18
3.2 Historic evolution of the coast - 19
3.3 Evolution of the coastline between 1958-2014 by analysis of aerial photos and images - 25
CHAPTER 4.
SURFING PRACTICES IN NAZARÉ - 26
Acknowledgements - 29
References - 29
CONTENTS
2
Abstract
The topic of this work is the coastal zone of Nazaré (located in central western mainland Portugal) and
adjacent o≠shore, in particular the submarine canyon, summarizing and organizing available informa-
tion in order to be used by a wide public. The physical characterization, mainly focused on the geo-
morphology and coastal dynamics, is based on previously published works but also on new data. The
information here provided aims to help tourists not familiar with the region, namely those involved in
surfing practices, in order to understand the peculiar setting and the expected waves. An explanation
for the genesis of the Nazaré giant waves is also provided.
Photo taken at Nazaré promontory in November 1st, 2011 (from www.zonnorthcanion.com)
INTRODUCTION
1.1 OBJECTIVES
This work aims to present the general
characteristics of the Nazaré canyon
and adjacent beach, addressing the
geomorphology and coastal dynamics.
1.2 GEOGRAPHICAL SETTING
Nazaré is a town and a municipality in
the west sub-region (NUT III/Leiria
District), in western central Portugal.
The county is divided into three
administrative areas: Nazaré, Valado
dos Frades and Famalicão (Fig. 1.1). It
borders the Atlantic Ocean in the west
and its neighboring municipality is
Alcobaça.
Nazaré town occupies an area of 82.4
km2, which maximum length is 13 km, in
the East - West and 15 km in the North
- South. Nazaré hosts about two-thirds
of the population of the municipality,
having a little more than half of the entire
area. In the last ten years the resident
population has only increased by eight
individuals.
The landscape is mainly characterized
by areas with pinewoods associated to
higher elevations and agricultural lands
of lower elevations along the Alcoa’s
River valley and near Nazaré, dominated
by irrigation (Fig. 1.2). The following
landscape units can be considered:
• The Alcoa river valley, with the fertile
fields of Valado dos Frades and Cela,
which is occupied with arable crops
on irrigated land (corn and vegetable
orchards);
• The Nazaré beach develops along a
flattened coastal area, north and south of
the promontory;
• The Plateau of National Forest Valado
de Frades develops on the north and the
east of Nazaré. The urban settlement is
almost non-existent and the forest cover
has little biodiversity;
• The Cli zone is represented by woods
and some pine forests, alternating with
small areas of bare soil;
• The sites of Pederneira and Nazaré,
which were ancient seaports. At the top
of the headland is located the Sítio, a
relevant viewpoint.
In the past, Pederneira and Sítio were
separated by pinewood but, due to the
increasing urban pressure, they are now
almost connected due to the various
housing developments that have been
made between them.
1.
4
Fig. 1.1 - Geographic location of
Nazaré (a sector of the 1:500,000
map of the Igeo).
Fig. 1.2 - The Nazaré region,
as showed by the Google Earth (2012 image).
1.3 CLIMATE
For the climate characterization of the
Nazaré municipality, the values recorded
by the Aljubarrota and Leiria udometric
stations were used together with Alcobaça
climatological station (Câmara Municipal da
Nazaré - CMN, 2011). The annual average
temperature ranges from 12.5°C to 17.5°C.
The highest values are recorded during
June to September, which corresponds
to the period of the year with the highest
number of forest fire occurrences. In the
town of Nazaré, the daily average maximum
temperature never reaches 30°C in summer
and the average minimum daily temperature
could reach 4°C only in January. During
summer, temperatures reach higher values
but the variations in minimum temperatures
during the night are not significant because
the proximity to the sea.
The relative air humidity is high and
ranges between 60% and 87%, according
to the data from the meteorological station
of Alcobaça (1978-1990). The humidity
values decrease in the warm months,
which makes days drier. In the rainy
season the sea plays an important role as
humidity increases as a result of a larger
amount of evaporation.
According to the “Atlas do Ambiente”,
the average annual precipitation for the
municipality of Nazaré is 700 - 1000 mm.
The rainfall reaches its maximum during
the months of January (138 mm) and
December (128 mm) and the minimum
during the months of July (6 mm) and
August (10 mm), thus, following the
trend of the Mediterranean climate where
the rainfall is concentrated in the colder
months of the year.
The dominant winds are from NW and
SW quadrants, the latter associated
with atmospheric depressions. Given its
orientation E-W, the headland interferes with
the winds and has a great influence on the
dynamic conditions of the sea near the beach.
1.4 GEOLOGICAL SETTING
In the Nazaré region, a sedimentary record
ranging in age from the Lower Jurassic to
the Quaternary can be found (Figs. 1.3 and
1.4) (e.g. França & Zbyszewski, 1963; Dinis et
al., 2008). The lithologies are diversified and
comprise siliciclastics, marls and limestones.
Volcanic rocks also occur locally and granite
and metamorphic rocks outcrop at the
Berlengas archipelago (at SW).
Some important tectonic faults exist in
the region, namely the NE-SW trending
Leiria-Caldas da Rainha structure (e.g.
Dinis et al., 2012).
Fig. 1.3 - The onshore geology of the Nazaré region:
a: location. b: main geological units (Dinis et al., 2006).
Fig. 1.4 - Geological map of the Nazaré region (a sector of
the Carta geológica de Portugal, scale 1/1000000; LNEG, 2010).
j - Jurassic; k - Cretaceous; e - Eocene; n - Neogene;
q - Quaternary; faults represented in black.
6
This coast has sandy beaches that are
straight stretches of coarse sand to pebbles,
extending for several kilometers, limited by
rocky headlands (Henriques, 1996; Cascalho
et al., 2014). Belts of aeolian dunes border
the landward edge of the beaches, resulting
from sand being carried by the wind from the
upper beach sector (Henriques, 1996; André
et al., 2009; Ramos, 2014). In particular,
the presence of hard Cretaceous limestones
explains the presence of the Nazaré headland.
In the south, the sea clis are cut on Upper
Jurassic siliciclastics but up north of the
headland the clis are cut on soer Eocene
sandstones.
Some of the sands that, moved by littoral dri,
could reach the Nazaré canyon are transported
to deeper marine environments (Oliveira et
al., 2007, 2011, 2014), but the majority could
surpass towards south the Nazaré headland
(Duarte et al., 2014) (Fig. 1.5).
The adjacent continental platform has
outcrops of the rocky basement or a cover
of sands and sandy gravels. Sediments
recovered from the canyon consist mostly
of terrigenous mud and, locally, sands of
presumed turbiditic origin (e.g. Stigter et
al., 2007; Arzola et al., 2008; Lastras et
al., 2009; Martín et al., 2011; Ramalho et
al., 2014). The current dynamics records
demonstrate the presence of moderately
strong tidal currents in the upper and middle
canyon, directed predominantly along the
canyon axis and typically alternating in up
and down – canyon direction with a semi-
diurnal frequency. Submarine canyons are
referred as active conduits for transport of
particulate matter to the deep sea. In this
case, the sedimentary material derived from
the near-shore, (predominantly silt and clay)
is transported down the canyon and delivered
at the abyssal plain. Turbidity currents
strong enough to transport sand down the
canyon are rare, occurring only on centennial
or longer timescale.
Fig. 1.5 -The Nazaré coast, as provided
by satellite Landsat 5 TM image, 1994
(Edisat). along the shore, the light blue
band indicates the sand movements, by
littoral dri, that surpass towards south
the Nazaré headland.
1.5 GEOMORPHOLOGICAL SETTING
The onshore of Nazaré is essentially a region
of low relief (Figs. 1.6 and 1.7). The altitude
varies from sea-level to about 180 m, reached
in the town of Raposos (at SE), but about
50% of the county has less than 60 m of
altitude.
The alluvial plain of Nazaré occupies the
northern end of the SW-NE elongated
depression (Figs. 1.7 and 1.8). Usually the
limit of this depression corresponds to faults,
probably resulting from the intense late
Cenozoic compression. The alluvial plain has
continuity to Ponte das Barcas, to the south
towards Famalicão and Valado de Frades,
and ending at the east near the villages of
Casalinho, Maiorga and Fervença, located
about 8 km from the sea (Henriques et al.,
2006). The alluvial plain is crossed by two
small rivers, Alcoa and Areia, with torrential
regime.
Fig. 1.6 - Digital elevation model (DEM; based on STRM data) of the Nazaré region
onshore, with a 5x vertical exaggeration.
Fig. 1.7 - Geomorphological map of the coastal area between Nazaré and Peniche, including the Caldas da Rainha diapir valley
(masl - metres above sea level) (Dinis et al., 2006).
The Pederneira Lagoon (Figs. 1.7 and 1.8) is nowadays an extensive flat area known as valley of the Cela/Valado dos Frades and Maiorga, flanked
to the west by the hill of Serra da Pescaria and to the east by the Bárrio hills.
8
Fig. 1.8 - Morphological sketch of the
aluvial plain of Nazaré (made from
1:2000 topographic plants, 1974 and
1977) (Henriques et al., 2006).
Fig. 1.9 - Praia do Norte, Nazaré
canyon head and Nazaré bay
(Duarte et al., 2014).
Fig. 1.10 -The Pedra do Guilhim, a large
stack located near the Nazaré headland
(author: Maria Margarida Gouveia;
January 21, 2015).
The headland divides the littoral into two
beaches: in the north, the Praia do Norte; in
the south, the Praia da Nazaré – facing the
Nazaré Bay (Fig. 1.9). This latter is divided
by the mouth of the Alcoa River (Fig. 1.8): in
the north, the Praia de Banhos; in the south,
the Praia dos Salgados.
In the continuity with the Nazaré headland,
but separated from it by a few meters, there is
a stack of trapezoidal shape, large and steep
(the stone of Guilhim), and another much
smaller (the stone of Leme) (Fig. 1.10).
The relationship between the formation of the promontory and the Nazaré submarine canyon has wide acceptance. It is the largest submarine
canyon in Europe and is one of the largest canyons in the world. It is located 100 km north of Lisbon, with a direction ENE-WSW in the upper
part and E-W in the middle and lower part (Fig. 1.11).
It cuts across the continental shelf almost to the beach which morphology and geographical location allows it to capture (and eventually
redistribute) the particles derived from the continent (littoral dri and rivers input). This canyon has been reported in the literature as the major
active sediment conduit to the abyssal plain (Oliveira et al., 2007 in Silva et al. 2013). The canyon head is located very near the shore and reaches
20 m in depth and few meters in distance from the beach. Distally this large submarine valley leads to the Iberian Abyssal Plain, some 210 km
from the coast at a water depth of 5000 m (Figs. 1.12 and 1.13).
Fig. 1.11 - Schematic map of the Nazaré canyon area (Stigter et al., 2007).
Fig. 1.12 - Bathymetry map of the west iberian margin showing
the location of Nazaré canyon (Arzola et al., 2008).
10
Fig. 1.13 - Extent of side scan sonar coverage of Nazaré canyon. Contours are 100 m, 200 m, 500 m, 1000 m than every
1000 m; a-h represents strike profiles and dashed white lines represents dip profiles (adapted from Arzola et al., 2008).
The initiation of sediment wave topography
is due to heterogeneous deposition from
sediment gravity currents flowing over
discrete obstacles on the seafloor. The
basal coarse-grained bed load layer ‘feels’
the topography; consequently this lower
portion of the flow accelerates and bypasses
sediment across the downslope-facing flanks,
and decelerates and deposits sediment on
the upslope-facing flanks of the waves. In
contrast, the fine-grained suspended load is
thicker and less aected by topography, so
deposits a drape of roughly equal thickness
over both flanks. The result is a sequence
of interbedded sand-mud turbidites on the
upslope-facing flanks, and mud-dominated
turbidites on the downslope-facing flanks,
shown clearly in the Nazaré Canyon mouth
(Arzola et al., 2008; Lastras et al., 2009).
The radioisotope fluxes determined in the
lower part of Nazaré canyon by Van Weering
et al. (2002) suggest rapid accumulation of
sediments in the upper and middle part of the
canyon, from where it is episodically flushed
into the Iberian Abyssal Plain. This explains
the terrigenous signature of the sediments,
particularly around the canyon’s head. These
terrigenous particles were derived from the
erosion of beaches and clis, and transported
by the dominant north-south littoral dri
into the canyon with a possible contribution
from northern rivers, Mondego and Douro,
respectively (Guerreiro et al., 2009).
1.6 ANTHROPIC INTERVENTIONS
IN THE VICINITY OF NAZARÉ
Several man-made features are present in
the vicinity of Nazaré (Fig. 1.14): the jetties
of harbor, the artificial mouth of the Alcoa
River and the seawall located between the
Marginal Avenue and the inner edge of the
Praia dos Banhos.
The construction of Nazaré harbor was
finished in 1983 and is very important for
the fishing activity, leading to the economic
development of Nazaré. Besides the fishing
activity, recreational boating has known a
notable importance in the last two decades.
The progressive silting of the Alcoa River
estuary caused, in 2003, the flooding of
agricultural land along its margins. During
high tide, a large amount of sand was
deposited at the river mouth. The river
evidenced some displacement towards the
south (Fidalgo, 2013).
1.7 THE PICTURESQUE VILLAGE OF
NAZARÉ
The picturesque village of Nazaré was for
centuries the main sanctuary of the Marian cult
in Portugal, having an enormous importance
in the touristic development of this village.
According to Fidalgo (2013), the development of
this urban nucleus resulted from two migration
processes. One, during the 16th century (1542),
coeval with the silting of the harbor of Paredes,
that led to the migration of the population to
various locations of the Portuguese coast, of
which the Pederneira (a name given by the
existence on the site of a round pine tree, with
the size of “five spans of flint “(described by
Father António Carvalho da Costa in Fidalgo,
2013). The second migration, that profoundly
changed the social, geographical and economic
habits of the people of this coastal area has
presumably occurred during the second half of
the 18th century: the migration from the fishing
community of Ílhavo to Lavos, Gala, Cova,
Buarcos, Matosinhos, Peniche, Nazaré and
São Martinho do Porto, among others, formed
important new fishing colonies.
The famous traditional festival of Nazaré takes
place in September and lasts for three days, with
fireworks, bullFighting and performances in the
town theatre.
The image of Senhora da Nazaré, whose chapel
was built in 1370 by King Fernando was, for a long
time, considered as one of the most miraculous
images of all Christianity. The first hermitage was
built by Fuas Roupinho, from Porto de Mós, during
King Afonso Henriques reign. At that time, the
image was placed between two rocks on a place
called The Memory (Ortigão, 1876).
The first miracle, that caused the devotion of
D. Fuas and the construction of this hermitage,
happened in September 14th of 1182, when he
was hunting on a foggy day. When chasing a
deer, he almost fell o a cli into the sea. The
running horse that he was riding only stopped
when Fuas shouted for help to “Nossa Senhora
da Nazaré “, (our Lady of Nazaré), (Fig. 1.15).
The legend says that the horseshoes were
carved in the limestone forever.
Aer the construction of the hermitage in
honor of “Nossa Senhora da Nazaré”, many
miracles were recorded in a book where the
stories were authenticated by the witnesses’
signatures. From a copy of this book, a work has
been published in 1628 called, “Antiga Imagem
Sagrada de Nossa Senhora da Nazaré”,
(Ancient Sacred Image of our Lady of Nazaré),
by Manuel de Brito Alão (Ortigão, 1876).
The first buildings in Nazaré should have
been made in the northern area, sheltered by
the headland and developed in parallel streets
leading to the sea. The Nazaré, Praia de
Banhos, developed significantly during the 14th
century, was supported by the fishing activities
and tourism.
“In the 17th and 18th centuries, the monks of
Alcobaça tried to legally obtain the temporal
jurisdiction over the site of Nazaré and the
territory donated by D. Fuas Roupinho, but
these attempts have failed. Both remained
Fig. 1.15 - Representation
of the miracle experienced by Fuas
Roupinho, at the hermitage da memória
(sítio da Nazaré) (adapted from
www.turistaprofissional.com).
Fig. 1.16 - Old photo of the fishing
activities at the Nazaré beach
(unknown author and date).
Fig. 1.17 - Old photo of the fishing
activities at the Nazaré beach
(unknown author and date).
under the administration of the Confraria
de Nossa Senhora da Nazaré, supposedly
constituted in the 15th century by the men and
women of Pederneira village and placed under
royal protection, in the early 17th century”
(CLASNZR, 2014). According to Frei Manoel
de Figueiredo (Fidalgo, 2013), in 1780 y-
eight houses in areas next to the sea along the
promontory of Nazaré were listed, where the
fishermen kept their gear.
Until the seventies of the last century, fishing
activities (Figs. 1.16 and 1.17) represented about
two-thirds of the economy of Nazaré.
12
Fig. 1.18 - Old photo of the Nazaré beach
during summer, the later called Praia de
Banhos (unknown author and date);
www.google.pt/search?q=imagens+antigas+da+nazare&rlz
Fig. 1.19 - Old photo of the Praia de
Banhos during summer (unknown
author and date);
www.google.pt/search?q=imagens+antigas+da+nazare&rlz
The seasonality of these activities, coinciding with
the annual fishing rhythms - a great bustle in the
summer and almost inactivity during the winter
months - was always felt by the local population
as their major weakness: the Nazarenes always
lived this duality between the abundance during
the summer and the times of hunger during the
winter (Trindade, 2008).
At the end of the 19th century, during the
summer, the Praia de Banhos (Bathing beach),
(immediately south of the headland) received
a bather population that was larger than the
population of Sítio da Pederneira (Figs. 1.18, 1.19
and 1.20).
The designation of Village to Nazaré was
attributed to the urban area of the Praia da
Nazaré and the Sítio da Nazaré, by order of the
Ministry of Interior, on the 28th February of
1957 (Figs. 1.21 and 1.22).
Nazaré represented the struggle for survival
and the union of the fishing community had
a common goal: the sea (Fidalgo, 2013). The
decline of the importance of fishing activities
for the local economy in the past thirty years
has accentuated this dependence of summer
economic activity (Trindade, 2007).
Since 1983, with the inauguration of the harbor,
boats and shermen le the beach. The
organization of the social life of the fishermen
was based on a family structure formed
by almost matrilineal lineages. When men
married they abandoned their families of origin
and were integrated into their wives families.
Aer a few generations this generated a large
concentration of families in neighbourhoods
or streets, linked by the maternal side, which
allowed people to help each other in any tragic
situation.
This very particular social organization has
been disappearing and the typical fishermen
houses have been occupied by shops, and
also by the type of life of future generations,
not facing fishing as a professional activity to
follow. Today it is tourism that occupies most of
the population and is supported in activities like
hotels, trade and restaurants. In order to reinvest
in the image of Nazaré and its fishing tradition
in the 90s of last century, the Xávega art was
recreated (Trindade, 2008). The Xávega art
is a traditional fishing technique, dominant in
the Portuguese central coast (Nunes, 2006 in
Delicado et al., 2012) and practiced in Portugal
since the 18th century. This technique consists
of dragging “on edge” as vessels launch their
fishing nets and make the “siege” to the fish.
The fishing net is then pulled from the beach,
once with the help of oxen, currently using
tractors. Today it is a show enjoyed by tourists
and persists in this area.
Apart from this aspect of the fishing culture,
during Easter an ethnographic group has been
responsible for organizing an exhibition where
the costumes, the house, the tavern, the work
with the fishing nets, the popular games and
the recreation of scenes of everyday life can
be seen by tourists. The peculiar habits of the
fishing community that lived by the sea, made
Nazaré beach, since the mid-ies, one of the
most popular touristic destinations of Portugal
(Fig. 1.23).
Fig. 1.21 - Old photo of the Nazaré village (unknown author and date).
Fig. 1.20 - Old photo of the Nazaré headland and southern beach during summer, the later called Praia de Banhos (unknown
author and date); www.google.pt/search?q=imagens+antigas+da+nazare&rlz
14
Fig. 1.23 - Panoramic view of Nazaré, from the Sítio, beach exposed during low tide (author: Pedro P. Cunha; July 2004).
Fig. 1.22 - Old photo of the Nazaré village (unknown author and date); www.fotos.sapo.pt/rjoalmeida/fotos/?uid=muyithnzou9vgtdsvj71&aid=73
LITTORAL
MORPHODYNAMIC
AGENTS
2.
Between April and October, the weather
situation that influences the Iberian Peninsula
corresponds to the joint action of the Azores
anticyclone, centered on its most northerly
position, and a thermal depression located
on the peninsula. The resulting atmospheric
circulation of the joint action of these two action
centers determines a northern wind along the
western Portuguese coast, oen reinforced
during the aernoon due to a caving depression
(e.g. POEM, 2005).
The western Portuguese coast is aected by a
mesotidal regime, with semi-diurnal tides and
small diurnal inequality. At Nazaré coastal
reach, the tidal range has a minimum of 0.9 m
and a maximum of 3.8 m.
The western Portuguese coast is well exposed to
the North Atlantic wave regime, characterized
by a predominant swell from the NW quadrant
and a wider directional spread (SW to N) of
other waves, generally less energetic. The
oshore incident wave regime is characterized
by an average significant wave height (Hs) of
2-2.5 m, wave periods of 9-11 s corresponding
to WNW to NNW swell (Andrade et al., 2002;
Dodet et al. (2010) in Bosnic et al., 2014).
The oshore dominant wave direction and the
orientation of the coastline is determinant for
the resulting nearshore total available wave
energy (Fig. 2.1). The eect of refraction on
the wave field as it propagates into shallower
waters is significantly higher in the sections
least orientated with the annual average wave
direction, leading to a higher energy reduction
along those coastal areas. The NW dominant
oshore wave direction clearly benets the
perpendicularly oriented Peniche - Nazaré
reach, which shows only 11% reduction in wave
power density relatively to the oshore value,
thus becoming the near shore area with higher
wave energy resource (Mota & Pinto, 2014).
2.1 WINDS 2.2 TIDES
2.3 WAVES
Fig. 2.1 - Relationship between the coastline orientation and the available wave energy to the
coastline (adapted from Mota & Pinto, 2014).
The nearshore wave propagation in this area
is significantly disturbed by the complex
morphology of the Nazaré canyon head (Fig.
2.2), which interferes with the net southward
longshore sediment transport (e.g. Dias et
al. (2002) in Silva et al., 2013). The Nazaré
headland shelters the embayment at south,
inducing a less energetic wave regime at the
Praia da Nazaré (in particularly the Praia de
Banhos); here, the sea currents are weak and
do not exceed 0.2 m/s (Bosnic et al., 2014). The
beach located at north of the headland, called
Praia do Norte, has a more energetic swell (Fig.
2.3) and very active dynamics, both in terms
of curling and longshore dri of sediment.
The Praia do Norte is immediately located
northwards of the submarine canyon where
the changes in the wave refraction pattern
are related to the progressively smaller wave
breaking angles northward from the headland
(Silva et al., 2013); at this beach, the water
current velocity varies mostly from 0.3 up to
0.7 m/s.
16
1 - The refraction of the wave, due to the difference in depth
between the continental shelf and the submarine canyon. This
effect leads to a change in direction over the canyon (where the
waves travel faster).
2 - Overtopping a topographic barrier (steep vertical variation).
The abrupt depth reduction leads to a shoaling effect on the
wave (reduction of wave length and increase of wave height).
This effect occurs gradually with the approach of a wave to
the shore.
3 - Positive interference between the wave travelling from
the canyon and the wave propagating across the northern
continental shelf. This effect promotes a new increase of wave
height at the point of intersection of the two wavefronts.
4 - Littoral drift. The wave propagation promotes a current,
flowing along the beach with a northernly direction, which
deflects offshore near the cape, acting as a topographic barrier.
This current is enhanced by the water pile-up in the cove. The
current, flowing with an opposite direction to the wave propagation
intercepts the wavefronts, leading to an additional increase of the
shoaling effect.The combined effect of these processes significantly
increases the wave height, which can reach much higher values
than those observed offshore. These waves break when their
height is approximately equal to the local water depth. The results
are spectacular, with giant waves breaking on the cliffs of the
headland (Figs. 2.4, 2.5 and 2.6).
Fig. 2.2 - Praia do Norte location and spatial coverage of the bathymetric grids used in the morphodynamic modelling (Silva et al., 2013).
Fig. 2.3 - Wave dissipation model of
the Praia do Norte (Silva et al., 2013).
Attending to his “V” transversal geometry,
E-W orientation, low longitudinal slope (10
- 20%) and canyon’s head deeply carved on
the coast line, the Nazaré submarine canyon
is a typical gouf-type canyon (Guerreiro et al.,
2009). It is 230 km long and 5 km below sea
level at its deepest part. It is big enough to hold
a considerable volume of water and any swell is
funneled all the way along the narrow canyon to
the Praia do Norte and adjacent headland.
According to the Instituto Hidrográfico (Cardoso,
2013; written communication), the arrival of a strong
swell, from the west/northwest quadrants, results in:
Fig. 2.4 - Strong waves at the Praia da Nazaré (Praia de Banhos);
www.google.pt/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0cacqjrw&url=http%3a%2f%2f
www.surfguru.com.br%2fnoticias%2f2013%2f10%2fscooby-e-maya-tentam-superar-onda-gigante-de-Mcnamara-em-Portugal.html&ei=9hjkvlk2iswtu7
Fig. 2.5 - Giant wave reaching the Nazaré headland;
www.almasurf.com/arquivos/image/2012/529041_409111969172415_1437498536_nbrunoaleixo.jpg
Fig. 2.6 - Giant wave breaking at the Nazaré headland (author: Bruno Aleixo);
www.noticiasaominuto.com/desporto/171169/Mcnamara-partilha-foto-impressionante-da-nazare#.uvxnuvl_uvm
According to Quaresma (2006), under the
project "EUROSTRATAFORM", whose
objectives included the specific study of
submarine canyons and their role in sediment
dynamics of European continental shelves, the
data obtained revealed also the propagation
of internal waves of large amplitude, forcing
pulses of strong currents.
The higuest ocean waves along the whole the
Portuguese shore occur, more frequently at
the Praia do Norte. The submarine canyon
of Nazaré plays a decisive role in the local
movement of water and sediments, but can also
generate giant waves.
During winter, big storms in the North Atlantic
Ocean generate swells that reach the western
Iberian margin. Severe stormy waves are
frequent in the western Portuguese coast. As an
example, on January 21, 2013 the Portuguese
Hydrographic Institute registered waves 19
m high and winds of 107 km/hour oshore
of Nazaré, typical values of severe storms. At
November 1, 2011, Garrett McNamara surfed
one gigantic wave generated by an intense storm
at the near Ireland oshore. This achievement
promoted Nazaré to the world. This site is now
a “magnet” for surfers searching for extreme
wave conditions (Figs. 2.7 and 2.8).
Usually, when the large open-ocean swells
approach the coast they start to slow down by
interaction with the ocean bottom. However, at
Nazaré oshore the ocean swells get focused in
the submarine canyon that points to the coast
and do not lose energy until they reach the near
shore. As the waves emerge at the canyon head,
they reach very shallow bottom and became
suddenly very high.
The results of the Siam project (first integrated
assessment of climate-driven impacts
and adaptation measures at a country-
scale) suggested that storminess along the
Portuguese margin may increase by the end
of the 21st century. This increase comes out as
markedly seasonal, with extreme events. This
modification could increase 15-25% the present
day erosions rates (Andrade et al., 2006).
Fig. 2.7 - Surfing with extreme wave conditions at Praia do Norte;
www.google.pturl?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0cacqjrw&url=http%3a%2f%2fsicnoticias.
sapo.pt%2fdesporto%2f2014-02-02-ondas-gigantes-e-Mcnamaraatrairamcentenas-de-curiosos-a-nazare&ei=knjkvitccoasufavg_
ge&bvm=bv.85970519,dd24&psig=afqjcnf08hgjbo3c8jri2gcecxf6pdyiow&ust=1424345435280804
Fig. 2.8 - Surfing with extreme wave conditions at Praia do Norte;
www.regiaodanazare.com/getjournalnewsthumb.ashx?fb=8292
18
Fig. 3.1 - Presumed Portuguese coastline at ca. 18 kyrs BP (A), 3 kyrs BP (B) and in the
Present (C) (adapted from Dias, 2004).
THE EVOLUTION
OF THE NAZARÉ
COAST
3.
B C
By 18 kyrs BP (Before Present), at the Last
Glacial Maximum (LGM), the landscape of
western Iberia was signicantly dierent from
today (Fig. 3.1A). The glacial ice caps were quite
expanded, covering part of the North Atlantic,
Northern Europe (at about the latitude 50ºN)
and half of North America (reaching latitude 40º
N). Due to the accumulation of ice at continental
glaciers and mountain glaciers, in Portugal the
sea level was between 120 to 140 m below the
present sea level (Dias, 1985, 1987). Because
of this low sea level, the paleo-coastline was
located near the edge of the continental shelf,
several kilometers from the present coastline
(Dias, 2004). At that time, the polar front was
located at the latitude of northern Portugal
(e.g. McIntyre, 1973), and the temperature of
water near the coast reached values below
4°C (e.g. McIntyre et al., 1976; Molina-Cruz
& Thiede, 1978). Near the Portuguese coast,
icebergs experienced an accelerated melting
(e.g. Guillien, 1962). On land, there was a strong
contrast between the cold environment along
the Atlantic coast, with abundant snow, strong
winds and high cloudiness. In the rest of the
Iberian Peninsula, the rainy seasons were much
more durable than currently, experiencing the
highest rainfall in autumn and spring (Daveau,
1980 in Dias, 2004). The modern vestibular
reaches of rivers, corresponded to very deep
valleys, were undergoing an intense erosive
fluvial incision.
3.1 EVOLUTION DURING
THE LAST 18 KYRS
A
In the Portuguese platform, the relative sea
level seem to have risen at a moderate rhythm
until about 16 kyrs BP, reaching a level ca. 100
m below the present sea level.
Until about 13 kyrs BP a stabilization period
was experienced. The rapid sea level rise that
occurred between 13 kys and 11 kyrs BP flooded
a significant part of the fluvial valleys.
At 11 kyrs BP, in the Iberian Peninsula the
climatic conditions were warm, due to an
interglacial period. Aer that, climate changed
to glacial conditions and the sea level lowered
to 60 m below the present level (Dias, 1987).
The sedimentation of Pederneira lagoon began
when the sea level reached the mouth of the
Alcôa river (-30 m at 8000-9000 yrs BP)
recording events since the early Neolithic and
the Atlantic climatic period (Dinis & Tavares,
2009). For two millenniums the sea level rise
was very fast but decreased between 5 kyrs
and 3 kyrs BP, reaching approximately the
present level (Fig. 3.1B). During the high-stand
sediments were mainly deposited in estuarine
or lagoon environments (Figs. 3.2 and 3.3).
Fig. 3.2 - Map of lagoons of Pederneira,
Alfeizerão and Óbidos at 2000 yrs B.C.
(author: Joaquim Pereira Da Silva;
date: 1982).
Fig. 3.3 – Map of the lagoons of Pederneira
and Alfeizerão during the Neolithic period
(10000 – 3000 B.C.) (adapted from Weinholtz
(1967-1978) in Monteiro, 1995).
3.2 HISTORIC EVOLUTION OF THE COAST
During historical times, the Portuguese coastal
setting has undergone profound changes (Figs
3.1C, 3.4, 3.5, 3.6 and 3.7). Whether as a result
of natural forcing, either due to the human
activities (deforestations and brush clearing,
agriculture, etc.), the fact is that intense
sediment supply to the coast was reached. It
seems that before the start of our era, the main
estuaries became almost filled and begin to
export to the coast large amounts of sediment.
At the time of Roman occupation, in the area
surrounding the lagoon of Pederneira, the
sea water reached far in the interior of the
estuaries. Figure 3.6 shows a picture from
1592, representing the Pederneira village and
the Fort at the headland (Fidalgo, 2013). During
the seventeenth century, the Pederneira lagoon
could have been navigable but only with small
boats.
20
Fig. 3.4 - The Oldest map of Portugal (author: Fernando Alvaro Sêco; date: 1560).
Fig. 3.7 - Map of província da Estremadura (date: 1846).
Fig. 3.5 – Palaeogeographic reconstruction of the lagoons of
Pederneira and Alfeizerão in the beginning of the 16th century
(adapted from Weinholt (1967-1978) in Monteiro, 1995).
Fig. 3.6 - Plan of Pederneira village, 1592 (Fidalgo, 2013);
the Pederneira lagoon is already almost filed with sediments.
The Pederneira lagoon became fully filled, mainly fed by large areas of loose ground and intensive agriculture and deforestation in the Alcôa drainage
basin, within a geological structure favorable to clastic transport (Dinis & Tavares, 2009).
During the twentieth century, many human activities dramatically reduced the sediment supply to the coast (Dias, 2004) leading to relevant changes in
physiography (Figs. 3.8, 3.9, 3.10, 3.11 and 3.12).
22
Fig. 3.8 - Plan of Nazaré at 1:25 000 scale (author: Manuel Francisco da Silva; date:1912).
Fig. 3.9 - Map of central Portuguese coast with bathymetry oshore
and topography onshore, 1:150 000 scale (date: 1915).
Fig. 3.10 - Map of central Portuguese coast with an oshore bathymetry; 1:150 000 scale (date:1912).
“The shoreline is oen considered as an
indicator of short and long-term coastline
changes that are central to defining the coastal
hazard zone. Despite its common usage, the
shoreline has been given several definitions
based on dierent approaches: physical,
geological, biological, or coastal engineering.
Boak & Turner (2005) describe a wide
variety of shoreline definitions. Depending
on the definition, the shoreline position can
vary up to hundreds of meters. The choice
of the period over which the waterline is
averaged to determine the shoreline will also
cause some dierences between shoreline
definitions“(Almar et al., 2012).
Fig. 3.11 - Topographic map of the central
Portuguese coast; 306-b, 1:25000 scale
(date: 1942).
24
Fig. 3.12 - Topographic map of the central
Portuguese coast, 306-b, 1:25000 scale
(date: 2003).
Fig. 3.13 - Photo of praia de Banhos, in Nazaré
(author: Margarida Porto Gouveia; january 20,
2015).
Fig. 3.14 - Evolution of the limit beach – aeolian dunes during the period 1958 to 2014
(source of the image used for plotting: 2014 Google Earth).
Fig. 3.15 - Evolution of the Nazaré shoreline during the period 1958 to 2014
(source of the image used for plotting: 2014 Google Earth).
3.3 EVOLUTION OF THE COASTLINE
DURING 1958-2014 BY ANALYSIS OF
AERIAL PHOTOS AND IMAGES
Understanding the behavior of beach
morphological response to meteorological and
oceanographic forcing ranges is an important key
for integrated coastline management. Beaches
are one of the most mutable environments in
the world. Analysis of aerial photos is one of the
methods used by geomorphologists and Earth
scientist to establish reference scenarios and to
quantify morphological changes, like shoreline
position or aeolian dune configuration, for example.
This requires baseline data, diagnostic indicators
and related measurements (Carapuço et al., 2014).
The establishment of monitoring programs in
sandy shores can be considered as a starting point
to understand present-day shoreline evolution.
Topo-bathymetric data acquired along several
years, and the respective DEMs, can provide
accurate information for shoreline evolution.
Usually the best indicators are the shoreline
position and the limit beach-aeolian dunes.
The recent evolution of the coastline performed
in this coastal stretch, was based on dated aerial
photos coverages of 1958, 1991, 2002, and satellite
digital images (Google Earth) of 2006, 2008,
2009 and 2014, respectively. Geo-processing tools
such as ArcGIS software were used.
Praia da Nazaré is considered as a beach-
dune system, because its inner boundary is
established by active aeolian dunes. The Praia
de Banhos is located between the cli of Sítio
and the harbor. The inner edge of this beach is
made by the retaining wall of the avenue and
not by dunes (Fig. 3.13) and is, therefore, included
in the beach system with an upper limit shore face
(Henriques, 1996).
This analysis reveals that between 1958 and 2014,
both north and south of the promontory, the active
aeolian dunes moved toward the beach (Fig. 3.14).
The evolution of shoreline, expressed by changes in
the limit beach face – berm (Fig. 3.15) documents a
trend for progradation, in contrast to other beaches of
the western coast of Portugal.
26
Fig. 4.1- First estimate of the height for the wave that
Garrett McNamara surfed on November 1st , 2011
(source: sicnoticias.sapo.pt, seen in February14th, 2014).
Fig. 4.2- Measurement of the wave surfed by Garrett McNamara on January 28th, 2013 (34 m)
(source: sicnoticias.sapo.pt).
In 2010, the municipal company “Nazaré
Qualifica” invited the U.S.A. surfer Garrett
McNamara, one of the world’s best big wave riders,
to develop a three-year project titled North Canyon.
Throughout this project, this athlete hit successive
world records in the size of waves, showing the city
of Nazaré and Portugal to the world. Also other
Portuguese athletes successfully challenged the
waves of Nazaré canyon.
On November 1st, 2011, G. McNamara, surfed
a giant wave that later achieved the Guinness
World Record for the largest wave surfed and
wons the Billabong XXL Award for the biggest
wave (Nazaré Qualifica (2013); in Ferreira, 2013).
“The largest wave successfully surfed had a face
estimated at 23.77 meters (78 feet) in height”,
writes the famous book (in surfertoday.com,
February, 2nd, 2015). However, the previous
estimated height for this wave was 31 m (Fig. 4.1).
On January 28th, 2013, Garrett McNamara surfed
a higher wave than the record hit in 2011, reaching
ca. 34 meters (Fig. 4.2). This wave received
a major highlight of the international press,
including international newspapers by The Times
(Fig. 4.3), El Pais and CNN television network
(Lusa, 2013). On the same day at Nazaré, Antonio
Silva and Ramon Laureano also surfed a wave of
over 25 meters (SurfTotal [ST], 2013).
SURFING
PRACTICES
IN NAZARÉ
4.
Fig. 4.3 - News about the Nazaré giant waves in
The Times;
www.dn.pt/inicio/tv/interior.aspx?content_id=3023617&seccao=media
Fig.4.4 - Garrett McNamara surfing
in Praia do Norte at November 18th, 2014.
www.facebook.com/163839373642847photos/a.203403679686416.6
1249.163839373642847/999298920096884/?type=1&theater.”
Another historical day at Praia do Norte, Nazaré
was on October 24th 2013, in which surfers
like Garrett McNamara, Carlos Burle, Sylvio
Mancusi, Rodrigo Koxa, Maya Gabeira, Felipe
“Gordo” Cesarano, Hugo Vau, Eric Rebiere,
Pedro Scooby and Andrew Cotton were present.
Images of surf experts as Hugo Vau, Andrew
Cotton, Kealii Mamala, Tom Butler, Sebastian
Steudner or Rodrigo Koxa, surfing the giant waves
of Praia do Norte, returned to run the world, over
the weekend of November, 29th and 30th, 2014
although the Nazaré canyon has not generated
anything close to the size of the largest wave ever
ridden.
During 2014, worldwide surfers challenged the
limits at Praia do Norte. Despite some fears, the
sea conditions allowed the capture of memorable
images (Figs. 4.4. and 4.5).
The North Canyon Project - exploration
program of big waves, for surfing and stand
up paddle, and promotion of Nazaré - remains
high, “with great movement on social
networks, many followers in Praia do Norte,
and guaranteed impact inside and outside the
country,” according to the news in Diário de
Notícias of December 4th , 2014.
28
Fig. 4.5 - Garrett McNamara surfing in Praia do Norte at November 19th, 2014;
www.facebook.com/163839373642847/photos/a.203403679686416.61249.163839373642847/1000777359949040/?type=1&theater
All these achievements supported by the
increasing number of surf schools and camps,
makes Portugal a required spot for a significant
number of domestic and foreign tourists coming
from Europe and all over the world during all
the seasons (Ferreira, 2013).
According to António D’Orey, a Portuguese
surfer, Nazaré is not only known by the giant
waves that have long been mediated lately
but also for the quality of their current waves.
The big-wave surng is considered dierent
from the usual surf (e.g. which is practiced in
Supertubos championship in Peniche) (D’Orey
interview, 2015). The Portuguese mainland is
always the place where the waves are larger and
even in days of small waves many surfers can
be found there. It is also one of the first places in
western Portugal to receive a new curling NW.
For example, a new swell reaches the Praia
do Norte in the morning but the Sintra coast
only in the aernoon; it also makes someone
want to go there to spend the day to take full
advantage of certain waves. At the Praia do
Norte, the waves usually display a triangle or
wedge geometry.
A wave, when approaching the beach, could
interfere with another wave coming sideways,
promoting the sudden swelling of the waves in
contact. The blistering burst area progressively
enlarge laterally. This allows the surfer to be in
the right position (in the highest part of the wave
before it bursts) to choose whether to go right
or le. Another important factor in the quality
of the wave is the fact that as it swells fast
when it bursts, it forms a very predictable tube,
searched by surfers. Regarding the Nazaré
giant waves, what makes it a unique place is
precisely the brutal wave swelling when two
waves of dierent directions clash transforming
a 5 m wave into a 15 m wave. The Jet Ski just
has to put the surfer at the point where the wave
is higher and then the surfer chooses to go right
or le where the wave rapidly loses strength
and height.
Although Garret McNamara surfed big waves
in various parts of the world, we can recognize
in Nazaré some similarities with the seas of
Mexico and Hawaii. G. McNamara has no
doubts in regard to Praia Norte : “a unique
place in the world where the waves have a lot of
personality and are very special.” “In fact”, he
said, “all in Nazaré is special” and therefore,
he returns, year aer year to compete, but
also to “share with the greatest number of
people” the adventures of giant wave surfing
that in the last year have contributed to attract
thousands of people to Nazaré (In: Público
and Lusa on January 21st, 2013).
The Nazaré gigant waves revealed to be an
excellent trigger for the transfer of scientific
knowledge in a language comprehensible for
all types of public (Carapuço et al., 2014).
REFERENCES
Almar, R., Ranasinghe, R., Sénéchal, N., Bonneton, P., Rolvink, D., Bryan, K., Marieu, V. (2012) - Video-based detection of shorelines at complex Meso-
macro tidal beaches. Journal of Coastal Research, V. 284, pp. 1040-1048.
Andrade, C., M.C. Freitas, C. Cachado, A.C. Cardoso, J.H. Monteiro, P. Brito, and L. Rebelo (2002) - Coastal Zones. In: Santos FD, Forbes K, Moita R (eds)
Climate change in Portugal. Scenarios, impacts and adaptation measures. SIAM Project, Gradiva, pp. 173–219.
Andrade, C., Oliveira Pires, H.; Silva, P.; Taborda, R., Freitas, M.C. (2006) - Zonas Costeiras. In: Santos, F.D.; Moita, R. & Miranda, P. (Eds). Alterações
Climáticas em Portugal, Cenários, Impactos e Medidas de Adaptação, Projecto SIAM II, Gradiva, Lisboa, pp. 169-206.
André, J., Cunha P., Dinis, J., Dinis, P., Cordeiro, F. (2009) - Características geomorfológicas e interpretação da evolução do campo dunar eólico na zona
costeira entre a Figueira da Foz e a Nazaré. Pub. Ass. Port. Geom.,VI, pp. 39-44.
Arzola, R.G., Wynn,R.B., Masson D.G., Weaver, P.P.E. (2008) - Sedimentary features and processes in the Nazaré and Setubal submarine canyons, West
Iberian margin, Elsevier, V.250, pp. 64-88.
Bosnic, I., Duarte, J., Taborda, R., Cascalho, J., Silva, A., Oliveira, A. (2014) - Modelling nearshore dynamics at Norte beach (Nazareth). Actas das 3as
Jornadas de Engenharia Hidrográfica, ISBN 978-989-705-073-2, Lisboa, pp. 229-232.
Câmara Municipal da Nazaré (2011) - Plano Municipal de Emergência, parte IV, Secção 2, 92 p.
Carapuço, M.M., Pinto, J.P., Duarte, J., Silva, A.N., Taborda, R. (2014) - Communication triggers in marine science: the Nazaré wave example. IMSCC
2014 - 1st International Marine Science Communication Conference.
Cardoso, J. L. G. (2013) - Onda gigante e canhão da Nazaré.. Revista da Marinha, 973, pp.34-36.
Cascalho, J., Duarte, J., Taborda, R., Ribeiro, M., Silva, A., Bosnic, I., Carapuço, M., Lira, C. and Rodrigues, A. (2014) - Sediment textural selection during
sub-aerial headland bypassing. An example from Nazaré coastal system (Potugal). Actas das 3as Jornadas de Engenharia Hidrográfica, ISBN 978-
989-705-073-2, Lisboa, Portugal, pp. 297-300
CLASNZR (2014) - Pré -Diagnóstico do Concelho da Nazaré. Câmara Municipal da Nazaré, 123 p.
Delicado, A., Schmidt, L., Guerreiro, S., Gomes, C. (2012) - Pescadores, conhecimento local e mudanças costeiras no litoral Português. Revista de Gestão
Costeira Integrada, V.12 (4), Lisboa, pp. 437- 451.
Dias, J.M.A. (1985) - Registos da migração da linha de costa nos últimos 18000 anos na plataforma continental portuguesa setentrional. 1ª Reunião do
Quaternário Ibérico, I, 281-285.
Dias, J.M.A. (1987) - Dinâmica sedimentar e a evolução recente da Plataforma Continental Portuguesa Setentrional. Dissertação de doutoramento,
Universidade de Lisboa, 341 p.
Dias, J.M.A. (2004) - A história da evolução do litoral português nos últimos 20 milénios. Evolução Geohistórica do litoral português e fenómenos
correlativos. Actas. Universidade Aberta, pp.157-169.
Dinis, J. L., Henriques, V., Freitas, M.C., Andrade, C., Costa, P. (2006) - Natural to anthropogenic forcing in the Holocene evolution of three coastal
lagoons (Caldas da Rainha valley, western Portugal). Quaternary International, 150, pp. 41–51.
Dinis, J.L., Tavares, A. (2009) - Condicionantes naturais e antrópicas na evolução holocénica de 3 lagunas do centro de Portugal (Óbidos, Alfeizerão e
Pederneira). Vila Nova de Santo André. Biblioteca Municipal. Escola Superior de Educação João de Deus, pp. 25-41.
Dinis, J.; Rey, J.; Cunha, P. P.; Callapez, P. & Pena dos Reis, R. (2008) - Stratigraphy and allogenic controls of the western Portugal Cretaceous: an
updated synthesis. Cretaceous Research, 29, pp. 772-780.
Dinis, J.; Lopes, F. C.; Rodrigues, A. & Cunha, P. P. (2012) – The “Nazaré fault”. An illusion exposed by data analysis. Proceedings of the 7th Symposium
on the Atlantic Iberian Margin, Lisboa, 16-20 December 2012, p. 43.
Duarte, J., Taborda, R., Ribeiro, M., Cascalho, J., Silva, A., Bosnic, I. (2014) - Evidences of sediment bypassing at Nazaré headland revealed by a experiment
bypassing at Nazaré headland. Actas das 3as Jornadas de Engenharia Hidrográfica, ISBN 978-989-705-073-2, Lisboa, Portugal, pp. 289-292.
Ferreira, M.S.B.P. (2013) - Modelo Sistémico do Setor Surf. Estudo do Subsetor do Surf Formação e Ensino em Portugal. Dissertação de mestrado em
ACKNOWLEDGEMENTS
This work was undertaken within the scope of project “Inov.C - Promoção do Empreendedorismo e Inovação Parte 2”. Research was supported by the
MARE – Marine and Environmental Sciences Centre, University of Coimbra.
António D’Orey is grateful for the information provided regarding the importance of giant waves in Praia do Norte to the surf practices; Prof. A. Campar
de Almeida (Univ. Coimbra) for some assistance with bibliographic access, Salma Tifratine (PhD student - Université Hassan II - Faculté des Sciences
Casablanca) for the help with the drawing of several Figures in GIS; and Fernando Magalhães, Isabel Anjinho and José Nunes André for providing with
several Figures.
30
Gestão do Desporto, Universidade de Lisboa, 154 p.
Fidalgo, C. (2013) - O povoamento na área da Lagoa da Pederneira: da ocupação Romana até ao século XII. Biblioteca da Nazaré, 256 p.
Fidalgo, C. (2013) - O progresso e a identidade cultural. O Ideário patrimonial. Praxis que se entrecruzam. Colóquio de turismo e património, V.1, pp.
15-30.
França, J. C.; Zbyszewski, G. (1963) - Carta geológica de Portugal na escala 1:50 000, Notícia Explicativa da Folha 26-B Alcobaça, Serviços Geológicos
de Portugal, Lisboa, 51p.
Guerreiro, C., Oliveira, A., Rodrigues, A. (2009) - “Gouf” Canyons: a Comparative Study Based on the Silt-clay Mineralogy of Bottom Sediments from
Oporto, Aveiro and Nazaré Submarine Canyons (NW of Portugal). Journal of Coastal Research, V.56, pp.722–726.
Henriques, M.V. (1996) - A Faixa litoral entre a Nazaré e Peniche. Unidades geomorfológicas e dinâmica actual dos sistemas litorais. Dissertação de
doutoramento, Universidade de Évora, 575 p.
Henriques, M.V., Dinis, J.L. (2006) - Avaliação do enchimento sedimentar holocénico na planície aluvial da Nazaré (Estremadura Portuguesa). X
Colóquio Ibérico de Geografia, Évora, PDF079, 16 p.
http://www.aaaio.pt/public/ioand148.htm, consultado a 3 Fevereiro, 2015.
http://www.npr.org/blogs/thetwo-way/2013/01/31/170753700/Portugals-monster-the-mechanics-of-a-massive-wave
http://www.tvi24.iol.pt/sociedade/temporal/mau-tempo-ondas-de-19-metros-na-nazare, consultado a 16 janeiro 2015.
http:// praiadonorte.com.pt/nazare/canhão-da-nazare
Lastras, G., Arzola, R. G., Masson, D .G., Wynn, R. B., Huvenne, V. A. I., Hühnerbach, V., Canals, M., (2009) - Geomorphology Geomorphology and
sedimentary features in the Central Portuguese submarine canyons, Western Iberian margin. Geomorphology, V.103, pp. 310-329.
Martín, J., Palanques, A., Vitoruino, J., Oliveira,A., Stigter, H.C. (2011) - Near Bottom particulate matter dynamics in the Nazaré submarine canyon under
calm and stormy conditions. Deep Sea Research II,58, pp. 2388-2400.
Monteiro, J. (1995) - Um Século de imagens da Nazaré no Bilhete-postal Ilustrado. I Jornadas sobre Cultura Marítima. Nazaré. Vol. 1, pp. 81-103.
Mota, P., Pinto, J. (2014) - Wave energy potential along the western Portuguese coast. Renewable Energy, V.71, pp. 8–17. doi:10.1016/j.renene.
Oliveira, A., Santos, A. I., Rodrigues, A., Vitorino, J. (2007) - Sedimentary particle distribution and dynamics on the Nazaré canyon system and adjacent
shelf (Portugal), Marine Geology, 246, 2-4, pp. 105-122.
Oliveira, A., Stigter, H. C. D., Palanques, A., Martı, J. (2011) - Near-bottom particulate matter dynamics in the Nazare under calm and stormy conditions.
Deep Sea Research II, 58, pp. 2388–2400.
Oliveira, A., Duarte, J., Silva, A, Taborda, R. (2014) - Dark grey sea foam formation in the “Norte” Beach (Nazaré). Actas das 3as Jornadas de Engenharia
Hidrográfica, Lisboa, Portugal, pp. 321-324.
Ortigão, R., Pimentel, E. (1876) - As praias de Portugal. Guia do Banhista e do Viajante. Livraria Universal de Magalhães e Moniz. Porto, pp. 99-104.
Quaresma, L. (2006) - Observação de Ondas Internas Não-Lineares Geradas Sobre O Canhão Submarino da Nazaré, Dissertação de Tese de Mestrado
em Ciências Geofísicas. Universidade de Lisboa, 112 p.
Ramalho, P., Adão, H., Kiriakoulakis, K., Wol, G. A., Vanreusel, A., Ingels, J. (2014). Temporal and spatial variation in the Nazaré Canyon (Western
Iberian margin): Inter-annual and canyon heterogeneity eects on meiofauna biomass and diversity. Deep-Sea Research I, 83, pp. 102-114.
Ramos, R.I.H. (2014) - Contribuição dos métodos geofísicos para o modelo evolutivo da região de Santo André desde o último máximo glaciário. Tese
de Doutoramento. Universidade de Lisboa, 208p.
Silva, A., Taborda, R. (2012) - Integration of beach hydrodynamic and morphodynamic modeling in a GIS environment. Springer Science, pp. 201-210.
Silva, A.N.; Taborda R.; Antunes C. Catalão, J., Duarte, J. (2013) - Understanding the coastal variability at Norte beach, Portugal. Proceedings 12th
International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Especial V. 65, pp. 2173-2178.
Soares, J. (2002) - Os mitos da Lagoa. Edição da Câmara Municipal da Nazaré, 130 p.
Stigter H. C., Boera, W, Mendes, P, A.J, Jesus, C.C., Thomsen, L., Bergha, G., Weering, T.C.E. (2007) - Recent sediment transport and deposition in the
Nazaré Canyon, Portuguese continental margin. Marine Geology, 246, pp. 144-164.
Trindade, J.M. (2007) - Nazaré, a mais típica praia portuguesa. In V International Tourism Congresso of Leiria and Oeste. URL: cassiopeia.ipleiria.pt/
esel.../3902_03_JoseTrindade_4bf50b0b97a87.pdf
Van Weering,T., Weaver,P. (2007) - Canyon Processes, an Introduction. Marine Geology, 246, pp. 65-67.
... For each area of the Mediterranean and Atlantic coast, average bottom slopes m were obtained from available bathymetric surveys [54,[77][78][79][80]. Bathymetric data were obtained for the winter seasons (during 2015-2016 [77][78][79][80]) to assess a range value of coastal slope m similar to the coastal slope and wave climate recorded during the video monitoring. ...
... For each area of the Mediterranean and Atlantic coast, average bottom slopes m were obtained from available bathymetric surveys [54,[77][78][79][80]. Bathymetric data were obtained for the winter seasons (during 2015-2016 [77][78][79][80]) to assess a range value of coastal slope m similar to the coastal slope and wave climate recorded during the video monitoring. Wavelength in offshore was assessed through wave propagation modeled for the offshore areas of Sicily [35] and Portugal [81]. ...
... Average bottom slope m was obtained through available bathymetric surveys. The water depth at the breaker zone was derived from literature[78,[82][83][84][85]; wavelength in deep water was assessed from the SWAN model (reported in Scicchitano et al.[35]) and wave model of Spanish Harbor Authority (SI-MAR 1,041,058 point-9.75° W and 39.50° N; SIMAR 1,042,065 point-9.5° ...
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... It is an extremely popular place for surfing, making these waves an additional attraction. These waves reach heights of 30 m or more ( Figure 7) and occur because of the existence of the Nazaré canyon, which is the largest submarine canyon in Europe and one of the largest in the world (Cunha and Gouveia, 2015). The coast of Nazaré does not present a situation of concern in terms of erosion, but the existing beaches are systematically deprived of sand by the deeper zones, forcing the annual artificial nourishment of the beaches. ...
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Antunes do Carmo, J.S., 2018. Climate change, adaptation measures, and integrated coastal zone management: The new protection paradigm for the Portuguese coastal zone. Journal of Coastal Research, 34(3), 687-703. Coconut Creek (Florida), ISSN 0749-0208. The efforts made to reduce the causes and mitigate the effects of global climate change continue to be critical in coastal areas. Many adaptation strategies implemented in coastal areas remain inadequate or ineffective. Using primarily events and interventions carried out along the Portuguese Atlantic coast, this work aims to show the paradigm shift that has occurred in Portugal since the last century (the 1990s) within the scope of the National Coastal Zone Management Strategy, taking into account the new guidelines for the implementation of coastal defence works. In this context, this paper also aims to assist coastal communities in carrying out operational coastal management by presenting and discussing management tools and primary options that should be considered in any adaptation programme that is to be implemented. Both nonstructural and structural measures are considered. Action plans, warning systems, emergency plans, and evacuation plans belong to the first category. Education and training are also considered, because they play a key role in the sustainability of coastal areas, especially in the coming generations. Structural measures are adaptation options that are designed to increase the safety of people and reduce risks. They are discussed and grouped into categories that include accommodation, protection, and retreat. Recent cases of successful accommodation and protection measures implemented along the Portuguese coast are also presented and discussed. ADDITIONAL INDEX WORDS: Storms, multifunctional options, management tools, public participation.
... It is an extremely popular place for surfing, making these waves an additional attraction. These waves reach heights of 30 m or more ( Figure 7) and occur because of the existence of the Nazaré canyon, which is the largest submarine canyon in Europe and one of the largest in the world (Cunha and Gouveia, 2015). The coast of Nazaré does not present a situation of concern in terms of erosion, but the existing beaches are systematically deprived of sand by the deeper zones, forcing the annual artificial nourishment of the beaches. ...
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The efforts made to reduce the causes and mitigate the effects of global climate change continue to be critical in coastal areas. Many of the adaptation strategies implemented in coastal areas remain inadequate or ineffective. Using primarily events and interventions carried out along the Portuguese Atlantic coast, this work aims to show the paradigm shift that has occurred in Portugal since the last century (the 1990s) within the scope of the National Coastal Zone Management Strategy and taking into account the new guidelines for the implementation of coastal defence works. In this context, this paper also aims to assist coastal communities in carrying out operational coastal management by presenting and discussing management tools and primary options that should be considered in any adaptation programme that is to be implemented. Both nonstructural and structural measures are considered. Action plans, warning systems, emergency plans and evacuation plans belong to the first category. Education and training are also considered, as they play a key role in the sustainability of coastal areas, especially in the coming generations. Structural measures are adaptation options that are designed to increase the safety of people and reduce risks. They are discussed and grouped into categories that include accommodation, protection and retreat. Recent cases of successful accommodation and protection measures implemented along the Portuguese coast are also presented and discussed.
... On the one hand, the adjacent deep allows a greater volume of water, thus generating more fruitful catches at their doorstep comparatively to other coastal fishing towns (Van Ginkel, 2001;De Leo et al., 2010). On the other hand, the canyon and the consequent oceanographic conditions may create very rough sea, endangering fishing practices (Cunha and Gouveia, 2015) (Fig. 1). ...
Conference Paper
Nazaré is a picturesque fishing town highly sought by tourists during summer. One of its natural attractions is the submarine canyon. Despite its attractiveness to extreme surfers and tourists, this canyon presents a paradox for fishermen: on the one hand, the adjacent deep allows a greater volume of water, thus generating more fruitful catches at their door comparatively to other coastal fishing towns. On the other hand, the canyon and the consequent oceanographic conditions may create very rough sea, endangering fishing practices. Just nearby the canyon is located the recently deployed Nazaré artificial reef (NAR), which is the first of its kind off the western coast of Portugal. The artificial reef was deployed aiming to improve social and economic resilience of the local communities, mainly by creating a safer area to fish and to find commercially exploitable marine resources with more certainty in the future (outer reef modules), and by stimulating diving tourism (inner reef modules). Our study has shown that the reef is now mature, colonized by abundant and diverse macrobenthic assemblages likely to enhance biodiversity and food availability for fish. Thus the NAR may have been a valuable contribution to an apparently social and economic positive impact on the local fishing community that can be corroborated by the presence of good biological indicators (e.g. fish biomass and benthic biodiversity), derived from experimental fisheries and scientific diving. It is also presented fisheries socio-economic indicators, namely related to patterns of use found via non-intrusive direct observations.
Thesis
Le déferlement des vagues, qui se produit de l'océan vers la zone côtière, est un phénomène d'écoulement diphasique complexe qui joue un rôle important dans de nombreux processus, notamment sur le transfert de matière, de quantité de mouvement et d'énergie entre l'air et l'océan. Les récentes tentatives de modélisation se heurtent au manque de connaissances physiques des plus petits détails des processus de déferlement. En outre, aucune loi d'échelle universelle pour les variables physiques n'a été trouvée jusqu'à présent.Une méthode de préservation de la quantité de mouvement, basée sur des travaux récents de la littérature, a été développée pendant la thèse afin d'atteindre les plus fins détails du processus de déferlement pour les ondes capillo-gravitaires. Cette méthode réduit l'échange non physique de la quantité de mouvement entre deux fluides pendant la simulation, ce qui permet d'effectuer des simulations très précises de déferlement de vague. Cette méthode a été vérifiée sur des cas de vérification de la littérature et validée par des expériences réalisées en laboratoire, telles que l'impact d'une goutte d'eau sur une surface libre et le déferlement d'une vague plongeante sur une plage. Ces vérifications et validations confirment l'utilisation de la méthode développée lors de l'étude suivante sur le déferlement des vagues.Dans la littérature, la plupart des résultats expérimentaux et numériques ont été réalisés pour des vagues en eau profonde. L'étude se concentre sur l'influence de la profondeur sur la dynamique du déferlement. La géométrie de surface, les anneaux de vorticité sous-marins et l'énergie totale sont étudiés pour plus de 170 simulations précises du déferlement d'une vague de Stokes sur un fond plat. Les nombreux résultats des simulations ont permis la génération de carte de déferlements pour trois différentes profondeurs d'eau. Les types de déferlements plongeant et glissant ont été subdivisés en fonction des observations faites. Ainsi, les études réalisées au cours de la thèse ont permis d'accroître les connaissances sur le déferlement d'ondes capillo-gravitaires de profondeurs d'eau intermédiaires.
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This chapter aims to introduce the processes and the consequences resulted from coastal erosion.
Thesis
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Este livro é o resultado do 1º Volume da TESE DE MESTRADO EM ESTUDOS DO PATRIMÓNIO apresentada e defendida em Março 2011, Universidade Aberta, Departamento de Ciências Sociais e Gestão, sob a orientação do Sr. Professor Doutor João Luís Cardoso.
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This work aims to characterize and understand the textural selection process related to headland sediment bypassing at three adjacent beaches (Norte, Prainha and Nazaré) located at the west coast of Portugal. To characterize sediment median grain size variability across the study site, 72 samples were collected and photographed with a digital single-lens reflex camera. This procedure generates a set of 261 digital images that were processed using the image autocorrelation method in order to compute the median sediment grain size. Preliminary results show that the Nazaré headland (between Norte beach and Nazaré bay) can act as a filter to the coarser sediment particles transported by the southward longshore drift, during the observed field conditions. The coarser particles (of coarse sand) were often found updrift of the Nazaré headland (at Norte beach), while at the downdrift side (Prainha beach) these particles are scarcer.
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Climate change is one of the major challenges human societies are facing. Coastal communities are particularly vulnerable, as their homes and livelihoods are increasingly exposed to risks from coastal erosion and sea level rise. Fishermen that live on and from the coast have a privileged perspective of coastal changes. As a result of their activity, fishermen have a knowledge that, despite not being technical, is based on experience and is local-specific. In spite of being well documented in scientific literature, the role of local knowledge - lay, ecological, indigenous or even stakeholder knowledge, as it has been diversely described in the literature - in planning and environmental related decisions remains unclear. In Portugal, this is an issue that remains largely unexplored and there are only a few studies within the social sciences that focus on fishing communities. In this sense, this study intends to contribute to an issue that is still in a very embryonic state in Portugal. Based on evidence from a set of in-depth interviews with local fishermen in three areas of the Portuguese coast - Vagueira in the Aveiro region in the north, Costa da Caparica in the Lisbon area and Quarteira in the southern coast of Algarve - this paper examines the perceptions of fishermen about coastal and climate changes, coastal planning and interventions, public participation and their role on coastal management processes. These coastal towns, all former fishing villages, have already experienced threatening situations (storm surges, coastal inundation of inhabited areas) and are marked by strong coastal defences: groynes, seawalls and regular sand renourishments. The analysis of the interviews revealed some important results. The first is that fishermen, due to their activity, their proximity to the sea and the fact that there is a large intergenerational reproduction (the activity is passed over from parents to their children) have a very rich and multifaceted knowledge of the sea and the coast. They have a clear notion of coastal evolution, an accurate memory of past events and a comprehensive understanding of coastal changes and their multiple causes. They acknowledge that, despite the fact that coastal defences built in recent decades have solved the problem in some places, they are also a problem and the cause of erosion in nearby coastal stretches. The analysis also showed some differences between case studies: while in Vagueira and Costa da Caparica fishermen are critical of hard defence structures, in Quarteira they seem to be fairly satisfied with the effects produced by the defence structures and sand renourishments. Regardless of that, in all three places, fishermen point out alternative technical solutions based on their practical knowledge of the specific areas. They admit that while their knowledge is not scientific - and therefore may not have the same value as expert knowledge - it is still worthy. They emphasize the practical and place-specific nature of their knowledge, which adds value to the more general knowledge of experts, and thus should be taken into account. But, according to the fishermen in these coastal stretches, this has not been the case. And we concluded that not only their knowledge is not incorporated into technical solutions, but they are also not consulted about coastal management decisions that directly affect them or their activity. We posit that, on the one hand, fishermen come from a traditionally disadvantaged social standing that has been made worse by EU fishing policies, which since 1986 have been weakening this activity in Portugal. The social devaluation of this activity seems to have been internalized by the fishermen and seems to translate into a low status self-perception. Thus, despite being aware of the relevance of their knowledge, they have not been able to make this knowledge available to experts and decision makers. Fishermen only show some capacity to intervene when represented in associations or unions, which highlights the importance of collective action and marks an important difference between our three case studies, and may also explain the state of greater frailness of fishing in Vagueira, the only place where they are not collectively represented. In addition to this inferior social position, there seems to be a certain “cultural incompatibility” between fishermen and experts, almost as if they spoke different languages altogether, making more difficult the dialogue between the two sides and the incorporation of local knowledge into technical decisions.
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Remote video imagery is widely used to acquire measurements of intertidal topography by means of shoreline detection, but, up to now, problems of accuracy were still encountered in the challenging case of energetic waves in nonuniform, meso macro tidal environments. Unique, simultaneous, video-based and global positioning system (GPS)-based measurements of shoreline were undertaken at Truc Vert (France), a beach with such characteristics. An innovative video method, referred to herein as the Minimum Shoreline Variability (MSV) method, was developed to cope with highly variable spatiotemporal shoreline properties. The comparison of video-based and GPS-derived shoreline data sets showed that using images averaged over short periods (30 s), rather than the traditionally used 10-min averaged images, significantly improved the accuracy of shoreline determination. A local video-derived, swash-based shoreline correction was also developed to correct for the MSV error, which was found to be linearly correlated to local swash length. By combining shorter time-averaged images and video derived local swash correction factors, the horizontal root mean square error associated with MSV shorelines was reduced to 1.2 m, which is equivalent to errors reported at more uniform, microtidal, and less-energetic beaches.
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Mean sea leveI and coastline evolution since the Last Glacial Maximum, in Portugal, is not well known in the different details. The sarne is true for the generality of the world coastal zones. However, the main features and the general picture of that evolution are already known. The main forcing mechanisms are quite well established. This paper presents a short criticaI synthesis of that knowledge under the form of a story.
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Norte beach stands in a coastal stretch fully exposed to the high energetic North Atlantic wave regime. The beach is located updrift of the Nazare submarine canyon head, a sedimentary sink that captures the southward directed longshore drift. Systematic monitoring of Norte beach has been conducted by a coastal video monitoring system since 2008. A total of 31 monthly coastlines were extracted and analyzed in the period between December 2008 and May 2012. Results show a rare high seasonal coastline variability which exceeds 160 m in the southward sector (adjacent to the headland) and 70 m at the central and north sectors. These coastline variations are related with modifications in the planform beach configuration: beach oscillates between a straight (generally from June to August) and an arcuate configuration (during the remaining months of the year). Results suggest that Norte beach variability depends mainly on longshore drift gradients rather than with cross-shore sedimentary transfers. The intense wave refraction over the canyon head, associated with the westerly swell waves, generates a sedimentary convergence at the centre of the beach promoting the increase of the beach curvature, while, northern and/or short waves (more frequent in summer) tend to linearize the beach. This work contributed with valuable information about the sedimentary dynamics of the Norte beach and showed that this site is a suitable candidate to evaluate longshore drift from shoreline changes.