SantosFerreira E Dias A TrigoTeixeira C Santos J Leal N Oliveira and J Peleja Instituto Portuário e dos Transportes Marítimos IP Instituto Superior Técnico ID: 801399
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THE STABILIZATION OF THE FARO-OLHÃO INLET AND ITS INFLUENCE ON THE MORPHODYNAMICS OF CULATRA ISLAND AND ARMONA INLET
Santos-Ferreira* , E. Dias* , A. Trigo-Teixeira** , C. Santos*** , J. Leal* ,
N. Oliveira*
and
J. Peleja*
* Instituto Portuário e dos Transportes Marítimos, I.P.
** Instituto Superior Técnico
*** Faculdade de Ciências e Tecnologia da
Univ
. NOVA
Slide2SumaryINTRODUCTIONGEOLOGY AND GEOMORPHOLOGY
METHODS
EVOLUTION OF ARMONA INLET AND CULATRA ISLAND
FARO-OLHÃO INLET OPENING AND EVOLUTIONDISCUSSION AND CONCLUSIONS
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Slide3IntroductionStudy area is located in the Faro lagoon - Ria
Formosa;
Large structural and
morphodynamic diversity and it is the most important wetland area in southern PortugalGeological environment: marshes that cover about two thirds of the area. The system consists of a series of barrier islands at the southern most part.
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Slide4IntroductionThey act as a protection from the sea and are separated by migrating inlets, some are fixed artificially, establishing the communication between the lagoon and the ocean.The islands and peninsulas are separated by six tidal inlets which allow water, sediment, chemicals and nutrients to be exchanged between the lagoon and the ocean.
Two bars (Faro-
Olhão
and Tavira) are artificial, stabilized with jetties.4
Slide5IntroductionThe evolution of the Ria
Formosa lagoon is largely determined by
morphodynamics
found in coastal lagoons:considering the phenomena of erosion and sedimentation, littoral transport.It is presented a study of the morphodynamics
of
Culatra
island and consequent evolution of
Armona
inlet since the XIX century, defining the average progression and development in different periods.
It is presented an evaluation of the influence of the opening of Faro-
Olhão
inlet (1929) on the evolution of
Culatra
island and Armona inlet.
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Slide6Geology and Geomorphology
Most of the formations had their origin in the Quaternary geological period.
The geological history show a complex evolution, including marine transgression and regression phases, erosion, coastal sediment transport, and seismic activity.
Marshes are the dominant geological environment > are alluvial formations of black clay, whose progression to the sea is blocked by sedimentation and by the islands. It is worth mentioning the presence of large masses of sand that make the barrier islands of the coast.
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Slide7Geology and Geomorphology
Presently, the system of barrier islands of Faro lagoon consists of:
two peninsulas (
Ancão and Cacela) which are respectively the western and eastern limits of the system; five barrier islands (from west to east:
Barreta
,
Culatra
,
Armona
,
Tavira
and Cabanas);
a vast body of water, the lagoon.
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Slide8Geology and Geomorphology
The islands and peninsulas are separated by six tidal inlets (
Ancão
, Faro-Olhão, Armona, Fuzeta
,
Tavira
,
Cacela
), which allow the exchange of water, sediment, chemicals and nutrients between the lagoon and the ocean.
The area of the lagoon is
12 000ha
and the area of the peninsulas and the barrier islands is about
2 000ha.
The Western side of the system is more energetic, directly exposed to the dominant wave action from W and SW (68%);
The Eastern
side is exposed to the "
Levante
" - SE winds from the Mediterranean, (25%).
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Slide9MethodsTo carry on an analysis of the evolution of Culatra
island and Nova and
Armona
inlets:Compilation of all available information from the XIX century till the present;Digitalization of the information, and subsequent integration into a GIS, where the coordinate system of all the information was defined; Perform the operations of spatial analysis leading to the study of coastal evolution. Development of digital terrain models (DTM) for each survey available;
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Slide10MethodsAn hydrodynamic study of the lagoon complex was used to correlate the information, and to allow the interpretation of the system behavior.Recent experimental data, from 1999 and 2000, referring the velocity, flow and tide, in the several inlets of the lagoon, was also used.
The influence of the Faro-
Olhão
jetties in the littoral drift, and in the evolution of the Culatra island, is also discussed.10
Slide11Evolution of Armona Inlet and Culatra Island
Armona
inlet is the most important for the water exchange between the lagoon and the sea.
Since 1873 the width has been narrowing, slowly first, but since 1955 much more rapidly. It is established the natural rate of closure of this inlet, as well as assess the influence of the opening and stabilization of the Faro-Olhão inlet. It is presented the evolution in some periods, using the existing topography, and using also some GIS tools.
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Slide12Evolution of Armona Inlet and Culatra Island
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1873
Slide13Evolution of Armona Inlet and Culatra Island
From 1873 to 1929
In this period the Faro-
Olhão inlet was closing at rate of 14m per year, in average.1929 > opening of the Faro-
Olhão
inlet > first phase
1873 >
t
he total width of the
Armona
inlet was 4050m.
1930 > the total width of the
Armona
inlet was 3300m.13
Slide14Evolution of Armona Inlet and Culatra Island
Armona
inlet DTM in 1873, 1916 and 1930.
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Slide15Evolution of Armona Inlet and Culatra Island
Difference between 1873 to 1916
hydrography
;Difference between 1916 and 1930 hydrography.
The brownish colors represent sedimentation, the blue ones erosion.
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Slide16Evolution of Armona Inlet and Culatra Island
From
1930 to 1950
First phase of Faro-Olhão construction: 1929 – 1930Final construction of the jetties: 1950 -1955;1930-1950: period of a slowing down of the closing of the Armona
inlet, with an average rate of 8m per year. So this inlet presented in 1950 an opening of 3150m.
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Slide17Evolution of Armona Inlet and Culatra Island
From
1950 to
the presentFrom 1955 till 2002 Armona inlet closed with an increased rate of 48m per year;
In 1980 > still identify the Nova and
Armona
channels;
In 2002 the Nova channel has disappeared and only one channel was present in the inlet;
In 2007 the width of
Armona
inlet was only 540m.
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Slide18Evolution of Armona Inlet and Culatra Island
DTM 1980
and 2002.
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Slide19Evolution of Armona Inlet and Culatra Island
Difference between 1930 to 1980
hydrography
;Difference between 1980 to 2002 hydrography; The reduction of the inlet width is accompanied by the channel deepening.
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Slide20Evolution of Armona Inlet and Culatra Island
3D Model of the
Armona
inlet (2002) spring ebb tide and spring flood tide.20
Slide21Evolution of Armona Inlet and Culatra Island
Evolution of the
Armona
and Nova channels, from 1873 to 2007. 21
Slide22Evolution of Armona Inlet and Culatra Island
Evolution of
Culatra
and Armona islands, from 1873 to 2007.22
Slide23Evolution of Armona Inlet and Culatra Island
Evolution of the
Armona
inlet, from 1873 to 2007.23
Slide24Faro-Olhão Inlet Opening And EvolutionDTM of the Faro-
Olhão
inlet, for the years 1955, 1967, 1976, 1985 and 2008.
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Slide25Faro-Olhão Inlet Opening And EvolutionFaro-
Olhão
inlet from 1929 to 1950
No significant changes in this inlet since its opening in 1929 till the conclusion of the jetties, in 1955.25
Slide26Faro-Olhão Inlet Opening And EvolutionFaro-
Olhão
inlet from 1955 to 2008
The Faro-Olhão inlet, as its stabilization works were designed, and an aerial photograph as it was in 2007. 26
Slide27Faro-Olhão Inlet Opening And EvolutionSedimentation and erosion for the Faro-
Olhão
inlet, for the periods 1955-1985, and 1985-2008.
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Slide28Faro-Olhão Inlet Opening And EvolutionDiscussion of the Faro-
Olhão
inlet evolution
Evolution of the Faro-Olhão inlet, from 1958 to 2010.28
Slide29Faro-Olhão Inlet Opening And EvolutionThe velocity pattern in Faro lagoon.
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Slide30Discussion and Conclusions
It is clear the importance that the opening of the Faro-
Olhão inlet had both in littoral drift and in the evolution of the old Nova channel and consequently in the evolution of the inlet of Armona, after the junction of the two channels.
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Slide31Discussion and Conclusions
It seems that there is a tendency in
Armona island to increase to the west, and not to erode that edge, so that the existing human settlement in this island is not expected to be at risk in the near future. The tendency of Faro-Olhão inlet to reach a balance in the long term may be at risk if the
Armona
inlet closes.
In this case, the closing of this inlet will probably force the opening of a new inlet somewhere near of the Faro-
Olhão
inlet.
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Slide32Discussion and Conclusions
A further study using a finite element circulation model is planned, using the data from Ventura Soares (2001), with 2000 topography for calibration, but using 2011 topography for the study.
It seems important to try to understand the flow pattern in the Faro-Olhão inlet, and the reason of the deepening so far away from the mouth defined by the breakwaters.
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Slide33Thank You33