DOCSLIB.ORG

Wave and Tidally Induced Processes on Rocas Atoll: Geomorphological Implications and Future Projections

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Wave and Tidally Induced Processes on Rocas Atoll: Geomorphological Implications and Future Projections Mirella Borba Santos Ferreira Costa Front Pages Wave and tidally induced processes on Rocas Atoll: geomorphological implications and future projections Thesis presented to the Oceanographic Institute of the University of São Paulo, in partial fulfilment for the degree of Doctor of Science in Oceanography, with emphasis in Geological Oceanography. Advisor: Prof. Dr. Eduardo Siegle São Paulo 2015 University of São Paulo Oceanographic Institute Wave and tidally induced processes on Rocas Atoll: geomorphological implications and future projections Mirella Borba Santos Ferreira Costa Thesis presented to the Oceanographic Institute of the University of São Paulo, in partial fulfilment for the degree of Doctor of Science in Oceanography, with emphasis in Geological Oceanography. Julgada em ___ / ___ / _____ ____________________________________________________ Prof. Dr. ____________________________________________________ Prof. Dr. ____________________________________________________ Prof. Dr. ____________________________________________________ Prof. Dr. ____________________________________________________ Prof. Dr. ii “Rocas está com a sua evolução quasi terminada. Poucos anos faltarão para se completar, para se tornar uma ilha na verdadeira acepção da palavra. Como precursores, prevemos a sua futura denominação: “Ilha de Rocas”, augurando também, quem sabe ? a sua habitabilidade ? um posto de pesca ? uma base aérea militar ou comercial ? uma estação meteorológica ? Tudo é possível e um futuro próximo nos dirá.” Capitão Tenente Osmar A. de A. Rodrigues Revista Marítima Brasileira, 1940 iii *Acervo fotográfico da Reserva Biológica do Atol das Rocas (Outubro de 2015) iv Contents Acknowledgements ................................................................................................................. viii Resumo ...................................................................................................................................... ix Abstract ..................................................................................................................................... xi Publications produced during the PhD Candidature............................................................... xiii List of Figures .......................................................................................................................... xiv List of Tables ............................................................................................................................ xix 1 INTRODUCTION ..................................................................................................................... 1 1.1 Objectives ...................................................................................................................... 3 1.2 Study area ..................................................................................................................... 4 1.3 Thesis layout .................................................................................................................. 7 2 WAVE CLIMATE AND EXTREMES ON ROCAS ATOLL .............................................................. 8 2.1 Introduction .................................................................................................................. 8 2.2 Methods ........................................................................................................................ 9 2.2.1 Global model ....................................................................................................... 10 2.2.2 Local model ......................................................................................................... 10 2.2.3 Definition of wave climate and extremes ........................................................... 12 2.3 Local model validation ................................................................................................ 13 2.4 Results ......................................................................................................................... 17 2.4.1 Typical conditions ................................................................................................ 17 2.4.2 Directional wave climatologies ........................................................................... 19 2.4.3 Seasonality .......................................................................................................... 20 2.4.4 Tide and wave climate ......................................................................................... 23 2.4.5 Wave extremes ................................................................................................... 23 2.4.6 Return periods ..................................................................................................... 28 2.5 Discussion .................................................................................................................... 31 2.5.1 Offshore wave climate ........................................................................................ 31 2.5.2 Lagoon wave climate ........................................................................................... 32 2.5.3 Extreme events .................................................................................................... 34 3 WAVE AND TIDAL FLUSHING ON ROCAS ATOLL .................................................................. 36 3.1 Introduction ................................................................................................................ 36 3.2 Methods ...................................................................................................................... 37 3.2.1 Measurements of waves, currents and water level ............................................ 37 v 3.3 Results ......................................................................................................................... 38 3.3.1 Tides .................................................................................................................... 38 3.3.2 Currents ............................................................................................................... 40 3.3.3 Water exchanges through the passes ................................................................. 42 3.3.4 Waves, current at larger reef pass, and lagoon water level ............................... 42 3.4 Discussion .................................................................................................................... 45 3.4.1 Atoll morphology and flow pattern ..................................................................... 45 3.4.2 Drag coefficient at the main reef passage .......................................................... 47 3.4.3 Tidal influence on wave pumping ....................................................................... 48 4 REEF ISLANDS MORPHODYNAMICS ON ROCAS ATOLL ....................................................... 51 4.1 Introduction ................................................................................................................ 51 4.2 Methods ...................................................................................................................... 52 4.2.1 In situ wave data ................................................................................................. 53 4.2.2 Morphological surveys ........................................................................................ 53 4.2.3 Historical data ..................................................................................................... 55 4.3 Results ......................................................................................................................... 56 4.3.1 Incident wave spectra ......................................................................................... 56 4.3.2 Reef islands and shingle bank morphology ......................................................... 57 4.3.3 Morphological changes ....................................................................................... 60 4.4 Discussion .................................................................................................................... 69 4.4.1 Response to incident wave energy ..................................................................... 69 4.4.2 Morphological adjustment of reef islands .......................................................... 71 5 RESPONSE OF WAVE REFRACTION TO SEA LEVEL RISE ON ROCAS ATOLL: IMPLICATIONS FOR REEF ISLANDS MORPHODYNAMICS ..................................................................................... 74 5.1 Introduction ................................................................................................................ 74 5.2 Methods ...................................................................................................................... 75 5.2.1 Topographic and bathymetric surveys ................................................................ 75 5.2.2 Numerical wave model........................................................................................ 77 5.3 Results ......................................................................................................................... 78 5.3.1 Atoll topography.................................................................................................. 78 5.3.2 Overall wave refraction ....................................................................................... 81 5.3.3 Wave vectors convergence ................................................................................
Load more

Recommended publications
  • This Keyword List Contains Indian Ocean Place Names of Coral Reefs, Islands, Bays and Other Geographic Features in a Hierarchical Structure
    CoRIS Place Keyword Thesaurus by Ocean - 8/9/2016 Indian Ocean This keyword list contains Indian Ocean place names of coral reefs, islands, bays and other geographic features in a hierarchical structure. For example, the first name on the list - Bird Islet - is part of the Addu Atoll, which is in the Indian Ocean. The leading label - OCEAN BASIN - indicates this list is organized according to ocean, sea, and geographic names rather than country place names. The list is sorted alphabetically. The same names are available from “Place Keywords by Country/Territory - Indian Ocean” but sorted by country and territory name. Each place name is followed by a unique identifier enclosed in parentheses. The identifier is made up of the latitude and longitude in whole degrees of the place location, followed by a four digit number. The number is used to uniquely identify multiple places that are located at the same latitude and longitude. For example, the first place name “Bird Islet” has a unique identifier of “00S073E0013”. From that we see that Bird Islet is located at 00 degrees south (S) and 073 degrees east (E). It is place number 0013 at that latitude and longitude. (Note: some long lines wrapped, placing the unique identifier on the following line.) This is a reformatted version of a list that was obtained from ReefBase. OCEAN BASIN > Indian Ocean OCEAN BASIN > Indian Ocean > Addu Atoll > Bird Islet (00S073E0013) OCEAN BASIN > Indian Ocean > Addu Atoll > Bushy Islet (00S073E0014) OCEAN BASIN > Indian Ocean > Addu Atoll > Fedu Island (00S073E0008)
    [Show full text]
  • With Special Emphasis on the Equatorial Oceanic Islands
    insects Article Synthesis of the Brazilian Poduromorpha (Collembola: Hexapoda) with Special Emphasis on the Equatorial Oceanic Islands Estevam C. A. de Lima 1,2,* , Maria Cleide de Mendonça 1, Gabriel Costa Queiroz 1 , Tatiana Cristina da Silveira 1 and Douglas Zeppelini 2 1 Laboratório de Apterygotologia, Departamento de Entomologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro 20940-040, Brazil; [email protected] (M.C.d.M.); [email protected] (G.C.Q.); [email protected] (T.C.d.S.) 2 Laboratório de Sistemática de Collembola e Conservação—Coleção de Referência de Fauna de Solo—CCBSA—Universidade Estadual da Paraíba Campus V, João Pessoa 58070-450, Brazil; [email protected] * Correspondence: [email protected] Simple Summary: Endemic Collembola species are bioindicators of environmental quality since native species abundance is particularly sensitive to environmental disturbances. Oceanic island biota generally present high percentages of endemic species, and the vulnerability of these species is higher than those of the continents. The objective of this work was to carry out a survey of the Collembola species of the order Poduromorpha in the Brazilian oceanic islands and synthesize a distribution list of this order for Brazil. Our results reveal four new species of Collembola Poduromorpha for Brazilian oceanic islands that may be useful for the conservation strategies of these island regions and a contributor to the knowledge of the order in Brazil. Citation: de Lima, E.C.A.; de Mendonça, M.C.; Queiroz, G.C.; da Silveira, T.C.; Abstract: We present new species and records of Poduromorpha for the Brazilian oceanic islands and Zeppelini, D.
    [Show full text]
  • Ascidians from Rocas Atoll, Northeast Brazil
    ORIGINAL RESEARCH published: 16 June 2015 doi: 10.3389/fmars.2015.00039 Ascidians from Rocas Atoll, northeast Brazil Sandra V. Paiva 1, Ronaldo R. de Oliveira Filho 1 and Tito M. da Cruz Lotufo 1, 2* 1 Graduate Program in Tropical Marine Sciences, Universidade Federal do Ceará, Fortaleza, Brazil, 2 Departament of Biological Oceanography, Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brazil Rocas Atoll is the only one of its kind in the South Atlantic—and the first Brazilian marine biological reserve. This is the first report about the ascidians from Rocas. A total of 12 species were found, 5 of them not hitherto described: Ascidia viridina sp. nov., Didemnum rochai sp. nov., Leptoclinides crocotulus sp. nov., Polysyncraton maurizeliae sp. nov., and Trididemnum rocasensis sp. nov. One Caribbean species, Didemnum halimedae, was also discovered in the region for the first time. Further, this is the first record of Didemnum digestum in the Atlantic. The results indicate a high degree of endemism in the ascidian fauna from Rocas Atoll, where didemnids are presently the most important members. Keywords: Ascidiacea, Tunicata, biodiversity, coral reef, taxonomy Edited by: Wei-Jen Chen, National Taiwan University, Taiwan Introduction Reviewed by: Greg W. Rouse, Ascidians are benthic marine invertebrates that are present throughout the marine environments University of California San Diego, from the intertidal to the deep sea. Currently, over 3000 species have been formally described USA (Lambert, 2005), but only 461 have been found in the Atlantic Ocean (Rocha et al., 2012). Francoise Monniot, Muséum National d’Histoire Naturelle, Despite their importance as one of the major components of benthic communities, their France presence is still ignored in many regions due to the lack of collections or specialists.
    [Show full text]
  • Colonization and Growth of Crustose Coralline Algae (Corallinales, Rhodophyta) on the Rocas Atoll
    BRAZILIAN JOURNAL OF OCEANOGRAPHY, 53(3/4):147-156, 2005 Colonization and growth of crustose coralline algae (Corallinales, Rhodophyta) on the Rocas Atoll Alexandre Bigio Villas Bôas1*; Marcia A. de O.Figueiredo 2 & Roberto Campos Villaça 1 1Universidade Federal Fluminense (Caixa Postal 100644, 24001-970Niterói, RJ, Brasil) 2Instituto de Pesquisas Jardim Botânico do Rio de Janeiro (Rua Pacheco Leão 915, 22460-030 Rio de Janeiro, RJ, Brasil) *[email protected] A B S T R A C T Crustose coralline algae play a fundamental role in reef construction all over the world. The aims fo this study were to identify and estimate the abundance of the dominant crustose coralline algae in shallow reef habitats, measuring their colonization, growth rates and productivity. Crusts sampled from different habitats were collected on leeward and windward reefs. Discs made of epoxy putty were fixed on the reef surface to follow coralline colonization and discs containing the dominant coralline algae were fixed on different habitats to measure the crusts’ marginal growth. The primary production experiments followed the clear and dark bottle method for dissolved oxygen reading. Porolithon pachydermum was confirmed as the dominant crustose coralline alga on the Rocas Atoll. The non-cryptic flat form of P. pachydermum showed a faster growth rate on the leeward than on the windward reef. This form also had a faster growth rate on the reef crest (0.05 mm.day-1) than on the reef flat (0.01 mm.day-1). The cryptic protuberant form showed a trend, though not significant, towards a faster growth rate on the reef crest and in tidal pools than on the reef flat.
    [Show full text]
  • Assessing Long-Term Changes in the Beach Width of Reef Islands Based on Temporally Fragmented Remote Sensing Data
    Remote Sens. 2014, 6, 6961-6987; doi:10.3390/rs6086961 OPEN ACCESS remote sensing ISSN 2072-4292 www.mdpi.com/journal/remotesensing Article Assessing Long-Term Changes in the Beach Width of Reef Islands Based on Temporally Fragmented Remote Sensing Data Thomas Mann 1,* and Hildegard Westphal 1,2 1 Leibniz Center for Tropical Marine Ecology, Fahrenheitstrasse 6, D-28359 Bremen, Germany; E-Mail: [email protected] 2 Department of Geosciences, University of Bremen, D-28359 Bremen, Germany * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +49-421-2380-0132; Fax: +49-421-2380-030. Received: 30 May 2014; in revised form: 7 July 2014 / Accepted: 18 July 2014 / Published: 25 July 2014 Abstract: Atoll islands are subject to a variety of processes that influence their geomorphological development. Analysis of historical shoreline changes using remotely sensed images has become an efficient approach to both quantify past changes and estimate future island response. However, the detection of long-term changes in beach width is challenging mainly for two reasons: first, data availability is limited for many remote Pacific islands. Second, beach environments are highly dynamic and strongly influenced by seasonal or episodic shoreline oscillations. Consequently, remote-sensing studies on beach morphodynamics of atoll islands deal with dynamic features covered by a low sampling frequency. Here we present a study of beach dynamics for nine islands on Takú Atoll, Papua New Guinea, over a seven-decade period. A considerable chronological gap between aerial photographs and satellite images was addressed by applying a new method that reweighted positions of the beach limit by identifying “outlier” shoreline positions.
    [Show full text]
  • Redalyc.Population Dynamics of Siderastrea Stellata Verrill, 1868
    Anais da Academia Brasileira de Ciências ISSN: 0001-3765 [email protected] Academia Brasileira de Ciências Brasil PINHEIRO, BARBARA R.; PEREIRA, NATAN S.; AGOSTINHO, PAULA G.F.; MONTES, MANUEL J.F. Population dynamics of Siderastrea stellata Verrill, 1868 from Rocas Atoll, RN: implications for predicted climate change impacts at the only South Atlantic atoll Anais da Academia Brasileira de Ciências, vol. 89, núm. 2, abril-junio, 2017, pp. 873-884 Academia Brasileira de Ciências Rio de Janeiro, Brasil Available in: http://www.redalyc.org/articulo.oa?id=32751197008 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Anais da Academia Brasileira de Ciências (2017) 89(2): 873-884 (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 http://dx.doi.org/10.1590/0001-3765201720160387 www.scielo.br/aabc Population dynamics of Siderastrea stellata Verrill, 1868 from Rocas Atoll, RN: implications for predicted climate change impacts at the only South Atlantic atoll BARBARA R. PINHEIRO¹, NATAN S. PEREIRA², PAULA G.F. AGOSTINHO² and MANUEL J.F. MONTES¹ 1Laboratório de Oceanografia Química, Departamento de Oceanografia, Universidade Federal de Pernambuco, Av. Arquitetura, s/nº, Cidade Universitária, 50740-550 Recife, PE, Brazil 2Laboratório de Geologia e Sedimentologia/LAGES, Universidade Estadual da Bahia, Campus VIII, Rua da Aurora, s/nº, General Dutra, 48608-240 Paulo Afonso, BA, Brazil Manuscript received on June 16, 2016; accepted for publication on January 1, 2017 ABSTRACT Coral reefs are one of the most vulnerable ecosystems to ocean warming and acidification, and it is important to determine the role of reef building species in this environment in order to obtain insight into their susceptibility to expected impacts of global changes.
    [Show full text]
  • The Contribution of Wind-Generated Waves to Coastal Sea-Level Changes
    1 Surveys in Geophysics Archimer November 2011, Volume 40, Issue 6, Pages 1563-1601 https://doi.org/10.1007/s10712-019-09557-5 https://archimer.ifremer.fr https://archimer.ifremer.fr/doc/00509/62046/ The Contribution of Wind-Generated Waves to Coastal Sea-Level Changes Dodet Guillaume 1, *, Melet Angélique 2, Ardhuin Fabrice 6, Bertin Xavier 3, Idier Déborah 4, Almar Rafael 5 1 UMR 6253 LOPSCNRS-Ifremer-IRD-Univiversity of Brest BrestPlouzané, France 2 Mercator OceanRamonville Saint Agne, France 3 UMR 7266 LIENSs, CNRS - La Rochelle UniversityLa Rochelle, France 4 BRGMOrléans Cédex, France 5 UMR 5566 LEGOSToulouse Cédex 9, France *Corresponding author : Guillaume Dodet, email address : [email protected] Abstract : Surface gravity waves generated by winds are ubiquitous on our oceans and play a primordial role in the dynamics of the ocean–land–atmosphere interfaces. In particular, wind-generated waves cause fluctuations of the sea level at the coast over timescales from a few seconds (individual wave runup) to a few hours (wave-induced setup). These wave-induced processes are of major importance for coastal management as they add up to tides and atmospheric surges during storm events and enhance coastal flooding and erosion. Changes in the atmospheric circulation associated with natural climate cycles or caused by increasing greenhouse gas emissions affect the wave conditions worldwide, which may drive significant changes in the wave-induced coastal hydrodynamics. Since sea-level rise represents a major challenge for sustainable coastal management, particularly in low-lying coastal areas and/or along densely urbanized coastlines, understanding the contribution of wind-generated waves to the long-term budget of coastal sea-level changes is therefore of major importance.
    [Show full text]
  • Pacific Remote Islands Marine National Monument
    U.S. Fish & Wildlife Service Pacific Remote Islands Marine National Monument The Pacific Remote Islands Marine National Monument falls within the Central Pacific Ocean, ranging from Wake Atoll in the northwest to Jarvis Island in the southeast. The seven atolls and islands included within the monument are farther from human population centers than any other U.S. area. They represent one of the last frontiers and havens for wildlife in the world, and comprise the most widespread collection of coral reef, seabird, and shorebird protected areas on the planet under a single nation’s jurisdiction. At Howland Island, Baker Island, Jarvis Island, Palmyra Atoll, and Kingman Reef, the terrestrial areas, reefs, and waters out to 12 nautical miles (nmi) are part of the National Wildlife Refuge System. The land areas at Wake Atoll and Johnston Atoll remain under the jurisdiction of The giant clam, Tridacna gigas, is a clam that is the largest living bivalve mollusk. the U.S. Air Force, but the waters from Photo: © Kydd Pollock 0 to 12 nmi are protected as units of the National Wildlife Refuge System. For all of the areas, fishery-related Marine National Monument, and orders long time periods throughout their entire activities seaward from the 12-nmi refuge of magnitude greater than the reefs near cultural and geological history. These boundaries out to the 50-nmi monument heavily populated islands. Expansive refuges are unique in that they were and boundary are managed by the National shallow coral reefs and deep coral forests, are still largely pristine, though many Oceanic and Atmospheric Administration.
    [Show full text]
  • Celebrating 125 Years of National Geographic
    EpicSOUTH AMERICA CELEBRATING 125 YEARS OF NATIONAL GEOGRAPHIC AN EXHILARATING & COMPREHENSIVE VoyaGE ABoarD NATIONAL GEOGRAPHIC EXPLORER | 2013 TM As astonishing as the photos in National Geographic. And an exhilarating life adventure: A Lindblad-National Geographic South America Expedition TM Lindblad Expeditions and National Geographic have joined forces to further inspire the world through expedition travel. Our collaboration in exploration, research, technology and conservation will provide extraordinary travel experi- ences and disseminate geographic knowledge around the globe. EPIC “Pertaining to a long poetic composition, usually centered upon a hero.” In this case, a continent. Dear Traveler, This expedition, Epic South America, is indeed a long poetic composition—from 10° north latitude to 35° south. It would be a 2,700 nautical mile voyage on South America’s west coast but, because of what we fondly refer to as “Brazil’s bump,” it’s about 4,000 nautical miles on the east coast. It visits eight distinctly different countries with spectacularly diverse geography—physically, culturally and naturally. For reasons that make little sense to me personally, South America played a very limited role in historic teachings when I went to school. We were Old World-centric, and rarely, if ever, discussed the vibrant, turbulent and complex history of this New World continent. So, on this voyage you can fill the gap so clearly left in the curriculum many of us experienced. To celebrate 125 years of the National Geographic Society, a most essential institution, we have assembled a most remarkable aggregate of staff and guest speakers, including my friends National Geographic Fellow Tom Lovejoy, and National Geographic Explorers-in-Residence Wade Davis and Johan Reinhard.
    [Show full text]
  • Patterns of Coral Reef Development on Tarawa Atoll (Kiribati)
    BULLETIN OF MARINE SCIENCE, 69(3): 1191–1207, 2001 CORAL REEF PAPER PATTERNS OF CORAL REEF DEVELOPMENT ON TARAWA ATOLL (KIRIBATI) Gustav Paulay and Alexander Kerr ABSTRACT Tarawa Atoll lies in the equatorial upwelling region, has the largest human population of any Pacific atoll, and has an unusual, asymmetrical form: the triangular lagoon is largely enclosed along the east and south, but communicates with the ocean through a submerged barrier reef along its entire western border. How do these unusual character- istics affect reefs? After characterizing lagoonal reefs, the interactions and influence of various physical and biotic factors are examined. Coral cover and diversity increase from northwest to southeast as a consequence of polarized exchange with the surrounding ocean. Macroalgae are abundant in the central lagoon, probably as a result of high pro- ductivity and low levels of herbivory, the latter a likely consequence of overfishing. Coral communities of these central reefs are dominated by clonal, fragmenting species of en- crusting Montipora and branching Acropora. A substantial loss of coral cover and diver- sity occurred in the southeastern lagoon apparently a few hundred years ago. As a conse- quence of this mortality, much of the reef habitat and associated communities of the southeastern lagoon were lost, and patch reefs in the area developed into sand-dominated shoals by intense bioerosion and burial. The high productivity of the region has also resulted in high rates of mobile sediment production through bioerosion and the accumu- lation of skeletal remains of a rich suspension and deposit feeding lagoonal biota. The productivity and sediment production in turn had major geomorphological consequences, creating an atoll with an unusually wide, sand-dominated rim and shallow, sediment- choked lagoon, and may have been partly responsible for the submergent nature of the western barrier reef through the impact of inimical lagoonal backwaters.
    [Show full text]
  • A Coupled Wave-Hydrodynamic Model of an Atoll with High Friction: Mechanisms for flow, Connectivity, and Ecological Implications
    Ocean Modelling 110 (2017) 66–82 Contents lists available at ScienceDirect Ocean Modelling journal homepage: www.elsevier.com/locate/ocemod Virtual Special Issue Coastal ocean modelling A coupled wave-hydrodynamic model of an atoll with high friction: Mechanisms for flow, connectivity, and ecological implications ∗ Justin S. Rogers a, , Stephen G. Monismith a, Oliver B. Fringer a, David A. Koweek b, Robert B. Dunbar b a Environmental Fluid Mechanics Laboratory, Stanford University, 473 Via Ortega, Y2E2 Rm 126, Stanford, CA, 94305, USA b Department of Earth System Science, Stanford University, Stanford, CA, 94305, USA a r t i c l e i n f o a b s t r a c t Article history: We present a hydrodynamic analysis of an atoll system from modeling simulations using a coupled wave Received 18 April 2016 and three-dimensional hydrodynamic model (COAWST) applied to Palmyra Atoll in the Central Pacific. Revised 11 October 2016 This is the first time the vortex force formalism has been applied in a highly frictional reef environ- Accepted 28 December 2016 ment. The model results agree well with field observations considering the model complexity in terms Available online 29 December 2016 of bathymetry, bottom roughness, and forcing (waves, wind, metrological, tides, regional boundary condi- Keywords: tions), and open boundary conditions. At the atoll scale, strong regional flows create flow separation and Coral reefs a well-defined wake, similar to 2D flow past a cylinder. Circulation within the atoll is typically forced by Hydrodynamics waves and tides, with strong waves from the north driving flow from north to south across the atoll, and Surface water waves from east to west through the lagoon system.
    [Show full text]
  • The Case-Study of Fongafale, Atool of Funafuti
    Shoreline of human-impacted coralline atolls: need for a concerted management. The case-study of Fongafale, atoll of Funafuti, Tuvalu Caroline Rufin The atoll of Funafuti (Tuvalu archipelago) is located in the South Pacific Ocean at latitude 8.31° South and longitude 179.13° East (Figure 1). According to its morphology, Fongafale island (atoll of Funafuti) can be split into three distinct geographical areas, i.e. the northern, central and southern parts. The present study deals with the central part, which results from the deposition of sediments from the two other areas following North and South longshore drifts. Marshall •• Islands, 1o·N Kiribati! . ~ ~· ... ' ... .. ·. ~ Samoa .. o_. •• Vanuatu b •! ; . b\ Fiji ,::::1 . ~ 0 Tonga .. ' '· : .... 2o·s New .. ~.'•. ' •• Caledon~. • • • 100· 110· 180' 170' 160"W Source : from Mclean et Hosking. 1991 Figure 1 Localisation of Tuvalu within the Pacific Bassin. 436 Coral reefs in the Pacifie: Status and monitoring, Resources and management Through the example of Fongafale island, the present study is aimed at thinking about the manage­ ment of low coralline islands confronted with erosion problems most often in relation with excessive coastal planning. This thought will be developed in terms of global geography while taking into account ail the environmental conditions. Our purpose will be not to demonstrate which of the two factors, Man or Nature, is the more disturb­ ing. However, from the analysis of our data set it is clear that the contribution of the former is greater than that of the latter. We will first draw a schedule of Fongafale lagoon shoreline from aerial pictures and topographical readings; it will be essential to understand the environmental problems which this atoll is submitted to.
    [Show full text]