Atualizado: 27 de ago. de 2020
A doutoranda Mirella Borba Santos Ferreira Costa (IOUSP) apresentou trabalho realizado no âmbito das atividades do GT1.1 – Respostas da Linha de Costa – coordenado pelos profs. Eduardo Siegle e Tereza Araújo, no 2014 Ocean Sciences Meeting. O evento é organizado pela American Geophysical Union e ocorreu em Honolulu no Hawaii entre os dias 23 a 28 de Fevereiro, reunindo aproximadamente 5000 participantes. O trabalho apresentado foi “Shoreline changes analysis at Rocas Atoll as a tool to improve spatial planning strategies” (Costa, M.B.S.F; Macedo, E.C.; Siegle, E.).
Trabalho de campo no Atol das Rocas
Praias arenosas do Atol das Rocas
Abstract:
SHORELINE CHANGES ANALYSIS AT ROCAS ATOLL AS A TOOL TO IMPROVE SPATIAL PLANNING STRATEGIES – Mirella B.S.F. Costa; Eduardo C. Macedo; Eduardo Siegle Rocas Atoll, the only atoll at South Atlantic Ocean, is one of the world’s smallest and most pristine atolls. It is managed by the Brazilian government as a no-take marine protected area where permissions are only given for research activities. Due to the small size of its reef island (Farol islet), shoreline erosion is one of the main concerns for local managers, which may affect the existence of seabird and turtle nesting sites, as well as the human presence. The goal of this work is to investigate the erosion on Farol islet using aerial photographs and tridimensional DGPS surveys. Results show that although the reef island is higher on the oceanward (about 4m above mean sea level) this margin is been historically eroded. However, the lagoonward margin which does not exceed 1–2 m in height is increasing over time. Overall, land area approximately doubled from 1984 to present. Results presented in this study show that the entire footprint of the islands is able to change so that erosion at the local scale (on one portion of an island) may be compensated by accretion on other parts of the shoreline. Furthermore, these results contribute to spatial planning of the Farol islet on Rocas Atoll.
Atualizado: 27 de ago. de 2020
Entre os dias 27/06/2013 e 27/07/2013 foi realizada a segunda expedição para a Reserva Biológica do Atol das Rocas, como parte das atividades do GT1.1 Respostas da Linha de Costa do inctAmbTropic. A expedição teve por objetivo obter um conjunto de dados in situ sobre os processos hidrodinâmicos que controlam a geomorfologia das ilhas no interior do atol. Foram obtidos dados de onda, correntes e marés, através do fundeio de 3 ADCP`s no interior do atol e 1 ADCP na porção externa. Além disso, dados da morfologia tridimensal das ilhas recifais e “run up” foram obtidos ao longo do período de estadia no Atol. O trabalho faz parte do doutorado de Mirella Costa que está sendo desenvolvido no IO/USP (http://ldc.io.usp.br), sob a orientação do Prof. Eduardo Siegle.
Esta segunda expedição contou com o apoio do Analista Ambiental, Eduardo Macedo, do ICMBio PARNAMAR Fernando de Noronha e do Prof. Carlos A.F. Schettini (UFPE). Também contribuiram para o sucesso da campanha o Prof. Natan Pereira (UNEB), o doutorando Miguel Loiola (UFBA) e mestrando Tiago Albuquerque (UFBA).
Trabalho de Campo no Atol das Rocas
A primeira expedição havia ocorrido no segundo semestre de 2012 (out-nov), onde foi medido o mesmo conjunto de dados, contudo durante um período de alta energia, caracterizado pela entrada de ondulações de direção norte. Os resultados da primeira campanha serão apresentados pela doutoranda Mirella na sessão oral “Reef Forms” do 8th IAG International Conference on Geomorphology, a ser realizado em Paris (França) (http://www.geomorphology-iag-paris2013.com).
ABSTRACT
Morphological response of reef island on rocas atoll (South Atlantic Ocean) to Seasonal energetic wave conditions. Costa M., Macedo, E., Siegle E.Reef islands on Rocas Atoll, the only atoll in the South Atlantic Ocean, are located at its leeward side, being protected from waves most part of the year but subjected to the impact of energetic swells from the north from November to February. With the aim of assessing the morphological evolution related to the incoming waves, in situ measurements were conducted in November 2012, covering a series of energetic wave conditions. Waves were measured by an ADCP (Nortek Aquadopp profiler) deployed at 1.2 km distance from the reef island and 0.9 km from the reef rim during 28 days. Simultaneously, the morphology of the entire reef island was surveyed with the use of a Differential Global Positioning System (DGPS). High energy waves with peak periods of about 13 s and significant wave heights of 2 m presented a weekly recurrence followed by a gradual decay. Morphological surveys show that the northwestern side of the island, which has been historically eroded, undergoes larger morphological changes. However, in contrast, there was an increase in volume on the beach island. The tridimensional terrain elevation models clearly show the removal of submerged banks dispersed on the reef rim and their deposition over the beach. This is thought to be due to the intense wave set-up generated by waves breaking on the leeward reef edge, moving the sediments in the opposite direction to that of the overall gravity-driven outflow. The results suggest that the sediment redistribution by seasonal northern swells contribute to sediment accretion on the reef island, thereby reducing the long-term erosion of this portion of the island.