Plantilla trabajo Geomorfo

7º Simpósio sobre a Margem Ibérica Atlântica - MIA12
16-20 de Dezembro de 2012, Lisboa
Avaliação do transporte longitudinal na praia de Ofir (NO Portugal)
Assessment of the longshore transport at Ofir beach (NW Portugal)
S. Fernández-Fernández (1), V. Martins (2,3), P.A. Silva (4), T. Abreu (5), P. Baptista (3), C.
Bernardes (3), P. Miranda (2), J. Pais-Barbosa (6), M.V.L. Rocha (4), F. Rocha (2), A.M. Bernabeu (1),
D. Rey (1)
(1) Dpt. Geociencias Marinas y O.T., GEOMA, Universidad de Vigo, 36310 Vigo, España,
[email protected]
(2)
Dpt. Gêociencias, GeoBioTec, Universidade de Aveiro, 3810-193 Aveiro, Portugal
(3) Dpt. Gêociencias, Centro de Estudos do Ambiente e do Mar (CESAM), Universidade de Aveiro, 3810-193
Aveiro, Portugal
(4) Dpt. Física, Centro de Estudos do Ambiente e do Mar (CESAM), Universidade de Aveiro, 3810-193 Aveiro,
Portugal
(5) Dpt. Eng.Civil, Centro de Estudos do Ambiente e do Mar (CESAM), ESTGV-Instituto Politécnico de Viseu,
3504-510 Viseu, Portugal
(6) Centro de Investigação em Ciências Geo-Espaciais, FCUP - Rua do Campo Alegre, s/n, 4169-007 Porto,
Portugal
Abstract:
A sand tracer experiment was performed at Ofir-Apúlia beach (NW Portugal) in order to study the
longshore sediment transport under medium-energy wave conditions.
th
The fieldwork was carried out during a single tidal cycle on the 19 March 2012, in a sheltered beach
sector between two groins. The dyed sand was placed covering an area of the beach face, at low
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tide, with 1 m per 0.1 m thickness. In the following low tide, sediments cores with 15 cm length
were gathered and divided into slices of 5 cm. Furthermore, local oceanographic conditions were
monitored using two pressure transducers and an electromagnetic current meter. Beach topography
was surveyed with the INSHORE (INtegrated System for High Operational REsolution in shore
monitoring) system mounted on a motor-quad vehicle. In the laboratory, the density of the dyed
sand was determined for each layer of the cores.
The results disclosed that the number of samples with dyed sand, as well as the density of dyed
grains, decreased considerably with depth, probably owing to local beach accretion, and with the
distance to the source. For that reason, the superficial layer (0-5 cm) was considered the most
representative for sediment transport computations. The tracer was driven southward in response
to the swell and wind-waves induced currents observed. The estimated total longshore transport
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rate was 0.0016 m .s . The empirical longshore formula proposed by the CERC (1984) predicts a
similar value, while the Kamphuis formula (2002) underestimates this value, as it has already been
reported by others researchers.
Palavras chave: traçadores de areia, transporte sedimentar, fórmulas empíricas, praia de Ofir
Key words: sand tracer, sediment transport, empirical formula, Ofir beach