Measuring and modelling over wash hydrodynamics on a barrier island

Ana Matias, Ana Rita Carrasco, Carlos Loureiro, Umberto Andriolo, Gerd Masselink, Martha Guerreiro, Andre Pacheco, Robert McCall, Oscar Ferreira, Theocharis Plomaritis

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Abstract

Overwash hydrodynamics datasets are mixed in quality and scope, being hard to obtain due to fieldwork experimental difficulties. Aiming to overcome such limitations, this work presents accurate fieldwork data on overwash hydrodynamics, further exploring it to model overwash on a low-lying barrier island. Fieldwork was performed on Barreta Island (Portugal), in December 2013, during neap to spring-tides, when significant wave height reached 2.64 m. During approximately 4 hours, more than 120 shallow overwash events were measured with a video-camera (at 10 Hz), a pressure transducer (at 4 Hz) and a current-meter (at 4 Hz). This high-frequency fieldwork dataset includes runup, overwash number, depth and velocity. Fieldwork data along with information from literature were used to setup XBeach model in non-hydrostatic mode. The baseline model had variable skills over the duration of the overwash episode, performing better during the rising tide than during the falling tide. Model average number of events RMSE (root-mean-square-error) was 7 events each 30 minutes. The baseline model was forced to simulate overwash with different nearshore morphology, grain-size and lagoon water level. An average decrease of about 30% overwash was obtained due to changes in the nearshore morphology, mostly a small vertical growth of the submerged bar. The coarser and finer grain-sizes tests produced an 11% change in overwash, with less overwash on the coarser barrier. Changing lagoon water levels had a reduced effect on overwash hydraulics.
Original languageEnglish
Title of host publicationProceedings of Coastal Dynamics 2017
EditorsTroels Aagaard, Rolf Deigaard, David Fuhrman
Place of PublicationHelsingor
PublisherUniversity of Copenhagen
Pages1616-1627
Volume1
ISBN (Print)n/a
Publication statusPublished - 12 Jun 2017

Keywords

  • storm impacts
  • hydrodynamics
  • XBeach
  • runup
  • nearshore topography
  • video data

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    Matias, A., Carrasco, A. R., Loureiro, C., Andriolo, U., Masselink, G., Guerreiro, M., Pacheco, A., McCall, R., Ferreira, O., & Plomaritis, T. (2017). Measuring and modelling over wash hydrodynamics on a barrier island. In T. Aagaard, R. Deigaard, & D. Fuhrman (Eds.), Proceedings of Coastal Dynamics 2017 (Vol. 1, pp. 1616-1627). University of Copenhagen. http://coastaldynamics2017.dk/onewebmedia/105_ana_matias.pdf