Measuring and modelling overwash hydrodynamics on a barrier island

Ana Matias, Ana Rita Carrasco, Carlos Loureiro, Umberto Andriolo, Gerd Masselink, Martha Guerreiro, A Pacheco, R.T. McCall, Óscar Ferreira, Theocharis A. Plomaritis

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientific

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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 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 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 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
Subtitle of host publicationHelsingør, Denmark
EditorsT. Aagaard, R. Deigaard, D. Fuhrman
Publication statusPublished - 2017
EventCoastal Dynamics 2017 - Kulturværftet, Helsingor, Denmark
Duration: 12 Jun 201716 Jun 2017


ConferenceCoastal Dynamics 2017
Internet address


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


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