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Experiments by Invited Researchers

 

Barrier Dynamics Experiment II (BARDEX II)

Project acronym: HyIV-Deltares-08
Name of Group Leader: Prof. Gerd Masselink
User-Project Title: Barrier Dynamics Experiment II (BARDEX II)
Facility: Delta Flume
Proceedings TA Project: LARGE-SCALE BARRIER DYNAMICS EXPERIMENT II (BARDEX II) ? EXPERIMENTAL DESIGN AND SOME PRELIMINARY RESULTS
Data Management Report: Report

This data can be requested from: Deltares, Mark Klein Breteler (mark.kleinbreteler@deltares.nl)


User-Project Objectives

A 4.5-m high and 30-m wide sandy barrier will be constructed in the Delta Flume with a lagoon situated to the landward. The barrier will be subjected to a range of wave conditions and varying sea/lagoon water levels, and the morphological response will be recorded. Five key objectives are identified, each of them linked to a specific Work Package:

  • WP1 – barrier hydrology: to observe, quantify and model the dynamic groundwater conditions within the barrier, subject to varying wave, water-level and back-barrier lagoon conditions.
  • WP2 – swash and berm dynamics: to examine the relative roles of advected bore-generated turbulence versus local boundary layer processes in the full column sediment transport processes in the swash zone; to resolve the role of barrier hydrology in controlling equilibrium morphological response at the beach face.
  • WP3 – swash-surf zone exchange and bar dynamics: to determine and quantify the dominant hydrodynamic and sediment transport mechanisms responsible for swash-surf zone sediment exchange; to identify key processes responsible for onshore and offshore bar migration.
  • WP4 – barrier overwash: to quantify overwash threshold for different wave and water-level conditions; to investigate the effect of groundwater gradients on overwash processes; to compare overwash processes on sand and gravel barriers.
  • WP5 – Sediment resuspension and bed morphology: to observe and measure vortex resuspension process and bedform dynamics under shoaling and breaking waves; to quantify changes in the magnitude and direction of sediment transport (bedload and suspended load) in the region just outside the surf zone.
  • WP6 – numerical modeling: to further develop and rigorously test advanced process-based cross-shore hydro-morphodynamic models that address bar and barrier dynamics, and barrier destruction through overwash.

Short description of the work carried out

The greatest achievement of BARDEX II is that the team, in collaboration with Deltares staff, managed to execute the complete test programme in the allotted time. Another major achievement is that of the vast amount of instrumentation deployed, the overwhelming majority worked and, as a result, an unprecedented data set was obtained.

Three major difficulties were encountered:

  • Although all data logging by the partners on their computers was time-synched through use of a time server, unfortunately the Delta Flume computer was operating under its own time. For the partners to directly compare their data with that collected by the Delta Flume system will not be an easy task.
  • The devices to record pump discharge from lagoon to sea (and vice versa) are unlikely to have yielded reliable data due to the need to always have a trickle discharge going through the pump to keep them ticking over and various other problems associated with the pump system. The pump discharge data was intended to be used to quantify discharge across and over the barrier, but this is unlikely to be possible.
  • The sand used in the flume was not what was requested. We requested a D50 of 0.8mm, and in the end we only had a D50 of 0.4mm. This meant that the initial first set of test conditions that was supposed to produce a berm actually resulted in the formation of a bar. We had to make adjustments to the test program and the resulting experimental sequence was far from ideal.

Highlights of important research results

It is really too early to be reporting on research highlights because the data analysis has only just commenced; however, some preliminary results from the work packages that have progressed their analysis furthest are provided below:

  • Measurement made in the surf zone during the BARDEX II experiment was revealed that breaking-induced surface-generated eddies can penetrate through the water column to hit the sea bed and suspend sand. The inherently intermittent nature of this turbulence and hence suspension is strikingly at odd with sand transport equations that assume sand transport to be related to the orbital flow to some power. Our quantitative understanding of the effects of breaking-induced turbulence on sand suspension is limited because of a lack of simultaneous and accurate measurements of turbulence and sand suspension under breaking waves.
  • Overwash Potential (OP), defined as the difference between the wave runup and the barrier elevation is used to define the overwash threshold condition, and to predict the morphological outcome of a particular overwash event. To make effective use of OP it is necessary to identify a reliable runup predictor. Twelve runup equations were tested for this purpose and the most reliable approach for the determination of OP during the BARDEX II experiment was the equation of Stockdon et al. (2006).
  • Sediment resuspension in the region outside the surf zone is complicated by the presence of bedforms in the nearshore, which alter the sand transport processes while modifying bed roughness in a complex feedback mechanism. Initial findings from analysis of the BARDEX II data indicate that sediment suspension in the nearshore appears to be controlled by a combination of near-bed turbulent bursting processes which results in near-instantaneous low concentration suspensions restricted to the bottom boundary layer, and vortex shedding from bedforms which results in higher concentration suspensions which are larger in scale than vertical eddy sizes, and perpetuate outside of the bottom boundary layer.

Publications
Gerd Masselink, Ian Turner, Daniel Conley, Gerben Ruessink, Ana Matias, Charlie Thompson, Bruno Castelle and Guido Wolters BARDEX II: Bringing the beach to the laboratory ? again! , 2013 Masselink, G, Turner, I.L., Conley, D.C., Ruessink, B.G., Matias, A., Thompson, C., Castelle, B. and Wolters, G., 2013. BARDEX II: Bringing the beach to the laboratory ? again! In: Conley, D.C., Masselink, G., Russell, P.E. and O?Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium, Journal of Coastal Research, Special Issue, No. 65, pp. 1545-1550. Plymouth, England, ISSN 0749-0208.
Ian L. Turner, Gabriel C. Rau , Martin S. Andersen, Martin J. Austin, Jack A. Puleo and Gerd Masselink Coastal sand barrier hydrology ? observations from the BARDEX II prototype-scale laboratory experiment , 2013 Turner, I.L., Rau, G.C., Andersen, M.S., Austin, M.J, Puleo, J. and Masselink, G. 2013. Coastal sand barrier hydrology ? observations from the BARDEX II prototype-scale laboratory experiment In: Conley, D.C., Masselink, G., Russell, P.E. and O?Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1886-1891, ISSN 0749-0208.
Ana Matias, Gerd Masselink, Aart Kroon, Chris E. Blenkinsopp, Ian L. Turner Overwash experiment on a sandy barrier , 2013 Matias, A., Masselink, G., Kroon, A., Blenkinsopp, C., and Turner, I.L., 2013. Overwash experiment on a sandy barrier In: Conley, D.C., Masselink, G., Russell, P.E. and O?Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium, Journal of Coastal Research, Special Issue, No. 65, pp. 778-783 Plymouth, England, ISSN 0749-0208.
Winnie de Winter, Daan Wesselman, Florent Grasso and Gerben Ruessink Large-scale laboratory observations of beach morphodynamics and turbulence beneath shoaling and breaking waves , 2013 De Winter, W., Wesselman, D., Grasso, F. and Ruessink, G., 2013. Large-scale laboratory observations of beach morphodynamics and turbulence beneath shoaling waves and plunging breakers. In: Conley, D.C., Masselink, G., Russell, P.E. and O?Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1515-1520, ISSN 0749-0208.
Bruno Castelle, Benjamin Dubarbier, Marion Tissier, Philippe Bonneton, Daniel Conley, Gerben Ruessink and Gerd Masselink Testing numerical hydrodynamic and morphodynamic models against BARDEX II Experiment data sets , 2013 Castelle, B., Dubarbier, B., Tissier, M., Bonneton, P., Conley, D.C., Ruessink, B.G. and Masselink, G., 2013. Testing numerical hydrodynamic and morphodynamic models against BARDEX II Experiment data sets. In: Conley, D.C., Masselink, G., Russell, P.E. and O?Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1745-1750, ISSN 0749-0208.
Charlie E. L. Thompson, Hachem Kassem and Jon Williams Nearshore sediment resuspension and bed morphology , 2013 Thompson, C.E.L., Kassem, H. and Williams, J., 2013. BARDEX II: Nearshore sediment resuspension and bed morphology. In: Conley, D.C., Masselink, G., Russell, P.E. and O?Hare, T.J. (eds.), Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1593-1598, ISSN 0749-0208.

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