Coastal Engineering 63 (2012) 1–2

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Coastal Engineering

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Editorial

BARDEX: A large-scale laboratory study of gravel barrier dynamics

1 http://www.hydralab.eu/.

Significant advances in the understanding of coarse gravel beacheshave been made in recent decades. The advent of community accessto large scale wave facilities has made it possible to complete nearfull scale simulations of cross shore processes with the interactionof the gravel beach. The European research scene is vibrant and alarge amount of knowledge has been built up from the programmesof applied research. The role of laboratory hydraulic modelling withstructures, sediments and ecology is recognised as bridging the gapbetween numerical modelling and field experimentation. Best prac-tice has been distilled and published recently on these topics as wellas on composite modelling which is the “balanced use of physicaland numerical models” (Frostick et al., 2011).

Almost ten years ago the results from gravel and mixed beach ex-periments from the Large Wave Channel (GWK) in Germany wereobtained (López de San Román-Blanco et al., 2006). This work led toimproved understanding of the interaction of profile development,swash and run-up and groundwater processes as well as berm dy-namics. This work was completed with European Community fundingand national funding in the UK from Defra (Department for Environ-ment, Food and Rural Affairs). The experimental data was used bythat particular research group, results were published and the datawas made available for use by the wider scientific community.

The more recent experience of large scale experiments with agravel beach at the Delta Flume in the Netherlands are the topic ofthis special issue. Why is this new data relevant to the understandingof coastal response? The unique aspect of the experiments completedduring the BARDEX experiment was the inclusion of the gravel barrierand the open sea, with wave attack and tidal variation, and the backbarrier lagoon. The interaction of the sea and lagoon dynamics is akey coastal management question on many coastlines, including theBritish Isles. Research confirming this was completed for Defra andpublished under the Barrier Beaches project (Stripling et al., 2008).At around the same time work was completed on the permeabilityof gravel beaches (She et al., 2007).

Each piece of work from the BARDEX experiments has contributedto the understanding of the behaviour of the beach and the resultshave generated a new level of understanding. The data is useful inits own right for those studying barrier processes as well as those un-derstanding management aspects of beaches.

The context of the experiments with a large homogeneous barrierof pebble sized material is described in the paper by Williams et al.Turner and Masselink examine the groundwater regime within thebarrier and the role of lagoon levels, above and below the sea level,in controlling groundwater flows and the swash behaviour. Theyalso quantify the permeability of the entire gravel barrier and the var-iation in that parameter which is a key to understanding groundwaterfluxes and exchanges. Masselink and Turner examine swash

0378-3839/$ – see front matter © 2012 Published by Elsevier B.V.doi:10.1016/j.coastaleng.2012.02.007

dynamics and the infiltration/exfiltration regimes. They concludethat the role of infiltration and exfiltration on the oscillatory bound-ary layer formation in swash is likely to be the largest contributionto asymmetry in transport. At the seaward toe of the barrier Thomp-son et al. examine the oscillatory bed shear stress and conclude withan empirical correlation that can be considered for improved predic-tion wave friction factors in such environments.

Matias et al. deal with swash, overtopping and overwash, and theresults from tracer experiments on the crest of the barrier. The role ofantecedent conditions, overtopping and crest build up, and the reduc-tion of overwash likelihood demonstrate the build up of ‘intertia’ inthe barrier. The authors present an “overtopping potential” parame-ter which can be used to distinguish the ratchet effect of barrier roll-over into a quiet lagoon, through overwash and sediment transport,from those conditions causing overtopping which temporarily ‘fixes’the barrier once again. The final paper by Williams et al. deals withthe use of the numerical model XBeach, in 1-dimensional cross-shore mode, which includes swash and groundwater processes. Vari-ous hydrodynamic and morphological results from the BARDEX ex-periments as well as from storm measurements at Slapton barrierbeach on the south coast of the UK are simulated with the model.The results from the model are sensitive to initial profile shape,beach permeability and some aspects of the hydrodynamic interac-tion with the beach clearly need to be improved. However, this typeof model should be able to be used in conjunction with semi-empirical and parametric methods for barrier prediction and to ex-plore the consequences of different beach management scenarios.

This special issue contains a wealth of information on the resultsarising from this specific experiment of cross-shore processes and re-sponse. The insights should be of value to coastal scientists and engi-neers wishing to enhance their own understanding of the keyprocesses, explore controlled laboratory data in their investigationof barrier dynamics or validate the prediction of numerical models.The BARDEX datasets once again demonstrate the value of maintain-ing large experimental facilities and funding the scientific communityto undertake innovative research in them. The wider scientific com-munity can now obtain the datasets through the HydralabProgramme.1

By way of conclusion some future steps that might be taken aresummarised here. The cross-shore experiments in large-scale flumesare extremely useful for understanding storm response and beach re-covery processes. The integration of longshore processes will be re-quired for a full explanation of barrier response and hence some

2 Editorial

challenges remain to be resolved to provide a full 3-dimensional de-scription of barrier beach dynamics. Medium scale experimental ba-sins have been used successfully for many years to explorelongshore processes (e.g. Simons et al., 1995). It is an exciting pros-pect to consider what new insights into coastal response and man-agement could be provided from controlled experiments in a verylarge wave basin; however practicalities may dictate that the bestway forward will be to undertake a further in-depth explorationand synthesis of the existing cross-shore datasets from, for example,the GWK and Delta Flume and to validate predictive methods, beforeensuring the consistent inclusion of longshore processes. Validationof new methods could then be undertaken using field datasets pro-vided by one of the integrated monitoring programmes that under-pins beach management (in the UK) (Rogers et al., 2010).

References

Frostick, L.E., McLelland, S.J., Mercer, T.G. (Eds.), 2011. Users Guide to Physical Modellingand Experimentation: Experience of the HYDRALAB Network. CRC Press/Balkema,Leiden, The Netherlands.

López de San Román-Blanco, B., Coates, T.T., Holmes, P., Chadwick, A.J., Bradbury, A.,Baldock, T.E., Pedrozo-Acuña, A., Lawrence, J., Grüne, J., 2006. Large scale

experiments on gravel and mixed beaches: experimental procedure, data docu-mentation and initial results. Coastal Engineering 53, 349–362.

Rogers, J., Hamer, B., Brampton, A., Challinor, S., Glennerster, M., Brenton, P., Bradbury,A., 2010. Beach management manual, CIRA Report C685, Second edition.

She, K., Horn, D., Canning, P., 2007. Influence of permeability on the performance ofshingle and mixed beaches. Research Scoping Study. Joint Defra/EA Flood andCoastal Erosion Risk Management R&D Programme: R&D Technical ReportFD1923/TR. Report accessed 1 November 2011 at http://randd.defra.gov.uk/.

Simons, R.R., Whitehouse, R.J.S., MacIver, R.D., Pearson, J., Sayers, P.B., Zhao, Y.-D.,Channell, A.R., 1995. Evaluation of the UK coastal research facility. Proceedings ofCoastal Dynamics '95, ASCE, Gdansk, Poland, September 1995, pp. 161–172.

Stripling, S., Bradbury, A.P., Cope, S.N., Brampton, A.H., 2008. Understanding barrierbeaches. Joint Defra/EA Flood and Coastal Erosion Risk Management R&D Pro-gramme: R&D Technical Report FD1924/TR. Report accessed 1 November 2011 athttp://randd.defra.gov.uk/.

Richard J.S. WhitehouseHR Wallingford, Howbery Park, Wallingford, Oxon OX10 8BA,

United KingdomTel.: +44 1491 822434.

E-mail address: r.whitehouse@hrwallingford.com.