Turbulence and the Beach, guest post by Hachem Kassem


Me inBardexII

Hachem surveying the beach in between wave runs during the BARDEX II experiments.



Hachem Kassem, an SMMI PhD researcher based in Ocean and Earth Science, gave a talk as part of the SMMPG seminar series, on turbulence and its role is shaping the beach. His talk, enthusiastically called “Turbulence and the Beach” answered our much sought after question, ‘what does Hachem actually study?’. Attempting to present the most complex problem in classical physics to an audience of non-physicists, Hachem presented ample examples of turbulence in nature and engineering from the daily cup of coffee to the raging storms on Jupiter. Art depicting nature such as van Gogh’s Stormy night, and a selection of historical quotes often highlighting the frustration of those who endeavoured to study this problem, where heavily featured, with quotes like:

Turbulence was probably invented by the Devil of the seventh day of creation (when the Good Lord wasn’t looking (Bradshaw, 1994, J. Exp. Fluids)


‘this area of research has quite a lot in common with studies of alleged paranormal phenomena, precognition, telepathy , ghosts, messages from the underworld, and so on” (McComb, 1990, the Physics of Fluid Turbulence).


Hachem then went to describe the two classical theories in the field, from energy cascades to the quest for order among chaos. This was a nice introduction into his specific area of research which focuses on ‘coherent turbulence structures’, which he described as bundles of energetic eddies that play an important role in momentum exchanges near boundaries, such as the sea bed. Hachem is interested in the role played by such motions in mobilising sediment on the sea bed under waves, tidal currents and/or combinations of both. He briefly introduced the concept of sediment transport then gave an example of how beaches change their profiles between summer and winter due to the different wave conditions they experience. He then introduced his PhD as ‘a study of these swirly energetic things that move sediment under waves!”. An overview of three major experiments that he conducted followed, starting with the large European Hydralab ‘Barrier Dynamics Experiment 2’ or BARDEX II. During that experiment, a team of international researchers built a life-scale beach, over a 100 m long, and subjected it to different types of waves, monitoring everything from turbulence to sediment transport, and of course changes in the beach profile. Hachem briefly mentioned the different mathematical tools he employs to analyse the role of these motion, and showed how different waves result in different beach layouts and patterns in the transport of sand. His second experiment was the very first to be conducted in the brand new HR Wallingford Fast Flow Facility, a unique scientific facility where he studies how currents interact with waves, and result in different patterns of bedforms on the seabed. Hachem concluded with some videos from his latest endeavour, another experiment at the unique CT Scan lab in Canada, where they actually used a medical CT Scanner to image how the sand moves under currents.



HR Wallingford’s Fast Flow Facility Experiment



Hachem is currently a Research Fellow in Coastal morphodynamics, and a Postgraduate Research Student in Coastal Sediment Dynamics at the University of Southampton, based at the National Oceanography Centre, Southampton. He graduated with a BEng (Hons) in Civil Engineering from London SouthBank University, before completing an MSC Engineering in the Coastal Environment (Distinction) at the University of Southampton.


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