Even if this not the case for natural beaches, I am thinking that mega-nourishments and artificial islands in particular might be exposed to additional currents to the longshore drift generated by breaking waves.
Dear Antonios,
I think you can find answer to your question in the attached publications.
Best wishes, Vladimir
Well, although many times the cross shore sediment transport is cyclic in some instances there might be a permanent loss of material.
I would also consider tidal cycles if the area is sensitive to it. That can create additional velocity components.
Dear Vladimir,
I found very interesting and useful your papers, especially the one about the 'Calculation of Longshore Sediment Transport' and the Local Approach. I will contact you in case I need any further assistance.
Thank you,
Antonios
Dear Maurizio,
Thank you very much for your very helpful answer, By the way, do you know any field sites where the phenomena you describe occur, or do you have any other relevant feedback?
Dear Antonios,
I have analysed a case of cross-shore coastal erosion where the material transported crosshore (either during extreme events or typical during circulation in typical events) was permanently lost due to a deep sink in the bathymetry no much offshore from the coast. That site is the Maronti bay on the Isle of Ischia (Italy).
The impact of the tidal cycles is evident around the coasts of UK, see the South Coast (English channel).
Hope this was helpful,
Maurizio
Hello Antonios,
First of all I advice that you have a look at the web site of Prof. Leo van Rijn of Delft University of Technology, at http://www.leovanrijn-sediment.com/
Secondly, the sediment transport at a coastal sector depends on the wave, wind, current and sea level (including tide) climate (both prevailing and predominant) as well as on the coastal slope and sea bottom and beach bathymetry and sediment properties.
Longshore currents are basically induced by waves coming obliquely to the beach alignment, while on-offshore transport is due to perpendicular to almost perpendicular wave incidence, inducing rip currents and sometimes undertow. Increasing oblicity leads first to meandering currents, then increasing further to only longshore currents. The larger the obliquity angle the stronger the longshore current. Furthermore the sediment transport depends on the sand bed thickness and the soil type beneath it (silt, clay, rock) which may affect bed roughness and on the availability of sand sources at the boundary of your coast sector and the presence of coastal structures or river estuary as well as on the grain size and specific density. Sediment budget is also influenced by the wind transport to the beach and onshore dunes. Finally take into account that bathymetric charts are limited in accuracy and resolution and the technology with which they were obtained so comparing two charts from different times remote many years may lead to significant sediment volume estimate errors. Finally, offshore islands if placed remote from the coast are also affected by the geosprophic, tide and wind induced currents in combination with the wave induced wave stirring and sediment extraction from the sea bed and suspension temporary in the water column where the general currents can transport them even if the currents are weaker than the Shields limit criterion. Offshore island may lead to refraction and diffraction induced currents in the shore side of the island due to longshore gradient development in the surf zone between the unshadowed coast (larger breakers) and the shadowed sector (smaller breakers). This is due to the different wave induced setup at the beach at the exposed sector(s) (higher elevation) than in the shadowed sector (lower elevation), generating currents transporting sediments in the shadowed sector, which may become spits or even tombolos.
Wish you success in your sedimentological study.
Dear Sergiu,
Sorry for my late reply, but I have just had the opportunity to read your answer. Thank you very much for this extensive description of sediment movement. I found very interesting your point about the geostrophic currents as they are not wave generated; and yes I will have a look at Leo van Rijn web page.
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