Nans BUJAN Ph.D. page
Click on the menu to see a presentation of the beginning of my work on the dynamics of sandy beaches of the
French Mediterranean shore.
The purpose of the work presented here is to estimate the sediment movements within different given sediment cells of the Gulf of Aigues-Mortes region (France). These movements are linked to the hydrodynamic forcings where winds and storms prevail.
The Languedoc Roussillon shore is mainly characterised by a strong off shore wind regime, microtidal (less than 30cm) barred dissipative sandy beaches, and a storm dominated wave environment (mean significant wave height is 0.80m and reaches 3m during storm events).
Languedoc Roussillon barrier beach aerial view. One can distinguish the external bar, the dune, overwash deposits and the pond.
Credit: EID Méditerranée.
The building of houses and tourism facilities in the 70's has often taken place directly in replacement of the dune itself without consideration of the dynamics of the sediments. Groins were then constructed to contain the increasing erosion in the urban areas, leading to the Languedoc-Roussillon shoreline as we know it: an alternation of heavily urbanized areas and natural areas undergoing strong erosion.
Those boundaries can be natural (estuaries, headlands) or artificial (groins, jetties).
The present work focuses on the characterisation of the movement of sediments on the different boundaries of the sediment cell for given conditions (fair weather, storms). Sand can be displaced in various directions:
- Offshore where sand can be lost irremediably if carried further off the depth of closure. Strong offshore winds, rip currents, and undertow can contribute to such flows.
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On the sides of the sediment cell with the littoral drift caused by the angle of incidence of the waves. This drift can be affected by the presence of shore normal structures such as groins.
- Onshore where sandbars can connect to the beach and wind carries the sediment inland. Overwash processes can also deposit sand inland during storms.
Overwash fan, Villeneuve-Les-Maguelone.
Credit Photo: EID Méditerranée.
Study of all these mechanisms aims to characterize the dominant sediment transport process for a given site. Coupled modeling/field approach is used to do so.
Wind and wave conditions are used as input for a wave driver (Ref/Dif) model and a circulation (Shorecirc) model.
Output is currents over the bottom that can be used to assess the sediment transport.
On site measures are performed between 0 and 20m deep with currentometers (4 ADVs, 5 ADCPs) and wave gauges.
