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The impact of tides and waves on near-surface suspended sediment concentrations in the English Channel

Guillou N., Rivier A., Chapalain G., Gohin F.

Oceanologia

2017

No. 59 (1)

28--36

Numerous ecological problems of continental shelf ecosystems require a refined knowledge of the evolution of suspended sediment concentrations (SSC). The present investigation focuses on the spatial and temporal variabilities of near-surface SSC in coastal waters of the English Channel (western Europe) by exploiting numerical predictions from the Regional Ocean Modeling System ROMS. Extending previous investigations of ROMS performances in the Channel, this analysis refines, with increased spatial and temporal resolutions, the characterization of near-surface SSC patterns revealing areas where concentrations are highly correlated with evolutions of tides and waves. Significant tidal modulations of near-surface concentrations are thus found in the eastern English Channel and the French Dover Strait while a pronounced influence of waves is exhibited in the Channel Islands Gulf. Coastal waters present furthermore strong SSC temporal variations, particularly noticeable during storm events of autumn and winter, with maximum near-surface concentrations exceeding 40 mg l−1 and increase by a factor from 10 to 18 in comparison with time-averaged concentrations. This temporal variability strongly depends on the granulometric distribution of suspended sediments characterized by local bimodal contributions of silts and sands off coastal irregularities of the Isle of Wight, the Cotentin Peninsula and the southern Dover Strait.

Towards validating a last generation, integrated wave-current-sediment numerical model in coastal regions using video measurements

Carniel S., Sclavo M., Archetti R .

Oceanological and Hydrobiological Studies

2011

Vol. 40, No.4

11-20

This paper presents the first steps in the implementation of a morphological numerical model to be applied in the Bevano River region, a shallow water area in the Adriatic Sea, with the aim of helping the identification and assessment of erosional patterns and bottom morphological modifications induced by severe marine storms. The numerical modeling, performed using a fully 3D coupled wave-current-sediment version of the ROMS model, has been complemented with in situ data analysis and observations: a first qualitative validation of the results was given by the analysis of images acquired via an ARGUS video station. Hydrodynamic modeling highlighted how shear bottom stresses and bottom currents fields were heavily influenced by severe storm situations, and had large effects on the morphology of shallow regions. The correlation between the wave-current induced bottom stresses and the resulting topography was investigated. Nearshore hydrodynamics modeling results demonstrated the dominant role played by alongshore sediment transport, with the magnitude of both cross- and along-shore wave-induced currents strongly depending on wave height and direction. We found a good qualitative conformity between the results of the numerical models applied during a "Bora" storm and the corresponding video observations; both techniques indicated the migration of the existing sandbar within the range of about 40 m seaward. Results show how integrated numerical open source tools, often used in oceanography, are becoming suitable for both preliminary investigations and for planning the effective littoral management, and how their calibration can be supported by the use of new low cost techniques, such as video measurements.