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Abstract: In situ observations were combined with 3D modeling to gain understanding of and to quantify the suspended sediment transport in the Gulf of Lions (NW Mediterranean Sea). The outputs of a hydrodynamic–sediment transport coupled model were compared to near-bottom current and suspended sediment concentration measurements collected at the head of seven submarine canyons and at a shallow shelf site, over a 6-month period (November 2003–May 2004). The comparisons provide a reasonable validation of the model that reproduces the observed spatial and time variations. The study period was marked by an unusual occurrence of marine storms and high river inputs. The major water and sediment discharges were supplied by the Rhone, the largest Mediterranean river, during an exceptional flood accompanying a severe marine storm in early December 2003. A second major storm, with moderate flooding, occurred in February 2004. The estimate of river input during the studied period was 5.9Mt. Our study reveals (i) that most of the particulate matter delivered by the Rhone was entrapped on the prodelta, and (ii) that marine storms played a crucial role on the sediment dispersal on the shelf and the off-shelf export. The marine storms occurring in early December 2003 and late February 2004 resuspended a very large amount of shelf sediment (>8Mt). Erosion was controlled by waves on the inner shelf and by energetic currents on the outer shelf. Sediment deposition took place in the middle part of the shelf, between 50 and 100m depth. Resuspended sediments and river-borne particles were transported to the southwestern end of the shelf by a cyclonic circulation induced by these onshore winds and exported towards the Catalan shelf and into the Cap de Creus Canyon which incises the slope close to the shore. Export taking place mostly during marine storms was estimated to reach 9.1Mt during the study period. [Copyright &y& Elsevier]

Abstract: This paper describes an integrated study of a typical Mediterranean flood event in the Gulf of Lions. A flood with a 5-year return interval occurred in the Têt River basin and adjacent inner-shelf in the Gulf of Lions, northwest Mediterranean, during April 2004. Data were collected during this flood as part of event-response investigations of the EU-funded Eurostrataform (European Margin Strata Formation) project. Southeasterly storm winds led to a flood which directly modified the inner-shelf hydrodynamics. Sediment delivery to the coastal zone during this flood represented more than half of the mean annual discharge of the Têt River to the Gulf of Lions. This river transported a large amount of sand in suspension, representing 25% of the total suspended load, and as bedload representing 8% of the total load, during this event. Sand introduced in the nearshore was transported northwards during the peak storm and nourished a small delta. Fine sediments were separated from coarse sediments at the river mouth, and were advected southwards and seawards by the counter-clockwise general circulation. Fine-grained sediments were transported via a hypopycnal plume along the coast towards the southern tip of the Gulf of Lions and the Cap Creus canyon. The along-shore currents, which intensified from north to south of the Gulf of Lions, particularly between the Cap Creus promontory and the Cap Creus canyon, favoured the transfer of fine-grained sediments from the continental shelf of the Gulf of Lions towards the continental slope. Our results show that floods with a few-year return interval in small coastal rivers can play a significant role in the transport of sediments on microtidal continental margins and their export from the shelf through canyons. [Copyright &y& Elsevier]