Sediment dispersal from a typical Mediterranean flood: The Têt River, Gulf of Lions

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 Tˆet 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.

Three-dimensional modelling of wave-induced current from the surf zone to the inner shelf

“…Locally, the Canet harbour in the south of the domain disturbs the longshore drift by shifting it offshore. These results are consistent with the development of sand spits growing northwards at river mouths, sand bars and harbours, as observed by Delpont and Motti (1994); Bourrin et al (2008) and in the LiDAR bathymetry. Downstream from the harbour, since the beginning of the storm, a cyclonic eddy and a return current along the northern breakwater of the harbour are generated, as discussed by Trampenau et al (2004).…”

“…A recent LiDAR (Light Detection and Ranging) survey (Fig. 8) shows a sand spit developing northwards of the breakwaters of the Canet-en-Roussillon harbor, followed by a deep pit, as observed by Bourrin et al (2008). Thereafter, complex double crescentic sandbar systems, classified as low tide terraces (LTT) by Aleman et al (2011), are observed.…”

“…During east or south-east storms, this general counterclockwise circulation is intensified in the inner shelf but is opposed by an alongshore northward littoral drift. Evidence of this drift has been provided by Anguenot and Monaco (1967) with radioactive tracers, by Delpont and Motti (1994) with aerial and SPOT images, multi-date remote sensing by Certain (2002) and by Bourrin et al (2008), who analyzed bathymetric and sediment data. The Têt is a small river with an average water discharge of less than 10 m 3 s −1 , with exceptional peaks two orders of magnitude higher during high precipitation events (Serrat et al, 2001).…”

Biogeochemical characterization of the riverine particulate organic matter transferred to the NW Mediterranean Sea

“…Furthermore, the Mediterranean shore is characterized by numerous coastal rivers that discharge significant amounts of water and sediment, mainly during the occurrence of short but violent flash flood events (Serrat et al, 2001;Bourrin et al, 2008). Several studies on the Rhône River have shown that the terrestrial particulate organic matter (POM) may be qualified as enough fresh, labile and modern POM to drive degradation processes (Bourgeois et al, 2011;Cathalot et al, 2010) and to sustain dense macrofaunal communities in surface sediments of the prodelta (Darnaude et al, 2004;Hermand et al, 2008).…”

Internal structure of event layers preserved on the Andaman Sea continental shelf, Thailand: tsunami vs. storm and flash-flood deposits

“…Not all tempestites comprise all these features, and they may also be observed in offshore tsunami deposits . Flash floods can comprise a large percentage of a river's yearly discharge and can form hyperpycnal flows due to high suspension load (Mulder et al, 2003;Bourrin et al, 2008). These criteria have also been established for tsunami backwash flows (Le Roux and Vargas, 2005).…”