Sorted Bedforms Developed on Sandy Deposits Derived from Small Ephemeral Streams (Catalan Continental Shelf)

Abstract

Multibeam echosounder data and sediment samples were used to characterize sorted bedforms on the inner shelf off Lloret and Tossa de Mar (NW Mediterranean Sea). The sorted bedforms are formed by a sequence of coarse-grained (coarse sand) and fine-grained (fine to medium sand) domains, with little topographic relief (up to 1 m). They exhibit elongated shapes and are oriented nearly perpendicular to the shoreline, at water depths ranging from 10 to 40 m. The sorted bedforms display lateral symmetry in backscatter and bathymetric relief with high backscatter centred on the bathymetric depression. They appear associated with elongated sand deposits fed by short, ephemeral streams that extend across-shelf over the infralittoral prograding wedge down to 40 m water depth. Sorted bedforms are better developed in deeper waters (20–40 m), probably due to stronger hydrodynamic conditions in the shallower sector of the shelf, which prevent the development or maintenance of these morphological features. The morphological evolution of these bedforms indicates that they are persistent features, showing small changes in their boundaries over a decadal timescale.