Morphodynamics of Ridge and Runnel Systems during Summer

Morphological analysis of ridge and runnel systems is carried out for a 1.6 km long straight shoreline at the Truc Vert Beach (French Atlantic Coast). Foreshore has been investigated through high-resolution shoreline cartography and topographic surveys recorded during summers, from 1999 to 2001. Hydrodynamic data are from the VAG-ATLA wave model and a TRIAXYS wave buoy. 1999 shoreline maps show three rhythmical ridge and runnel systems with an average wavelength of 480 m. The SSW-NNE trend bars were about one meter high. Runnels were SW-NE oriented. The crosshore profiles of 1999 point out the shoreward sediment's transfer of both berm and bar. During summer 2000, bars and channels are disrupted, whereas 2001 surveys show an irregular and double system of nearshore and foreshore bars. The shoreline map analysis underlines a conceptual model of ridge and runnel systems described by four phases: from the nearshore bar formation to the bar welding to the foreshore and system organization. These rythmical systems migrate longshore to the south.