DOI 10.4461/GFDQ.2013.36.1
ARNAUD-FASSETTA G.
Dyke breaching and crevasse-splay sedimentary sequences of the Rhône Delta, France, caused by extreme riverflood of December 2003
Pages 7-26
Abstract
Crevasse splays caused by the flood event of December 2003 in the Rhône Delta (Mediterranean France) offered the opportunity to study the «stage I» of Smith & alii (1989), as contemporary analogues for quantifying lateral erosion and overbank deposition in the flood plain. From two study cases («Petit Argence» and «Claire Farine»), main hydrogeomorphological impacts of December 2003 flood event and sedimentary facies associated with each crevasse-splay sub-environment (crevasse channel, crevasse-splay lobe, proximal and distal flood basin) are detailed. Fluvial landforms, sediment-body geometries and sedimentary-facies characteristics are determined using a combination of topographic maps, remote sensing data, field measurements, and laboratory analyses. Spatial distribution of hydraulic parameters such as mean flow velocity, bed shear stress, and specific stream power is derived from relationship with mean flow depth, sediment structure, sediment grain size, sediment thickness, and distance from the Petit Rhône channel/dyke breach. Sedimentological analysis highlights different gradients of downstream thickness, fining, and sorting of sediments. The 3-D geometry of crevasse splays is reconstructed with calculation of the sedimentary volume deposited or eroded in the delta-plain area. Sediment balance (674,227 ± 33,711 m3) derived from December 2003 crevasse splays is correlated with the delta-plain sediment balance.