Flow recession as a driver of the morpho-texture of braided streams

Braiding has been widely studied in humid-temperate climates though rarely in arid environments. Morpho-texture of braided streams refers to the morphological-textural organization in a braid-cell (stream section including bars, anabranches and chutes) that may strongly relate to different processes and hydrological regimes. The objective of this study is to compare the morpho-texture of braided streams governed by diverse flow recessions in different climates. Measurements were conducted in the wadis Ze’elimand Rahaf, southeast hyper-arid Israel, in the Mediterranean Barranca-de-los-Pinos, central Spain and in humid-temperate braided systems, the La-Bléone River, Haute-Provence, France and in the Saisera and Cimoliana torrents, northeast Italy. Terrestrial laser scanning was used to produce point clouds and high resolution digital elevation models of the braid-cells.Wet braid-cells in humid-temperate environments were surveyed by a Total Station. Roughness and the upper tail of grain size distributions were derived from the scanned point clouds or from Wolman sampling. We found that anabranches are commonly finer-grained than the bars in dryland systems and in semi-arid sandy braided systems, contrary to the humid-temperate braided systems. In both climates, chutes are similar or coarser-grained than the bars which they dissect, in accordance with their steeper gradients due to the considerable bar-anabranch relief. The Saisera’s morpho-texture is similar to that of the dryland braided channels, despite the very humid-temperate environment in which it is located, due to its short-lived, ephemeral type hydrograph. Hydrograph shape, specifically the duration of flow recession, typical of a climate but not confined to it, determines the morphotexture of braided streams and the textural differentiation between a depositional bar and the adjacent anabranches. The morphotexture of chutes and bars results also from local erosional processes affected by local topography, i.e. ungraded longitudinal profiles, and is not solely determined by flow recession. This new morpho-textural model enables identifying primary depositional and erosional braiding processes.