Braided wadis in SE hyper-arid Israel and humid counterparts in the French pre-alps and in NE Italy were studied. Terrestrial Laser Scanning and electronic theodolite measurements of morphological units produced point clouds, from which high resolution accurate Digital Elevation Models (DEMs) were extracted. Roughness and upper tail grain size distribution percentiles were derived from the DEMs or by standard physical sampling.
Results indicate that dryland anabranches are finer-grained than the bars, contrary to humid braided rivers. Bar-dissecting chutes are similar to or coarser-grained than the bars, in accordance with their steeper gradients. Surprisingly, the morpho-texture of the steep, braided Saisera, having the highest annual precipitation, has similarity to that of desert channels.
In deserts the sorting of bar deposits is low due to high bedload discharges, whereas rapid flow recessions are responsible for mass deposition and minimal winnowing in anabranches. Therefore, channels are finer-grained than bars. This process is associated with the mid-channel deposition of central bars. However, the steeper chutes and coarser anabranches are associated with erosive processes (chute cutoffs and multiple bar dissection), allowing winnowing to occur also during rapid recession. Hence, in deserts coarser-grained anabranch patches are essentially chutes. Lengthy flow recession in humid braided channels allows winnowing of fines, thereby generating armored channels, the finer sedimentary particles often deposited downstream as unit bars. Although the steep Saisera is located in a humid region, it is ephemeral with rapid short recessions responsible for a morpho-texture similar to that of desert braided streams.
It is, thus, the hydrologic regimen, important in many of Stanley Schumm's observations, which simplifies our understanding of the morpho-textural variability of braided rivers.
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