Continuous monitoring of bedload discharge in a small, steep sandy channel

• Bedload flux first ever continuously monitored in a natural steep sandy channel.
• The bedload fluxes reported herein are among the highest observed in a natural setting.
• The quasi-flat channel bed is actually braided, which produces variability in bedload flux.
• Bedload texture expresses bar-anabranch textural differentiation but also equal mobility.

SummaryThis paper reports on bedload flux and texture monitored in a natural, steep, sandy ephemeral channel draining a small gullied sandy watershed, the Barranca de los Pinos (1.32 ha), Spain. Bedload flux was continuously monitored with two independent Reid-type slot samplers; bedload texture was determined from the sediment collected in the samplers. Channel morphology was surveyed with a high spatial resolution with a Terrestrial Laser Scanner.The monitored instantaneous bedload fluxes are among the highest measured in natural rivers, characterized by high temporal and spatial variability related to the presence of bedforms, shallow bars and sand sheets, and to the reworking of the dry bed between and at the end of individual flow events. The grain size distribution of the bedload indicates equal mobility; but bedload texture fluctuates, depicting the transport of coarser bar surfaces and of finer-grained anabranch surfaces as well as of the overall bed subsurface.