Width variations control the development of grain structuring in steep step‐pool dominated streams: insight from flume experiments

• Published in: Earth surface processes and landforms 2020-05, Vol.45 (6), p.1430-1440
• Main Authors: Saletti, Matteo, Hassan, Marwan A.
• Format: Article
• Language: English
• Subjects: Creeks & streams; Experiments; Flumes; Fluvial geomorphology; Granular forces; Jamming; Particle interactions; Restoration; River engineering; River restoration; Rivers; Sequences; Shear stress; Stability; Steep channels; Step‐pools; Streams; Variation; Width
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.4815

ABSTRACT We report results from flume experiments designed to study the effect of width variations on the formation and stability of steps in steep streams. To physically model channel width changes we inserted multiple trapezoidal elements in the flume. Two competing effects are in play: a fluidic effect, suggesting that steps are more likely to form in wide areas because of deposition enhanced by lower shear stress, and a granular effect, suggesting that steps are more likely to form in narrow areas because of particle jamming. Our experiments show that width variations enhance the formation of steps. Although steps can form in every location, those in narrow/narrowing areas are more common, more stable and they occupy a larger portion of the channel width. These results stress the importance of particle interactions in coarse‐bedded streams and help river engineers by providing a new element to consider when designing step‐pool sequences in river restoration projects. © 2020 John Wiley & Sons, Ltd. We run flume experiments to study the effect of width variations on the formation and stability of steps in steep streams. The results show that width variations enhance step formation, and, although they can form in every location, steps in narrow/narrowing areas are more common, more stable and they occupy a larger portion of the channel width. These results stress the importance of particle interactions in coarse‐bedded streams, and are relevant for river engineers designing step‐pools in river restoration projects.