Paper publication alert

Fine Sediment in Mixed Sand‐Silt Environments Impacts Bedform Geometry by Altering Sediment Mobility

S. I. de Lange, I. Niesten, S. H. J. van de Veen, J. H. Baas, J. Lammers, K. Waldschläger, D. Boelee, and A. J. F. Hoitink
doi: https://doi.org/10.1029/2024WR037065

The fourth paper of Sjoukje’s Phd project just got published! Underwater bedforms, such as dunes, are often found on the bed of rivers and deltas. These rhythmic undulations have specific shapes and sizes, and they affect how water flows. When the bed of the river is made up of sand, we can predict the dune height and length. However, mixtures of different‐sized sediments are common in rivers, and it is unknown how this impacts the geometry of the dunes. Therefore, we did experiments in a flume, a laboratory facility to simulate a river, and we tested different sediment bed mixtures. We found that replacing part of the base material with non‐cohesive fine particles leads to longer dunes, likely caused by increased mobility of the base material. However, for weakly cohesive fine particles, the effect was the opposite, and the dunes became shorter, probably due to the limited mobility of the sediment. Finally, we observed that under high flow conditions, the bed became unstable and different dune shapes occurred. We found that the friction the water experiences is not directly impacted by the sediment bed mixtures, but is mostly affected by the shape of the bedforms.

Conceptual diagram of non‐dimensionalized dune height against transport stage, indicating the impact of the presence of non‐cohesive and cohesive fine sediment in the bed at relatively low transport stages, and the increased variability of bedform height due to flow instabilities at high transport stages. The dark gray shading indicates the 5 and 95percentiles of data aggregated from Venditti et al. (2016) and Bradley and Venditti (2019). Data from this study are shown with dark gray markers. No data are available for the light gray shaded area. The dashed lines show the estimated course of the confidence intervals.