Fine sediment in mixed sand-silt environments impact bedform geometry by altering sediment mobility

Research output: Contribution to journalArticlepeer-review

Electronic versions

Documents

DOI

  • S.L. de Lange
    Wageningen University
  • I. Niesten
    Wageningen University
  • S.H.J. van de Veen
    Wageningen University
  • Jaco Baas
  • J. Lammers
    Wageningen University
  • K. Waldschlaeger
    Wageningen University
  • D. Boelee
    Wageningen University
  • A.J.F. Hoitink
    Wageningen University
Geometric characteristics of subaqueous bedforms, such as height, length and leeside angle, are crucial for determining hydraulic form roughness and interpreting sedimentary records. Traditionally, bedform existence and geometry predictors are primarily based on uniform, cohesionless sediments. However, mixtures of sand, silt and clay are common in deltaic, estuarine, and lowland river environments, where bedforms are ubiquitous. Therefore, we investigate the impact of fine sand and silt in sand-silt mixtures on bedform geometry, based on laboratory experiments conducted in a recirculating flume.
We systematically varied the fraction of sand and silt for different discharges, and utlized an acoustic Doppler velocimeter to measure flow velocity profiles. The final bed geometry was captured using a line laser scanner. Our findings reveal that the response of bedforms to an altered fine sediment percentage is ambiguous, and likely depends on, among others, bimodality-driven bed mobility and sediment cohesiveness. When fine, non-cohesive material (fine sand or coarse silt) is mixed with the base material (medium sand), an increased dune height and length is observed, possibly caused by the hiding exposure effect, resulting in enhanced mobility of the coarser material. However, weakly cohesive fine silt suppresses dune height and length, possibly caused by reduced sediment
mobility. Finally, in the transition from dunes to upper stage plane bed, there are indications that the bed becomes unstable and dune heights vary over time. The composition of the bed material does not significantly impact the hydraulic roughness, but mainly affects roughness via the bed morphology, especially the leeside angle.
Original languageEnglish
Article numbere2024WR037065
JournalWater Resources Research
Volume60
Issue number7
Early online date25 Jul 2024
DOIs
Publication statusPublished - Jul 2024
View graph of relations