Simulated Dynamics of Mixed Versus Uniform Grain Size Sediment Pulses in a Gravel-Bedded River

Authors

Muneer Ahammad, Virginia Tech
Jonathan A. Czuba, Virginia TechFollow
Allison M. Pfeiffer, Western Washington University
Brendan P. Murphy, Simon Fraser University
Patrick Belmont, Utah State UniversityFollow

Document Type

Article

Journal/Book Title/Conference

Journal of Geophysical Research: Earth Surface

Author ORCID Identifier

Muneer Ahammad https://orcid.org/0000-0002-3995-6507

Jonathan A. Czuba https://orcid.org/0000-0002-9485-2604

Allison M. Pfeiffer https://orcid.org/0000-0002-3974-132X

Brendan P. Murphy https://orcid.org/0000-0001-8025-1253

Patrick Belmont https://orcid.org/0000-0002-8244-3854

Volume

126

Issue

10

Publisher

Wiley-Blackwell Publishing, Inc.

Publication Date

9-29-2021

Keywords

Sediment pulse, bed mobility, sediment transport, bedload transport model, bed elevation change, sediment supply

First Page

1

Last Page

23

Abstract

Mountain rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes. Once emplaced in the river, the movement of this sediment depends on flow, grain size distribution, and channel and network geometry. Here, we simulate downstream bed elevation changes that result from discrete inputs of sediment (10,000 m³), differing in volume and grain size distribution, under medium and high flow conditions. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. This work builds on a Lagrangian, bed-material sediment transport model and applies it to a 27 km reach of the mainstem Nisqually River, Washington, USA. We compare observed bed elevation change and accumulation rates in a downstream lake to simulation results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of synthetic sediment pulses by comparing the results against a baseline condition (without pulse). Our findings suggest that bed response is primarily influenced by the sediment-pulse grain size and distribution. Intermediate mixed-size pulses (~50% of the median bed gravel size) are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed-size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform-size pulse. This work has important implications for river management, as it allows us to better understand fluvial geomorphic responses to variations in sediment supply.

Comments

© 2021. American Geophysical Union. All Rights Reserved.

Recommended Citation

Ahammad, M., Czuba, J. A., Pfeiffer, A. M., Murphy, B. P., & Belmont, P. (2021). Simulated dynamics of mixed versus uniform grain size sediment pulses in a gravel-bedded river. Journal of Geophysical Research: Earth Surface, 126, e2021JF006194. https://doi.org/10.1029/2021JF006194