A New Method for In Situ Measurement of the Erosion Threshold of River Channels

The vast majority of alluvial deposits have some degree of cohesion, typically due to the presence of clays and/or organic matter. Determining the threshold fluid shear stress, τc, necessary to entrain these sediments is essential for predicting erosion rates and morphodynamics of rivers, tidal chan...

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Bibliographic Details
Published in:Water resources research 2022-08, Vol.58 (8), p.n/a
Main Authors: Dunne, K. B. J., Arratia, P. E., Jerolmack, D. J.
Format: Article
Language:English
Subjects:
Aggregation
Alluvial channels
Alluvial deposits
Alluvium
Calibration
Channels
Clay
Cohesion
Cohesive sediments
critical shear stress
erosion
Erosion rates
Fluid flow
Fluvial deposits
Gravel
Gravel beds
Hydrodynamics
In situ measurement
Laboratories
Measurement
Mechanical stimuli
Methods
Microcontrollers
Morphology
Organic matter
River banks
river channel
River channels
River erosion
Rivers
Sand
Sand & gravel
Sediments
Shear stress
Surface chemistry
Tidal inlets
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Summary:The vast majority of alluvial deposits have some degree of cohesion, typically due to the presence of clays and/or organic matter. Determining the threshold fluid shear stress, τc, necessary to entrain these sediments is essential for predicting erosion rates and morphodynamics of rivers, tidal channels, and coasts. Cohesive sediments present a greater challenge than noncohesive sand and gravel beds due to the sensitivity of τc to such factors as compaction, aggregation, and particle surface chemistry. All of those factors may be altered if bed and bank sediments are extracted for later analysis in the laboratory. Environments with mixed cohesive and noncohesive materials are common, such as sand‐bedded rivers with muddy banks; it is therefore desirable to have a method for in situ measurement of τc across a very wide range. We present a novel instrument that is capable of reproducibly determining τc for submerged cohesive and noncohesive sediments in situ. The instrument has several advantages over alternative methods, including ease of implementation in the field, and a fluid shear that is more representative of natural flows. The device incorporates common and low‐cost components integrated with an Arduino microcontroller, which may receive commands from a mobile phone. We demonstrate our instrument's capabilities in gravel, sand, and clay‐sand mixtures prepared in the laboratory, and present a proof of concept field deployment in a wadeable stream. Additionally, we provide the necessary schematics, parts lists, code, and calibration procedures for the interested reader to build their own version of the instrument. Key Points The threshold entrainment stress of mud is a function of many variables and therefore should be measured in situ We have developed a new instrument for the in situ measurement of cohesive sediment threshold entrainment stress We demonstrate the instrument's capability on natural and synthetic muds, and noncohesive sediments
ISSN:0043-1397
1944-7973
DOI:10.1029/2022WR032407