Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat, West Indies

The wavelength of stationary water‐surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand‐bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of...

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Bibliographic Details
Published in:Sedimentology 2017-12, Vol.64 (7), p.1817-1845
Main Authors: Froude, Melanie J., Alexander, Jan, Barclay, Jenni, Cole, Paul, Manville, Vern
Format: Article
Language:English
Subjects:
Antidunes
Bed forms
Diagnostic systems
flash flood
Flash flooding
Flash floods
Floods
Flow velocity
Flumes
Gravel
gravel lenses
lahar
Lenses
palaeoflow
River beds
Sand
Sedimentary structures
Surface waves
Upstream
Valleys
Velocity
Wave data
Wavelength
Wavelengths
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Summary:The wavelength of stationary water‐surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand‐bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of the lenses was empirically related to antidune wavelength, and thus could be used to estimate flow velocity and depth. This study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting, testing the previously published relationship at a field‐scale. Trains of stationary and upstream migrating water‐surface waves were prevalent during the flash flood in October 2012 in the Belham Valley, Montserrat, West Indies. Wave positions and wavelengths were assessed at 900 sec intervals through the daylight hours of the event within a monitored reach. The wave data indicate flow depths up to 1·3 m and velocity up to 3·6 m sec−1. Sedimentary structures formed by antidune growth and change were preserved in the event deposit. These structures include lenses of clast‐supported gravel and massive sand, with varying internal architecture. The lenses and associated low‐angle strata are comparable to sand‐bed structures formed from stationary and upstream migrating waves in flume experiments, confirming the diagnostic value of these structures. Using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow.
ISSN:0037-0746
1365-3091
DOI:10.1111/sed.12375