Short wave modulation due to infragravity waves in the nearshore zone, with applications
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Authors
Abdelrahman, Saad M. M.
Subjects
Infragravity
Longshore Current
Sediment transport
Surf zone dynamics
Longshore Current
Sediment transport
Surf zone dynamics
Advisors
Thornton, E.B.
Date of Issue
1986-09
Date
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
The omni-present low frequency wave motion (30-300 sec) contains a substantial
fraction of the total wave energy inside the surf zone. A more complete description of
nearshore wave processes considers incident short period wind waves superposed on,
and interacting with, long standing waves. The wind waves are modulated in
amplitude, wavenumber and direction due to relatively slowly varying depth changes
caused by the long waves. The energy in the wind wave band is enhanced by side band
growth at the sum and difference frequencies of short and long waves (order 15% at
the shoreline). The modulation is identified in the analysis of field data as a positive
correlation between the long waves and the wind wave envelope near the shoreline.
Considering oblique incident waves, a steady longshore current showing a
non-vanishing current at the shoreline is found as a result of the non-linear interaction
between monochromatic incident and infragravity waves. An analytical solution
describing the unsteadiness of the longshore current is developed. Applying the derived
longshore current solution, longshore sediment transport is reformulated to include the
infragravity waves, giving improved comparisons with field measurements.
Type
Thesis
Description
Series/Report No
Department
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NPS Report Number
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Format
128 p.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.