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Storm-driven changes in rip channel patterns on an embayed beach

Storm-driven changes in rip channel patterns on an embayed beach
Storm-driven changes in rip channel patterns on an embayed beach
This paper introduces a semi-automatic computer algorithm designed to detect rip current channels in video imagery. As a case study, this method is applied to 3.3 years of video data from an embayed beach to demonstrate the link between antecedent surf zone morphology, wave energy and up/down transitions in beach state. An objective measure of rip channel change was developed to define six significant rip reconfiguration events and relate these events to wave energy. Over the period of study no complete resets of the nearshore morphology occurred. The analysis indicates that direct correlation of rip patterns with the instantaneous wave conditions is not a useful way to demonstrate how rips and waves interact. The average wave energy over a period of ten days, combined with storm duration were good indicators of rip channel change, demonstrating that in general, beach morphology responds with a time lag to changes in forcing. Rip channels with a short cross-shore length and narrow alongshore spacing responded faster to changes in wave conditions than rips with a long cross-shore length and wider alongshore spacing. To force changes in the rip morphology, longer rip channels required wave events of higher energy and/or a longer duration. Offshore islands protect the beach under certain wave approach angles, sometimes resulting in a dual-width surf zone, which was narrow at the sheltered end and wide at the exposed end of the beach. The wider surf zone end was characterised by three dominant and persistent rip channels, whereas the narrow surf zone section contained a number of smaller rips which evolved rapidly under wave forcing. Our observations demonstrate the importance of rip channel size in controlling the response time of nearshore morphology.
Rip currents, Rip channels, Video imagery, Beach state, Sand bars, Nearshore morphology
0169-555X
179-188
Gallop, S.L.
c14133fc-9141-47d9-ae9c-84c2513ea8ad
Bryan, K.R.
02d42071-7100-4ef5-9bba-4b14bdbd9277
Coco, Giovanni
8a6c97e1-2a44-4f03-ad8d-e03dbc2908db
Stephens, S.A.
e4ffd370-0569-479f-a11e-894131d9747c
Gallop, S.L.
c14133fc-9141-47d9-ae9c-84c2513ea8ad
Bryan, K.R.
02d42071-7100-4ef5-9bba-4b14bdbd9277
Coco, Giovanni
8a6c97e1-2a44-4f03-ad8d-e03dbc2908db
Stephens, S.A.
e4ffd370-0569-479f-a11e-894131d9747c

Gallop, S.L., Bryan, K.R., Coco, Giovanni and Stephens, S.A. (2011) Storm-driven changes in rip channel patterns on an embayed beach. Geomorphology, 127 (3-4), 179-188. (doi:10.1016/j.geomorph.2010.12.014).

Record type: Article

Abstract

This paper introduces a semi-automatic computer algorithm designed to detect rip current channels in video imagery. As a case study, this method is applied to 3.3 years of video data from an embayed beach to demonstrate the link between antecedent surf zone morphology, wave energy and up/down transitions in beach state. An objective measure of rip channel change was developed to define six significant rip reconfiguration events and relate these events to wave energy. Over the period of study no complete resets of the nearshore morphology occurred. The analysis indicates that direct correlation of rip patterns with the instantaneous wave conditions is not a useful way to demonstrate how rips and waves interact. The average wave energy over a period of ten days, combined with storm duration were good indicators of rip channel change, demonstrating that in general, beach morphology responds with a time lag to changes in forcing. Rip channels with a short cross-shore length and narrow alongshore spacing responded faster to changes in wave conditions than rips with a long cross-shore length and wider alongshore spacing. To force changes in the rip morphology, longer rip channels required wave events of higher energy and/or a longer duration. Offshore islands protect the beach under certain wave approach angles, sometimes resulting in a dual-width surf zone, which was narrow at the sheltered end and wide at the exposed end of the beach. The wider surf zone end was characterised by three dominant and persistent rip channels, whereas the narrow surf zone section contained a number of smaller rips which evolved rapidly under wave forcing. Our observations demonstrate the importance of rip channel size in controlling the response time of nearshore morphology.

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More information

Published date: 15 April 2011
Keywords: Rip currents, Rip channels, Video imagery, Beach state, Sand bars, Nearshore morphology
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 349603
URI: http://eprints.soton.ac.uk/id/eprint/349603
ISSN: 0169-555X
PURE UUID: add4d98a-3c78-44ac-90fc-89338cd5d7f9

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Date deposited: 07 Mar 2013 14:32
Last modified: 14 Mar 2024 13:16

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Contributors

Author: S.L. Gallop
Author: K.R. Bryan
Author: Giovanni Coco
Author: S.A. Stephens

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