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Rock topography causes spatial variation in the wave, current and beach response to sea breeze activity

Rock topography causes spatial variation in the wave, current and beach response to sea breeze activity
Rock topography causes spatial variation in the wave, current and beach response to sea breeze activity
We hypothesized that beach profiles that are perched on natural rock structures would be better protected from waves and currents than profiles that are not fronted by rock. In southwest Western Australia many beaches, such as at Yanchep, are perched on Quaternary limestone. Yanchep Lagoon is fronted by a low-crested limestone reef that partially encloses a coastal lagoon. The spatial variation of waves and currents around the rock structures were quantified during the sea breeze cycle at locations: (1) offshore; (2) 20 m seaward of the reef; (3) inside the lagoon; and (4) in the surf zone. The spatial variation in the beach profile response was measured at two beach profiles: (1) the Exposed Profile that was not fronted directly seaward by outcropping limestone; and (2) the Sheltered Profile which was fronted seaward by submerged limestone at 2 m water depth and that was near the lagoon exit at the end of the limestone reef. The Sheltered Profile had greater volume changes during the cycle of the sea breeze whilst the Exposed Profile recovered more by overnight accretion when wind decreased. The lagoonal current drove the strong response of the Sheltered Profile and may have contributed to the lack of overnight recovery of the beach together with the seaward rock formation impeding onshore sediment transport. The different direction and speed responses of bottom-currents in the surf zone fronting the two profiles reflected the local variation in geology, the influence of the jet exiting the lagoon, and wave refraction around the reef that was measured with GPS drifters and wave-ray tracing using XBeach. Major spatial variation in waves, currents and beachface behavior at this perched beach shows the importance of the local geological setting.
perched beach, geological control, hard-bottom, rock platform, coastal structures, coastal lagoon
0025-3227
29-40
Gallop, Shari L.
c14133fc-9141-47d9-ae9c-84c2513ea8ad
Bosserelle, Cyprien
9b81c52f-ca84-4c68-b3e5-341b175be924
Pattiaratchi, Charitha
270222fc-4e18-4365-8128-6b554d183347
Eliot, Ian
4ea8eee0-06c3-4107-8724-921097963352
Gallop, Shari L.
c14133fc-9141-47d9-ae9c-84c2513ea8ad
Bosserelle, Cyprien
9b81c52f-ca84-4c68-b3e5-341b175be924
Pattiaratchi, Charitha
270222fc-4e18-4365-8128-6b554d183347
Eliot, Ian
4ea8eee0-06c3-4107-8724-921097963352

Gallop, Shari L., Bosserelle, Cyprien, Pattiaratchi, Charitha and Eliot, Ian (2011) Rock topography causes spatial variation in the wave, current and beach response to sea breeze activity. Marine Geology, 290 (1-4), 29-40. (doi:10.1016/j.margeo.2011.10.002).

Record type: Article

Abstract

We hypothesized that beach profiles that are perched on natural rock structures would be better protected from waves and currents than profiles that are not fronted by rock. In southwest Western Australia many beaches, such as at Yanchep, are perched on Quaternary limestone. Yanchep Lagoon is fronted by a low-crested limestone reef that partially encloses a coastal lagoon. The spatial variation of waves and currents around the rock structures were quantified during the sea breeze cycle at locations: (1) offshore; (2) 20 m seaward of the reef; (3) inside the lagoon; and (4) in the surf zone. The spatial variation in the beach profile response was measured at two beach profiles: (1) the Exposed Profile that was not fronted directly seaward by outcropping limestone; and (2) the Sheltered Profile which was fronted seaward by submerged limestone at 2 m water depth and that was near the lagoon exit at the end of the limestone reef. The Sheltered Profile had greater volume changes during the cycle of the sea breeze whilst the Exposed Profile recovered more by overnight accretion when wind decreased. The lagoonal current drove the strong response of the Sheltered Profile and may have contributed to the lack of overnight recovery of the beach together with the seaward rock formation impeding onshore sediment transport. The different direction and speed responses of bottom-currents in the surf zone fronting the two profiles reflected the local variation in geology, the influence of the jet exiting the lagoon, and wave refraction around the reef that was measured with GPS drifters and wave-ray tracing using XBeach. Major spatial variation in waves, currents and beachface behavior at this perched beach shows the importance of the local geological setting.

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More information

Published date: 1 December 2011
Keywords: perched beach, geological control, hard-bottom, rock platform, coastal structures, coastal lagoon
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 349588
URI: http://eprints.soton.ac.uk/id/eprint/349588
ISSN: 0025-3227
PURE UUID: a7f153a9-d42d-481a-9f11-38185209652f

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Date deposited: 07 Mar 2013 14:28
Last modified: 16 Jul 2019 21:41

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Contributors

Author: Shari L. Gallop
Author: Cyprien Bosserelle
Author: Charitha Pattiaratchi
Author: Ian Eliot

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