Spectral signatures for swash on reflective, intermediate and dissipative beaches

Hughes, Michael G., Aagaard, Troels, Baldock, Tom E. and Power, Hannah E. (2014) Spectral signatures for swash on reflective, intermediate and dissipative beaches. Marine Geology, 355 88-97. doi:10.1016/j.margeo.2014.05.015

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Author Hughes, Michael G.
Aagaard, Troels
Baldock, Tom E.
Power, Hannah E.
Title Spectral signatures for swash on reflective, intermediate and dissipative beaches
Journal name Marine Geology   Check publisher's open access policy
ISSN 0025-3227
Publication date 2014-09-01
Year available 2014
Sub-type Article (original research)
DOI 10.1016/j.margeo.2014.05.015
Open Access Status Not yet assessed
Volume 355
Start page 88
End page 97
Total pages 10
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Subject 1910 Oceanography
1907 Geology
1906 Geochemistry and Petrology
Abstract In this paper we synthesise a large data set gathered from a wide variety of field deployments and integrate it with previously published results to identify the spectral signatures of swash from contrasting beach types. The field data set includes the full range of micro-tidal beach types (reflective, intermediate and dissipative), with beach gradients ranging from approximately 1:6 to 1:60 exposed to offshore significant wave heights of 0.5-3.0. m. The ratio of swash energy in the short-wave (f > 0.05. Hz) to long-wave (f < 0.05. Hz) frequency bands is found to be significantly different between the three beach types. Swash energy at short-wave frequencies is dominant on reflective and intermediate beaches and swash at long-wave frequencies is dominant on dissipative beaches; consistent with previously reported spectral signatures for the surf zone on these beach types. The available swash spectra were classified using an automated algorithm (CLARA) into five different classes. The ordered classes represent an evolution in the spectrum shape, described by a frequency downshifting of the energy peak from the short-wave into the long-wave frequency band and an increase in the long-wave swash energy level compared to a relatively minor variation in the short-wave swash energy level. A universally common feature of spectra from all beach-states was an f-4energy roll-off in the short-wave frequency band. In contrast to the broadly uniform appearance of the short-wave frequency band, the appearance of the long wave frequency band was highly variable across the beach-states. We incorporate the results presented here and previously published observations into the morphodynamic beach-state model, and propose an ordered sequence of swash spectra under increasing and decreasing incident wave energy level. This extension of the beach-state model to include the swash zone leads to the following propositions for morphodynamic controls on the nature of the swash spectrum. (1) The short-wave part of the swash spectrum is relatively constant in form across all beach-states (f-4 energy roll-off) and the energy density per unit frequency is controlled by the beach face gradient alone. (2) The spectral bandwidth of the energy roll-off varies directly with offshore wave energy level and inversely with beach face gradient (or beach-state), in a manner consistent with the non-linear wave breaking criterion. (3) The infragravity part of the swash spectrum is highly variable in form across all beach-states and the energy level is related to the offshore wave energy level and surf zone morphology.
Keyword Beach erosion
Beach-state model
Coastal morphodynamics
Swash zone
Wave runup
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Civil Engineering Publications
Official 2015 Collection
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Citation counts: TR Web of Science Citation Count  Cited 10 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 10 times in Scopus Article | Citations
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Created: Tue, 01 Jul 2014, 10:13:13 EST by System User on behalf of School of Civil Engineering