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Abstract: Rhythmic surfzone sandbars often appear to be coupled to longshore shoreline patterns. Several works have suggested that temporal variations in such patterns ("beach states") are correlated with incident wave forcing. Surf zone morphodynamics have been modeled extensively, but the majority of such numerical models treat the shoreline simply as a fixed boundary, or model the shoreline response separately. Overall, the behaviour of shoreline dynamics as a coupled system of shoreline and sandbar is still relatively unexplored. Here, video imagery is used to test whether the bar and the shoreline are a part of the same dynamic or coupled system, or whether they vary in response to the forcing in some more complex and perhaps independent manner. Video images reveal a range of complicated behaviours with both the sandbar and the shoreline varying from alongshore uniform into a crescentic pattern with varying degrees of regularity. The application of wavelet analysis allows quantification of shoreline/sandbar patterns and the extent to which such patterns are coupled. The shoreline usually mirrors crescentic sandbar patterns (but with a phase ranging from 0 to 180 degrees) even though it tends to straighten following periods of calm conditions, regardless of the sandbar shape. As anticipated, changes between different beach states can be triggered by extreme wave events but it appears evident that other variables in either the forcing conditions (wave period or angle of wave approach) or the antecedent shoreline-sandbar configuration can also play a substantial role. Overall, it appears that nearshore circulation patterns might increase the coupling of the bar and shoreline. In contrast, periods of weaker breaking merely induce swash-backwash patterns, which are independent from offshore breaking and therefore do not provide the mechanism for coupling.

To cite this article: Coco, Giovanni; Bryan, KR; Green, MO; Ruessink, BG; van Enckevort, IM J and Turner, Ian L. Video Observations of Shoreline and Sandbar Coupled Dynamics [online]. In: Townsend, Murray Robert (Editor); Walker, David (Editor). Coasts and Ports 2005 : Coastal Living - Living Coast; Australasian Conference; Proceedings. Barton, A.C.T.: Institution of Engineers, Australia, 2005: 471-476. Availability: <http://search.informit.com.au/documentSummary;dn=499866127156897;res=IELENG> ISBN: 0646451308. [cited 29 Jun 17].

Personal Author: Coco, Giovanni; Bryan, KR; Green, MO; Ruessink, BG; van Enckevort, IM J; Turner, Ian L; Source: In: Townsend, Murray Robert (Editor); Walker, David (Editor). Coasts and Ports 2005 : Coastal Living - Living Coast; Australasian Conference; Proceedings. Barton, A.C.T.: Institution of Engineers, Australia, 2005: 471-476. DOI: Document Type: Conference Paper, Research ISBN: 0646451308 Subject: Coastal zone management; Wavelets (Mathematics)--Data processing; Shorelines--Monitoring; Video recording--Data processing; Affiliation: (1) NIWA, National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand
(2) Earth Sciences Department, University of Waikato, Hamilton, New Zealand
(3) NIWA, National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand
(4) Department of Physical Geography, Institute for Marine and Atmospheric Research, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
(5) Department of Physical Geography, Institute for Marine and Atmospheric Research, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
(6) Water Research Laboratory, School of Civil and Environmental Engineering, University of New South Wales

Database: Engineering Collection