Analysis of observed two- and three-dimensional nearshore bar behaviour
Shore-parallel sandbar systems often exhibit considerable quasi-regular alongshore variations, such as crescentic plan shapes. Therefore, morphological change in such systems commonly consists of two- and three-dimensional variability. The former is related to overall on/offshore bar migration, wher...
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Published in | Marine geology Vol. 169; no. 1; pp. 161 - 183 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
15.09.2000
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Subjects | |
Online Access | Get full text |
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Summary: | Shore-parallel sandbar systems often exhibit considerable quasi-regular alongshore variations, such as crescentic plan shapes. Therefore, morphological change in such systems commonly consists of two- and three-dimensional variability. The former is related to overall on/offshore bar migration, whereas the latter is induced by the horizontal amplitude growth, migration, or length scale change of the quasi-regular topography. In this paper, we used a six-week data set of bathymetric surveys and video images of breaking-induced foam to quantify short-term (days–weeks) two- and three-dimensional variability in the bar-crest position of the double barred beach at Egmond aan Zee (Netherlands). The alongshore-uniform response was computed as the mean of each bar-crest line, whereas the alongshore non-uniform behaviour was characterised by the amplitude around each mean. A more sophisticated description of the inner-bar data set was provided by complex empirical orthogonal function (CEOF) analysis. The first complex mode, containing about 85% of the variance in the data set, corresponded to the amplitude growth and longshore migration of an approximately 600
m long alongshore non-uniformity. The longshore migration rate varied between 0 and 150
m/day and was found to be well related to the longshore component of the offshore wave energy flux. The second complex mode explained about 10% of the variance and largely described the alongshore-averaged cross-shore bar migration. The CEOF results suggest that short-term variability in bar-crest position is largely due to changes in the quasi-regular topography and not to alongshore-uniform on/offshore oriented behaviour. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 0025-3227 1872-6151 |
DOI: | 10.1016/S0025-3227(00)00060-8 |