Journal
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 116, Issue -, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2010JC006660
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Funding
- (New Zealand) Foundation for Research, Science and Technology
- Hanse Wissenschaftskolleg (Germany)
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Swash hydrodynamics were investigated on an intermediate beach using runup data obtained from video images. Under mild, near-constant, offshore wave conditions, the presence of a sandbar and the tidally controlled water depth over its crest determined whether most of the incoming waves broke before reaching the shoreline. This forced a change in the pattern of wave energy dissipation across the surf zone between low and high tide, which was reflected by changes to swash on time scales of a few hours. Significant runup height (Rs, defined as 4 times the standard deviation of the waterline time series), was found to vary by a factor of 2 between low tide, when most of the waves were breaking over the sandbar (Rs/Hs approximate to 1.5, where Hs is the offshore significant wave height) and high tide, when the waves were barely breaking (Rs/Hs approximate to 2.7). The increase in wave energy dissipation during low tide was also associated with changes in swash maxima distribution, a decrease in mean swash period, and increasing energy at infragravity frequencies. Bispectral analysis suggested that this infragravity modulation might have been connected with the presence of secondary waves.
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