| dc.description.abstract | I quantified scale effects on very small (~1 cm high, wavelength 20-30 cm) waves and on resulting wave-induced sediment mobility. The aim of this research is to gain and understanding of scale effects on wave dimensions, shape and ultimately wave-induced sediment mobility. Wave experiments were conducted in the Metronome tidal facility by measuring wave time series at various cross-shore positions over simplified straight coast and ebb delta bathymetries. A numerical wave model (SWASH) was employed to model waves after the Metronome experiments at a 500 times larger scale using Froude scaling. I found that, despite the very small-scale waves in the Metronome, surface tension and internal friction effects are minimal and only become significant for waves with wavelengths smaller than 0.1 m. Furthermore, the amount and rate of wave energy dissipation in the near-shore zone is similar across scales and is independent of model distortion. Total wave non-linearity in small-scale wave experiments is lower and barely translates into the development of wave skewness, whereas wave asymmetry clearly developed towards greater Ursell numbers. The different nature of non-linearity in small-scale wave experiments implies reduced on-shore transport fluxes. Sediment size scaling requirements for mobility similitude were derived for various assumed model distortions. It appears that increasing model distortion leads to a lower mobility in the 1:500 models, hence I was able to expand the scaling law for sediment size to include the effect of model distortion. As a final conclusion and recommendation for using waves in the Metronome, it is recommended to increase mobility through lowering sediment density or by generating higher and steeper waves. The latter is easier to put into practice and will also improve similitude of the surf zone similarity parameter through lowering it. | |
