THESIS
2015
xiv, 136 pages : illustrations (some color) ; 30 cm
Abstract
Detailed hydrodynamics within the swash-swash interactions are studied based on
experimental measurements. Two bores are generated using a double dam-break mechanism
and interact on a 1:10 impermeable sand-rough beach. Two series of experiments are
conducted. The first series is carried out to explore the overall features of swash-swash
interaction. The water levels in the reservoirs and opening times between the two gates of the
dam break mechanism are varied to generate a large number of different swash-swash
interactions. Experimental flow depth data is measured using acoustic displacement sensors.
The results are combined with estimated times of flow reversal, obtained from a model based
on the nonlinear shallow water equation, to determine the type of swash-swash interactio...[
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Detailed hydrodynamics within the swash-swash interactions are studied based on
experimental measurements. Two bores are generated using a double dam-break mechanism
and interact on a 1:10 impermeable sand-rough beach. Two series of experiments are
conducted. The first series is carried out to explore the overall features of swash-swash
interaction. The water levels in the reservoirs and opening times between the two gates of the
dam break mechanism are varied to generate a large number of different swash-swash
interactions. Experimental flow depth data is measured using acoustic displacement sensors.
The results are combined with estimated times of flow reversal, obtained from a model based
on the nonlinear shallow water equation, to determine the type of swash-swash interaction.
Two types of interactions are identified: wave capture interaction, when the interaction with
the second bore occurs during the uprush of the first bore, and weak wave-backwash
interactions when interaction happens during the backwash of the first bore. The second
series of experiments investigates the detailed hydrodynamics of these two types of swash-swash
interaction by using a combined particle image velocimetry and laser induced
fluorescent system, which enables comparisons to be made between wave capture interaction,
weak wave-backwash interaction and the single swash event.
The results of the first series of experiments show that the relative strength of the bores
at the initial shoreline and time between their arrivals determines the initial type of
interaction, however the type as well as the intensity of the interaction may vary throughout the swash-zone for the same swash event. The results of the second series of experiment
show that during wave capture and weak wave-backwash interactions, the fluid of the first
bore is advected upwards, then mixed with the fluid of the second bore by highly turbulent
vortices generated at the front of the second bore because of the relative velocity differences
between the two bores.
Discussions of the results obtained in the experimental study highlights that swash-swash
interaction results in large shoreward local fluid accelerations and strong turbulence
intensities in particular with a large vertical fluctuating component. In addition, the velocity
gradients indicate that the bed shear stress also increases during interaction. All these factors
indicate that swash-swash interactions have the potential to enhance shoreward sediment
transport in the swash zone.
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