The swash zone, characterised as the part of the beach intermittently exposed to atmosphere and water, plays an integral part in the overall evolution of beach fronts. Knowledge and understanding of the hydrodynamics associated with this zone is therefore imperative, however at present is relatively limited. This is a direct result of the complexities associated with obtaining accurate measurements in the field, as the swash zone is notorious for its high velocity flows and extremely shallow water depths.
The experimental research carried out in this project relies upon the similitude inherent between the infamous dam break wave problem and the swash solutions derived from non linear shallow water equations by Shen and Meyer (1963). The dam break model also is capable of modelling this intermittent dry/wet nature associated with the swash zone, as mentioned above. Experiments focus on three main aspects of swash cycle: the down rush component, bed shear stress measurements and maximum uprush run-up lengths. For all cases, various combinations of bed slope, initial water depth, reservoir lengths and bed roughness are examined.
AnuGA- a recently developed hydrodynamic modelling tool, was used to compare depth and velocity profiles with collected down rush data, for different values of Mannings n. It was found to model the flow regime quite accurately, with differences in friction values influenced by bed roughness. AnuGAs output was also employed with the shear stress equations, in order to draw comparisons with measured bed shear stress data. Greater magnitudes of peak shear stress were observed in the uprush cases as compared with the down rush cases, for similar depth and velocity characteristics.
Maximum run-up length values were measured and the average dimensionless run-up height calculated to be approximately 1.27. This was found to be much smaller than Peregrine & Williams (2001) proposed value of 2. Interestingly however, the obtained value is much closer to Morrisons (2006) findings of 1.05.