Modeled Swash and Runup on Natural Beach

Runup position is commonly used to delineate the region that is affected by wave up-rush from the dry land. The earliest attempts at runup prediction were completely empirical and based on deep water wave conditions and beach slope. However, advances in technology and understanding have provided the opportunity for improved tools in estimation of swash characteristics and runup. Through the straight-forward integration of the phase-averaged energy and momentum equations in the surf zone, a rational prediction for the wave height, setup, and longshore current is developed. The computation of swash zone hydrodynamics, however, necessitates use of a probabilistic representation and additional assumptions before cross-shore integration of the equations of motion. As such, the model depends on empirical relations and comparison to data. While the formulation was based on small-scale laboratory experiments initially, we have recently collected high-quality measurements of swash and runup hydrodynamics on a natural beach. Use has been made of a permanently mounted laser scanner to detail the position of the swash zone free surface position over a wide range of wave and water level conditions. The present effort constitutes a detailed comparison of the field data and numerical results. The model, in present form, demonstrates reasonable predictive skill throughout the swash for most low and moderate wave conditions. For energetic seas, however, swash hydrodynamics and runup statistics are under-predicted. The deficiency may be due, in part, to our expectation that the low frequency components are a larger fraction of the overall energies for larger wave conditions, and the model lacks a dedicated low-frequency infragravity generation mechanism.