Numerical prediction of wave transformation, velocity, and bottom stress in the inner surf and swash zone

Abstract

A physical model study was conducted in a narrow wave flume to verify a previously developed numerical model for predicting the hydrodynamic response to irregular waves on a rough impermeable slope. In the physical model study, one case was run using a narrow banded TMA spectrum and a rough impermeable composite slope. The composite slope consisted of a 1:10 slope fronted by a 1:35 slope. The incident and reflected waves were resolved at 13 locations along the 1:35 slope using a three gage array. In addition, the free surface was measured along the 1:10 slope at 15 locations. A vertical stack of three capacitance sunup gages was used to measure the waterline oscillation along the 1:10 slope. Also, velocities were measured using a laser Doppler velocimeter (LDV) at 11 horizontal locations along the 1:10 slope at several elevations. A logarithmic profile was shown to exist for many phases of the onshore and offshore flows in the surf zone. Inside the swash zone, the logarithmic profile was more clearly established during the offshore flow. The measured and computed hydrodynamic responses were compared to evaluate the capability of the model in predicting the flow on a rough slope in the swash zone. The incident wave time series at two locations was specified at the seaward boundary of the numerical model. The measured and computed time series of both the reflected wave time series at the seaward boundary and the water line oscillation on the slope were plotted. The ability of the model to predict the detailed time varying quantities as well as the general wave characteristics of wave reflection, sunup, and flow velocity on the rough impermeable slope indicate that the model could be used to predict the swash zone hydrodynamics. The model showed a strong sensitivity to changes in the friction factor along the 1:10 slope. Improvements in the estimation of the bottom friction factor are needed to better predict the bed stress in the swash zone.