Measurements and Analysis of Near-Shore Breakers in a Model-Scale Surf Environment

This paper describes the development and deployment of a new type of wave sensor, termed the ΔF2luID (pronounced delta fluid), for detailed measurements of a wave's profile during wave breaking. A large-scale laboratory measurement campaign was carried out to characterize the shoaling and breaking of waves in shallow water in a model-scale surf environment. Experiments were conducted in the Hydraulic Wave Basin Facility at the University of Iowa, with a compound planar beach installed opposite the wavemakers, which was used to produce eight wave conditions spanning deep water wavelengths from 2 to 6.5 meters (periods of 1.1 to 2 seconds) and wave amplitudes of 6.5 to 18 centimeters. The ΔF2luID sensors were co-located with ultrasonic wave gauges and arrayed across the shoaling and breaking regions of the wave field, and data from the two sensor types were hybridized to produce wave profiles that accurately captured the steepening wave profile, the overturning or spilling wave face, and the receding waterline on the wave back. A wave-by-wave statistical analysis is presented, which shows that the wave field achieves stationarity within a short duration after starting the wavemaker, and that wave heights follow an approximately normal distribution. Within the stationary process, median wave heights show a local maximum that corresponds to the observed breaker line location, after which median wave heights quickly diminish and wave height variance grows considerably. Ensemble mean wave profiles clearly show the evolution of the wave profiles across the shoaling region, with the transformation from a nonlinear, sharply-peaked wave to an overturning/plunging breaker, followed by a bore-like spilling profile. Ensemble wave profiles are used to quantify the wave set-up and the approximate normalized energy flux along the cross-shore direction, showing a gradual rise in mean water level as waves approached the shore, which grow with wavelength and wave height. Energy dissipation was evident as the waves passed through the shoaling and breaking regions, with a much more gradual rate of dissipation observed for shorter and shallower waves. A preliminary parameterization of the face profile of a breaking wave produces a good agreement with existing theoretical models, which hold promise for parameterizing wave profiles across the surf zone using non-optical measurement techniques.