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