Surface Wave and Roller Dissipation Observed with Shore-based Doppler
Marine Radar
Abstract
Surface wave energy and dissipation are observed across the surf zone.
Utilizing the concept of surface rollers, a new scaling is introduced to
obtain the energy flux and dissipation related to rollers from Doppler
velocities measured by a shore-based X-band marine radar. The
dissipation of wave energy and hence the transformation of the incoming
wave height (or energy) is derived using the coupled wave and roller
energy balance equations. Results are compared to in-situ wave
measurements obtained from a wave rider buoy and two bottom mounted
pressure wave gauges. A good performance in reproducing the significant
wave height is found yielding an overall root-mean-square error of 0.23
m and a bias of -0.13 m. This is comparable to the skill of numerical
wave models. In contrast to wave models, however, the radar observations
neither require knowledge of the bathymetry nor the incident wave
height. Along a 1.5 km long cross-shore transect on a double-barred,
sandy beach in the southern North Sea, the highest dissipation rates are
observed at the inner bar over a relatively short distance of less than
100 m. During the peak of a medium-severe storm event with significant
wave heights over 3 m, about 50% of the incident wave energy flux is
dissipated at the outer bar.