Energy Spectra of Irregular Surf Waves

Abstract

The investigations under consideration are based on synchronous measurements of water level deflections n(t) at some positions in a beach profile with a slope of approximately 1:40. Surf conditions are studied during a severe storm surge as well as during periods of attenuating wave action. By the use of a FOURIER ANALYZER 40 energy spectra are calculated which are also presented in integrated form (co-cumulative spectra). Because of different site arrangements it is possible to analyze the deformation of the spectra due to tide dependent changes of the water depth as well as due to coastward decreasing water depth. It happens that there are some phenomena associated with certain frequency bands. With the water depth decreasing the energy densities in surf spectra are distributed over a wider frequency band. In the present case unbroken waves are characterized by energy spectra in which at least 90 % of the energy is represented by FOURIER components in the frequency range 0 - f - 0.5 Hz. Increasing distribution of the energy densities over a wider frequency band represents at first breaking and finally broken waves. Sometimes the amount of energy coastward of the surf zone is higher than seaward of the breakers. This phenomenon can be explained by refraction effects caused by local nearshore bathymetry. All of there investigations were sponsored by the DEUTSCHE FORSCHUNGSGEMEINSCHAFT (German Research Foundation).

Anomalous Dispersion of Fourier Components of Surface Gravity Waves in the Near Shore Area

“…An explanation like this would be in accordance with the author's previous finding of increasing energy densities at higher frequencies at the expense of the energy densities associated with lower frequencies (BUSCHING, 1976).…”

“…Compared to the storm surge measurements the dispersion in this case is minimal in the total frequency range at position 106.5 m and with the water depth decreasing the weak dispersive property is preserved at frequencies f >0.1 Hz, where in the present case appreciable values of energydensity are to be found in the respective energy spectra, see BUSCHING, 1976. In order to demonstrate the so-called ANOMALOUS DISPERSION with its effect on the deformation of the waves, Fig.…”

“…Later on in this respect the spectrum analysis was used by the author (BUSCHING, 1974(BUSCHING, , 1975(BUSCHING, , 1976).…”

The Energy Spectra of Surf Waves on a Coral Reef

“…of Oceanography, Univ. of Hawaii, Honolulu, Hawaii periods, and energy spectra are thus modified significantly but information on such a modification is very limited (Bushing, 1976), particularly for correlated field measurements. Knowledge of wave characteristics leeward of a reef is necessary in numerous engineering endeavors, such as the assessment of beach stability, design of coastal structures, prediction of dynamic response of small boats in marinas in waters partly protected by a reef, artificial shoal, and submerged breakwaters.…”