Über die Änderung von Wellenperioden im Brandungsgebiet : Verteilung der Wellenenergie in Brandungsspektren)

The investigations under consideration are based on storm surge measurements of synchronous water level deflections [eta(t)] at some positions in a beach profile with a slope of approximately 1:40 in front of steep foredunes. 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 as well presented as co -cumulative spectra. Because of different site arrangements it is possible to analyze the deformation of the spectra due to tidal dependent water depth as well as due to coastward decreasing water depth. There are some phenomena associated to 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 breaking and finally broken waves. Sometimes the total amount of energy at an inshore measuring station is bigger than at a station 15m further offshore.