FIELD INVESTIGATIONS IN SURF ZONES

Hans Henning Dette, Alfred Fohrboter

Abstract


During storm surges considerable wave energies are dissipated in surf zones; the energy transfer rates are in the order of one up to two powers of ten higher than outside the surf zone. A breaker parameter s introduced by FOHRBOTER (1974) with regard to a quantitative breaker classification, especially of the intermediate types between surging and spilling, was found to be convenient for practical application. The breaker parameter e is in close relation with the horizontal asymmetry parameter a of the breaking wave. With decreasing breaker parameter the asymmetry is increased and reverse. Within the longshore currents macro-turbulences were discovered. The periodical fluctuation parameter y was found to increase nearly linearily with decreasing breaker parameter; the narrower the area is, where the main energy is dissipated the smaller becomes the mean periodical fluctuation which seems to be independent of the wave period but reaches up to 7 and more fluctuations within the wave period. The mean longshore currents velocities reached up to 1.5 m/s above the seabottom; th£ coefficient of variation was scattering considerably between 400 per cent at low velocities (v,= 0.1 m/s) and 20 per cent at the highest velocities (v.= 1.5 m/s). The instantaneous longshore current velocities were nearly symmetrically distributed around the mean velocity, the mean amplitudes were nearly constant and reached approx 0.35 m/s whereas the periodical fluctuation decreased from 2.6 s at low mean velocities up to 1.7 s at high velocities.

Keywords


surf zone; field investigation

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