Comparison of model and beach scour patterns.
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Artificial or natural barriers may be divided into two classes, those from which waves are reflected and those on which waves break. Any intermediate type that gives a combination of reflection and breaking may set up severe erosive action of the beach in front of barriers. When the reflected waves are superimposed on the incident waves a stationary spatial envelope of the combined incident and reflected waves is produced. The crests of the sand bed in a model study appeared fairly closely under the nodes of the envelope and troughs of the scoured sand bed appeared under the loops of the envelope. The predominant scouring pattern had a spacing between crests equal to one-half the wave length. Wave data taken during hurricane Beulah (October 1967) at Galveston were obtained from the Coastal Engineering Research Center. The wave data were analyzed, using spectral methods, and equivalent wave height and period at maximum spectral density were obtained. At Galveston the average spacing between sand wave crests was greater than the deep water wave length and about twice as long as the average wave length at 18 ft depth. The relationship between average scour depth and the average wave height is approximately equal to 0.160 for the East Beach area and equal to 0.142 for the Groin area.