Charles B. Chesnutt, Cyril J. Galvin


Reflection coefficients and profile changes were measured during four lengthy experiments in two relatively long, narrow wave tanks. Each tank had a periodic wave generator at one end and a 0.2 mm movable sand bed at the other end. Generator period (1.90 sec), water depth (2.33 ft), nominal wave height before reflection (0.36 ft), and initial sand slope (1:10) were constant In the four experiments. Measured reflection coefficients (K = H /H.) ranged from 0.05 to 0.30, with the typical time variation of K related to profile changes as follows: K increased by a factor of 3 to 4 within the first minutes while a steep foreshore was built on the undeformed profile; K fluctuated and dropped to a lower value as the inshore widened; K increased as the offshore steepened. Large variations in K near the end of the experiments appeared to result from minor profile changes. The apparently similar experiments showed very different rates of profile development, implying control by other variables such as water temperature or tank geometry. "Equilibrium" in these experiments was never reached, even after as many as 375 hours of wave action.


reflection; lab profile; H/L ratio

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