Random Wave Transformation and Sediment Transport Across Barred and Terraced SandBeaches

摘要

Two irregular wave tests were conducted over a permeable fine sand beach inequilibrium, recording time series of the free surface and horizontal velocity at 17 cross-shore locations. The first part of this study supplements the results of Herrman et al. (1997), obtained using a 1:16 impermeable smooth slope. The exponential gamma distribution, with measured mean, standard deviation, and skewness, is shown to be capable of describing the probability distributions of the above data in a unified manner over the beach profiles, in mean water depth h > 1 cm. In the swash zone, the skewness, s, approaches 2 and the root-mean-square wave height Hrms approaches squareroot h. Cross-shore variations of the mean and standard deviation of mid-depth horizontal velocity are adequately predicted in the shoaling and surf zones using linear long-wave theory locally. In addition to cross-shore data, two velocity profiles were measured and horizontal velocity statistics were shown to be fairly constant over depth. An attempt is also made to synchronize free surface and velocity time series to obtain information about incident and reflected wave spectra in shallow water. Total wave spectra are examined to check for the existence of long period standing waves over the profiles. Finally, sheet flow and energetics-based sediment transport models are used with the measured horizontal velocities to try to predict the equilibrium profiles obtained in this experiment. The energetics model is shown to predict these profiles more accurately than the sheet flow model. In the milder wave conditions of the second test, the energetics model predicts equilibrium II.