Journal of Waterway, Port, Coastal, and Ocean Engineering

Three irregular wave tests were conducted on a 1:16 smooth impermeable slope to investigate the detailed cross-shore variations of the probability distributions and statistics of the free surface elevations and middepth horizontal velocities in the shoaling, surf, and swash zones. The exponential gamma distribution with the measured mean, standard deviation, and skewness is shown to be capable of describing the measured probability distributions in a unified manner, although the agreement becomes worse in the lower swash zone. The probability distribution of the free surface elevation whose lower limit is imposed by the beach face in the swash zone becomes exponential with the skewness s= 2 and the standard deviation σ=$\overline{\mathit{h}}$ with $\overline{\mathit{h}}$= mean water depth. These upper limits of s and σ/$\overline{\mathit{h}}$ in the lower swash zone are in qualitative agreement with the data in the region of $\overline{\mathit{h}}$≳ 0.4 cm in these small-scale tests. The cross-shore variations of the mean (undertow) and standard deviation of the middepth horizontal velocity measured in the shoaling and surf zones can be predicted fairly accurately using the simple relationships derived using linear long-wave theory together with the measured values of $\overline{\mathit{h}}$ and σ. The adopted distribution and these simple relationships will need to be verified using extensive data on sand beaches of various profiles.

Streamer sediment traps were used to measure the distribution of longshore sediment flux in the surf zone at 29 locations along the southeast coast of the United States and the Gulf coast of Florida. Measurements were conducted on both barred and nonbarred coasts under low-wave energy conditions. Results indicate that longshore sediment flux decreases logarithmically upward in the water column throughout the surf zone, and the rate of upward decrease is largest in the trough and smallest in the swash due to stronger mixing energy in the swash. Six types of cross-shore distribution patterns of longshore sediment transport (LST) were found. These six distribution patterns are controlled by nearshore morphology, breaker type, and energy dissipation pattern. For low-wave energy coasts, the swash (nonbarred coast) and inner surf (barred coast) zones contain significant contributions to the longshore sediment transport rate. The cross-shore distribution pattern of the longshore sediment transport rate along nonbarred coasts was well reproduced using energy-dissipation and shear-stress approaches developed mainly from laboratory studies.

The present paper outlines the numerical calculation of wave interactions with a thin vertical slotted barrier extending from the water surface to some distance above the seabed, and describes laboratory tests undertaken to assess the numerical model. The numerical model is based on an eigenfunction expansion method and utilizes a boundary condition at the barrier surface that accounts for energy dissipation within the barrier. Numerical results compare well with previous predictions for the limiting cases of an impermeable barrier and a permeable barrier extending down to the seabed. Comparisons with experimental measurements of the transmission, reflection, and energy dissipation coefficients for a partially submerged slotted barrier show good agreement provided certain empirical coefficients of the model are suitably chosen, and indicate that the numerical method is able to account adequately for the energy dissipation by the barrier. The effects of porosity, relative wave length, wave steepness, and irregular waves are discussed and the choice of suitable parameters needed to model the permeability of the breakwater is described.

A nondimensional wavemaker curve of a characteristic water wave amplitude is constructed from the landslide length, the initial landslide submergence, the incline angle measured from the horizontal, the characteristic distance of landslide motion, and the characteristic duration of landslide motion. This wavemaker curve applies broadly to water waves generated by unsteady motion of a submerged object, provided the motion is governed by only one characteristic distance scale and one characteristic time scale. An analytical solution of solid block motion provides the characteristic distance scale and time scale. Two-dimensional experimental results on a 45° incline confirm that a wavemaker curve for solid block landslides exists as a function of the nondimensional initial submergence and what is called the Hammack number. Water wave amplitudes generated by solid block landslides can be predicted from the wavemaker curve if the solid block motion is known. Criteria for the generation of linear water waves are given.

The long-term cross-shore dynamics of the surf zone affected by storms is investigated. The validity of the hypothesis of equilibrium bottom profiles in the coastal zone is examined using bathymetric measurements of some coastal regions in Israel for the period 1968–1995. It is shown that the power law of depth variation as a function of offshore coordinate (Dean's profile) is satisfied on the average for nonbarred profiles. Bar development for the period of the last five years is analyzed. A mathematical model for description of time-dependent sea bottom deformation under the action of wind waves in the surf zone is developed. It is found that, besides the known static solutions of the balance equation for sediment transport, which correspond to the equilibrium bottom profile with zero net sediment transport, there exists a solution corresponding to the profiles of dynamic equilibrium when the surf zone is a “carrier” of sediment transport from the coast to the sea or in the opposite direction. Both equilibrium bottom profiles satisfy the power asymptotic law near shore. A class of steady-state solutions of the sediment balance equation, which correspond to the “traveling” bottom profiles, is studied also. Such “wave” solutions may be used for the description of the long-term processes of the beach migration. Data available on the deviation of bottom profiles from equilibrium are used to estimate an anticipated speed of the long-term beach deformation.

The mechanism by which a suspended fine-sediment-induced pycnocline, or lutocline, is generated under wave action is examined. The steady-state form of the turbulent kinetic energy balance is used along with commonly invoked phenomenological arguments to obtain a formula for the height of the lutocline as a function of wave and suspended sediment properties. This formula is then used in conjunction with data on equilibrium heights of lutoclines of a suspended clay mixture in a wave flume to show that the formula holds promise as a first-order predictor of lutocline height. This height is also shown to correlate empirically with wave energy.

Comparison of predicted with observed attenuation of pressure fluctuations shows that wave heights can be estimated with observations from a pressure sensor that is buried a known depth in fine sand. The attenuation of pressure fluctuations within the sand bed under unbroken shoaling waves, bores in the surf zone, and swash near the shoreline was measured with vertical stacks of buried pressure sensors. The attenuation increased with increasing frequency and depth below the bed surface, consistent with previous observations under nonbreaking waves in deeper water and with model predictions based on poro-elastic theory. In the limit of an infinitely deep soil skeleton that is much more compressible than the pore fluid, the predicted pressure fluctuations decrease exponentially with increasing burial depth, and the attenuation is independent of the sediment properties. For the fine-grained sand beds considered here, this exponential limit accurately predicts the observed attenuation.