Journal of Waterway, Port, Coastal, and Ocean Engineering

Characteristics of groups of high ocean waves are studied in varying water depths using field measurements and laboratory simulations. Field data were collected from a shore‐perpendicular line of gages at the Coastal Engineering Research Center Field Research Facility during one storm with onshore winds. Laboratory data were obtained over a plane 1:30 slope by generating the energy spectrum measured offshore in the field. Parameters indicative of wave grouping are observed to vary little outside the surf zone, but decrease greatly after wave breaking occurs. Field and laboratory parameters are generally consistent although some laboratory parameters sensitive to details in the record appear to be distorted by standing wave oscillations in the flume. In particular, the modulation period or time lag between successive groups and the length of the group containing the highest wave in the record are distorted in the laboratory.

Shallow tidal rivers exhibit bore during the propagation of tides of large ranges. The parameters of tidal propagation—the attenuation constant and the phase constant—continually change in a shallow river during a tidal cycle. As a result, the water surface slopes increase during flood and decrease during ebb at corresponding depths of flow. Tidal flux is retained during ebb and the low water is elevated. This is the reason for the formation of “bore” and also the variations of the observed low water levels in different reaches along a shallow river. The height of the bore is obtained from the slope of the water profile just at the turn of the tide from ebb to flood. The veracity of these computations are checked from the observed tidal data of the river Hugli in the state of West Bengal, India.

Wave reflection from a submerged horizontal plate in shallow water varies with the plate width to wavelength ratio and the submergence depth ratio. For a particular submergence, the reflection coefficient increases alternately to a peak value and then decreases to zero. The conditions for these maxima and zero reflections can be explained by examining the energy fluxes across the fluid regions around the plate. The total reflection consists of three components; those reflected from each end and that beneath the plate. The underflow is governed by the pressure difference between the two ends and can be either in a seaward or shoreward direction depending on the plate width to wavelength ratio. Superposition of reflections from the two edges can be additive or subtractive as their phases differ. The additive interference, reinforced by the seaward energy flux beneath the plate, produces the maximum reflection. On the other hand, when the two end reflections are out of phase and the energy flux beneath the plate is zero or shoreward, the incident wave energy is fully transmitted to the lee side.

A method of force‐coupling the nonlinear response of a pile foundation to the linear response of a structure is presented. Basically, this method successively corrects the three boundary forces and three boundary moments for each pile at the pile‐structure interface by comparing the nonlinear response of the pile‐soil system to a linear quasi‐tangent modulus response. Convergence is assumed when all six values per pile are within a stated tolerance. This technique has been employed in the analysis of approximately 40 major and a number of smaller offshore structures in the Gulf of Mexico and has been found to be an efficient and accurate way of coupling a structure to its foundation. It is shown that this method accounts for certain lateral nonlinearities that are inherent in most pile‐soil system responses and why these can produce large errors using other modeling techniques. Examples of convergence criteria, interpolation algorithms, and computer solution times are also given.

Diffraction of solitary waves by a semi‐infinite thin barrier is studied both theoretically and experimentally. A theoretical solution is developed based on the linear shallow water wave theory. The linear wave theory compares reasonably well with the experimental data in the vicinity of the barrier. Nonlinear and dispersive effects are not important in the region examined. The formation of a vortex behind the tip of the barrier is observed and is an important factor in estimating the wave amplitudes in the shadow zone.

A simple mathematical model to predict suspended sediment concentration due to wave agitation is formulated using the diffusional approach. The classical Schmidt equation is solved to obtain the vertical distribution for time‐averaged sediment concentration. The diffusion coefficient is assumed to be proportional to the product of shear velocity at the bed and orbital velocity just outside the boundary layer. A bed layer concept is proposed to evaluate the absolute values of sediment concentration as a function of the height from the bed knowing the wave parameters such as the wave height, period and the mean water depth and the sediment characteristics such as the grain size and the specific gravity. Laboratory experiments are used to evaluate the dimensionless diffusion coefficient and the bed layer thickness in terms of the dimensionless parameters controlling the phenomenon. The present formulation is compared with the experimental data of other investigators and a reasonable agreement between the two is obtained.

The interfacial friction coefficients in a two‐layered stratified flow have been studied in a closed 15 m long rectangular duct with fresh water flowing over a quasi‐stagnant salt water pool. A one‐dimensional flow model along Schijf‐Schoenfeld's line for open channels was developed and used. The average interfacial friction coefficient was found to be best correlated with the number ${\mathrm{RF}}^2\text{,}$ in which R and F are the Reynolds and Froude numbers respectively, and with the relative density difference $\Delta \rho /\rho$ used as an independent parameter. There is dose agreement with re‐analyzed data from an earlier study while one data point from the Mississippi estuary falls on a smooth extrapolation of the appropriate curve. The interfacial friction coefficient cannot be uniquely correlated with either the Reynolds number or the Froude number or the Keulegan number. This is in agreement with the results of a literature review on the subject.

Effects of various geometry parameters on tidal flushing and internal circulation in small‐boat basins (marinas) of rectangular planform were determined in physical hydraulic models by means of a photographic technique incorporating the use of a photodensitometer. The schematic model marinas tested were scaled to have surface areas, water depths, and tide ranges comparable to “prototype” marinas in the Pacific Northwest: Results are presented in terms of spatial average tidal flushing (exchange) coefficients for each configuration tested, and by contour drawings of equal local per‐cycle exchange coefficients for a number of configurations, all at the same tide range. Emphasis is placed on planform geometry and aspect ratio, those variables over which designers may have most latitude in designing a marina for a specific site. Effects of basin length to width ratio are delineated for basins with typical single asymmetric entrances.

An analytical formulation is presented for the calculation of the water wave field in and around a circular region of wave damping, such as might occur over a kelp bed. Figures show the instantaneous wave field and wave amplitude along several transects across the circular damping region.

A useful and computationally simple method is given for estimating the wave breaker height and angle behind structures on a uniformly sloping bottom. The breaking wave height behind a structure is assumed to be proportional to the product of refraction, shoaling and diffraction coefficients with the incident wave height at the tip of the obstacle. The solution is obtained by iterating over breaking depth and starting angle at the tip of the structure, together with a breaking condition. The diffraction coefficient can correspond to either monochromatic or directionally random waves. A simplified procedure for calculating the diffraction coefficient of random directional waves is given in an appendix. The method has been verified with limited field and laboratory data. Possible refinements as well as limitations are discussed.

Explicit equations based on the dispersion relation for linear waves are used to derive an analytical solution to the problem of wave height variation due to shoaling, refraction and frictional dissipation on a beach with straight, parallel contours where the depth is a power function of the distance from the shoreline. The solution is simple enough to be handled by a handheld calculator and as accurate as the underlying linear wave theory justifies.

The field and laboratory data for wind shear stress coefficient at the air-water interface are reanalyzed. The major discrepancy between the field and laboratory data for wind shear stress coefficient is removed by adjusting the laboratory data to the same elevation as the field data. The adjusted laboratory data for wind shear stress follow closely the corresponding field data. Based on this result, it is concluded that wind shear stress coefficient is independent of fetch length. Finally, the Charnock hypothesis is tested statistically based on the available data. The results of the test indicate that the roughness parameter, z^o, varies linearly with (V*²/g) in the laboratory. However, the corresponding variation is not linear for field conditions contrary to the results reported in previous studies.

Experimental evidence shows that two commonly-used estimates of significant wave height behave differently during the shoaling process. Further, the estimates behave differently for monochromatic and irregular wave conditions. Although the mechanics that force these differences are not fully understood, it is important to recognize that the differences exist. It is also vital to identify which wave height parameters are of interest in a study and to assure that they are treated in a consistent manner.