Journal of Waterway, Port, Coastal, and Ocean Engineering

Examination of the impact of dredging when employed in support of engineering requirements for river system development on the Mississippi River system reveals that the dredge provides the river engineer with a means of rapidly altering channel configuration and accelerating morphologic processes. In this respect, dredging constitutes a morphologic agent responsive to engineering requirements. This application is overshadowed by the volume of material moved and the number of reaches involved in dredging operations for navigation channel maintenance. Dredging and disposal of dredged material in support of channel maintenance implies the repeated moving of alluvial sediments from the main channel region toward the periphery of the channel. The combined use of dredging, contraction dikes, and disposal of dredged material in the dike fields can induce major changes in the cross‐sectional characteristics of a river. This direct physical displacement of bed material and the resulting change in channel shape can retard the movement of bed‐load sediments through a river system. In both the Columbia and Mississippi River systems this lateral redistribution of sediment by dredging, when combined with contraction works, has constituted an agent for long‐term morphologic change.

The modification and application of a hydrodynamic water quality model to predict the water elevations, the depth average velocity components, and the depth mean nitrogen concentrations in Poole Harbor and Holes Bay, in Dorset, England, are described. The main objectives of the study are to ascertain the influence of the nitrogen discharge from Poole Sewage Treatment Works on the corresponding concentrations across the harbor. Comparisons were undertaken, both with and without nitrogen inputs from Poole Sewage Treatment Works, of the concentration distributions of total oxidized nitrogen and ammoniacal nitrogen across the harbor, for inflows from two rivers and three sewage treatment works. Limited field measurements were available of velocities and nitrogen concentrations, allowing a check on the accuracy of the model predictions. A number of difficulties had to be overcome in the hydrodynamic modeling, including treatment of the open boundary conditions, representation of the advective terms, with particular reference to the narrow harbor entrance, and simulation of extensive flooding and drying of shallow regions throughout the tidal cycle.

A knowledge of sediment transport due to wave action is required to understand the dynamic process of nearshore morphology; however, these phenomena of sediment transport due to waves are complicated by the unsteady characteristics of the flow, the presence of turbulence and the interactions between the fluids and the sediment. These unsteady phenomena are much more complicated than those of steady uniform flows. Profiles of mean and unsteady concentrations are derived from the mass conservation equation using the diffusion coefficient profile adapted from the eddy viscosity profile, taking into account changes of the friction factor and boundary layer thickness in the presence of suspension. The theoretical profiles are expressed explicitly as functions of the friction factor, velocity and shear stress profile parameters, and the settling velocity of the sediment relative to the fluid velocity. The tabulated data available and the present experimental data of the mean concentration are used to fit the theoretical profile. The analysis shows that the friction factors in the presence of suspension decrease from the sediment‐free values in the same manner and magnitude as the von Karman constant.

The effects of laminar viscosity on the evolution of a steady Stokes wave train are investigated by employing a boundary‐layer method. It is assumed that the nonlinearity of the second order in the wave slope, $0(\mathrm{ka}{)}^2\text{,}$ is in the same order of magnitude as the viscous effect; i.e., $0(\mathrm{ka}{)}^2=0(k\delta )\text{,}$ where $\delta =\sqrt{v/2\omega }=\mathrm{the}$ Stokes boundary layer thickness. A nonlinear Schrödinger equation with a dissipation term is derived as the governing equation for the wave envelope. It is shown that the viscosity not only reduces the wave amplitude but also causes a phase shift in the same order of magnitude.

Wave interactions with a sediment trench are examined both theoretically and experimentally. The envelope of the wave amplitudes in front of the sediment trench is measured to evaluate the wave reflection from the trench. Detailed pore water pressure measurements are also made above and within the sediment trench. It is found that the wave reflection is practically zero when the trench is filled with sand. It is also shown that potential theory describes adequately the velocity and pressure field when the trench is not filled with sand. However, when the trench is filled with sand, the Biot consolidation theory gives a better description of the pore water pressure field under wave loading than other theoretical models.

A semi‐empirical model for surf zone wave height decay is adapted to the parabolic equation method in order to include the effect of depth‐limited wave breaking in combined refraction/diffraction calculations. Several examples for plane beaches are presented in order to show correspondence between the empirical model, its numerical formulation, and previous laboratory data. The model is then applied to the study of wave breaking and diffraction around offshore islands of various planforms. An analytic method for constant depth, which can be used to extend computed solutions to the farfield downwave of the island, is provided, and several simple examples treating the island as a finite width breakwater are examined.

An alternative to rubble mound construction, with or without precast concrete armor units, is recommended which comprises flexible membranes filled with cement mortar in situ. The placement of these for greatest stability is suggested by maximizing surface contact of sausage type units. Results of tests to derive an economical mortar mix are described. Construction details are outlined together with comparative costs for a marina breakwater.

The vertical distribution of suspended sediment under broken waves is considered. Close to the seabed, the turbulence is dominated by the wave‐boundary layer, which determines the amount of suspended sediment very close to the bottom. Away from the bottom, the main contribution to the turbulence intensity originates from the surface generated turbulence due to wave breaking. This is described by application of the transport equation for turbulent kinetic energy. The production of kinetic energy is estimated from the energy loss in a hydraulic jump. The vertical distribution of suspended sediment is obtained from the diffusion equation. The theoretical findings are compared with laboratory experiments and field measurements.

Information from a bidirectional electromagnetic current meter and surface‐piercing, continuous resistance wave staff is shown to provide good estimates of the angle of wave approach within the surf zone. Spectra of surface elevation fluctuations (η) define limits to the primary frequencies in the incident wave field, which are then used to define the wave‐driven components in the onshore (x) and alongshore (y) velocity spectra. Cross spectra between η and x and y give squared coherence values used to weight the wave contribution to the motion in any frequency band. A weighted orbital vector for each frequency band is calculated: the angles corresponding to each band are then further weighted according to the proportional contribution of the variance in the velocity in that frequency band to the total variance in the onshore and offshore velocities. Summation of the individual angle contributions gives a wave angle representative of the energy distribution in the peak of the incident wave spectrum. A test of the technique is made by comparing wind and wave angles, and wave angles calculated for adjacent instrument pairs.

Ice‐bonded sediment is present in tundra cliffs and gravel structures in the southern Beaufort Sea. Thermoerosion of the frozen sediment under wave action can be important in determining the rate of coastal retreat and the severity of erosion of a gravel structure. The thermal processes involved in the thermoerosion of the frozen sediment are examined assuming the transport capacity of the wave action exceeds its melting capacity. The location of the melting surface of the frozen sediment is determined by solving the heat conduction equation in the frozen sediment exposed to the wave action, which causes the convective heat transfer between the sea water and the frozen sediment. Analytical solutions are presented for simplified one‐dimensional problems. A two‐dimensional finite element method based on a fixed domain approximation is proposed to facilitate the numerical computation. The example computation made for a frozen gravel causeway indicates that the melting of the frozen gravel will occur rapidly under the assumed storm conditions if the melted sediment is removed by the wave action.

This paper examines the character and dissipation of a bore initially generated from a wave overtopping a berm and subsequently running inland. A simplified relation is developed to provide depth and speed of the bore at any distance inland. This information can be used to establish safe setback and floor elevations for structures built on artificial islands.

The recession rate of the bluffs at four sites on the Chesapeake Bay is related to three factors: the height of the bluff, the local potential littoral drift rate, and the overfill ratio, which is used in an analog of bluff slumping to beach nourishment. Results show that these factors can distinguish between the dissimilar erosion rates at the four sites.

Previous studies investigated the correlation between predictions of existing cross-shore transport models using observed surf zone parameters and the measured beach face responses from Torrey Pines Beach, California. Following the Torrey Pines experiment, 3 more Nearshore Sediment Transport Study (NSTS) data sets were obtained by the present writer: (1) from Scripps Beach, California; (2) from Virginia Beach, Virginia; and (3) from Santa Barbara, California. These results are presented to enable testing of cross-shore transport models.

Various wave energy spectrum models have been suggested in terms of two independent statistical parameters, e.g., significant wave height and a characteristic period. Alternatively, they are represented by a coefficient and the wind speed parameter. A general spectrum model is derived here that encompasses a large class of single peak two parameter wave energy spectrum models including P-M, Bretschneider, ISSC and ITTC. The two independent parameters chosen are the significant wave height and the peak frequency. The relationship of these quantities to other statistical parameters for the different spectrum models is established.