Journal of Waterway, Port, Coastal, and Ocean Engineering

A method for estimating an upperbound on the total energy of the wind wave spectrum in shallow water is extended to define a depth‐controlled zero‐moment wave height for irregular waves. The method requires an estimate of the peak frequency of the wave spectrum, knowledge of the Phillips' equilibrium coefficient, a, and water depth, h. A method for estimating α from the peak frequency of the sea spectrum and windspeed is given. Results indicate that the depth‐controlled zero‐moment wave height is generally less than the depth‐limited monochromatic wave height, $H_d\text{,}$ and appears to vary with the square root of depth.

A model is developed to describe the turbidity plume induced by dredging a ship channel using an hydraulic dredge. The model predicts the suspended sediment concentration within the plume and the resulting sediment deposition alongside the dredged channel. The model applies to a dredging operation in a water body in which the current is primarily along the channel axis and the channel depth is large enough that no significant suspended sediment reaches water surface. Results of field measurements are presented and compared with model. It is shown that the model describes the qualitative feature of prototype data and that the calibrated model parameters agree with independent observations by other investigators.

An improved capacitance wavestaff is described and used to measure wave height transformation in a surf zone; and the assumption is tested that wave height decays linearly across a surf zone. Acceptable frequency response in the instrument could be obtained only if sensor wires were smaller than or equal to 0.35 mm in diam. Simultaneous measurements of wave height were taken at points distributed across a surf zone during four field experiments at Virginia Beach, Virginia. Pairs of wavestaffs were repositioned along a line perpendicular to the shore line. Wave height decay across this surf zone was found to be nonlinear, and the observed pattern appears to be categorizable into three zones: (1) One in which there is a rapid decay in height due to turbulence induced by the breaking process; (2) one in which there is a nearly constant decay due to a balance between turbulence and wave shoaling affects; and (3) one in which there is a rapid decay of remaining wave energy as a wave propagates up the beach slope against the force of gravity. Energy is dissipated less rapidly by spilling breakers than plunging breakers, and, thus, spilling breakers produce greater runup at the shore line.

Wave‐induced pressures are an important design consideration for oil and natural gas pipelines buried in the marine environment. Realistic problems are three‐dimensional in nature and involve waves approaching the buried pipeline at oblique angles and special pipeline geometries. For fluid flow in a sandy soil where liquefaction does not occur and fluid acceleration terms are negligible, Darcy's law can be used. Assuming that the soil structure and fluid are incompressible, results will show the wave‐induced pressure in the domain being governed by the Laplace equation with associated boundary conditions on the domain boundaries. The pressure distribution on the pipeline is obtained using the boundary integral equation method (BIEM). The BIEM is economical because the computations are performed only on the two‐dimensional surface boundaries of the solution domain rather than throughout the entire three‐dimensional domain. The first problem analyzed is the two‐dimensional case where the pipeline is parallel to the wave crests. The numerical solutions show good agreement with finite element and analytical solutions. For waves approaching at oblique angles, the periodic pressure distribution on the pipelines is obtained. Finally, solutions are obtained for soils of different properties. Future work is proposed in order to apply the techniques to more general problems.

In an earlier paper, a three‐layer model of an oscillatory rough turbulent layer was simplified to a two‐layer model. The model consisted of an overlap layer in which the turbulent viscosity varied linearly with height, and an outer layer in which the viscosity was constant. This paper improves the theory from the earlier paper: Turbulent viscosity is allowed to decrease linearly above the overlap layer until a certain height is reached, after which the viscosity is held constant. The viscosity everywhere is assumed time independent. The theory is compared with observations by other researchers. The agreement between theory and experiment is reasonably good. Also, a theoretical derivation of the wave friction factor is given, which for the larger excursion amplitudes agrees well with a previously established semi‐empirical friction factor formula.

Seven West Coast sites are selected having from one to three years of nearshore directional wave measurements several times a day during the period 1979–82. Time series of daily net longshore transport are estimated using the energy flux method, based upon measured $S_{\mathrm{xy}}\text{.}$ Investigations are made on frequency and cumulative distributions of transport, and from these, a number of statistics characterizing the degree of episodic transport are generated. The transport is found to be very episodic, with almost half of the gross transport occurring during only 10% of the time. The maximum transport occurring in a single day each year produced between ten times, and more than 600 times, the mean daily net transport. Inferences concerning the design requirements for sand bypass systems are drawn from the statistics of episodicity.

A mathematical model is developed to predict the flow characteristics in the downrush of regular waves and the critical condition for initiation of movement of armor units on the slope of a coastal structure. The analysis of water motion on the slope is based on the standing‐wave solution of the finite‐amplitude shallow‐water equations with an implicit account of the effects of wave breaking. This simple model neglects the effects of permeability, bottom friction and water depth. In addition, use is made of an empirical runup relationship. A stability analysis of armor units is performed including the drag, lift and inertia forces acting on an armor unit which vary along the slope with time over the period of wave downrush. Comparison is made with the largescale test data on riprap stability from an earlier study. The predicted critical stability number follows the same trend as the observed zero‐damage stability number, although the agreement is qualitative.

Using various types of basic empirical results, equations are developed for average volumetric concentration of sediment moving as bed load in nearshore wave environments. Laboratory and natural situations have appreciably different dependences of bed‐load concentration on peak flow velocity, with laboratory sediment concentrations being commonly larger than those in nature. Critical examination of published concentration measurements isolates several subsets of near‐bed data for quartz sands which allow the two expressions for bed‐load concentration to be evaluated. Field and laboratory results in separate categories exhibit distinct functional trends and some quantitative magnitudes agreeing with calculated bed‐load concentrations, so that calculation might give a reference value useful for suspended‐load computation. Evidence permits a firm conclusion that laboratory near‐bed processes and suspended sediment concentrations in usual conditions do not pertain to important field situations.

A statistical study of the gravimetric gradation characteristics of quarrystones used for shoreline protection against small wave attack is described. A nonparametric method based on order statistics is used to determine the minimum sample size required so that the probability is θ that at least β of the population will be between the jth and kth observations. It is also found that riprap quarrystone obtained after secondary crushing exhibited the Log-Pearson Type III distribution.

The use of the stability parameter for calculating the weights of armor units in models of rubble mound breakwaters is shown to have little justification. An alternative scaling method based on similarity criteria is developed and the results of the two methods are compared. It is shown that the use of the stability number causes little error but that this is fortuitous rather than physically meaningful.

Many coastal engineering problems require an estimate of the seaward limit of sediment transport, defined as the minimum depth at which no measurable change in water depth occurs. A procedure to estimate this limit depth was evaluated using measurements collected at the Coastal Engineering Research Center's Field Research Facility located on the Atlantic Ocean. The data consisted of measured wave characteristics and accurate repetitive nearshore surveys which extended out to a depth of 30 ft (9 m). Ten unique data points were used in the evaluation with measured limit depths ranging from 18 to 21 (3.9 to 6.4 m). These depths were overpredicted by an average of 4.6 ft (1.4 m). This difference could be reduced to 1.3 ft (0.4 m) by adjusting the coefficients in the equation. A reasonable correlation was also obtained using a simple multiple of wave height.