Journal of Waterway, Port, Coastal, and Ocean Engineering

Charleston Harbor, South Carolina, has undergone pronounced changes in salinity regimes because of the diversion of the Santee River into the Cooper River in 1942 and rediversion of the Cooper into the Santee in 1985. The mean monthly harbor surface salinity changed from 30.1 ppt to 16.8 ppt as a result of the diversion, and has again increased to 22.0 ppt since rediversion. Postdiversion monthly mean Cooper River discharge was $418m^3{s}^{-1}\text{,}$ but since rediversion, the monthly mean discharge has decreased to $122m^3{s}^{-1}$ and become less variable. Regression models for salinity variability in Charleston Harbor and Cooper River have been developed. Based on these models, discharge alone explains 78% of the salinity variance during the postdiversion period, but accounts for only 1% of the salinity variance after rediversion because of the near constant discharge. Thus, the estuary is presently much more susceptible to salinity changes due to far‐field forcing from the coastal ocean.

A review of the Morison‐equation approach to the evaluation of wave loads on cylindrical members in harmonic flow is presented. The results presented show the most comprehensive picture to date of the Reynolds number‐displacement ratio dependence of the drag and inertia coefficient in the small‐displacement‐ratio range and demonstrate the important effect of the Reynolds number in the case of both smooth and rough cylinders. Results from oscillating‐cylinder tests are compared with wave‐tank results for both regular and random waves. Finally, a wake model applied to the high Reynolds number case is shown to correlate the drag coefficient for both rough and smooth cylinders quite well.

A numerical method for calculating the transient, second‐order interaction of ocean waves with large fixed offshore structures of arbitrary shape is described. The development of the flow together with the associated fluid forces is obtained by a time‐stepping procedure in which the flow at each time step is calculated by an integral‐equation method based on Green's theorem. The nonlinear free‐surface boundary conditions and Green's theorem defined on the instantaneous free surface are first expanded about the still‐water level by a Taylor series expansion and terms up to second order are retained through a perturbation procedure. The stability and numerical accuracy of the proposed solution and the treatment of the radiation condition to second order are discussed. The procedure is applied to the two‐dimensional, vertical‐plane case of a submerged circular cylinder subjected to regular incident waves. Comparisons with a previous second‐order theory and a previous experimental study are presented and indicate favorable agreement.

New methods are suggested for scheduling advance maintenance dredging on isolated reaches of navigation channels based on economic and reliability analysis. For reaches where sedimentation occurs regularly as a result of gradual slumping, quiescent deposition, or regular erosion due to waves and wakes, the problem reduces to a deterministic least‐cost replacement problem. Where sedimentation rates are uncertain, the risk of sediment encroachment into the navigational channel becomes a concern. Where sedimentation rates are probabilistic and independently distributed in time, encroachment probabilities and expected dredging costs can be calculated for a variety of dredging schedules. This risk and cost analysis allows explicit specification of risk‐cost trade‐offs in dredge scheduling. These methods are applied to an example case where existing dredging costs are compared with those estimated using these new dredge scheduling techniques. Extensions of these methods could be applied to multiple‐reach dredge scheduling, sizing sediment traps, and scheduling dredging with explicit consideration of environmental impacts.

The present paper describes random wave forces acting on a slender structural member in the vicinity of the water surface, taking account of the intermittency of submergence. A brief review is initially given of available formulations for fully submerged portions of a member, these being based on the Morison equation applied in conjunction with linear wave theory. The Morison equation is generally linearized in order to estimate spectral densities, while its nonlinearity is retained in order to estimate probability densities and consequently extreme force values. For sections located near the free surface, the intermittency of submergence drastically alters the statistics of the water particle kinematics in the random wave field and consequently those of the wave forces. Expressions for the spectral density of the force and the probability density of the force maxima are derived. Numerical results relating to these and to the vertical distribution of extreme forces are presented, and the effects of including the intermittent submergence near the free surface are illustrated.

A consistent theory is presented for generating arbitrary, finite‐amplitude, long waves at any location in a two‐dimensional, constant‐depth wave tank using a vertical paddle‐type wavemaker. The theory consists of solving an inverse evolution problem of the Korteweg‐de Vries equation; given specific initial data the boundary motion that produces that data is determined. The theory also suggests the appropriate method for calculating the force on the wavemaker. Application of this theory allows for the laboratory generation of very detailed single waveforms at arbitrary lengths away from the wave‐maker; this formalism obliterates the limitations of the existing shallow‐water wavemaker algorithms which can only reproduce wave motions either of periodic or of constant form. A series of laboratory experiments is described where relatively arbitrary single waves are specified as initial data, the theory calculates the correct boundary motion, the waves are generated and then compared with the initial data as appropriate. The experiments also demonstrate the limitations of this theory, which, even though capable of generating the leading wave emerging after a long wave breaks, it cannot model the details of the tail of the breaking wave.

An experimental study is conducted in order to identify the major physical processes leading to the breakout of half‐buried submarine pipelines from the seafloor under ocean‐wave action. Both the hydrodynamic loading on the exposed surface of the pipe as well as the pore‐pressure distribution on the buried surface were measured. The resulting displacement histories of the pipe were recorded and analyzed in order to identify the critical pipe‐soil‐wave conditions for the detachment of the pipe from the seabed. The paper examines the balance of the pipe under the combined lift and drag loading from the water wave. The experimental coefficients of drag, lift, and added mass have been calculated by the least squares method and compared with theoretical predictions. As for the soil response, a simple theoretical model is worked out to describe the pore‐pressure resistance force at the soil‐pipe interface. An experimental breakout force‐time power law is obtained and compared with the theoretical model.

The amount of general cargo that is transported through public wharves in a port is not necessarily constant for a certain point of time; it will change depending on the relative location of the port to other ports in a country. In this paper, a method to determine the optimum allocation and size of ports in a country is proposed from a national economic point of view. The total cost spent in transporting general cargo consists of two kinds of costs; i.e., the total inland transportation cost and the total port cost. The former cost is a linear function of the amount of cargo transported; while the latter cost is a nonlinear function and is not easy to treat. Consequently, the total port cost is approximated by a piecewise linear function. Thus, the application of the separable programming technique to this type of allocation problem has proved successful. The optimum berth planning of ports in a country can be executed efficiently and easily with the aid of the procedures herein developed.

Small-scale tests were performed to examine the effect of opposing current on the breaking condition of regular waves shoaling on a uniform slope. A simple empirical formula is proposed for predicting the breaking condition of shoaling waves on opposing current.