Journal of Waterway, Port, Coastal, and Ocean Engineering

A mathematical model is developed to simulate the filling/emptying of navigation locks and to compute the stress on mooring lines of barges during lockage. The model, verified for different filling and emptying systems (end-filling systems with valves-in-gate or loop culverts and wall culverts with side-ports), reproduces satisfactorily the hydraulic transient generated in the lock chamber and the hawser force. A procedure is proposed to design the optimal valve operation for end-filling systems, which gives the minimum lockage time, keeping the hawser force below the admissible value. It is concluded that valving at a progressively increasing rate diminishes the lockage time in comparison to a valve operated at a constant rate.

Continually changing shipping industry practices, cargo composition, world markets, and competition among ports are making revenue estimates uncertain. This paper demonstrates the application of Monte Carlo simulation for scrutinizing sources of uncertainty and their impact on investment risk. Strengths and weaknesses of Monte Carlo simulation are discussed using the Port of Colombo development project in Sri Lanka as a case example.

The behavior of water waves in the vicinity and within an inlet through an idealized barrier island is studied. Two mathematical approaches are used: the first treats the waves in the ocean and bay with Fourier transforms; and the second uses “buffer” domains, which permit the far-field waves to be treated by eigenfunction expansions. The first method is used to treat an inlet with reflective vertical sidewalls. In nature, inlets lined with armor stone absorb wave motion; therefore, the second method is used with impedance boundary conditions at the inlet sidewalls to reduce the wave energy propagating down the channel and into the bay. Wave patterns in the inlet can vary significantly with the angle of incident wave and so can the direction of the radiated wave field in the bay.

Bulk commodity export terminals are equipped with very expensive infrastructure. The massive capital outlay also is accompanied by large operating costs associated with major equipment such as shiploaders, reclaimers, and unloading stations. The port management is always interested in optimizing the deployment of its infrastructure with a view to minimizing the terminal's operating costs. This study deals with finding an optimal solution to an interesting situation where using one shiploader results in unacceptable ship waiting times and a high level of demurrage, whereas continuous deployment of two shiploaders results in inefficiency and high operating costs. This paper describes an approach for developing a strategy that considers a trade-off between the ship waiting cost and the cost of deploying the additional shiploader and results in the optimal deployment of resources. The approach is an integration of simulation, scenario building, and economic fundamentals. An actual bulk export terminal in Australia is used to demonstrate the applicability of this approach in assisting the port management in rational decision making.

A mathematical model is presented for calculating the change in volume and sand-bypassing rate at ebb-tidal shoals. Conceptually and mathematically, the ebb-tidal shoal is distinguished from bypassing bars that emerge from it and from attachment bars where the bypassing bars merge with the beach. The volumes and bypassing rates of these morphologic entities are calculated by analogy to a reservoir system, where each reservoir can fill to a maximum (equilibrium) volume. The ratio of the input longshore sand transport rate and the equilibrium volume of the morphologic feature is found to be a key parameter governing morphologic evolution. The analytical model gives explicit expressions for the time delays in evolution of the bypassing bar and the attachment bar, which are directly related to the delays in sand bypassing. Predictions of morphology change agree with observations made at Ocean City Inlet, Md. Examples of extension of the model by numerical solution are given for a hypothetical case of mining of an ebb-tidal shoal and for an idealized case of bidirectional longshore sand transport, in which updrift and downdrift bypassing bars and attachment bars are generated.

This paper presents a numerical model for long-wave interaction with vertically walled porous structures. Based on depth-integrated equations of motion, the model is suitable for weakly nonlinear, weakly dispersive transient waves propagating in both variable-depth open water and porous regions. Comparisons with experimental data for problems with one horizontal dimension show that a single choice of empirical parameters for hydraulic conductivity gives accurate numerical predictions for various sizes of rocks used in the construction of porous breakwaters. A rigorous experimental comparison of a porous breakwater gap shows that the numerical model is excellent in predicting the waveform and phase of the transformed wave. In this paper attention is focused on the reflection, transmission, and diffraction of solitary waves by a porous breakwater.

The behavior of the lutocline as a measure of fine sediment mixing in high-concentration estuaries is briefly examined with reference to the Jiaojiang estuary in China. A lutocline mixing index is introduced and shown to correlate empirically with the rate of turbulent kinetic energy production in such a way that with increasing energy production lutocline mixing increases. Suspended sediment concentration and energy production together govern the turbulent mixing length, hence lutocline mixing, which appears to be measurably modulated by sediment settling, interparticle interaction, and cohesion. Further understanding of lutocline response to tidal forcing will require direct and long-term measurements of turbulent fluxes, especially within the zone of lutocline occurrence and in the high-concentration suspension underneath.