Journal of Waterway, Port, Coastal, and Ocean Engineering

An absorbing-generating boundary condition is derived for the two-dimensional-horizontal nonlinear shallow equations using the method of characteristics. It assumes local superposition of the incoming and outgoing long waves at the boundary, and uses a relationship between the flux and surface elevation of the waves. This boundary condition allows the outgoing waves to leave the computational domain through the boundaries with a minimum of reflection, while specifying incoming waves at the same boundaries. The boundary condition's absorbing properties are tested for both linear and nonlinear waves for a range of amplitudes and of angles of incidence. Its performance is compared to the classical Sommerfeld radiation condition for the linear case and is shown to cause significantly less reflection errors, especially for oblique angles. Also, a case of simultaneous absorption and generation of waves at the same boundary is analyzed where it is shown that the errors are of the same order as for the case of absorption only. Finally, the boundary condition is extended to include known currents.

Time series of wave, mean current, tidal stage, and wind data collected at Perdido Key, Fla. are analyzed to assess the influence of a large, dredged, microtidal inlet with sizeable shoals on the surrounding wave conditions. The relative importance of different wave transformation processes is addressed, with the aim of providing practical guidelines for modeling wave transformation numerically. A monochromatic wave transformation model that includes wave shoaling, diffraction, breaking, and refraction due to both bathymetric gradients and horizontal gradients in tidal currents is tested against the field data. A two-dimensional (2D) (vertically averaged) hydrodynamic model is used to specify the mean flow, which serves as one input to the wave model. The wave model yields wave heights that, on average, compare well with measurements (within 1%, on average), but produces high spatial variation in wave direction, where waves propagate along a contour. Neglect of wind in the model is suggested to be one reason for the scatter evident in comparisons between measured and modeled wave conditions. Wave conditions west of Caucus Shoal, on the west side of Pensacola Pass, are governed primarily by wind and bathymetric control. Tidal currents exert little influence on waves outside of the shoals that flank the inlet.

Goa has a 125-km-long coastline of which two-thirds consists of beautiful sandy beaches. There are mainly 17 beaches having significant importance of tourism. Sporadically, surf drownings have been reported at a few stretches of the beach. Longshore currents were measured at 2-week intervals from November 1993 to October 1994 along these beaches to identify the zones of strong longshore currents and rip currents. Entire beaches were found to be unsafe for swimming during the southwest monsoon season. Parts of stations 5 and 6 in Harmal beach, 16 at Vagator beach, 51–54 at Miramar beach, 75 and 76 at Valsao beach, 84 at Majorda beach, and 116 at Palolem beach are observed to have the risk of permanent rip current zones; and they are unsafe places for swimming all through the year. Parts of Colva, Benaulim, and Agonda beaches, which are suitable for surf swimming, are identified.

In the sheetflow regime, the concentration of the sediment is so high that particle/particle interaction plays an important role. In this study, a numerical simulation of the sediment transport in the sheetflow regime is performed on the basis of the Distinct Element Method (DEM) with a focus on particle/particle interaction. The characteristics of the vertical velocity profile of sediment particles in the sheetflow regime, which were reported in previous experiments, are reproduced well by the present simulation. Furthermore, the mechanism to determine the velocity profile of the sediment particles is clarified from the viewpoint of the granular material dynamics. Finally, the half-cycle averaged sediment transport rate under an action of sinusoidal oscillating flow is estimated from the result of the simulation under the quasi-steady assumption and is compared with the result of previous experiments.

Japan's Kobe Port was severely damaged during the Hyogoken Nanbu Earthquake of January 17, 1995, suffering a nearly total loss of operations and direct losses estimated to be about $5.5 billion. This paper summarizes the causes of this damage, and uses this experience as a case study to show that the economic benefits of including seismic risk reduction methods in the design and construction of ports in areas of moderate-to-high seismicity can far exceed the increases in initial construction costs. The paper also describes and illustrates an “acceptable seismic risk” evaluation procedure for assessing the viability of alternative seismic risk reduction strategies for a given port.

Two simple numerical models are presented to estimate the root-mean-squared velocity for random nonbreaking waves obliquely incident on partially reflecting coastal structures. The structures considered are vertical permeable structures with a free surface or crowned. The models are also capable of simulating the case of an impermeable vertical wall. Results depend on the input spectrum, breakwater geometry, and porous material characteristics. All this information is considered in the calculated complex reflection coefficient, which has information not only on the modulus of the reflection for each of the wave components, but also on the reflection-induced phase shift.

A new kinematic undertow profile model is developed to relate the mean horizontal velocity, bottom shear stress, and boundary layer thickness in a simple but general manner. The model combines a logarithmic profile in the bottom boundary layer with a parabolic profile in the interior layer. Use of a logarithmic profile is justified using our laboratory measurements for regular waves spilling on a rough, impermeable slope. Two forms of the model are presented, each with one calibration coefficient associated with the mean bottom shear stress. By adjusting the calibration coefficient at each measuring line, the model is shown to be capable of predicting the measured undertow profiles both inside and outside the surf zone for our rough slope case and for smooth slope cases from the literature. The model does not predict the overshoot in the bottom boundary layer for the rough slope case outside the surf zone. The predicted velocity profile for the smooth slope case in the bottom boundary could not be verified due to a lack of data. The predicted boundary layer thickness agrees with the measurements for the rough slope case and appears to be reasonable for the smooth slope cases. The model predicts the shear velocity in the transition region and inner surf zone reasonably well for the rough slope case, and it underpredicts the shear velocity outside the surf zone. This model is shown to be simple and versatile, but it will need further validation using irregular wave data and varying bottom geometry before it can be used in practical applications.