Journal of Waterway, Port, Coastal, and Ocean Engineering

Probably the best set of observations of wave growth in shallow water presently available has been acquired in 1996 by Young and Verhagen in Lake George, Australia. These observations were taken during nominally ideal conditions of a constant wind, in fetch-limited conditions, over water with a constant depth (wind from the North or South, along the main axis of the elongated lake). However, we found a north-south stratification in the data that Young and Verhagen ignored. This stratification suggests that the wave growth was affected by the tapering of the lake in southern-wind conditions but not in northern-wind conditions (when the upwind lake is wider). This interpretation was supported by computations with a numerical wave model. We therefore removed the southern-wind data and reanalyzed the northern wind data to reformulate the growth curves for the significant wave height and peak period. For young sea states (relatively deep and transitional water depths), we find considerably higher (by 30%)—but not longer—waves than the original authors, in agreement with a widely accepted compilation of other wave growth data. For fully developed conditions (in shallow water), our results agree well with those of the original authors.

The storm surge generated by Hurricane Hugo (1989) is reproduced for the purposes of (1) evaluating the significance of including inland flooding areas and corresponding levels of spatial resolution and (2) assessing the spatial variability of near-inlet boundary forcings with respect to storm surge hydrographs. The study focuses on the coastal regions of South Carolina, incorporating inundation areas between Charleston and Shallotte Inlet and including Winyah Bay and the Waccamaw River. The region of interest is modeled with five variations of an unstructured, finite-element mesh, including a localized coarse grid with and without floodplains, a localized fine grid with and without floodplains, and a large-domain approach that includes floodplains and the continental shelf and deep ocean. Simulation results demonstrate that the inclusion of inland flooding areas significantly improves the description of storm surge generation within coastal regions. While the large-domain approach is shown to be beneficial, it is determined that the coarse mesh resolution of the floodplains is sufficient. Computed water surface elevations at specific locations surrounding Winyah Bay Inlet indicate that storm surge hydrographs are highly spatially dependent near inlets, as opposed to the astronomical tides, which exhibit minimal variance in space around the inlet environment.

The first detailed observations of the motion and loading of a mussel (shellfish) aquaculture long-line are described in order to identify the dominant modes of flow-structure interaction and provide a baseline for prediction of future structures. A long-line is typically a $120\mathrm{m}$ long sequence of surface floats beneath which is looped rope bearing the mussel crop. Accelerometer and load cell data from sensors mounted on the structure along with remote radar data are examined in the context of wave and current measurements. The mussels comprise the largest mass and drag element of the structure, and the tidally affected pretensioning of the mooring lines dominates the background load. However, waves and currents increase the maximum load by potentially 100% over this value. The floats at each end of the long-line follow the wave orbital motion reasonably well, more so than the floats in the middle of the backbone. The mussel-laden loops of rope (droppers) clearly respond differently to the floats, implying flexibility in the vertical dimension. This suggests that flow around the droppers, which influences mussel feeding ability and hence production, is complex and highly three-dimensional.

This paper reviews the feasibility in function and design of an alternative to the jetty-hardened coastal inlet to develop tidal exchange between the ocean and an estuary. The proposed alternative is a subseabed (buried) tidal siphon. The proposed siphon will be best suited for inlets where navigation is not required and a tidal lag can be tolerated. The four main objectives of this paper are: (1) to present the immediate reasons for coastal inlet closures; (2) to identify the tidal exchange best suited for the tidal siphon; (3) to determine the shallowest functional depth of the inlet/outfall; and (4) to evaluate the hydraulic performance of the designed tidal siphon. It was determined the best tidal exchange for the tidal siphon is in the lower one-third of the stable tidal prism, the stability prism, and the reasonable depth for the offshore inlet/outfall structure is the depth of closure. Based on an analytical evaluation, the tidal siphon as designed preformed as required. Collection of field data included offshore wave height and length, turbidity as a function of elevation from the oceanbed, tidal range in the lagoon and tidal lag as a function of offshore tide, and inlet velocity as a function of tidal phase. The estuary used in this study is a recently constructed tidal inlet at the Batiquitos Lagoon in Carlsbad, Calif.

Although detached, low-crested breakwaters are frequently employed for beach stabilization, no design tool is available nowadays that reliably predicts the transmissivity of these structures for a wide range of engineering conditions. With this in view, the paper presents a semiempirical model where the predictive equations have been obtained starting from a crude schematization of the physical processes that govern wave transmission. The obtained results are encouraging and show good agreement with a large ensemble of experimental data.

In this note, partially discontinuous elements are employed to solve the singular integrals in the simulation of waves in a numerical wave tank. A higher-order boundary element method (HOBEM) is employed in combination with a time-marching method to solve the system of partial differential equations. By using a predictor–corrector time integration scheme, we solve an integral equation at each time step by uncoupling the kinematic and dynamic free-surface conditions. Different progressive wave types are used at the inflow boundary, a special form of the Sommerfeld/Orlanski type open boundary condition is employed at the outflow boundary, and linear regular and irregular waves have been simulated. The results show that the adopted HOBEM, along with the open boundary condition, is accurate and robust, and furthermore, results have been obtained for a nonlinear Stokes wave.

Tension leg platforms (TLPs) are compliant-type offshore structures generally used for deepwater oil/gas exploration. Dynamic analysis of three triangular TLP models under regular waves is presented, considering the coupling between various degrees of freedom. The analysis considers various nonlinearities developed due to change in tether tension, change in buoyancy, and hydrodynamic drag force. The hydrodynamic characteristics of the wave loading on the structure are computed using Airy’s wave theory and Stokes’ fifth-order theory. The hydrodynamic coefficients $C_d$ and $C_m$ vary along the water depth. The low frequency drift response and the high frequency springing response are not considered in the present study. The equation of motion has been solved in time domain using Newmark’s integration scheme. Numerical studies are conducted to compare the coupled response of triangular TLPs under regular waves using Airy’s wave theory evaluated with Chakrabarti’s modification and that obtained by using Stokes’ fifth-order nonlinear wave theory. Results show that the coupled response in surge and pitch degree of freedom obtained using Stokes’ theory is lesser than that obtained using the Airy’s theory. Additionally, the presence of current in the wave field increases the responses in all degrees of freedom in all the cases taken for the study.

The bed sediments in most rivers and estuaries usually consist of mixtures of sand and mud formed by silt and clay particles. Past studies of mud have focused mainly on the cohesive properties of the mud due to the presence of clay particles. Only limited attention has been given to the erosion behavior of mixtures of sand and noncohesive silt particles. Although a number of experiments have shown that the presence of silt particles in predominantly sand bed results in an increase in the critical shear stress of sand fraction, the mechanism responsible for this change is not clear and no general formula is available for prediction. In this note a simple two-fraction formulation is presented for determining the relative critical shear stress of sand fraction in a noncohesive sand-silt mixture. The formulation is broadly consistent with the mechanism that the presence of silt causes the changes in bed roughness with corresponding reduction of shear stress exerted on the sand particles. The calculated relative critical shear stresses for the sand fraction at varying silt contents and the mean silt particle sizes show good agreement with the available experimental data.