Journal of Waterway, Port, Coastal, and Ocean Engineering

A simple method is developed for representing wave refraction and shoaling in the vicinity of a beach‐nourishment project. The method applies for the case of a one‐line model of shoreline evolution in which the active profile is displaced seaward or landward without change of form. The model can include the presence of shore‐perpendicular structures and background erosion. It is recommended that shoreline modeling of beach‐nourishment projects be carried out by conducting an ad hoc transformation in which the preproject contours are represented as straight and parallel. The simple method is compared to the results of a one‐line model, which includes a more detailed grid‐based refraction and shoaling algorithm. For all cases tested, the simple method of representing refraction and shoaling results in shoreline evolution in good correspondence with the detailed method. The models are used to illustrate the effects of several features of beach‐nourishment projects of engineering interest, including: shore‐perpendicular structures placed at the ends of a project with background erosion; and nourishing with material more and less transportable than the native.

Diversion boom approaches are developed to contain oil spills close to shore when high‐current velocities prevent normal booming operations. In the diversion boom configuration, one end is anchored outside the spill, while the other is secured to shore. The boom is angled to the current to deflect the oil towards a shore pickup point. Boom configuration (planform shape) must be designed for each site‐specific current environment to prevent leakage under the boom. A mathematical model relating mooring points, boom parameters, and current is developed, calibrated, and validated. The model is applied, as a representative example, to the design of a boom configuration for the Northeast Petroleum terminal on the Piscataqua River, N.H. Current information is obtained, and trial configurations are evaluated employing the model and using a leakage criterion of 0.31 m/s (0.6 knots) for the maximum normal component of current. The recommended design is found to behave as predicted in a demonstration experiment (without oil). Thus, the model and design procedures are observed to be suitable for diversion configuration design in high‐speed currents.

A finite element computer modeling system called TABS‐2 has been developed by the U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. TABS‐2 has been used to model shallow water flow in estuaries. Accurate modeling of the flow in estuaries using TABS‐2 requires the use of very large two‐dimensional finite element meshes. The task of constructing such meshes has traditionally been the most time‐consuming and error‐prone part of the modeling process. Most automatic mesh‐generation schemes are not well suited for estuarine modeling because the regions modeled are typically highly complex and irregular. As a result, the meshes are often constructed manually by coding the mesh in an ASCII file. Manual construction of large meshes is very tedious and can take several weeks to complete. To overcome this difficulty, a mesh generation scheme well suited for estuarine modeling has been developed involving a trian‐gulation algorithm and a variety of mesh editing tools. The scheme makes it possible to generate large meshes of several thousand elements in a relatively short period of time. In addition, the scheme results in meshes with favorable geometric properties, leading to stability and accurate solutions.

A small‐scale experimental study was performed to investigate wave runup on rigid full‐length and truncated circular cylinders under regular and random sea conditions. Wave elevations were measured around one‐half of the cylinder circumference together with the total in‐line wave force. The regular wave data were compared with predictions obtained using linear diffraction theory, and the results were consistent with the findings of earlier researchers. A regression analysis was performed on the regular wave data to obtain a relationship between the wave runup and the velocity head. The resulting empirical equation can be used to make preliminary estimates of wave runup on truncated circular cylinders. An approximate formula for predicting the time‐dependent wave force on a truncated cylinder is presented. Transfer functions relating the enhanced wave‐surface‐elevation spectrum and the wave‐force spectrum to the incident‐wave spectrum are derived. The validity of the wave‐force approximation and the adequacy of the linear transfer functions are examined in light of the new experimental data. As in the case of regular waves, the random‐wave spectrum model does not adequately predict the root‐mean‐square (RMS) surface elevation at the front of the cylinder, but does provide a reasonably good estimate of the wave force on full‐length and truncated cylinders. Extreme value estimates based on standard statistical procedures are compared with the experimental data and generally found to be conservative.

A model is developed for tidal flushing of a small, well‐mixed embayment, based on the classic tidal prism flushing formation. Both a flushing expression and a steady‐state concentration expression for a nonconservative tracer are derived. The return flow factor is identified as an important, but previously poorly constrained, input to the flushing model. A model for estimating the return flow factor is derived considering the fate of the plume of effluent water, which exits the embayment mouth on ebb tide, mixes with coastal waters, and partially returns to the embayment on flood tide. The predicted return flow factor depends primarily on the relative phases and speeds of the embayment channel currents and coastal currents and on the amount of mixing that occurs outside the embayment. The return flow factor model is solved for a range of representative cases, and the results are plotted for reference. The complete flushing model is compared to the results of a dye study performed in a marina basin in Indian River Bay, Del., with favorable results.