Journal of Waterway, Port, Coastal, and Ocean Engineering

A previously developed model for nonhydrostatic free surface flow is adapted to simulate breaking waves in the surf zone. The model solves the Reynolds-averaged Navier-Stokes equations in a fraction step manner with the pressure split into hydrostatic and nonhydrostatic components. The hydrostatic equations are first solved with an approximate Riemann solver. This approach is particularly well suited for simulating discontinuous flow associated with breaking waves because the model prediction converges to the classical solution for a turbulent bore, which closely resembles breaking waves in the surf zone. The hydrostatic solution is then corrected by including the nonhydrostatic pressure. The model uses a sigma coordinate discretization in the vertical direction, which has been previously demonstrated to yield significant truncation errors with highly skewed grids over large bottom slopes. This potential problem is investigated in the context of highly skewed (but transient) grids that occur with steep breaking waves.

Numerical simulations of cross-shore wave transformation and associated wave setup were performed for 100,000 realistic combinations of wave height, period, and beach profile. Results of numerical simulations were compared with a widely used empirical predictor of wave setup, and the outcome was a large variability in setup relative to that calculated by the empirical predictor. The variability, comparable in magnitude to the scatter around the empirical predictor developed with field observations, arose from wave energy dissipation over the cross-shore profile that was not taken into account. The beach-face slope commonly used in empirical predictors can be a poor descriptor of wave transformation across the beach profile, where most of the wave energy dissipation and setup generation occurs. Shoreline setup appears to be far more dependent on accurate characterization of the offshore profile (e.g., bar location and depth) than the beach-face slope.

A 170 km tidal channel connects the lower Columbia River ports of Portland and Vancouver to the Pacific Ocean. An increasing incidence of low water levels during summer and fall sometimes limits the draft of ships using the channel and can delay transits. Reduced spring freshet water levels have also decreased shallow-water habitat for juvenile salmon. Records from Tongue Point (km-30, 1925-date), and Vancouver (km-175, 1902-date) were used to analyze historic changes. Mean water levels (MWL) at Vancouver have dropped $\sim 0.3–1.5\mathrm{m}$ since 1902, depending on flow. Lower low water (LLW) at the lowest river flows has decreased $\sim 0.4–0.5\mathrm{m}$ since 1940. Vancouver LLW has dropped more than MWL and higher high water (HHW), increasing tidal range. Tides in the Columbia and many other river ports are evolving because of a combination of changing ocean tides and local alterations, including both harbor development and river-flow modification. Assessments of climate change impacts on harbors need to consider both factors.

On the basis of the recently proposed boundary value problem for the nonlinear shallow water equations and the extension of its available solutions for swash zone flows, we propose regression curves for the prediction of the maximum runup and the maximum rundown induced by impulsive waves on a frictionless, uniformly sloping beach. This class of input waves is generally used to represent tsunami waves generated by seismic fault dislocations or submarine landslides. Therefore, they have important applications in the coastal engineering practice. Regression formulas are expressed as functions of both the wave height and the wave steepness and are validated through comparison with maximum runup laws and breaking conditions already available in the literature.

The fall velocity of fine particles was measured in a column of height 2.50 m and diameter of 0.30 m to model the settling properties of cohesive sediments in lakes and large reservoirs. In contrast to the traditional particle-size-based methods, an approach relying on time and depth variation of sediment concentration was employed to estimate the mean value of fall velocity at any depth and time. Particles at greater depths, particularly for the samples with a higher rate of sediment concentration, accelerated faster and remained at higher velocities for a longer duration owing to a higher rate of flocculation. As a particular property of cohesive sediments, particles for all concentrated samples and in all depths reached their maximum fall velocity at around the same time—15 min after the start of the tests. The low concentration samples reached higher maximum velocities because of the lower rates of hindering, but for a much lower duration in comparison to the higher concentrated samples. An empirical equation is developed to estimate the maximum fall velocity of particles for cohesive sediments where the ratio of flocculation to hindering is highest.