Journal of Waterway, Port, Coastal, and Ocean Engineering

This study examines the estimated tsunami loads on five California coastal bridges. The quantities of interest include the horizontal and vertical forces and overturning moment. The simulations and analysis are conducted for two stages: (1) initial impact and overtopping and (2) full inundation. The first stage starts from the time when the tsunami water free-surface elevation reaches the low chord of the bridge superstructure, the water free surface rises and reaches the top of the bridge barrier where it overtops the bridge and starts to flow on the bridge deck, and until the bridge is totally inundated. The second stage occurs when the bridge first becomes fully inundated, i.e., end of the first stage, and until the most critical events, (1) the maximum tsunami water velocity, (2) the maximum tsunami momentum flux, and (3) the maximum tsunami mass flux, have occurred. The first part of the initial impact and overtopping stage leads to a combination of lateral (horizontal) and uplift (upward vertical) forces. The maximum uplift force during Stage 1 is found to occur when the tsunami water free-surface elevation reaches the top of the bridge barrier right before the water overtops the bridge and starts to flow onto the bridge deck. It is observed that the time interval representing the initial impact of the tsunami on the bridge superstructure leads to the maximum horizontal force, downward vertical force, and overturning moment. The overall maximum uplift force is found to be in tsunami scenarios in which the bridge superstructure is totally inundated, i.e., in Stage 2, if total inundation actually occurs. Analyzing a deck-girder bridge with a failed, i.e., removed, first seaward girder shows a 15% reduction in the maximum horizontal force. The uplift force is found to be approximately 25% larger for the bridge with a failed first girder. A design procedure is proposed to compute the maximum horizontal and vertical forces on bridge superstructures based on the simulation results. Good agreement between numerical predictions and formula estimations of the tsunami forces is observed. The proposed design procedure is intended to provide estimations of tsunami loads on bridge superstructures.

The response of physical models of beach profiles to random breaking waves was studied to investigate size-selective sediment transport and cross-shore profile evolution. Three types of beach profiles with different sediment mixtures were considered and subjected to waves until profiles reached equilibrium. Size-selective sediment transport was evident in the experiments, with the mean sediment size varying up to 20% along the beach profiles. Consistent coarsening and fining of the surface sediment in the experiments revealed size-selective sediment transport governed by cross-shore variations in energy dissipation, affecting important beach profile features such as sandbar structures and offshore and foreshore slopes. The theoretical basis of the transport phenomenon was described by analyzing the relationship between the transport processes and essential wave and hydrodynamic parameters obtained using a new set of numerical models. The results showed that beach profile changes and associated sediment grain sorting are most sensitive to instantaneous total water velocity and local energy flux under propagating waves.

Beach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations.

A dike erosion model is developed to predict the temporal and cross-shore variations of vertical erosion depth under irregular wave action. The product of the erosion rate and the turf resistance force is related to the rate of erosion work by turbulence generated by wave energy dissipation caused by wave breaking and bottom friction. The turf resistance force is expressed using the turf thickness and the surface and underneath resistance parameters. The empirical parameters are calibrated using available data. The calibrated model is shown to reproduce the relation between the limiting velocity and steady flow duration, the erosion rate on a seaward grassed slope, and the eroded profile evolution of a seaward clay slope. The turf resistance parameters are uncertain and will need to be calibrated for specific dikes.

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours.

This paper presents the results from several experiments aimed at determining the effectiveness of combined caissons with an internal rubble mound to dissipate incident sea wave energy. Techniques for assessing the reflection coefficient from wave tank data are discussed via a comparison between the established two- and three-probe methods and a new method using four probes. It is shown that obtaining reliable results for the incident and reflected waves requires the determinant of the linear system derived from the Fourier transform to be sufficiently greater than zero. This requirement was always satisfied for the three- and four-probe methods, but it was not always satisfied for the two-probe method. The experiments showed that the calculated reflection coefficient decreased when the ratio of the water depth, $D$, to the wavelength, $L$, increased. Increasing the caisson chamber width $b$ and the upper frontal opening $h$ also substantially decreased the reflection coefficient. Plotting the reflection coefficient as a function of $b/L$ shows that, to keep the reflection coefficient lower than 0.4, the $b/L$ ratio must be greater than 0.15. The effects of a slight variation of the still water level, such as those caused by tides or climate changes, were also analyzed. If the geometrical dimensions are appropriately designed, then the combined caisson can be effective for rising water levels. This occurs when the water level rise leads to an increase of the surface exposed to the armor layer.

The spatial variation of damage on different sections of the trunk and head of a low-crested stone structure on a fixed bottom is examined using a cross-shore numerical model extended to oblique waves. The computed wave transmission coefficient and damage on the front slope, back slope, and total section of the trunk are compared with available data consisting of 188 tests. Similarity of trunk and head damage for a low-crested breakwater is proposed to predict damage on the front head and back head using the numerical model. The agreement is mostly within a factor of 2; however, the model overpredicts damage on the back head of a submerged structure. An experiment was conducted in a wave flume for a low-crested stone structure located inside the surf zone on a sand beach. The model is shown to reproduce the measured cross-shore wave transformation on the beach with and without the structure as well as the measured small damage on the structure. Sand deposition inside the porous structure will need to be accounted for in order to predict toe scour and accretion.

Hopper sedimentation is the result of precipitation of typically fine sediment from a homogenous, high-concentration mixture, which is not completely deficient of turbulence. If hopper sedimentation or loading is accomplished through a single-inflow system, or if the irregularity of the inflow concentrations is pronounced or simply terminated, then the hopper mixture will clear. Whereas turbulent mixing is redundant, when the mixture is homogeneous, it may take an active role when the mixture is clearing. The role of turbulence on hopper sedimentation has been the focus of several studies, and a common perception of turbulence (or at least of mixing) is that it delays sedimentation. Existing measurements of sedimentation rates in a closed-flume experiment, engineered to provide input to a hopper sedimentation model, revealed that turbulence in a clearing mixture is not necessarily associated with a delay in sedimentation. The experiment showed that sedimentation was boosted by adding a current to a clearing mixture, which infers that turbulence, under certain conditions, may act as a sedimentation agent on the excess sediment in suspension. Therefore, the interactions between turbulent mixing and settling in high-concentration mixtures were examined theoretically. Analytical solutions for clearance of excess concentrations were derived for the limiting cases of (1) still-water clearance and (2) clearance when the amount of turbulence is abundant. When examining these analytical solutions, a potential for enhanced sedimentation was revealed. It was found that mixing-induced dilution of concentration weakens the hindrance in settling to a degree that enhances sedimentation. The analytical findings prompted a more elaborate analysis of the mechanism using a numerical model, which encompassed time- and depth-varying turbulence. This allowed the experimental setup and the observed settling effects to be simulated. The potential of the enhancing sedimentation mechanism was analyzed under more general conditions with the numerical model.