Journal of Waterway, Port, Coastal, and Ocean Engineering

To gain a better understanding of the wave forces that led to the failure of numerous causeway-type coastal highway bridges along the U.S. Gulf coast, a series of experiments was conducted on a realistic, 1:5 scale reinforced concrete bridge superstructure. The experimental setup is unique compared to other wave-in-deck studies in that the stiffness of the horizontal support system can be varied to represent different dynamic properties of the bridge system. The bridge specimen is subjected to a wide range of regular and random wave conditions at multiple water levels. In addition to measuring pressures and forces, the experiments measure the dynamic response of the bridge specimen using strain gauges, displacement sensors, and accelerometers. This paper presents the innovative experimental setup, and a preliminary analysis of the data showing the effect of wave height, wave period, and water level, on the forces experienced by the bridge superstructure.

During nine small-scale laboratory experiments simulating combined wave overtopping and storm surge overflow on a trapezoidal levee, time series measurements of flow thickness and velocity were acquired at a location on the levee crest and at a location on the landward-side slope. Flow thickness and velocity were combined to estimate time series of the instantaneous discharge. Comparisons of the calculated overtopping discharge time series at the two locations revealed that the time series of instantaneous discharge was the same at both locations with the only difference being a short phase lag. Individual peaks of the discharge time series were examined, and an empirical expression was determined for the root-mean-squared discharge peak. The largest discharge peaks were overestimated by the Rayleigh distribution. For locations on the landward-side slope where the friction slope is approximately the same as the levee slope, it is possible to derive a stream power probability density function based on the overtopping discharge cumulative exceedance probability. The stream power probability density function may be a useful tool for assessing erosion potential of overtopped earthen levees.

Wave-induced overwash of sand dunes may cause rapid profile changes and possible dune destruction, thus increasing the flood risk landward of dunes. Accurate modeling of the wave overwash processes is therefore essential in predicting dune profile evolution during overwash events. However, available field and laboratory data are very limited. We measured dune profile evolution and overwash transport rates for three tests with different initial dune geometries in front of a low-crested vertical wall exposed to the same wave conditions in a wave flume. In all three tests, the transition from minor to major overwash occurred rapidly but the resilience of the dune against destruction depended on its initial geometry. During minor overwash, offshore sediment transport caused most of the dune crest lowering. These tests are used to assess a numerical model for wave overtopping and overwash of a dune. The numerical model is shown to be in agreement with the measurements of the free surface elevations, fluid velocities, and dune profiles. However, beach erosion in front of the exposed wall is underpredicted.

Singularities play a significant role in the characterization of time series. The temporal characteristics of fluctuating significant wave height time series are investigated in this study. The hourly time series from 24 stations located off the west coast of the United States are used for the analysis. The multifractal nature of these time series is unveiled by employing a wavelet-based method. The wavelet transform modulus maxima method is applied to obtain the multifractal spectra (singularity spectrum) of the significant wave height series. The multifractal spectra and their parameters such as peak, min and max Hölder exponents, skewness coefficients, and support lengths are calculated. The peak Hölder exponent ranged from 0.30 to 0.46 throughout the study area. Hölder exponents that are less than 0.5 indicate that the time series exhibits an antipersistent random walk. The spatial variation of parameters is depicted through kriging maps. Different spatial variation patterns can be seen from the maps. It is clear that deep offshore stations have relatively higher Hölder exponents than coastal areas. This change can be related to the wave generation mechanism, by way of physical interpretations. Since the stations located in the deep offshore can receive more swell waves than coastal zones and are open to large-scale storms, they may tend to be more persistent and have greater Hölder exponents. Also, the type of the singularities occurring in deep offshore and in the coastal zones is assessed by considering the wave generating mechanisms.