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Waterborne debris impacts during inundation events are a widely observed threat to structures in coastal communities. This study investigates the probability of impact and magnitude of wave–current (N = 1,170) and current-only (N = 156) debris events on exposed and sheltered buildings within a 10 × 10 building array, using laboratory measurements of structural loading response, flow hydrodynamics, and video recordings of flow transport and impact. A methodology based on a structural system with a single degree of freedom is implemented to estimate the applied debris impulse from collisions and to investigate the dynamic impact of waterborne debris on structures. Results show that the debris collision probability varies greatly, between 42% for unsheltered rows and 2% for nine rows of sheltering. Given a collision, the normalized debris impulse in sheltered buildings is at maximum 0.8 times the impulse for unsheltered conditions, and this reduction increases as the number of sheltering rows increases. Using empirical exceedance probabilities of the applied debris impulse, a framework is developed to estimate the maximum structural loading response within a building array, along with a comparison with data and existing standards. The effect of the impact duration on the relation between the applied debris impulse and the maximum structural response is also discussed. [ABSTRACT FROM AUTHOR]

A probabilistic framework is presented for evaluation of hurricane wave and surge risk with particular emphasis on real-time automated estimation for hurricanes approaching landfall. This framework has two fundamental components. The first is the development of a surrogate model for the rapid evaluation of hurricane waves, water levels, and run-up based on a small number of parameters describing each hurricane: hurricane landfall location and heading, central pressure, forward speed, and radius of maximum winds. This surrogate model is developed using a response surface methodology fed by information from hundreds of precomputed, high-resolution Simulating Waves Nearshore ( SWAN) + Advanced Circulation Model for Oceanic, Coastal and Estuarine Waters ( ADCIRC) and One-Dimensional Boussinesq Model ( BOUSS-1D) runs. For a specific set of hurricane parameters (i.e., a specific landfalling hurricane), the surrogate model is able to evaluate the maximum wave height, water level, and run-up during the storm at a cost that is more than seven orders of magnitude less than the high-fidelity models and thus meets time constraints imposed by emergency managers and decision makers. The second component of this framework is a description of the uncertainty in the parameters used to characterize the hurricane through appropriate probability models, which then leads to quantification of hurricane risk in terms of a probabilistic integral. This integral is then efficiently computed using the already established surrogate model by analyzing thousands of different scenarios (based on the aforementioned probabilistic description). This allows the rapid computation of, for example, the storm surge that might be exceeded 10% of the time based on hurricane parameters at 48 h from landfall. Finally, by leveraging the computational simplicity and efficiency of the surrogate model, a simple stand-alone PC-based risk-assessment tool is developed that allows nonexpert end users to take advantage of the full potential of the framework. The proposed framework ultimately facilitates the development of a rapid assessment tool for real-time implementation but requires a considerable upfront computational cost to produce high-fidelity model results. As an illustrative example, implementation of hurricane risk estimation for the Island of Oahu in Hawaii is presented; results demonstrate the versatility of the proposed approach for delivering accurate tools for real-time hurricane risk estimation that have the ability to cross over technology adoption barriers. [ABSTRACT FROM AUTHOR]

Observations of wave properties during Hurricane Ike are presented for eight temporary gauges in mean depths of 8.7-15.8 m over a 360-km section of coastline. These gauges cover both the strong (left) and weak (right) sides of the tropical cyclone, with one gauge immediately adjacent to landfall. Maximum significant wave heights are large over the entire section of the coast and reached 5.8 m near landfall but were at some locations significantly limited by the finite depths with significant wave height-to-depth ratios nearing 0.5 at landfall. Nondirectional spectral shapes changed sharply over the course of the storm, from strongly peaked profiles before landfall to much flatter, sometimes multipeaked, spectra as the hurricane came ashore. After landfall, the spectra on Ike's strong side reverted to the sharply peaked form, whereas the weak side spectra were broader and often had multiple peaks. No waves during the storm appeared to be in equilibrium with local winds and water depths, although heights on the strong side of the storm were close. [ABSTRACT FROM AUTHOR]

Often, nearshore radiation stresses are approximated using the monochromatic wave assumption, although this can have significant errors when the incident waves have finite frequency and/or directional spread. Consequently, the resulting wave-driven currents could be predicted erroneously or, when fitting to observations, biased model parameters such as the bottom friction coefficient may result. We develop and test a moments-based reduced spectral wave model which includes the leading order effects of wave frequency and directional spreading. This model solves the evolution equations of wave moments, which are integrations of the wave action balance equation multiplied by weighting functions over frequencies and directions. An assumption of analytical Gaussian distribution for the frequency-direction spectrum is made to develop a simple five-parameter system that contains information on the wave height, period, direction, frequency bandwidth, and directional bandwidth. Using this model, we investigate the finite bandwidth effects on the wave field and radiation stresses. The directional spreading is found to have a strong impact on the radiation stress, with a larger directional bandwidth resulting in smaller radiation stresses. However, the frequency spreading has much less impact. The spectral wave breaking based on the roller concept is considered in this wave model. After coupling with a circulation model based on the shallow water equations, simulation results compare favorably with the DUCK94 field data for waves and longshore currents but show strong dependence on the directional bandwidth. [ABSTRACT FROM AUTHOR]

Airborne bathymetric lidar surveys taken in Florida before and after the severe 2004 and 2005 hurricane seasons show infilling of seventeen dredged nearshore borrow pits. During these seasons, groups of pits captured volumes that were the equivalent of up to four years of net longshore transport, even though only one of the seventeen pits studied was inside the presumed depth of closure. Unsurprisingly, dimensionless infilling increased strongly with the ratio of wave height to pit depth. For open coast pits with large alongshore lengths, cross-shore infilling appeared to dominate over longshore infilling but both processes may be of comparable importance in shorter pits. Infilling of three borrow pits adjacent to ebb shoals was found to be considerably larger than on open coasts. Bathymetric changes in borrow pits occurred at greater depths than on nearby undisturbed profiles. Crude estimates of the long term infilling rates from tropical cyclones indicate that annual infilling volumes may be equivalent to more than one quarter of the expected net longshore transport at some locations. However, the episodic nature of hurricanes means that infilling events will be highly irregular. [ABSTRACT FROM AUTHOR]

The behavior of rip currents with changing bar and gap lengths was tested in a series of laboratory experiments using video-tracked floating drifters. Qualitatively, currents showed strong differences in overall character with changing topography. As narrow gaps became wider, the circulation tended to first travel parallel to the shoreline instead of immediately offshore, although strong offshore-directed flows were found for all topographies. Quantitatively, the width of the rip neck was found to increase slowly when compared to the increasing width of the rip channel. Maximum offshore and longshore velocities showed little dependence on bar or gap lengths, and were found to scale well with the predicted rate of generation of circulation. Finally, volumetric offshore flow rates through the rip channel showed no proportionality with the bar length as predicted by the mass transport hypothesis of rip current strength. [ABSTRACT FROM AUTHOR]

This paper describes nonintrusive optical techniques to measure large-scale O(10 m×10 m) flows in a laboratory wave basin. Numerous drifters with weak positive flotation are tracked discretely and automatically using a video camera mounted near the laboratory ceiling. Processed drifter tracks are used for dense estimates of mean surface currents over the visible area. Examination of the drifter tracks also shows that waves are imaged and therefore basic wave properties may also be estimated, although this requires some further assumptions. These video based flow observations are presumed to have less precision than in situ measurements; however, the density of measurements from the video far exceeds that which can be obtained using fixed instruments, providing the method’s major advantage. [ABSTRACT FROM AUTHOR]

Part I. Focuses on a study of the extension and testing of two sets of Boussinesq-type equations to include surf zone phenomena. Views on surf zone model; Model verification; General types of waves; Discussion and conclusion.

The article announces that the study paper "Numerical study of sandbar migration under wave-undertow interaction" by Jinhai Zheng and colleagues, published in the March/April 2014 issue has been chosen as the 2014 Best Paper Award winner by the editorial board of the periodical.