Journal of Waterway, Port, Coastal, and Ocean Engineering

A tidal bore is a wave propagating upstream as the tidal flow turns to rising. It forms during spring tide conditions when the flood tide is confined to a narrow funneled channel. To date, theoretical and numerical studies rely upon physical experiments to validate the developments, but the experimental data are limited mostly to visual observations and sometimes free-surface measurements. Herein turbulent velocity measurements were obtained in a large-size laboratory facility with a fine spatial and temporal resolution. The instantaneous velocity measurements showed rapid flow deceleration at all vertical elevations, and large fluctuations of all velocity components were recorded beneath the bore and secondary waves. A comparison between undular (nonbreaking) and breaking bores suggested some basic differences. In an undular bore, large velocity fluctuations were recorded beneath the first wave crest and the secondary waves showing a long-lasting effect after the bore passage. In a breaking bore, some large turbulent stresses were observed next to the shear zone in a region of high velocity gradients, while some transient flow recirculation was recorded next to the bed. The effects of bed roughness were tested further. The boundary friction contributed to some wave attenuation and dispersion, and the free-surface data showed some agreement with the wave dispersion theory for intermediate gravity waves. The instantaneous velocity data showed however a significant effect of the boundary roughness on the velocity field next to the boundary $\left(z/d_o<0.2\right)$ for both undular and breaking bores. Overall the findings were consistent with field observations of tidal bores and highlighted the significant impact of undular (nonbreaking) bores on natural systems.

A probabilistic hydrodynamic model for the wet and dry zone on a permeable structure is developed to predict irregular wave action on the structure above the still water level. The model is based on the time-averaged continuity and momentum equations for nonlinear shallow-water waves coupled with the exponential probability distribution of the water depth. The model predicts the cross-shore variations of the mean and standard deviation of the water depth and horizontal velocity. The model is compared with four test series in which measurement was made of the wave overtopping rate and probability as well as the water depth, velocity, and discharge exceeded by 2% of incident 1,000 waves. The agreement is mostly within a factor of 2. Damage progression of a stone armor layer is predicted by modifying a formula for bed load on beaches with input from the hydrodynamic model. The damage progression model is compared with three tests that lasted up to 28.5 h. The model predicts the eroded area of the damaged armor layer well but overpredicts the deposited area because it does not account for discrete stone units deposited at a distance seaward of the toe of the damaged armor layer.

A model for the production of isovel contours in a normalized form, which can be used for estimation of discharge in artificial and natural channels by using a single point of measurement, has been introduced previously by Maghrebi in 2006. Herein, for the first time, application of the model to a tidal river with partially reverse flow, which is caused by opening a sluice gate located asymmetrically close to the right bank of the Ohta floodway in Hiroshima, Japan, is presented. An acoustic Doppler current profiler was used to measure the velocity profiles at different verticals (with several points at each vertical) and then discharge was calculated. In addition, estimated discharge based on each measured point with the aid of the model was obtained. For the measured points away from the low magnitude of isovel values, the predicted discharges are comparable with the measured one. Due to the fluctuations of the measured velocities, instead of a single point of measurement, vertical and horizontal groupings of the measured points were used to estimate the discharge. It is generally proposed to select the measured points from the regions with the corresponding high values of isovels in the range of $u/V<-0.5$ and $u/V>0.5$ . The overall results have shown that minimum errors are associated with the horizontal groupings.

A two-dimensional time domain, fully nonlinear numerical wave tank (NWT) based on potential theory, the mixed Eulerian-Lagrangian approach, and the boundary element method was developed and applied to land-based oscillating water columns (OWCs) with compressed air inside the chamber. The nonlinear free-surface condition inside the chamber was specially devised to represent both the viscous effect of the water column motion and the pneumatic effect of the time-varying pressure. The latter not only influenced the water column motions, but also generated radiated waves to interfere with incident and reflected wave fields. Both linear and quadratic models are used for the viscous and pneumatic effects. The regular-wave cases are also compared with irregular-wave cases. The developed NWT was verified through comparison with viscous-flow-based numerical and experimental results for both narrow-gap and wide-gap chambers at two different skirt depths, with and without air ducts. All of the NWT simulations correlated well with experimental values for a variety of wave and chamber conditions, so that the developed numerical tool can be practically used for the optimal design of land-based OWCs. The fully nonlinear simulations were also compared with linear simulations. In case that had the same skirt depth and air duct area, the efficiency of the wide-gap chamber was generally higher than that of the narrow-gap chamber over a wider range of wavelengths, due to the larger amount of compressed air and the corresponding higher flow velocities.

Traditionally, solitary waves are generated in the laboratory setups using the Goring’s methodology that considers a wave of permanent form during the generation process. In this study, we propose a new methodology for solitary wave generation using piston-type wavemakers by considering the evolving nature of the wave during the generation process. This proposed methodology is tested by conducting a series of experiments in a wave tank. In the experiments, generation of solitary wave profiles predicted by Boussinesq’s and Rayleigh’s theoretical solutions are accomplished using both the New and Goring methodologies. Waves generated using the Goring methodology served as a benchmark to assess the performance of the proposed New methodology. Comparisons of experimental observations and theoretical solutions for various wave characteristics have shown that the New methodology is capable of generating more accurate solitary waves with less attenuation as waves propagate compared to the Goring methodology. Proposed solitary wave generation methodology is expected to be useful in various laboratory investigations to study different aspects of long wave theories and to simulate tsunamis and internal waves, among others.