Journal of Waterway, Port, Coastal, and Ocean Engineering

A two-dimensional numerical model for the solution of the nonlinear shallow water equations (NSWEs) using the discontinuous Galerkin finite element method (DGFEM) is presented. A new adaptation of the thin-film approach is developed for the wetting/drying treatment. The model is applied to a number of test cases that can be characterized as swash flows, or as cases that are particularly useful for swash flow modeling. The DGFEM model shows robustness and provides accurate predictions of water depth, velocities, and shoreline movement. For the case of bore collapse on a plane beach the model performs well against a state-of-the-art finite volume swash code. The new wetting/drying algorithm is tested against a previous algorithm within the same framework for simulating a solitary wave propagating on a beach with bottom friction, showing a noticeable improvement in the shoreline prediction. The model is also tested against a more subtle test case, including generation of subharmonic edge waves, in order to test the effectiveness of DGFEM in reproducing second-order effects. The model simulates the excitation and development of the subharmonic edge waves when compared with the analytical solutions in the literature. Overall, it is shown here for the first time that the DGFEM technique can be used to simulate accurately a wide range of swash zone flows and therefore swash zone processes.

For the design of offshore wind turbines, the airgap height of a service platform above still water level (SWL) is dependent on the maximum level of wave run-up in seas. A number of laboratory model tests were carried out in a wave flume to evaluate and predict the wave run-up on a tripod foundation in regular and irregular waves. Comparison of the measured data with the predictions by existing methods revealed that the empirical formulae for wave run-up on monopile foundations cannot straightforwardly be applied to the tripod foundation for the sake of more complex structural geometry and associated hydrodynamics. Hence, the run-up coefficients m for measured regular and irregular wave run-ups are derived with the velocity stagnation head theory and then fitted against wave steepness. The hindcast results using the fitted m show good agreement with measurement, thus enabling fast prediction of wave run-ups on tripod foundations in practice. In addition, an exceptionally large wave-up has been recorded in the irregular wave tests, which affirms the occurrence of a similar phenomenon in Horns Reef 1 wind farm some years ago.

NavTEL is a new decision support tool for the short-term (36 h) planning of ship routes and the management of underkeel clearance in estuarine navigation channels. NavTEL uses a deterministic method and is coupled with the TELEMAC-MASCARET system for numerical modeling of hydrodynamic and sediment transport in the estuary with a two-dimensional approach. In its present version, NavTEL allows (i) daily simulations to be automatically prepared and launched; and (ii) simulation outputs to be postprocessed to find the safest ship route and to predict underkeel clearances at specified locations. As the reliability of the results relies on the accuracy of water-level predictions, numerical simulations were performed with measured river discharges, storm surge forecasts, and time-varying friction coefficients for bed roughness. Even though NavTEL was initially developed for the Atlantic Port of Bordeaux located in the Gironde Estuary, its kernel has a modular structure allowing the tool to be adjusted to different port configurations and types of water bodies. Finally, examples of graphical outputs and reports generated by NavTEL are shown for an application of a container ship coming into the port of Bordeaux.

The effects of sea level rise on storm surge energy transformation and flood and ebb current magnitudes are examined in two distinct New Hampshire estuarine systems. The Great Bay estuary is characterized by strong tidal dissipation along a long (13 km) and deep (20–25 m) rocky channel (ebb-dominated Piscataqua River) that connects to a large (flood-dominated) estuarine bay with extensive mudflat areas, whereas the (ebb-dominated) Hampton/Seabrook estuary has minimal tidal dissipation through a short (1 km) and shallow (5–7 m) sandy inlet that connects to an extensive salt marsh with narrow tidal channels. Numerical simulations are conducted using the finite-volume coastal ocean model (FVCOM) with forcing provided by the tides, with and without 0.01 annual exceedance probability storm surge estimated by the North Atlantic Comprehensive Coastal Study (NACCS) and further with and without sea level rise scenarios for year 2060 in Hampton/Seabrook (0.73 m) and 2100 in Great Bay (1.92 m). Results for the Great Bay estuary show that although the maximum sea surface elevation is higher during storm events, upstream linear wave energy loss (about 50%) of the storm surge with and without sea level rise is similar to tidal wave energy loss under present nonstorm conditions. Corresponding depth-integrated currents increase by 10%–30% with sea level rise, 23%–52% with the storm surge, and 32%–97% for the combined event. However, results from the Hampton/Seabrook estuary show that energy loss through the inlet increases from 2% to 4% for no storm and present-day sea level to 30%–40% for storm surge with sea level rise, partially mitigating inland inundation. Depth-integrated current magnitudes in the Hampton/Seabrook inlet increase by a factor of 4 under sea level rise and storm surge. Model results suggest that sea level rise has significant impacts on current speeds in both estuaries and that the energy decay of the tidal wave and storm surge depends on the nature of the estuarine system, with greater change associated with estuaries with shallow, narrow inlets somewhat reducing the effects of inland flooding.

The salinity distribution in the estuarine channel network of a partially mixed estuary was investigated by quantifying salt intrusion length and stratification with response to tidal circulation, seasonal variation, topography, and river discharge. The studied Karnafuli River estuary responds to a power-law relationship between discharges and salt intrusion lengths with exponent −0.64. In the river network, two salinity sinks were identified, that is, a river confluence and a channel bend. At the estuary, the surface salinity level during the dry period increased by 1.2–1.9 times that of the wet period due to residual salinity. On the other hand, the surface salinity level during the wet period decreased due to high river discharge. Again, a high salinity pulse was observed during flood tide and lower concentration was found in surface salinity during ebb tide. The spring–neap transition also causes salinity variation, reaching the lowest concentration at the end of the neap tide-wet period. Applying a subgrid scale Horizontal Large Eddy Simulation model in Delft3D, the spatial distribution of salinity showed that during flood tide the centrifugal force acted stronger than the opposing barotropic pressure gradient, and the centrifugal force moves the low-density water toward the river bend, which resists salinity intrusion. High salinity stratification was observed with high freshwater discharge and low stratification was found at a shallow water depth of the estuary. The surface salinity responds faster than the channel bottom salinity flux with changing forcing conditions (tide and discharge), while the bottom salinity circulation follows an unsteady process.

The September 28, 2018 earthquake and tsunami, which occurred north of Palu City, Indonesia, attracted widespread interest from the scientific community due to the unusually large tsunami that occurred after a strike-slip earthquake with a relatively small moment magnitude (M_W = 7.5). To understand the structural performance of buildings and infrastructure under hydrodynamic loads and their associated effects, the authors conducted field surveys in Palu City. Light wooden frame constructions and masonry infill walls were common in the area, some of which were severely damaged by the earthquake and tsunami. Reinforced concrete structures remained predominantly intact, although they suffered soil-related issues such as scour around rigid building members. Local structural failures caused by the loss of supporting soil were also observed during the field survey, resulting in an overall reduction in the stability of the inspected structures. Based on the observations made, knowledge gaps and research needs concerning coastal and structural scouring are discussed. These are tied into the latest community research activities and put in the context of a published ASCE standard chapter that discusses tsunami design.

In July 2018, Super Typhoon Maria moved in the northwestward direction, passed by the northern tip of Taiwan Island, and severely impacted the coasts along Fujian and Zhejiang Provinces, China. In this paper, the storm surge and wind waves induced by Typhoon Maria are numerically simulated using a weather research and forecasting (WRF) model and the wind–surge–wave modeling suite [semi-implicit cross-scale hydroscience integrated system model (SCHISM)—wind wave model III (WWMIII)]. Numerical results are compared against available field measurements, including winds, atmospheric pressures, storm tides, and wave parameters. Using the model results, the significance of waves on modulating storm surges during Typhoon Maria is examined. Wind waves contribute significantly to surge heights in the Taiwan Strait and in nearshore waters. The models are then employed to conduct numerical experiments by reducing the topographic heights of Taiwan to 25% of their original values so as to investigate their effects on wind fields, surges, and currents. From these results, we observe that reduced topography weakens the wind intensity on the eastern side of the island while intensifying the wind on the other side of the island by up to 10 m/s, which is due to the terrain-induced blocking and channeling effects. The scenario with reduced topography also shows elevated surge heights on the right-hand side of typhoon landfalling coasts but slightly attenuated surge in the Taiwan Strait. Storm surge tends to increase the southwestwardly flux via the Taiwan Strait with maximum current velocities increased by approximately 0.5 m/s, compared with the case induced by astronomical tides only. The reduced island topography slightly weakens the southwestwardly current, decreasing maximum flux by approximately 16%, relative to the hindcast simulation using the original island topography. The results in this study indicate that the presence of island influences the propagation of surge wave with elevated surge height and storm-induced flux in the Taiwan Strait, this blocking effect weakens with reduced island topographic heights; meanwhile, the terrain-induced channeling effect, which alters the typhoon circulation and further impacts the surge pattern, is prone to forming in the case of high island topography.

This paper presents a proof of concept that acoustic velocity and backscatter intensity measurements can provide essential information on ship wave–induced sediment transport processes in the littoral zone of a large river. Through a case study in the Hungarian section of Danube River, a combined application of an acoustic Doppler velocimeter (ADV) and a formerly calibrated acoustic backscatter sensor (ABS) is introduced for parallel measurements of 3D flow velocities and suspended sediment concentration (SSC) in a characteristic point of the near-bank zone. SSC times series detected by the ABS supported the calibration of the ADV backscatter, which eventually enabled the analysis of the temporal behavior of flow velocity and SSC conditions altered by ship waves. A suitable method for the separation of primary and secondary waves provided essential information on the turbulence intensities and sediment fluxes, and was found that the low-frequency primary waves are rather responsible for the lateral sediment transport instead of the dynamic secondary waves. The introduced data processing techniques and the main findings of the paper mean an important step toward the better understanding of the impacts of ship waves on the riverbanks, inherently playing a crucial role in the hydro-morphological and habitat conditions of river systems.

Tsunami waves are often very energetic and therefore pose a significant threat to coastal structures. However, most coastal defenses such as detached breakwaters are designed to protect against storm waves, with the consequence that tsunamis often lead to a catastrophic failure of these structures. This numerical study was inspired by the wave scenario, which occurred at Soma Port in Japan, during the 2011 Tohoku tsunami where a combination of tsunami-type waves and shorter period undular bores caused severe damage to a detached caisson breakwater. The objective herein is to analyze the role that undular bores play on breakwater stability in the case of a tsunami propagating over a gentle slope into shallow water. Two complementary wave models, one of Boussinesq type and the other of Reynolds-averaged Navier-Stokes (RANS) volume of fluid (VOF) type, are used to compute the propagation of a representative tsunami composed of multiple waves components and their impact on a detached breakwater. The presence of an undular bore is controlled by the balance between wave nonlinearity and dispersion. As the draw-down from the first wave reduces the water depth around the breakwater and leaves the structure almost completely exposed, only the second wave transforms into an undular bore. This causes wave breaking far offshore from the breakwater where a large amount of energy is dissipated ultimately resulting in much less-destructive wave impact at the structure. The undular bore influences the wave loading on the breakwater, though the bulk of the wave loads and the excessive bearing pressures were computed for the long-lasting overtopping process of the first wave. These findings facilitate the damage assessment of detached breakwaters as they relate some specific tsunami features to structural stability and failure mechanisms. The results also provide information regarding the applicability and usefulness of different numerical modeling approach for the analysis of the stability of detached breakwaters under tsunamis. For this particular case, even depth-integrated numerical models provide conclusive solutions. To the best of the authors’ knowledge, this is the first numerical study addressing breakwater stability with respect to the impact of undular bores under tsunami conditions.