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During tropical cyclones, processes including dune erosion, overwash, inundation, and storm-surge ebb can rapidly reshape barrier islands, thereby increasing coastal hazards and flood exposure inland. Relatively few measurements are available to evaluate the physical processes shaping coastal systems close to shore during these extreme events as it is inherently challenging to obtain reliable field data due to energetic waves and rapid bed level changes which can damage or shift instrumentation. However, such observations are critical toward improving and validating model forecasts of coastal storm hazards. To address these data and knowledge gaps, this study links hydrodynamic and meteorological observations with numerical modeling to 1) perform data-model inter-comparisons of relevant storm processes, namely infragravity (IG) waves, storm surge, and meteotsunamis; and 2) better understand the relative importance of each of these processes during hurricane impact.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/kUizy8nK3TU

Coastal wetlands protect the shoreline and infrastructure by attenuating wind waves and reducing storm surge. It is of importance to accurately quantify the flood protection provided by vegetation. Existing numerical models for hurricane waves and storm surge are based on the phase-averaged wave action balance equation and the nonlinear shallow water equations, respectively, with the wind forcing and vegetal drag as the free surface and bottom boundary conditions. To consider the interaction of waves and surge, the phase-averaged short wave and long wave (storm surge) models can be coupled in a staggered fashion. If the time step of the wave model and storm surge model are 30 minutes and 1 s, respectively, both models would exchange information every 30 minutes. There is no iteration between the wave and surge models at each coupling interval. An alternative to this state-of-the-practice of hurricane wave and storm surge modeling is to simulate the combined wave and surge motion driven by wind and attenuated by wetland vegetation using a phase-resolving Boussinesq model. The objective of this study is threefold: 1) to demonstrate the capability of modeling wave growth by wind, wave reduction by vegetation, and the total water level (wave setup, wind setup and wave runup) using the extended FUNWAVE-TVD model; 2) to analyze the energy balance of the combined wave and surge motion; 3) to examine the momentum balance with an emphasis on the vegetal drag owing to the combined wave orbital velocity and wind-driven current velocity.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/-o_kx4hPvC8

Modeling hydrodynamic processes in a salt marsh system is a challenging task, due to the complexity of topographic features and the scale of such features relative to the overall system size. With growing availability of high-resolution topographic measurements, like LiDAR-derived DEM data, it is increasingly desirable to run a high-resolution model in a large domain and for a long period of time to get trends of sedimentation patterns, morphological change and marsh evolution. However, high spatial resolution poses a big challenge in both computational time and memory storage. Vegetation dynamics in a marsh system needs to be properly taken care of with respect to the vegetation zones and elevation from the mean sea level. The interaction between micro-scale topography and vegetation canopy dominates the overall morphological evolution.

Surface gravity waves alter discharge and circulation near and within coastal inlets, affecting the exchange and transport of water masses, nutrients, sediments, and pollutants between inland waters and the ocean. Field observations and numerical simulations suggest that, during storms, wave forcing (radiation-stress gradients) owing to wave dissipation across the ebb shoal can enhance fluxes into the inlet (Bertin et al. 2009; Wargula et al. 2014). As a result, water levels may increase inside the bay (Olabarrieta et al. 2011; Dodet et al. 2013), creating an offshore-directed pressure gradient that may balance onshore fluxes during energetic waves, and may enhance offshore fluxes after the waves decrease. Spatial and tidal variability in water depths on the ebb shoal lead to complex wave breaking patterns that drive spatially and tidally asymmetric flows. Here, field observations and numerical simulations are used to evaluate the effects of waves on discharge and circulation, and the relative importance of wave radiation-stress and pressure gradients at an unstratified inlet during and following energetic waves.

Meteorological tsunamis, also called meteo-tsunamis, are significant ocean surface waves generated by atmospheric forcing. The waves typically result from energy transfer from atmosphere to ocean through the Proudman resonance phenomena, where translation speed of the storm system in the atmosphere coincides with the free wave speed of long surface waves. These tsunami-like waves can be hazardous, either through direct inundation of shorelines or through generation of harbor oscillations and other disruptions to maritime activities. The wide continental shelf bathymetry of the United States (US) East Coast provides a long potential fetch length for the resonant generation process, making the region particularly susceptible to meteo-tsunamis. In this study, we carry out a probabilistic analysis of potential meteo-tsunami hazard on the US East Coast, extending the earlier work of Geist et al. (2014) to include a wider range of storm conditions and additional response types including coastally-trapped edge waves. The work, carried out under the auspices of the National Tsunami Hazard Mitigation Program (NTHMP), extends the previous efforts of Geist et al. to include a representation of inundation and maritime hazards in at-risk areas. The work is conducted using the fully nonlinear Boussinesq wave model FUNWAVE-TVD (Shi et al., 2012), extended to include atmospheric pressure and wind forcing.

In hazard assessment studies that evaluate the damage caused to coastal structures by windstorm-generated surge and waves, the standard approach has been to estimate structural loading by applying phase-averaged wave propagation models (e.g., SWAN, STWAVE) and storm surge models (e.g., ADCIRC), coupled or not with each other. Bare-earth “Digital Elevation Models” (DEMs) have typically been used as a basis for model grid development, with sometimes empirical adjustments being made to beach profiles or dune crest levels to account for storm-induced erosion. In recent work, the latter approach has been improved by including real time morphodynamic changes in simulations, using models such as XBeach (e.g., Schambach 2017; Schambach et al., 2017), which are still based on the wave action conservation equation, including semi-empirical parameterizations of wave breaking and many formulations based on linear wave theory (e.g., phase/group velocity, radiation stresses,…), as well as low-order wave-wave interaction terms. Finally, structural damage has typically been estimated based on empirical damage curves, developed based on field surveys, that use flow depth and controlling wave crest height as inputs (e.g., Grilli et al., 2017). Neglected in this modeling approach, however, are dynamic set-up and runup effects, as well as strongly nonlinear wave interactions that occur near and in the surf and swash zones.

Significant progress has been made in the numerical modeling of wave-current interaction during the past decade. Typical coastal circulation and wave models, however, still only employ theoretical formulations which take depth-uniform mean flows into account, with realistic, non-uniform flows treated as being depth uniform through some chosen averaging procedure. Depending on the choice of average over depth, significant errors may arise in the estimation of properties such as group velocity and action density in realistic conditions. These errors, in turn, are fed back into the circulation model through incorrect representation of the vertical structure of wave forcing. A new framework for wave-current interaction theory for strongly sheared mean flows has been developed using vortex force formalism by Dong (2016). The resulting formulation leads to a conservation law for wave action identical to that of Voronovich (1976), and to expressions for wave-averaged forces in the Craik-Leibovich vortex force formalism. In this study, we are completing the development of a coupled NHWAVE/SWAN which implements the wave forcing formulation of Dong (2016) in a wave-averaged version of the non-hydrostatic model NHWAVE (Ma et al., 2012). The SWAN model is also being extended to incorporate a better representation of frequency and direction-dependent group velocity and intrinsic frequency in the neighborhood of the spectral peak, thus improving on the present practice of using quantities evaluated only at the spectral peak. The resulting model is being tested against field data collected in several recent experiments involving strong, vertically sheared currents in river mouths or straits.

Heavy ship traffic causes a growing concern with respect to public safety, potential damage of coastal structures, and corresponding environmental impacts. High-speed ship-generated wakes such as solitons, undular bores, and breaking bores behave differently compared to wind waves and have a great potential for damage in vulnerable areas such as low-energy coasts and wetlands. In this study, we are developing a multi-grid model framework for the Fully Nonlinear Boussinesq Wave Model, FUNWAVE-TVD (Shi et al., 2012), for simulating ship-wakes in both the operational scale and refined process scales using full two-way coupling. Physical processes in areas of interest requiring higher model resolution, such as the ship-wake generation region, wave breaking in the near-field, and wave evolution with wave-structure interaction in the nearshore field, will be modeled in refined grids embedded in the operational-scale domain. A dynamically adaptive grid algorithm is implemented in order to track a vessel and calculate the physical processes precisely in the wave generation and breaking region in the vicinity of the vessel. Both pressure source and panel source methods for ship wave generation will be tested in the model framework. A concept of nesting layers based on the hierarchical basis, and an efficient parallelization method in the context of the full domain partition are utilized to allow the model to deal with a large-scale computation efficiently in a High Performance Computing (HPC) system.

In this study, a two-layer landslide model is presented for investigating submarine landslides and generated waves that propagate over irregular bathymetry. The landslide is described as either a mudflow or a fully saturated granular flow, which are distinguished by using different rheological closure based on physical principles. Depth-averaged governing equations for the landslide are derived in a regular Cartesian coordinate system, and take into account the effect of vertical acceleration and interface traction from the upper-layer water. In addition, sediment erosion from basal boundary and water entrainment are also considered. Tsunami waves generated by the landslide are simulated by the three-dimensional non-hydrostatic wave model NHWAVE (Ma et al., 2012). The governing equations for both the lower-layer slide and the upper-layer water body are solved using a Godunov-type finite volume TVD scheme in space and a Strong Stability-Preserving (SSP) Runge- Kutta scheme in time.

The goal of this study is to investigate the role of wave-current interaction in tidal inlet hydrodynamics. A quasi-3D nearshore community model, NearCoM-TVD, is used to simulate circulation and waves at New River Inlet, NC, USA. Model skill for waves and circulation is evaluated at about 30 locations throughout the inlet, including a recently dredged navigation channel, a shallower channel, a flood tidal delta, and ebb tidal deltas, for a range of flow conditions in May 2012. Model skills for flow velocity and wave height are high in the channels. The numerical model also captures the sharp transition between wave-dominated and tide-dominated flows near the ebb tidal deltas. Model results demonstrate that wave intensity plays an important role in circulation (vortex) generation near inlet entrances.

This paper describes the recent developments in a suite of coastal engineering models using Godunov-type shock-capturing schemes. The developments include a depth-integrated, wave resolving Boussinesq model, a hydrostatic, wave-averaged circulation model, and a fully 3-D non-hydrostatic model in a surface-following $\sigma$ coordinate formulation. The models implemented with the shock-capturing TVD scheme show robust performances in modeling breaking waves, nearshore circulation and coastal inundation. In this paper, we present model equations in a conservative form, MUSCLE-TVD numerical scheme and model applications. We also point out some problems caused by the TVD scheme in the recent model applications.

Recent observations of the coastal impact of large tsunamis (e.g., Indian Ocean 2004; Tohoku 2011) and related numerical and theoretical works have made it increasingly clear that tsunami waves arrive nearshore as a series of long waves (so-called N-waves) with, often, the superposition of undular bores around each crest. Such wave trains are much more complex and very much in contrast with the solitary wave paradigm which for a long time was the accepted idealization of tsunami waves in both experimental and numerical work. The dissipation associated with these breaking bores can be very large, particularly over a wide and shallow continental shelf such as along the east coast of North America, particularly for the shorter waves associated with tsunamis generated by Submarine Mass Failures (SMFs). In this paper, we perform numerical simulations of tsunami coastal impact in the context of both idealized laboratory experiments and several tsunami case studies. We attempt to clarify the key physical processes at play in such cases, and discuss the parameterization of long wave dissipation and implications for models of coastal tsunami hazard assessment.

We establish a framework for describing the spatial and temporal distribution of entrained air bubbles under breaking surface waves. The computational framework is based on a large eddy simulation (LES) in 3-D together with a VOF treatment of the air-water interface. An Eulerian multiphase approach is used in order to track the entrained bubbles as a number density distribution. Examples of numerical results for breaking periodic surf zone waves are illustrated.

This paper demonstrates that numerical modeling tools such as a RANS-VOF model can be applied confidently to reduce the level of uncertainty from empirical guidance and provide for a deterministic quantification of the hydraulic response associated with any arbitrary Caisson breakwater superstructure geometry. The RANS-VOF model used for this paper is first satisfactorily validated against laboratory measurements (surface elevation, overtopping and pressure) of a caisson breakwater on a rubble-mound foundation and then applied to several prototype caisson breakwater superstructure geometries. Numerical simulations presented in this paper for prototype geometries demonstrate that curved/inclined parapets, when compared with vertical face caisson breakwaters with the same crest elevation, can lead to large increases in overtopping as well as downward forces. Expectedly, the landward forces are reduced by the implementation of a curved or recessed and inclined parapet when compared to a caisson with a completely vertical face. During large overtopping events, the model results show that much larger short-duration seaward loads can be generated for curved and inclined superstructures when compared to vertical face geometries. This is in general agreement with previous laboratory experiments as well as field observations of seaward caisson sliding and failure resulting from large overtopping events. Further, numerical experiments indicate that the overtopping response of a superstructure can vary noticeably due to small changes in the recessed length of an inclined or curved parapet. The numerical model also easily provides for the quantification of the variation of instantaneous and peak overtopping discharges along the crest of the caisson superstructure, and which can provide for useful guidance in the design of various crest infrastructure components, such as drainage systems, flow deflectors, wave power devices etc.

This paper provides a review of our recent developments in numerical models for predicting physical processes related to optical properties inside the surfzone. Model components in the developments include the bubble entrainment model, 2D and 3D multiphase two-fluid models for modeling quiescent phase of bubbles, turbulence models with influences of bubbles, bubble coalescence and breakup models used in the two-fluid models, and foam model for predicting foam patch generation and evolution inside the surfzone. The paper summarizes theories used in the model components and shows some numerical results from model tests.

Yellow River is famous for its high sediment concentration, which carries a huge amount of sediment into Bohai Sea during the flood season. In the mouth of Yellow River, the suspended sediment concentration (here after: SSC) are relatively high and the average depth is generally shallow. Recent studies indicated that in the shallow and micro-tide area, wave usually is a primary mechanism for bottom sediment resuspension. Most numerical studies of sediment transport in the Yellow River mouth didn't include the wave effects. To analyze the sediment transport in the Yellow River mouth with wave effect, a Coastal Sediment Transport Modeling System (CSTMS) was applied in this study.