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Abstract: Many low‐elevation, coral reef‐lined, tropical coasts are vulnerable to the effects of climate change, sea level rise, and wave‐induced flooding. The considerable morphological diversity of these coasts and the variability of the hydrodynamic forcing that they are exposed to make predicting wave‐induced flooding a challenge. A process‐based wave‐resolving hydrodynamic model (XBeach Non‐Hydrostatic, “XBNH”) was used to create a large synthetic database for use in a “Bayesian Estimator for Wave Attack in Reef Environments” (BEWARE), relating incident hydrodynamics and coral reef geomorphology to coastal flooding hazards on reef‐lined coasts. Building on previous work, BEWARE improves system understanding of reef hydrodynamics by examining the intrinsic reef and extrinsic forcing factors controlling runup and flooding on reef‐lined coasts. The Bayesian estimator has high predictive skill for the XBNH model outputs that are flooding indicators, and was validated for a number of available field cases. It was found that, in order to accurately predict flooding hazards, water depth over the reef flat, incident wave conditions, and reef flat width are the most essential factors, whereas other factors such as beach slope and bed friction due to the presence or absence of corals are less important. BEWARE is a potentially powerful tool for use in early warning systems or risk assessment studies, and can be used to make projections about how wave‐induced flooding on coral reef‐lined coasts may change due to climate change. [ABSTRACT FROM AUTHOR]

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours. [ABSTRACT FROM AUTHOR]

A comprehensive review of state of the art numerical modeling in the field of sea bed morphology during cyclonic events is of vital importance. In this study a high impact and devastating cyclone, Vardah (2016) is considered to understand the hydrodynamic conditions, whereas, the recent cyclone, Nivar (2020) is considered for investigating the morphodynamic changes along the continental shelf region off the state of Tamilnadu, India. Three different models are coupled intrinsically to simulate hydrodynamics of tides and surges, waves and morphodynamic conditions. Initially, the hydrodynamic and wave models are established and validated with field measurements for an extreme event. Then, morphodynamic model is coupled with validated wave and tide model. Furthermore, the validation of bed evolution is performed for two cases viz., currents only and combination of waves and currents. The combined effect of tides, waves and surges improves the morphodynamic predictions. The present paper emphasizes the spatial and temporal morphological changes along the radius of cyclone pertaining to the shelf region. It is observed that the impact of cyclone on morphodynamics is predominant upto half the radius of the cyclone along the coast and upto 25 m contour from the coast across the shelf region. In this study, the bed evolution and its rate of change at various locations along the coast and across the shelf are extensively discussed. [ABSTRACT FROM AUTHOR]

A coupled wave and hydrodynamic model was applied to the Kingston Basin of eastern Lake Ontario, a region with bathymetric variability due to channels and shoals, to assess the potential impacts on surface waves and wind-driven circulation of an offshore wind farm. The model was used to simulate a series of storm events with time-varying wind forcing and validated against wave, current and water level observations. The wind farm was simulated by adding semi-permeable structures in the surface wave model to represent the turbine monopiles, and by adding an energy loss term to the fluid momentum equations in the hydrodynamic model to represent the added drag of the monopiles on the flow. The results suggest that the wind farm would have a small influence on waves and circulation throughout the wind farm area, with spatial variability due to focussing of wave energy and re-direction of the flow. Overall, the results indicate that the wave height in coastal areas will be minimally affected with changes in significant wave height predicted to be < 3%. Larger changes to the strength of circulation occur inside the wind farm region with localized changes in current magnitude of up to 8 cm s − 1 . The results of this study may help to understand the impacts of future offshore wind farms and other offshore structures in the Great Lakes. [ABSTRACT FROM AUTHOR]

Small island developing states are among the most vulnerable areas to the impact of natural hazards and climate change. Flooding due to storm surges and extreme waves, coastal erosion, and salinization of freshwater lenses are already a serious threat and could lead to irreversible consequences in the coming decades. Reef flat mining is one of the most common practices to source the required material for the implementation of coastal protection measures, but concerns remain that partial removal of the protective reef could increase wave loading on the islands. However, the available data and knowledge on the effects of these mining pits are currently very limited. This study provides new insights on the effects that pits may have on nearshore hydrodynamics and wave runup. Results are based on a large numerical data set of fringing reefs, derived using the validated XBeach nonhydrostatic+ process‐based model. Model results indicate that excavation pits cause a decrease in infragravity wave energy around the fundamental mode of the reef, which is partly caused by reduced wave transmission. Additionally, changes in sea and swell wave energy are attributed to reduced transmission, a decrease in wave dissipation, and (triad) wave–wave interaction. Furthermore, in 13% of all modeled cases, an increase in wave runup is observed, mainly due to more sea and swell wave energy reaching the shoreline. This probability is lowest for narrow pits relative to the reef flat width or pits located further from shore. Plain Language Summary: Many small island states are among the most vulnerable areas to the impacts of climate change. Additionally, flooding due to storms, coastal erosion, and loss of freshwater supply already form a serious threat. Mining of dead coral sediments from the reef flat is a common practice to source material for coastal protection works. This could potentially lead to higher waves at the coastline through the partial removal of the reef, which breaks large waves. However, the knowledge on the effects of these mining pits is currently very limited. The present study provides improved explanations on the effects that a pit may have on waves and assesses the resulting risk of flooding it poses on these islands. The results are obtained by simulating a large set of different reefs and wave conditions using a numerical model named XBeach. These show that the effect of a pit can vary significantly, but in general, a pit causes lower waves near the shoreline. At some cases, larger waves at the shoreline were found, thereby increasing the risk of flooding. This risk is the lowest for pits that are located further from the coastline, or those that have narrow width relative to the reef width. Key Points: Coral Reef mining pits cause a variation in the nearshore hydrodynamics and wave runup during extreme eventsPits generally cause a decrease in nearshore wave height and extreme runup mainly due to lower infragravity wave energyPits with a relatively narrow cross‐shore width or with a location further from shore are least likely to cause an increase in runup [ABSTRACT FROM AUTHOR]

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For the design, assessment and flood control of water defences, hydraulic loads in terms of water levels and wave conditions are required and often obtained from numerical models. For these hydraulic loads to be reliable, accurate atmospheric forcing is required. Waves and surges are typically forced by surface stress. However, in most cases, the input for these models consists of 10-m wind velocities that are internally converted to surface stress by applying a particular drag relation. This procedure generally leads to inconsistencies, since the hydrodynamic, wave and atmospheric models often apply different drag relations. By means of a case study, we explored the consequences of this inconsistency in the drag formulation for a North Sea storm wave and surge hindcast. This was done by forcing the hydrodynamic and wave models using both the 10-m wind velocity and the surface stress fields computed by the atmospheric model. Our study results show significant differences between the wave parameter values and water levels computed with surface stress input and 10-m wind velocity input. Our goal is not to assess different drag parameterizations but to raise awareness for this issue and to plea for the use of a consistent drag relation in meteorological and hydrodynamic/wave models. The consistent use of one drag formulation facilitates the identification of problems and the eventual improvement of the drag formulation. Furthermore, we suggest using the so-called pseudo-wind, which is a translation of the surface stress to the 10-m wind speed using a reference drag relation. [ABSTRACT FROM AUTHOR]