Wave-tide interaction modulates nearshore wave height

Abstract

The combined hazard of large waves occurring at an extreme high water could increase the risk of coastal flooding. Wave-tide interaction processes are known to modulate the wave climate in regions of strong tidal dynamics, yet this process is typically omitted in flood risk assessments. Here, we investigate the role of tidal dynamics in the nearshore wave climate (i.e. water depths > 10 m), with the hypothesis that larger waves occur during high water, when the risk of flooding is greater, because tidal dynamics alter the wave climate propagating into the coast. A dynamically coupled wave-tide model BCOAWST^was applied to the Irish Sea for a 2-month period (January-February 2014). High water wave heights were simulated to be 20% larger in some regions, compared with an uncoupled approach, with clear implications for coastal hazards. Three model spatial resolutions were applied (1/60°, 1/120°, 1/240°), and, although all models displayed similar validation statistics, differences in the simulated tidal modulation of wave height were found (up to a 10% difference in high water wave height); therefore, sub-kilometre-scale model resolution is necessary to capture tidal flow variability and wave-tide interactions around the coast. Additionally, the effects of predicted mean sea-level rise were investigated (0.44-2.00 m to reflect likely and extreme sea-level rise by the end of the twentyfirst century), showing a 5% increase in high water wave height in some areas. Therefore, some regions may experience a future increase in the combined hazard of large waves occurring at an extreme high water.

Usable Science for Managing the Risks of Sea‐Level Rise

“…Coupling ice‐sheet models to GCMs (e.g., Golledge et al, ) will help in characterizing these feedbacks, but the computational expense of fully coupled GCMs poses a challenge to uncertainty quantification, so offline calculations (e.g., Howard et al, ) and reduced‐form representations of these relationships will remain useful for the foreseeable future. Dependencies can also extend to components of high‐frequency sea level variability (next section), either due to common drivers (e.g., Little et al, ) and/or interactions (such as nonlinear interactions between RSL, tides, surge, and waves; e.g., Arns et al, ; Lewis et al, ).…”

“…Future ESL frequencies and impacts depend upon local RSL rise and changes in the characteristics of coastal storms, tides, and waves, as well as their possible interdependencies (e.g., Arns et al, ; Lewis et al, ; Little et al, ). Projections based upon statistical models typically assume that RSL change is the only driver of changes in the ESL distribution (e.g., there are no changes in storm surge characteristics or tidal range; e.g., Buchanan et al, ; Buchanan et al, ; Hall et al, ; J.…”

Can wave coupling improve operational regional ocean forecasts for the north-west European Shelf?

“…Wave simulations are produced for the NWS using a configuration of the WAVEWATCH III (Tolman et al, 2014) spectral wave model (Saulter et al, 2017). The wave model is defined to cover the same domain extent as AMM15, but using a spherical multiple cell grid refinement approach (Li, 2012), which has variable horizontal resolution nesting from 3 km across much of the domain down to 1.5 km spacing for all cells adjacent to the coast and/or where the depth of a 3 km grid cell would be shallower than 40 m. A wave model global time step of 600 s is used. The wave model is forced by winds from the same ECMWF global atmospheric model as used for ocean forcing at 3-hourly temporal frequency.…”

Sensitivity of Flood Hazard and Damage to Modelling Approaches

“…For this event HWH s is 0.94 m, superimposed on HWL of 9.4 m. Larger waves during the more extreme coastal hazard condition at the time of tidal high water have a greater impact on wave runup, and contribute more directly as a source of flood hazard. A coupled wave-tide model applied to the Irish Sea has shown that wave-tide interaction can increase high water wave heights up to 20% in regions with larger tidal range [72]. Wave-tide interaction is extremely important within flood hazard assessments and must be accounted for in coastal hydrodynamic models to accurately generate the largest waves at high water, which have been shown here to generate the greatest physical and economic impacts of flooding.…”