Abstract
Wave overtopping and subsequent coastal flood hazard is strongly controlled by wind and water levels, and is especially critical in hyper-tidal estuaries where even small changes in wave heights can be catastrophic if they are concurrent with high spring tide. Wave hazard in estuaries is largely attributed to high amplitude shorter period, locally generated wind waves; while low amplitude longer period waves rarely impact low-lying coastal zones up-estuary. Here, the effect of wind and wave properties on up-estuary wave propagation and the sensitivity of significant wave height are investigated numerically along the shoreline of the Severn Estuary, southwest England, as an example. Representative values for wind speed and direction, wave height, period and direction are used to identify key combinations of factors that define the wave hazard generation. High amplitude, short period wind waves are sensitive to opposing winds, with a steepening effect that varies along the estuary shoreline, highlighting the effect of estuarine geometry on wave hazard. Low amplitude, long period wind waves respond with maximum variability in significant wave height to strong winds resulting in their propagation further up-estuary. Our results advance current understanding of the compound interaction between wind and waves, and identify critical conditions maximizing the hazard and hazard variability along the shoreline. The outcomes from this research can help to avoid economic losses from operational downtime in ports and harbors, inform sustainable coastal sea defense design and understand how wave hazard may vary under future climate due to changing storm tracks. Results can also be applied to the design of coastal infrastructure and facilitation of emergency response planning.
Highlights
This paper describes the effect of wind and wave properties on spatial variability and sensitivity of significant wave height along the shoreline of a hyper-tidal estuary
The difference between maximum significant wave height and the baseline scenario is plotted along the shoreline starting at Rhossili, South Wales and moving along the north shoreline of the estuary up to Gloucester, and along the south shoreline of the estuary to Woolacombe, Devon
The results presented here help to identify the contribution of individual factors to variability in coastal wave hazard in a hyper-tidal estuary
Summary
The highest waves superimposed on high water levels can cause an instantaneous uprush of water at the coast and push large volumes of water over seawalls or dikes in a short period of time (Hoeke et al, 2015; EurOtop, 2016). This has implications for run-up, wave overtopping, spray and subsequent coastal flooding, which is critical for users and property along the coastline (Allsop et al, 2008; Wolf, 2008; Bastidas et al, 2016; Thompson et al, 2017). Despite many seawalls designed to withstand this threshold, 4–8 people are killed each year in the UK through the direct effects of waves on seawalls (Allsop et al, 2005) and approximately 60 killed in Italy over the last 20 years (Allsop et al, 2003)
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