Longshore wave variability along non-straight coastlines

Abstract

The present paper demonstrates the role of wave direction and shoreline alignment on wave attenuation along a non-straight coastline. A numerical model was calibrated against measured data at six locations along a non-straight coastline and a hybrid method composed by wave case selection/simulation and nearshore time series reconstruction was applied to transfer 20 years of wave time series from offshore to nearshore. The results highlight the importance of the orientation of the coastline to different degrees of wave exposure to the wave attenuation process. The varying orientation of the coastline, at each of the six sites, resulted in non-uniform wave attenuation alongshore under different wave directions. The extreme wave conditions at each of the sites were also shown to vary significantly along the coast, e.g. ~18% alongshore (at-17 m Australian Height Datum-AHD) and as much as 34% from offshore (-70 m AHD) to nearshore (-17 m AHD). The results presented here reinforce the importance of assessing variations in wave attenuation along the coast as opposed to simply using the closest offshore wave dataset available. Improved understanding of nearshore wave attenuation along non-straight coastlines aids in better informing future coastal protection and management strategies.

Spatial Variability in Beach Morphology With Respect to Wave Exposure Along a Zeta-Shaped Coastline

“…The open ocean beaches of the Gold Coast are wave-dominated and microtidal (average tidal range = 1m; maximum spring tidal range = 2.1 m) (Kobashi et al, 2014). A detailed explanation of the Gold Coast open beaches wave climate is presented in Vieira da Silva et al (2018). Due to the exposure of the coastline and dominant SE wave energy source the importance of the longshore current is increased with respect to beach morphodynamics and variability in beach state as shown by Strauss et al (2006), Strauss and Tomlinson (2009) and .…”

“…Palm Beach is also characterised by a large offshore natural reef which influences wave transformation into the embayment. The Bilinga study site is located at the southern end of the coast, with the most sheltering of the dominant SE wave climate (Vieira da Silva et al, 2018). Bilinga is characterised by a large outer terrace located at the -5m AHD contour, which is an extension of the sand wave generated from the permanent sand bypassing system located at the southern end of the Gold Coast.…”

“…Palm Beach also displayed LBT morphology albeit a slightly lower energy state in the morphology with the offshore bar less well-defined and not as far detached from the shoreline as the sites to the north. Due to the nature of the well-developed offshore terrace at Bilinga and increased wave attenuation at the site under S-SE wave direction (Vieira da Silva et al, 2018) no longshore bar was present at Bilinga in the July 2017 survey (Figure 3e).…”

“…Vieira da Silva et al 2018analysed wave attenuation along the zeta-shaped Gold Coast embayment and found that wave attenuation will be uneven along a non-straight coastline with respect to the incoming wave direction. This has implications for sediment transport both under extreme wave events and milder conditions (Vieira da Silva et al, 2018).…”

Nearshore Wave Simulations and Wave Characteristics Analysis during Extreme Weather Events

“…Along the east coast of Australia, weather patterns dominate sea-wave and swell-wave formation (Vieira Da Silva, Murray, and Strauss, 2018). During summer, tropical cyclones are formed, while in winter east coast lows (ECLs) are formed.…”