Longshore wind, waves and currents: climate and climate projections at Ninety Mile Beach, southeastern Australia

Abstract

It is shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in southeastern Australia, is situated in a region that may experience noticeable changes in longshore wind, wave and ocean currents compared to present day climate variability as a consequence of the southward shifting subtropical ridge (STR) predicted in global climate change models. These changes could modify sediment transport in the littoral zone and impact the coastline position. Thirty-year hindcasts of winds, coastal currents and waves are shown to agree well with available observations and provide a long-term dataset of the climate variability. Hindcasts of coastal ocean currents and waves indicate that while the annual net mean wave and current transport are in opposing directions, their seasonal adjusted monthly anomalies are positively correlated. Furthermore they are also correlated with the position of the STR location index. On seasonal to annual time scales a weak connection between the transport variables and Southern Oscillation Index (SOI) is found. It appears that during multiple years of positive (negative) SOI conditions the STR is located north (south) of its mean monthly position, resulting in anomalous eastward (westward) transport. The four climate models used in this study indicate a southward shift in the STR for most months under a high emission future. In summer months the shift in the STR results in both increased summer westward wind-driven currents and westward wave forcing. Changes in winter months are less related to the STR location and it is discussed that the contraction and increased intensity of the westerly storm belt linked to Southern Annular Mode could possibly influence the transport. The analysis is presented at the coastal scale to provide insights into how these changes may affect net transport across the littoral zone in more detailed numerical nearshore sediment transport modelling.

Information for Australian impact and adaptation planning in response to sea-level rise

“…O'Grady et al (2015) has shown that the change in both wind-driven currents and waves in south-eastern Australia may lead to complex seasonal changes in longshore sediment transport with subsequent impacts on the near shore region.…”

Natural hazards in Australia: sea level and coastal extremes

“…Wave setup is an increase in mean water level due to the cross-shore Other coastal attributes, such as continental shelf width, bathymetric depth, coastline 125 orientation in relation to prevailing weather conditions, headlands, estuaries and shoreline 126 slopes, also influence extreme sea levels. The wider shelf regions along the tropical and much 127 of the southern Australian coastline ( Figure 3) are conducive to larger storm surges and tidal 128 ranges whereas the narrower shelves along the southeast, southwest and parts of the 129 southern coastline are exposed to wave-driven coastal extremes. Coral reefs, found along the 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63…”

Atmospheric Circulation Changes and their Impact on Extreme Sea Levels around Australia

“…35 Lowe et al, 2009]. Changes to wind-driven coastal currents, which could be considered using the modelling framework presented in this study (but is beyond the scope of this paper), is also potentially important in the context of coastal erosion and shoreline change [Gornitz, 1991;O'Grady et al, 2015].…”