A theory (involving tropical cyclones) on the formation of coarse-grained sand beach ridges in NE Australia

Abstract

AbstractA theory is presented that coarse-grained sand beach ridge plains in northeastern Australia have developed their final form (i.e. the height of the ridges above sea level) as a result of marine inundations generated by intense tropical cyclones. Although winds generated during such tempests are of more than sufficient velocity to transport coarse-grained sands the beach is typically inundated by the storm surge and waves during these events and hence there is no viable source for aeolian sand transport. Numerical storm surge and shallow water wave models are run for two sites (Cairns and Cowley Beach) and the results indicate that only wave run-ups generated by category 3 or more intense tropical cyclones can deposit the final units of sediment onto the sand beach ridges at these locations. It is suggested that as a sand beach ridge increases in height, via successive deposition of units of sand, progressively higher marine inundations are required to reach the ridge crest. The final height of the sand beach ridge is dependent upon the interplay of sediment supply rates to the coastal system and the intensity and frequency of tropical cyclones. If tropical cyclones are responsible for the final form of the sand beach ridges then these sequences can be used to assess the long-term climatology of intense tropical cyclones over this broad geographical region.