Field observations of retrogressive breach failures at two tidal inlets in Queensland, Australia

This paper describes observations of rapid beach erosion events which occur regularly adjacent to deep sandy tidal channels at Amity Point and Inskip Point on Australia’s east coast. The characteristics of these events are consistent with others which have been extensively studied and described in the scientific literature and which occur at several river and coastal locations elsewhere in the world. This connection has not previously been made. The geomorphological mechanism of retrogressive breach failure (RBF) events reported in the literature matches the study site observations well. It is concluded that the described Australian events are caused by breaching of fine, subaqueous, dilatant sand. This understanding will help coastal planning including the design of coastal defences.