Retrogressive Flow Slides in South-East Queensland

Konrad Beinssen and Ian Shipway

Abstract

‘Retrogressive breach failures’, also known as ‘retrogressive flow slides’, are relatively common but short lived natural events which can affect shorelines adjacent to sandy tidal channels in South East Queensland and elsewhere in the world. Their occurrence often goes unnoticed and unreported because they occur underwater and do not always reach the bank or beach, their active phase is relatively short lived and their timing cannot be predicted. One of the better known examples of such an event occurred at Inskip Point in September 2015 where it impacted the beach and undermined a camp site. This event was widely reported by the news media as a “sinkhole”.

The first part of the presentation will briefly cover the history of flow slide research, describe observations of retrogressive breach failure events at Amity Point and explain their geotechnical mechanism. The distinction between ‘static liquefaction’ and ‘retrogressive breaching’ flow slides will be explained. Both of these types result in geomorphologically similar post failure landforms. The second part of the presentation will place the Inskip Point instability event of September 2015 into the context of the breaching mechanism and present the stability risk assessment and risk management outcomes.

About the Speakers

Konrad Beinssen

Konrad Beinssen is currently an RHD student at the University of Queensland, researching erosion management at Amity Point on North Stradbroke Island. His background is in fisheries science (abalone fishery, coral trout fishery, Victorian bay and inlet recreational fishery and artificial reefs). He has held positions as Assistant Director of the (then) Victorian Fisheries and Wildlife Department, OIC of Davis Station in Antarctica, OIC of the Southern Section of the Great Barrier Reef Marine Park with QNPWS and manager of Sydney Universiy’s One Tree Island Research Station on the GBR. Konrad was an abalone diver for seventeen quota years, finishing his working life in 2005 and retiring to Stradbroke Island.

Ian Shipway

Ian Shipway is currently a Principal and director at EDG Consulting. His geotechnical consulting experience spans over 30 years with companies including Golder Associates and Coffey. Ian has worked over a broad range of different projects and fields within geotechnics in Australia, New Zealand and Asia covering civil infrastructure, mining infrastructure and developments associated with oil and gas. His major area of practice at the present is slope engineering, risk assessment.

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