Abstract

Arohi Saini
Supervisors: Kurt Iveson and Ana Vila-Concejo
Faculty of Science, School of Geosciences, The University of Sydney
2025
Thesis submitted in partial fulfilment of the requirements for the degree of
Environmental Studies (Honours), The University of Sydney, 2025 

This thesis investigates ephemeral beaches, characterised by their intermittent appearances, through a socio-physical perspective, focusing on Mackenzies Beach in Sydney, Australia. Research aims to understand how and why Mackenzies Beach forms, and how its ephemerality shapes its use and governance. By analysing satellite images, drone data, wave, storm, and El Niño Southern Oscillation data, the study identified the sequence of conditions favourable for the occurrence of this ephemeral beach: (1) highwave-energy events from storms, often during La Niña phases, must cause erosion at Bronte and Tamarama beaches, which is then deposited offshore within the larger embayment. (2) After the erosion, the conditions must be calm and storm-free with significant wave heights below 1.6 metres from the east-southeast. Those conditions facilitate shoreward transport of the offshore sand deposit, redistributing it to the three bays in the sediment compartment: Bronte, Tamarama and Mackenzies. (3) The sand stays on the three beaches only if those calm conditions are maintained; any storm can trigger erosion and disappearance of Mackenzies beach. If the erosion is not followed by the calm conditions described in (2), the sand only returns to Bronte and Tamarama. The beach's highly variable width across its appearances highlights the instability of ephemeral beach profiles, challenging the traditional coastal management strategies based on permanent beaches and assumptions of relatively stable land-sea boundaries. The study, using interviews, social media, drone imagery, and archival records, found that while an ephemeral beach hosts activities similar to those on permanent beaches, its transient nature creates uncertainty about who is responsible for its management and the rules governing its use, leading to various informal arrangements. The beach's ephemeral nature makes it difficult for the Council to allocate resources, such as lifeguards and rangers, leading to inconsistent enforcement of bans on activities like dog walking and topless bathing, which persist as informal activities. Furthermore, while the Tamarama Surf Life Saving Club (SLSC) has historically patrolled the beach informally, there has been no move by the State or the SLSC to formally include it in their official patrol duties, as the beach hardly appears long enough to warrant formalisation. Ultimately, this research shows that understanding the physical processes underlying the beach's ephemeral presence is key to understanding its varied use and management.

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About the Author

Just a pic of me doing archive research at the university in the middle of the night, end of May, with the heater on beside me and Subway for dinner :)

Hi everyone! I’m Arohi, and if you’re here, you probably share my curiosity about the “disappearing” Mackenzies Beach, affectionately called Maccas by locals. Just a year ago, I had no idea such a place existed. It was my then soon-to-be honours supervisors who mentioned, “Oh, there’s this incredible beach that sometimes shows up, but most of the time doesn’t.’ With my very basic understanding of coastal science, I thought, ‘Maybe it’s just tides temporarily covering the beach—I don’t see what’s so extraordinary about that.’ But they added, “It last appeared in the summer of 2023-24, and now it’s gone.” I wouldn’t say it was a lightbulb moment, but I was excited to share this with friends and family, and I believe that was when I realised: this is it; this is my honours project. The journey that followed was filled with incredible highs and challenging lows—like getting my (gloved) hands on the actual council meeting minutes from the 1940s and 50s, along with many sleepless nights of anxiety, fearing the project might be a disaster (spoiler: it wasn’t). Looking back, the process of researching and writing this thesis was truly unforgettable, and I wouldn’t hesitate to do it all over again. Mackenzies Beach is a truly captivating place (ask anyone!), not just because of its ephemerality, but also because of how it functions as a social space. Honestly, I’m even more excited now to share and learn about this beach than I was before starting this project. I hope my honours thesis helps satisfy some of your curiosity about this beach and inspires you to explore it even more!