Coastal Morphodynamics and Near Shore Processes

The GRG IMG_2013studies beach morphodynamics in a range of environments that include ocean and estuarine beaches. The research undertaken by Prof Andy Short is an international benchmark. Andy’s research on beaches includes an amazing database that not only includes long-term monitoring of Narrabeen beach (now continued by researchers at WRL-UNSW) but also beach morphodynamic data from all beaches around Australia and many around the world. Andy is now officially retired but still doing a lot of research, he lives in the South Coasts of NSW and now monitors Moruya beach.

PS_Windawoppa51-08From 2007 to 2011 we had an ARC Linkage project studying the management implications of the shoreline morphodynamics in Port Stephens where we studied the dynamics of a flood-tide delta and the surrounding estuarine beaches: Shoal Bay and Jimmy’s beach; this project was led by A/Prof Ana Vila-Concejo. We continue very much interested on estuarine beaches and are also researching some of the estuarine beaches in Sydney, Chowder Bay (next to SIMS) and Nielsen Park. And a monitoring program is planned for these beaches.

OLYMPUS DIGITAL CAMERAIn 2010 we started a program to investigate the morphodynamics of coral reefs which was led by A/Prof Ana Vila-Concejo. We have studied wave propagation over reefs and sediment transport on sand aprons. More details about this research can be found in the [coral reef research page] https://grgusyd.org/research/coral-reef-geology/

In 2015 we started a monitoring program for the ocean beaches of the Eastern Suburbs of Sydney which includes monitoring of Bondi, Bronti, Tamarama and Maroubra beaches. We also have a video-camera in Bondi beach which is a joint collaboration with A/Prof Rob Brander from UNSW (he installed it and run it until September 2015).  The collaboration with Rob Brander, both in beach morphodynamics and rip currents research, was a natural process once his former PhD student, Dr Jak McCarroll, joined us as a lecturer in 2015. Although this monitoring program, co-led by Dr Jak McCarroll and A/Prof Ana Vila-Concejo  is still young, it is already generating interest and we are working towards establishing collaborations with the local councils. Dr Jak McCarroll continues his research on rip currents.

Long term morphodynamics of coasts and continental shelves is led by A/Prof Peter Cowell who now lives in the north coast of NSW. His research involves the combined use of field data and computer modeling to yield information that is otherwise unattainable, with the application of formal methods for managing uncertainty. This approach is applied to estimation of sediment transport and coastal change relevant to coastal management and coastal impacts of climate change, as well as to geological exploration.

Rip current swimmer escape numerical modelling

Rip currents are a hazard to bathers on surf beaches worldwide, yet due to logistical and ethical concerns there has been minimal examination of how bathers caught in them should attempt to escape. This study presents the first numerical model of simulated bathers escaping from a rip current.

The model treats bathers as particles that move with the underlying flow, with an additional swimming velocity added, iterating until a safety condition, based on depth and current speed, is satisfied or until a maximum time limit is reached. Simulations compared the strategies of “stay afloat” and various fixed swim directions, using two bather heights and four swim speeds (up to 0.4 m/s).

fig10_concMod_FINAL

The overall optimal escape strategy was to swim parallel in the direction of alongshore flow. Time to safety was less for: (i) recirculating flow; (ii) taller bathers; and (iii) greater swim speeds. Across all simulations, 44% of “floaters” reached safety within 10 min, while 80% of slow swimmers (0.2 m/s) succeeded in the same time interval. This suggests that slow sustainable swimming may be a preferable escape action to floating. Optimal swim direction varied with start location, from onshore (near the shoreline), parallel to shore (mid-rip channel) and diagonally onshore (outer rip channel). Critically, no strategy succeeded in all scenarios at all locations across the surfzone, and small changes to input conditions (water level, start time and location, swim direction) had major impacts on outcomes.

-Jak

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