A process based approach to understand WA s complex coastline Jeff Hansen Ryan Lowe Graham Symonds Laura Segura Gundula Winter

Transcription

1 A process based approach to understand WA s complex coastline Jeff Hansen Ryan Lowe Graham Symonds Laura Segura Gundula Winter

2 WA s coastline is highly variable due to offshore and shore-attached coral and limestone reefs Wave interaction with reef structures is a fundamental factor controlling shoreline position and response over a wide range of spatial scales. Wave/reef interactions ultimately influence water quality and swimmer safety for example.

3 Relationship between reefs and beaches is complex and presents challenges to coastal management Limited mechanistic understanding of how spatial variations in waves, caused by reefs, ultimately determine beach width and response. Vast majority of literature on beach morphodynamics is from straight sandy beaches (e.g. East Coast of USA) and therefore likely not applicable to WA s beaches. A more complete understanding of processes is required to predict and mitigate impacts from climate change along WA s coast.

4 Monitoring of WA s coastline lacking compared to eastern states Need to better understand Australia s coastline highlighted in 2013 Marine Nation 2025 white paper. Capacity to understand and monitor WA s coast already exists, but needs to be directed into coordinated approach. Coastal dynamics not constrained by council/shire boundaries Coastal monitoring, once initiated, is low cost relative to the benefit gained. UNSW WRL CSIRO Secret Harbour Barnard et al., GRL 2011

5 Active research projects in WA Examples of UWA/CSIRO collaborative projects include: Garden Island Secret Harbour Ningaloo coast Garden Island Secret Harbour Ningaloo Reef

6 Garden Island shoreline variability Nearmap digitized shorelines Empirical orthogonal function analysis indicates dominant temporal and spatial signals in the shoreline movement.

7 Garden Island hydrodynamic experiment - May/June 2014 Gundula Winter Drifter release locations 100 m 8 days 2 release locations: Northern and southern channel Up to 15 drifters used each release hours each day

8 Single drifter deployments m/s Example of Drifter Retention from Reef 28 May 2014 Retention during big waves

9 Single drifter deployments m/s Example of Drifter Exits from Reef 3 June 2014 Ejection during small waves

10 Secret Harbour Two-week experiment quantifying impact of summer sea-breeze on beach morphology. Topographic beach surveys every 2 hours during daylight. Complimented by array of instruments in the surf zone. Before sea breeze After sea breeze Laura Segura

11 Fringing reef shoreline dynamics What mechanisms are leading to accreted shorelines onshore of fringing reefs? Mean flow patterns are not consistent with observed shoreline orientation. GPS drifter trajectories, Ningaloo reef?

12 Ripple crest are parallel to the shoreline Observations from recent pilot experiment suggest onshore migrating sand ripples may be the primary source of beach sediment not currents.

13 Summary WA s unique coastal morphology results in highly-variable shoreline response that is difficult to predict given current understanding and conceptual models. There is considerable need to broaden our understanding of coastal morphodynamics into mixed sand/reef environments, and this is presently underway at a variety of sites. The capacity exists to conduct fundamental and applied coastal research in WA.

14 Waterman s Bay Marine Centre Undersea Observatory IOMRC building

15 Observatory aims Establish a continuously operating array of instruments spanning a range of marine science disciplines offshore of the IOMRC Waterman s Bay Marine Centre. Provide relevant data in real-time, free of charge, to the public and governmental agencies (e.g. allow real-time assessment of coastal ocean conditions that can support marine safety and recreational coastal use). Establish long-term records of physical, chemical an biological variables to quantify environmental change. Build technical capacity within Western Australia to deploy coastal observing systems Australia wide and within the Indian Ocean rim. Link with industry partners to develop and test undersea instrumentation and infrastructure. Enhance Australia s marine science education, across all levels, by engaging students in the collection and analysis real-time ocean observations.

16 Schematics of similar observatories Ocean Networks Canada MBARI MARS station WHOI OceanCubes