From 1 - 10 / 1375
  • Multibeam bathymetry gridded at 20m resolution and projected to WGS84 UTM zone 50S from the North Perth Survey (GA reference GA-0332).

  • The Marine Survey Multibeam Bathymetry Web Map Service contains the highest-resolution multibeam bathymetry grids available for download on Geoscience Australia's website. These bathymetry grids were collected over numerous multibeam survey programs conducted in Australian mainland and Antarctic waters by both Geoscience Australia and our collaborators. Layers are grouped by survey or region and where available include both the Geoscience Australia and vessel survey identification numbers that contributed to the bathymetry grids. Bathymetry grids have been rendered over a rainbow colour-ramp with minimum and maximum depth values unique for each survey. These values are specified in each survey's layer description. The resolution of each bathymetry grid is also specified in each survey's layer description

  • This report presents the results of seabed mapping and habitat classification surveys completed in Darwin Harbour during 2011 and 2013 as part of the Northern Territory Government's marine habitat mapping program. This research aims to provide baseline data on the existing marine habitats and characteristics of the Darwin Harbour region. It is a collaboration between Geoscience Australia (GA), the Australian Institute of Marine Science (AIMS), the Department of Land Resource Management (DLRM) and the Darwin Port Corporation. Key objectives are to: - Produce detailed maps of the bathymetry and derived parameters such as slope and rugosity, - Classify the seabed into areas of hard and soft substrate, and, - Produce seabed habitat maps (or seascapes). Data collection was completed in two stages comprising a multibeam survey, undertaken on the MV Matthew Flinders in 2011 by DLRMs predecessor, the Department of Natural Resources, Environment, the Arts and Sport (NRETAS), GA, AIMS and the Darwin Port Corporation; and, a seabed sampling survey undertaken in 2013 on the MV John Hickman, by DLRM and GA. Data acquired from the surveys included continuous high-resolution multibeam sonar bathymetry and acoustic backscatter, video and still camera observations of seabed habitats and biological communities, and physical samples of seabed sediments. Key outcomes from the surveys include: 1. Improved understanding of the seabed of Darwin Harbour. The main seabed geomorphic features identified in Darwin Harbour include banks, ridges, plains and scarps, and a deep central channel that divides into smaller and shallower channels. Acoustically hard substrates are found mostly on banks and are associated with rocky reef and sponge gardens, and are often overlain by a thin veneer of sandy sediment. In contrast, plains and channels are characterised by acoustically soft substrates and are associated with fine sediments (mud and sand). 2. Classification of physical seabed properties to produce a Seascape Map for Darwin Harbour. Six seascape classes (potential habitats) were derived using an Iterative Self Organising (ISO) unsupervised classification scheme. These six classes are related to statistically unique combinations of seabed substrate, relief, bedform and presence of sediment veneer (quite often inferred from presence of epibenthic biota). The results presented in this report demonstrate the utility of multibeam acoustic data to broadly and objectively characterise the seabed to describe the spatial distribution of key benthic habitats. This is particularly important technique in high-turbidity settings such as Darwin Harbour where the application of satellite and aerial remote sensing techniques can be limited. The results of this study will be used for the planning and analysis of data from upcoming benthic biodiversity studies as they: - Provide robust near-continuous physical variables that can be used to predictive modelling of biodiversity; - Provide high-resolution coverage of near-continuous variables that describe the key physical characteristic of the seabed of the harbour, and; - Enhance survey sample design by providing indicative locations of likely similar biology communities.

  • Coastal communities in Australia are particularly exposed to coincident natural hazards, whereby tropical cyclones and extra-tropical storms cause damage to infrastructure and shorelines from severe wind, flood and storm surge. Because the climatic drivers of severe storms are stronger under certain conditions (e.g. during La Ni±a periods for tropical cyclones), these events can repeatedly impact the coast over periods of weeks to months. Historically, major episodes of beach erosion along southeast Australia have occurred during every decade over the last century, with the most severe in 1974 resulting from two extra-tropical storms in two months. <p>While the process of beach erosion is well understood in general terms, the response of a specific sector of coast to clustered storms may not be. For effective coastal management, this site specific knowledge becomes essential. Here we present a framework for integrating coastal geomorphology and coastal engineering approaches to model shoreline response to clustered storms at a spatial scale that can directly inform management agencies. We focus on two case study areas in southeast Australia, the beaches of the Adelaide metropolitan coast (South Australia) and Old Bar beach (central New South Wales) where erosion is a management priority. <p>For each site we adopt the coastal sediment compartment as the functional management unit, mapped for the Australian continent at multiple spatial scales, and use sub-surface information (boreholes, ground penetrating radar profiles) to estimate sediment volumes in the upper beach to foredune. These data are then used to inform shoreline response modelling linked to an event time series (observed and hind cast) as a separate project component. Future work includes assessment of `at-risk infrastructure at each site. This paper is a contribution to the Bushfire and Natural Hazard Cooperative Research Centre project Storm surge: Resilience to clustered disaster events on the coast.

  • <p>Knowledge of extreme ocean climate is essential for the accurate assessment of coastal hazards to facilitate risk informed decision making in coastal planning and management. Clustered storm events, where two or more storms occur within a relatively short space of time, may induce disproportionately large coastal erosion compared to non-clustered storm events. Therefore this study aims to develop a statistical approach to modelling the frequency and intensity of storm events on the eastern and southern coast of Australia, with a focus on examining storm clustering. This paper presents the preliminary analysis of the recently developed methods and results when they are applied to a study site on the central coast of New South Wales, Australia. This study is a key component of the Bushfire and Natural Hazards CRC Project Resilience to clustered disaster events on the coast storm surge that aims to develop a new method to quantify the impact of coincident and clustered disaster events on the coast. <p>Extreme storm events at a given site can be described using multivariate summary statistics, including the events maximum significant wave height (Hsig), median wave period, median wave direction, duration, peak storm surge, and time of occurrence. This requires a definition of individual storm events, and so the current methodology firstly involves the extraction of independent storm events from a 30-year timeseries of observations. Events are initially defined using a peaks-over-threshold approach based on the significant wave height. The value of 95% exceedance quantiles (2.93 m) is adopted. Subsequently, these events are manually checked against sea-level pressure data to examine if closely spaced events are generated by the same meteorological system, and if so the events are combined. This means that the final event set is more likely to consist of statistically independent storm events. <p>Various statistical techniques are applied to model the magnitude and frequency of the extracted storm events. A number of variations on the non-homogenous Poisson process model are developed to estimate the event occurrence rate, duration and spacing. The models account for the sub-annual variations in the occurrence rate, temporal dependency between successive events, and the finite duration of events. The results indicate that in the current dataset, closely spaced events are more temporally spread out than would be expected if the event timings were independent, which we term anti-clustering. A particular marginal distribution is fitted to each variable, i.e. a Generalised Pareto (GP) distribution for Hsig, and Pearson type 3 (PE3) distributions for duration and tidal residual. Empirical marginal distributions are employed for wave period and direction. The joint cumulative distribution function of all storm magnitude statistics is modelled by constructing dependency structure using Copula functions. Two methods are tested: a t-copula and a combination of a Gumbel and Gaussian copulas. Comparison of modelled and observed scatterplots shows similar pattern, and the difference of using the two methods is marginal. The goodness-of-fit tests such as Komologorov-Smirnov (K-S) tests, Chi-square tests and AIC and BIC are used to quantitatively evaluate the fitting qualities and to assess model parsimony, along with graphical visualisations e.g. QQ plots. <p>Based on this approach, a set of long-term synthetic time-series of storm events (106) is generated using the event magnitude and timing suggested by the optimised models. These long-term synthetic events can be used to derive exceedance probabilities and to construct designed storm events to be applied to the beach erosion modelling.

  • Hemipelagic, sediment drift deposits have been discovered and mapped on the Antarctic Peninsula shelf in 300-500 m water depth. The drift located adjacent to Andvord Bay covers 44.5 km2 and exhibits continuous and discontinuous parallel reflections that conform to peaks and valleys in the acoustic basement as observed in deep-tow boomer and sparker seismic records. This style of drift deposit is a common feature of deep oceanic sediments, but is not normally found in continental shelf environments.

  • Seagrass communities in the northwest of Torres Strait are known to disappear episodically over broad areas. Sediment mobility surveys were undertaken within two study areas during the monsoon and trade wind seasons, in the vicinity of Turnagain Island, to find out if the migration of bedforms could explain this disappearance. The two study areas covered sand bank and sand dune environments to compare and contrast their migration characteristics. Repeat multibeam sonar surveys were used to measure dune-crest migration during each season.

  • A symposium was held at the University of Wales, Swansea in July 2007 to honour the career and achievements of Professor Michael Collins. The symposium was organised by Michael's former postgraduate students as a tribute to his contributions over the past 30 years as a scientist, teacher, mentor and friend. About 30 of the 50+ Ph.D. and M.Sc. students that Michael has supervised over the years were fortunate to attend the symposium, which offered the opportunity for all of us to learn about the many different subjects and projects that Michael supervised and to renew our friendships with the Collins family, as well as the extended, academic Collins 'family'.