The upper Swan River estuary located in the eastern suburban area of Perth in Western Australia experiences periods of poor water quality in the form high nutrient levels, anoxic bottom water conditions and occasional nuisance algae blooms. It has long been suspected that oxygen uptake and nutrient release from estuarine sediments are major drivers for these poor water quality conditions. Geoscience Australia in conjunction with the Department of Water in Western Australia investigated water quality in the upper Swan River estuary through water and sediment quality studies in October 2006, September 2007 and May 2008. The objectives of these studies were (1) to characterise the distribution of sediments, in particular to identify areas of high nutrient release, (2) to better understand conditions leading to high oxygen consumption and nutrient release, and (3) to determine the influence of the bottom water oxygen status on nutrient release from sediments.

No abstract available

The historical record reveals that at least five tsunamis generated by earthquakes and volcanic eruptions along the Sunda Arc have impacted the West Australian coast (1883, 1977, 1994, 2004 and 2006). We have documented the geomorphic effects of these tsunamis through collation of historical reports, collection of eyewitness accounts, analysis of pre- and post-tsunami satellite imagery and field investigations. These tsunamis had flow depths of less than 3 m, inundation distances of up to several hundred metres and a maximum recorded run-up height of 8 m. Geomorphic effects include off-shore and near-shore erosion and extensive vegetation damage. In some cases, vegetated foredunes were severely depleted or completely removed. Gullies and scour pockets up to 1.5 m deep were eroded into topographic highs during tsunami outflow. Eroded sediments were redeposited as sand sheets several centimetres thick. Isolated coral blocks and rocks with oysters attached (~50 cm A-axis) were deposited over coastal dunes however, boulder ridges were often unaffected by tsunami flow. The extent of inundation from the most recent tsunamis can be distinguished as strandlines of coral rubble and rafted vegetation. It is likely that these features are ephemeral and seasonal coastal processes will obscure all traces of these signatures within years to decades. Recently reported evidence for Holocene palaeotsunamis on the West Australian coast suggests significantly larger run-up and inundation than observed from the historical record. The evidence includes signatures such as chevron dunes that have not been observed from historical events. We have compared the geomorphic effects of historical tsunami with reported palaeotsunami evidence from Coral Bay, the Cape Range Peninsula and Port Samson. We conclude that much of the palaeotsunami evidence can be accounted for via more traditional geomorphic processes such as reef evolution, aeolian dune formation and archaeological site formation.

This study examined the geomorphology of the sea bed, the spatial distribution of the various sediment types and the geomorphic evolution of Cockburn Sound.

There is growing global concern for the impact of increased fluvial sediment loads on tropical coral reefs and seagrass ecosystems. The Fitzroy River is a macrotidal, tide-dominated estuary in the dry tropics of central Queensland and is a major contributor of sediment to the southern Great Barrier Reef (GBR) lagoon. The estuary currently receives most of its sediment during large episodic flood events commonly associated with cyclonic depressions. The sediment dynamics of macrotidal estuaries and especially of wet-dry tropical systems, with intermittent flows and sediment discharge are poorly understood. Average annual sediment budgets for such a system are also difficult to estimate due to the sporadic nature of flood discharge events. Therefore we have estimated a long-term sediment accumulation rate of catchment-derived sediment trapped in the estuary using the Holocene stratigraphic sequence, determined from a series of sediment cores, dated with radiocarbon and optically stimulated luminescence (OSL), and integrated with industry borehole data. We estimate that 17,400 million tonnes (Mt) of river sediment has accumulated in the estuary during the last 8000 years. This suggests a minimum mean annual bulk sediment discharge of the Fitzroy River of 2000 kt yr-1. This estimated 2175 kilotonnes per year (kt yr-1) of bulk sediment is equivalent to 25% of the estimated average annual modern bulk sediment discharge of the Fitzroy River of 8800 kt yr-1, (Kelly and Wong, 1996) suggesting that the sediment trapping efficiency of the Fitzroy estuary during the Holocene has been approximately 25%. This implies that 75% of the river sediment has been exported from the estuary into Keppel Bay and the adjacent GBR lagoon during the Holocene. With minimal accommodation space left in the floodplain, modern sediment accumulation appears to be focussed around the mangroves and tidal creeks, which cover an area of 130 km2. Cores from the tidal creeks were dated using 137Cs, excess 210Pb, and OSL and display sedimentation rates of approximately 1.5 cm yr-1 for the last 45-120 years, or 1700 kt yr-1, and suggest a modern sediment trapping efficiency for the estuary of around 19%. These results provide useful insights into the long-term sedimentation and quantification of the sediment trapping efficiency of a subtropical macro-tidal estuary with episodic floods, where sediment trapping will vary seasonally and inter-annually.

Freshwater coastal aquifers provide an important resource for irrigated agriculture, human consumption and the natural environment. Approximately 18 million people live within 50 km of the coast in Australia, and many coastal communities are reliant on groundwater. These coastal aquifers are vulnerable to seawater intrusion (SWI) - the landward encroachment of seawater - due to their close proximity to the ocean. To assess the threat of SWI in Australia, a comprehensive literature review was undertaken with input from state/territory agencies. The literature review, in combination with contributions from stakeholders, identified sites within each of the states and the Northern Territory where SWI had been reported or where it was considered to be a serious threat. International Association of Hydrogeologists 2013 Congress poster

Measured probability distributions of shoreline elevation, swash height (shoreline excursion length) and swash maxima and minima from a wide range of beach types are compared to theoretical probability distributions. The theoretical distributions are based on assumptions that the time series are weakly steady-state, ergodic and a linear random process. Despite the swash process being inherently non-linear, our results indicate that these assumptions are not overly restrictive with respect to modeling exceedence statistics in the upper tail of the probability distribution. The RMS-errors for a range of exceedence level statistics (50, 10, 5, 2, and 1 percent) were restricted to <10 cm (and often <5 cm) for all of the swash variables that were investigated. The results presented here provide the basis for further refinement of coastal inundation modeling as well as stochastic-type morphodynamic modeling of beach response to waves. Further work is required, however, to relate the parameters of swash probability distributions to wave conditions further offshore.

Permeable, sandy sediments cover most of the continental shelf. The important role of pore-water advective flow on biogeochemical processes in these sediments has been highlighted in recent studies. Such flow can be driven by wave-action, water-density and interactions between topography and bottom currents, in addition to biological activity, and can create spatially complex and highly dynamic benthic environments in which processes vary on timescales ranging from minutes to months. It is well known that the patchiness of soft sediment (organic matter/bacteria, particle diversity, redox) is likely to be a major determinant of species diversity, but previous studies have not specifically defined patches based on a range of biologically-relevant physico-chemical variables, nor observed how patches change across time. This study, as part of the Surrogates Program in the Commonwealth Environmental Research Facilities Marine Biodiversity Hub, investigated temporal changes in the geochemistry, physical sediments and infauna of sandy sediments in Jervis Bay at two times.

Macrotidal coastal environments are characterised by complex patterns of sediment transport that have been poorly documented in the international literature. Of particular environmental concern is the transport of sediment from tropical coastal catchments, through estuaries and into coral reef environments. Consequently, knowledge of the distribution of benthic environments, and transport pathways of both fine and coarse sediment is required for the effective management of this issue. The Great Barrier Reef (GBR) is located on the continental shelf adjacent to the coast of tropical northeastern Australia. The GBR comprises an outer coral-dominated environment that encloses a large lagoon dominated by catchment-derived sediments. Keppel Bay is a macrotidal environment that represents the interface of the large catchment of the Fitzroy River with the southern GBR lagoon. We classified the benthic sediments of Keppel Bay into five distinct facies based on the statistical analysis of physical and geochemical sediment data and modelled seabed shear stress (the influence of waves and tidal currents). Multibeam sonar was employed to determine bedload sediment transport directions as indicated by bedform geometry, and to identify areas of sediment accumulation and erosion. Our findings suggest that much of the catchment-derived fine sediment accumulates in the mouth of the Fitzroy River. Outer Keppel Bay is dominated by relict palaeochannels, and the shoreward transport of sediment from the continental shelf. The Fitzroy River-Keppel Bay system provides a useful facies model for a seasonal, sediment-starved macrotidal depositional setting in which bedrock configuration and relict features dominate geomorphology, and restrict processes of modern sediment accumulation.

Keppel Bay is a macrotidal environment that represents the interface of the large catchment of the Fitzroy River with the southern GBR continental shelf. In this study, we assessed the distribution of sediments and their depositional characteristics using a combination of sediment sampling, and acoustic (sonar) seabed mapping tools. Using statistical techniques, we classified the seabed sediments of Keppel Bay into five distinct classes, based on sediment grainsize, chemical composition, and modelled seabed hear stress (the influence of waves and tidal currents).