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Model evaluation of RIMPUFF within complex terrain using an Ar-41 radiological dataset.
Get PDFThe newly updated atmospheric dispersion model RIMPUFF is evaluated using routine releases of 41Ar from the former HIFAR research reactor located at the Australian Nuclear Science and Technology Organisation (ANSTO) in Sydney, Australia. Predicting radiological dispersion for emergency response at this site proves challenging due to complex topographical conditions including a steep-sided river valley located between the reactor and the nearest residents. A large number of 41Ar measurements from a network of environmental gamma detectors are used to evaluate the model under a range of atmospheric stability conditions. Topographic and meteorological influences that potentially affect a released plume, such as channelling, wind shear, local terrain slope flows and strong inversions are explored. A sensitivity analysis using various combinations of meteorological station data for model input, including vertical wind and temperature profiles, also identifies model strengths and weaknesses within the complex terrain. Various model evaluation tools, such as relevant statistical indices and gamma dose contour plots, are used to evaluate this new version of RIMPUFF for emergency response purposes at ANSTO and for inclusion in the ARGOS Decision Support System
Modern and historical engineering components investigated by neutron diffractionon ENGIN-X
Get PDFThe ENGIN-X beamline is mainly used to determine residual strains/stresses deep within the interior of bulk engineering components. It is mainly used by scientists and engineers for the development of modern engineering processes and structural integrity investigations. ENGIN-X diffraction and transmission mode can be a very useful tool to measure strain, phase transitions, texture and material composition in spatial resolution in historical or archaeological artifacts and modern materials. The complexity of the shapes and sizes of the samples measured on ENGIN-X varies significantly between experiments, and this required the development of better planning, simulation and control software, SScanSS. In this paper an overview of recent developments in strain scanning on ENGIN-X and a highlight of current scientific research are presented. © 2012 The Japan Society of Mechanical Engineer
Benthic foraminifera: Their importance to future reef island resilience
Get PDFThe provenance, age and redistribution of sediments across Raine Reef (11°35’28”S 144°02’17”E),
northern Great Barrier Reef (GBR) are described. Sediments of both the reef flat and sand cay beaches are
composed predominantly of benthic foraminifera (35.2% and 41.5% respectively), which is a common
occurrence throughout the Pacific region. The major contemporary sediment supply to the island was identified
as Baculogypsina sphaerulata, a relatively large (1-2 mm exclusive of spines) benthic foraminifera living on the
turf algae close to the reef periphery, and responsible for beach sand nourishment. Radiometric ages of
foraminiferal tests of ranging taphonomic preservation (pristine to severely abraded) included in surficial
sediments collected across the reef flat were remarkably young (typically <60 years). Results indicate rapid
transport and/or breakdown of sand with a minimal storage time on the reef (likely <102
years), inferring a tight
temporal link between the reef island and sediment production on the surrounding reef. This study demonstrates
the critical need for further research on the precise residence times of the major reef sediment components and
transport pathways, which are fundamental to predicting future island resilience. © Copyright belongs to the authors
Emerging applications of nuclear and isotopic techniques in the environmental sciences
No full textNone available
Geological and geochemical field survey on the Sendai Plain following the 11 March 2011 Tohoku-Oki Tsunami
No full textA post-tsunami survey was carried out in May 2011 by members of a UNESCO-IOC International Tsunami Survey Team. The geological and geochemical survey was carried out along a transect extending 4.5 km inland north of Sendai airport, and focused on tsunami flow characteristics, sedimentation and erosion, as well as assessing the impact of saltwater contamination on the paddy fields . Tsunami inundation in this area reached c. 4.5 km inland, and the limit was marked by the elevated Tobu Highway, except where underpass structures allowed inundation further inland. The tsunami deposit generally thinned and fined inland, with the sandy deposit thinning landward from about 30 cm thickness in the coastal forest to less than 0.5 cm c. 2.8 km inland. Rip-up clasts were observed mostly near the base of the sandy deposits. Further inland, the deposit was dominated by mud, although it contained thin sand laminae one to a few grain-thick up to the limit of inundation near Tobu Highway. The thickness of the tsunami deposit was found to show large variability over short distances. Erosion and liquefaction features were also commonly observed. Ponded water was reported between the coastal forest and up to 2.6 km inland, while salt crusts were observed on numerous rice paddy fields up to the limit of tsunami inundation, where the water had evaporated. Conductivity measurements of ponded water, canals, irrigation and drainage channels revealed that the water was still saline to brackish, despite >60 mm of precipitation in the two months since the tsunami. Elevated concentrations of water-leachable chloride (salt) were measured both in mud and sand deposits, where seawater had stagnated and evaporated
Methane simulations at Cape Grim to assess methane flux estimates for South East Australia
No full textA transport model intercomparison for methane (TransCom-CH4) has been run involving twelve
models (Patra et al., 2011). We contributed simulations using two climate models, CCAM and
ACCESS. The CCAM simulations were nudged to NCEP analysed meteorology, which allows
simulated atmospheric concentrations to be compared to observations on synoptic timescales.
The ACCESS simulations were forced only with observed sea surface temperatures and are
consequently not expected to match observed synoptic variations. The TransCom experiment
involved simulating six CH4 tracers (with different prescribed fluxes) along with SF6, radon and
methyl chloroform. We have analysed hourly model output for Cape Grim and find that the
magnitude of the non-baseline signal differs, especially in winter, dependent on the CH4 flux
scenario used. The magnitude of the non-baseline signal also varies between models, although
these differences can be reconciled when methane is scaled by model-simulated radon
concentration. Comparison with observed CH4, also scaled using radon, suggests that the CH4
flux scenario with little or no wetland emissions in winter matches the observations. The
observations also indicate an apparent extra source of CH4 in October-November not seen in the
model simulations. However this appears to be an artefact of this analysis method which
assumes that radon emissions are known (and in this case constant in space and time). We have
found that the discrepancy between model and observations in spring appears to be due to a
poor simulation of radon, rather than CH4. Observed radon shows a larger seasonality than
modelled radon, which suggests that temporal and spatial variations in radon flux need to be
considered. It would also be helpful to understand why the simulated CCAM and ACCESS
radon (and non-baseline CH4) concentrations differ in magnitude. Comparisons with Cape
Grim output from the other participating TransCom-CH4 models may provide some insight
Field observations of erosion, deposition, and tsunami flow characteristics on the Sendai Coastal Plain after the March 2011, Tohoku-oki Tsunami, Japan
No full textHistorical and instrumental data show that the Pacific coast of Mexico has been exposed to destructive tsunamis over at least the past 500 years. This coast is also affected by hurricanes generated in the eastern Pacific. The great 1985 Mexico earthquake and its aftershock generated tsunamis that affected the Ixtapa-Zihuatanejo and Michoacán coast. The purpose of our study was two-fold, a) to determine whether we could distinguish storm from tsunami deposits, and b) whether tsunami deposits from historical events are preserved in the tropical environments of the Ixtapa-Zihuatanejo coast. Two anomalous sand units in the Ixtapa estuary are interpreted as the result of high-energy marine inundation events that occurred in the last century. Several lines of evidence using a multi-proxy approach (historical studies, interviews with local witnesses, geomorphological and geological surveys, coring and trenching, and laboratory analyses including grain size, micropaleontology, geochemistry, magnetic susceptibility and radiometric dating) indicate the occurrence of two tsunamis that we link to local events: the 1985 Mexico and possibly the 1979 Petatlan earthquakes. We thereby provide the first onshore geological evidence of historical tsunamis on the Pacific coast of Mexico. © American Geophysical Unio
Investigating the origin of salinity and aquifier interaction in a sesonally pumped confined aquifier system in southeast Australia (Western Port Basin)
No full textThis ongoing study aims to identify the different sources of fresh/saline water, pathways, mechanisms of
groundwater salinisation, and factors controlling salt-water intrusion in the Western Port Basin aquifer (Victoria,
Australia). The multi-layered aquifer is characterised by variable distributions of fresh and saline groundwater at the
coastline, which are speculated to result due to geological heterogeneity, and the influence of past sea levels. The
spatial salinity distribution observed indicates that the typical situation of a dense saltwater wedge underlying fresh
groundwater does not apply. Further to natural drivers, an understanding of the potential short and long term
effects of seasonal pumping for irrigation in the basin is desired, particularly whether it induces migration of water
from other areas in the basin or causes leakage from low-permeability horizons.
The impact of seasonal pumping on the variation and distribution of salinity was examined at a nested bore site 500
m from the coast. Analyses of chloride concentration and 18O in groundwater indicate various degrees of mixing
between seawater and fresh meteoric groundwater. Multi-depth sampling in the upper aquifer, identified high
salinity water with ~19% seawater mixture above slightly less saline water – with ~17% seawater; while samples
from the lower aquifer yielded significantly fresher groundwater (~4 to 7% seawater). This is likely to be due to the
relatively good connection between the upper aquifer and the ocean, and low-permeability material separating the
shallow and deeper aquifers. Seasonal salinity changes were observed as a response to pumping, with salinity in the
upper aquifer decreased by ~15.5% at the onset of pumping, and salinisation gradually increased once pumping
ceased by ~22%.
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Recent 14C dating of groundwater in the proximity of the pumping area revealed low radiocarbon activities (<25
pMC) and a lack of tritium, which rules out the possibility of modern recharge reaching the pumping area. A thick
Holocene clay cap (ranging from 10 to 30 m) covering significant areas and extending beneath the bay, limits rainfall
recharge to the basin margins where the aquifers outcrop. Beneath the shallow bay a paleoriver channel incised
deep into the bay floor sediments expose the aquifer to potential vertical and horizontal input from modern
seawater. However, the lack of long-term salinisation despite decades of pumping, and the relatively old
groundwater ages, imply buffering against saline intrusion by stores of relict fresh water. Incorporation of these
results into a conceptual model will contribute to an improved understanding of the groundwater flow system and
the long-term implications of pumping on future groundwater sustainability in the Western Port Basin
Irrigation bore water in the Condamine Catchment: baselining groundwater quality and assessing pathways of hydraulic connectivity
No full textThe expansion of coal seam gas production adjacent to the irrigation farming districts in the Condamine Catchment
has raised concerns about the impact of gas production on groundwater in adjoining aquifer systems. To assess the
risk, and to be able to detect any future changes in groundwater properties, existing groundwater chemistry data
sets need to be updated and expanded. Historically, the testing of groundwater chemistry in the Condamine
Catchment has focused on the Queensland Government groundwater-monitoring network, but it is unlikely that
these samples come from the same sand and gravel bodies from which the irrigation bores extract groundwater. We
report the result of 20 groundwater samples collected from bores that supply irrigation water for cotton and other
crops. These samples were collected in January 2014 at the end of the pumping season, when the aquifer system is
at peak stress for the year.
We compare the major ion chemistry recorded in the irrigation bores to that measured at selected sites from the
QLD government groundwater-monitoring network and with historical results reported in the literature. A
hydrochemical facies analysis of these data provides one assessment of the likelihood of hydraulic connectivity
between the Walloon Coal Measures, other bordering Great Artesian Basin formations and the valley filling
sediments of the Condamine Alluvium.
The results highlight variation in groundwater chemistry within the Condamine Alluvium, particularly in the Cecil
Plains and Dalby regions, where there are signs of water mixing. As a result, further research into the area to explain
the baseline data sets would provide a better understanding of hydraulic connectivity and the potential effects of
CSG on the groundwater