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This paper discusses the progress of the landslide susceptibility mapping in the wider Sydney Basin area to facilitate engineering and geological studies and land-use zoning; using induced decision trees. This study investigates the effect of the basic unit of this spatial modelling work (pixel resolution) on the accuracy of the modelling outcome, and reports on the effectiveness of using See5 pruned decision trees to model the landslide susceptibility of the Sydney Basin. Landslide susceptibility was determined from the landslide confidence value derived from the Laplace ratio of the rule based predicted classes. The modelling work has been carried out at 2 m, 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, and 40 m pixel resolutions for a trial area within the Sydney Basin. Ten different GIS based datasets derived from the same original datasets have been used each time as landslide causative factors. The optimum tree pruning parameters for each pixel resolution were identified by analysing the behaviour of misclassification errors. Performance of the models at different pixel resolutions was compared using ROC curves and five-fold cross validation accuracy. High density ALS elevation point clouds and large scale datasets allowed model development at a higher resolution (2 m) but the decision tree model at 10 m resolution performed better than the rest. The ratio between the square root of the mean landslide area of the inventory and the area covered by a single pixel has been developed as a worthwhile quantitative measurement of the adequacy of the model resolution. The validation results of the final modelling outcome show that landslide susceptibility descriptors fulfil the requirements of the LRM guidelines. The model has a conservative success of 90% according to the field validation and a cross validation accuracy of 92%. [ABSTRACT FROM AUTHOR]

Coal seam gas zonation in the Sydney Basin, NSW, Australia is related to basin hydrodynamics and hydrochemical facies evolution along the flow path from the subcrop to the basin center. Biogenic methane corresponds with meteoric water under hydrostatic pressure and persists down to the top of the geopressured zone (~ 800 to 1000 m). Thermogenic gases, including wet hydrocarbons, can reach up to relatively shallow horizons of less than 500–600 m depth. In the transition zone between the top of the geopressured and base of the hydrostatic zone, a mixed water and gas regime prevails, comprising brackish waters, and gases of mixed biogenic, thermogenic and inorganic origins, including CO 2 . Mechanisms for and the role of stress in the development of this layered hydrogeological and gas environment are investigated in this paper. The inverse relationship between effective horizontal stress and permeability in coals through regulation of cleat volumes is well documented, and there is evidence of regionally compartmentalized stress regimes with depth within the Sydney and other eastern Australian coal basins. This regional stress regime can be overprinted by the effect of localized geological features. It is hypothesized that the in situ stress regime plays an important role in the regulation of groundwater flow regimes and extents, resulting in the development of the reported gas content and compositional zonation. Analysis of regional gas and stress data obtained from public and private databases, as well as literature, supports this hypothesis. Changes in gas concentration and composition with depth correspond with discernable variations in horizontal stress anisotropy. Gas contents generally increase with depth down to a ‘peak gas’ horizon, below which concentrations decrease. This ‘peak gas’ zone is coincident with a horizontal stress anisotropy change from moderately high to low levels, associated with reverse to strike–slip faulting conditions, respectively. The stress release zone also marks the top of the thermogenic gas zone, identified by the first appearance of ethane in the vertical profile. This zone also hosts gases of mixed origins: biogenic, thermogenic and inorganic (CO 2 ) and represents a mixed (transitional) groundwater flow environment. The base of the mixed gas zone is the top of the ‘geopressured-only’ flow associated with thermogenic gases and is signaled by the return to high stress reverse faulting conditions below 850–900 m depth in the Sydney Basin. [ABSTRACT FROM AUTHOR]

Temperate Highland Peat Swamps on Sandstone (THPSS) and Coastal Upland Swamps in the Sydney Basin (CUSSB) are listed as endangered ecological communities under Australia's national and state legislation. They are threatened by a range of human and climate impacts. Across the region there are 3208 individual, valley-bottom, elongate-shaped, upland swamps that drain first- or second-order drainage lines and small catchment areas (mean = 0.25 km2). They occur at a median distance of 57 km from the coast in areas with an average annual rainfall of 1505 mm/year and average annual temperature of 15°C. Those closer to the coast occur on elevations as low as 160 m a.s.l., and those further from the coast, on plateau country, occur up to 1172 m a.s.l. (median 634 m a.s.l.). The valleys that contain these swamps terminate downstream at a valley constriction or bedrock step, behind which alluvial materials have accumulated, and peat has formed to produce relatively steep swamps (median slope 6.2 per cent). Understanding the spatial distribution and physical attributes of these systems, and having the accompanying maps as a resource, is critical for development of sound, well-informed conservation, rehabilitation and monitoring programs, and for analysing the ecosystem services they provide. [ABSTRACT FROM AUTHOR]

This study examined two underground coal mines in the Sydney basin and investigated the water chemistry impact from their wastewater discharges to surface receiving waters. One mine closed 17 years prior to the study, and the other was still active. The geology of both mine locations shared many similarities and some important differences that influenced their wastewater chemistry and its subsequent impact on receiving waterways. Water quality of wastewater discharges from the two mines and their receiving waterways was investigated over a 6-month period. Both mine discharges caused comprehensive modification to receiving water chemistry. The closed mine increased electrical conductivity (EC) 3.3 times from upstream (33 μS/cm) compared to downstream (108 μS/cm). In comparison, the active mine increased EC by 9.4 times (173 μS/cm) upstream to 1628 μS/cm downstream. Both coal mine wastes increased the concentration of different contaminants to levels that are potentially hazardous for receiving water ecosystems. The active mine increased bicarbonate concentration in the receiving water by more than 60 times to 743 mg/L. The closed mine increased zinc and nickel concentrations in its receiving stream by 70 and 20 times to 318 and 360 μg/L. The active coal mine discharge was dominated by sodium and bicarbonate ions compared to magnesium and sulphate ions in the closed mine drainage. Although both receiving waters were sodium and chloride dominated upstream of the mine waste, their ionic composition was strongly modified due to the inflow of coal mine wastes. Results from this study are a reminder that water pollution from coal mines is important for both active mines and for closed mines decades after mining activity ceases. [ABSTRACT FROM AUTHOR]

The Australian continent displays the most complex pattern of present-day tectonic stress observed in any major continental area. Although plate boundary forces provide a well-established control on the large-scale (>500 km) orientation of maximum horizontal stress (SHmax), smaller-scale variations, caused by local forces, are poorly understood in Australia. Prior to this study, the World Stress Map database contained 101 SHmaxorientation measurements for New South Wales (NSW), Australia, with the bulk of the data coming from shallow engineering tests in the Sydney Basin. In this study we interpret present-day stress indicators analysed from 58.6 km of borehole image logs in 135 coal-seam gas and petroleum wells in different sedimentary basins of NSW, including the Gunnedah, Clarence-Moreton, Sydney, Gloucester, Darling and Bowen–Surat basins. This study provides a refined stress map of NSW, with a total of 340 (A–E quality) SHmaxorientations consisting of 186 stress indicators from borehole breakouts, 69 stress measurements from shallow engineering methods, 48 stress indicators from drilling-induced fractures, and 37 stress indicators from earthquake focal mechanism solutions. We define seven stress provinces throughout NSW and determine the mean orientation of the SHmaxfor each stress province. The results show that the SHmaxis variable across the state, but broadly ranges from NE–SW to ESE–WNW. The SHmaxis approximately E–W to ESE–WNW in the Darling Basin and Southeastern Seismogenic Zone that covers the west and south of NSW, respectively. However, the present-day SHmaxrotates across the northeastern part of NSW, from approximately NE–SW in the South Sydney and Gloucester basins to ENE–WSW in the North Sydney, Clarence-Moreton and Gunnedah basins. Comparisons between the observed SHmaxorientations and Australian stress models in the available literature reveal that previous numerical models were unable to satisfactorily predict the state of stress in NSW. Although clear regional present-day stress trends exist in NSW, there are also large perturbations observed locally within most stress provinces that demonstrate the significant control on local intraplate sources of stress. Local SHmaxperturbations are interpreted to be due to basement topography, basin geometry, lithological contrasts, igneous intrusions, faults and fractures. Understanding and predicting local stress perturbations has major implications for determining the most productive fractures in petroleum systems, and for modelling the propagation direction and vertical height growth of induced hydraulic fractures in simulation of unconventional reservoirs. [ABSTRACT FROM PUBLISHER]