The goal of this study was to investigate how extreme hydraulic loading influences hydraulic pathways, and thus failure potential, of two soil absorption systems. A grid of tensiometers and piezometers were installed beneath and adjacent to the absorption trenches, and water height was manipulated to simulate different hydraulic loadings. At both sites, measured soil matric potentials along the trench sidewalls increased toward zero as water height increased over time, indicating that water was preferentially flowing laterally above the biomat zones. Saturated hydraulic conductivity ( Ks ) of the soil and biomat, and other hydraulic parameters were calibrated using inverse modeling procedures in HYDRUS-2D. We found generally good agreement between measured and predicted matric potentials. The calibrated model was then used to predict fluxes through different infiltrative zones under typical and extreme hydraulic loads. Modeling indicated that the overall infiltration rates through the biomat and subbiomat...

One feature of riparian zones is their ability to significantly reduce the nitrogen loads entering streams by removing nitrate from the groundwater. A novel GIS model was used to prioritise riparian rehabilitation in catchments. It is proposed that high-priority areas are those with a high potential for riparian denitrification and have nearby land uses that generate high nitrogen loads. For this purpose, we defined the Rehabilitation Index, which is the product of two other indices, the Nitrate Removal Index and the Nitrate Interception Index. The latter identifies the nitrate contamination potential for each raster cell in the riparian zone by examining the extent and proximity of agricultural urban land uses. The former is estimated using a conceptual model for surface–groundwater interactions in riparian zones associated with middle-order gaining perennial streams, where nitrate is removed via denitrification when the base flow interacts with the carbon-rich riparian sediments before discharging to the streams. Riparian zones that are relatively low in the landscape, have a flat topography, and have soils of medium hydraulic conductivity are most conducive to denitrification. In the present study, the model was implemented in the Tully–Murray basin, Queensland, Australia, to produce priority riparian rehabilitation area maps.

Regulators require the gas industry to assess the risks of unintentional release of chemicals to the environment and implement measures to mitigate it. Industry standard models for contaminant transport in aquifers do not explicitly model processes in the unsaturated zone and groundwater models often require long run times to complete simulation of complex processes. We propose a stochastic numerical-analytical hybrid model to overcome these two shortcomings and demonstrate its application to assess the risks associated with onshore gas drilling in the Otway Basin, South Australia. The novel approach couples HYDRUS-1D to an analytical solution to model contaminant transport in the aquifer. Groundwater velocities and chemical trajectories were derived from a particle tracking analysis. The most influential parameters controlling solute delivery to the aquifer were the soil chemical degradation constant and the hydraulic conductivity of a throttle soil horizon. Only 18% of the flow paths intercepted environmental receptors within a 1-km radius from the source, 87% of which had concentrations of <1% of the source. The proposed methodology assesses the risk to environmental assets and informs regulators to implement measures that mitigate risk down to an acceptable level.