Abstract Black Box ( Eucalyptus largiflorens F. Muell.), is a keystone tree species of lowland semi‐arid floodplain ecosystems in south‐eastern Australia. E. largiflorens woodlands are of high conservation value and threatened by climate change‐induced drought and irrigation water diversions due to their location on upper floodplain areas where flood frequency has declined. Water requirements of E. largiflorens have not been well quantified using empirical data. Accordingly, knowledge gaps exist in relation to volumes of environmental water required to maintain and improve ecological condition for disconnected floodplain woodlands. To further assist conservation and water resource management, we tested the use of drip irrigation to provide a variety of water regimes to experimental plots in order to monitor tree responses. Water was provided via irrigation delivery across four regimes representing known volumes of water, referred to as an environmental water provision, applied over a 22‐week period for two Austral summers. Benefits to trees were identified by measuring transpiration and plant water status using sap flow sensors and a Scholander pressure chamber, respectively. Results indicate that volumes of 0.3, 0.4, 0.7 and 0.8 ML increased transpiration and improved plant water status in comparison to a control, with delivery recommended to commence early autumn. Greater volumes (1.4 ML), substantially increased transpiration and improved water status, especially when delivered at a rate of ~25 mm week −1 compared to a monthly 'burst' which broadly represented natural, sporadic summer rainfall in the region. For an environmental watering provision of 25 mm week −1 , ~178 ha of E. largiflorens woodland can be watered with a 1 GL environmental water allocation. The study methods presented are relevant worldwide and our results further the collective understanding of the benefits environmental water provides to E. largiflorens .
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.
In environments with shallow ground water elevation, small changes in the water table can cause significant variations in recharge and evapotranspiration fluxes. Particularly, where ground water is close to the soil surface, both recharge and evapotranspiration are regulated by a thin unsaturated zone and, for accuracy, must be represented using nonconstant and often nonlinear relationships. The most commonly used ground water flow model today, MODFLOW, was originally designed with a modular structure with independent packages representing recharge and evaporation processes. Systems with shallow ground water, however, may be better represented using either a recharge function that varies with ground water depth or a continuous recharge and evapotranspiration function that is dependent on depth to water table. In situations where the boundaries between recharging and nonrecharging cells change with time, such as near a seepage zone, a continuous ground water flux relationship allows recharge rates to change with depth rather than having to calculate them at each stress period. This research article describes the modification of the MODFLOW 2000 recharge and segmented evapotranspiration packages into a continuous recharge-discharge function that allows ground water flux to be represented as a continuous process, dependent on head. The modifications were then used to model long-term recharge and evapotranspiration processes on a saline, semiarid floodplain in order to understand spatial patterns of salinization, and an overview of this process is given.
Abstract The water table fluctuation method of estimating recharge is widely used because it is conceptually simple and easy to implement. The major source of uncertainty in the recharge estimates come from the specific yield. The apparent specific yield has a dependence on the depth to water table that makes its measurement difficult (if not impossible) for appropriate use in the water table fluctuation method. This study has treated the specific yield as a conceptual parameter that cannot be measured and has constrained it using a rejection sampling approach using probabilistic estimates of net recharge from the chloride mass balance method and excess water derived from the difference between precipitation and remotely sensed actual evapotranspiration. The method developed here provided probabilistic estimates of the ultimate specific yield and a probabilistic time series of gross recharge, both important in shallow water table environments. An additional benefit of the method is that by jointly constraining the three different recharge types (i.e., excess water, gross, and net recharge) they are assured of being internally consistent. The method was implemented for 58 bores across four catchments in Northern Australia that may see increased development in coming years.
EXECUTIVE SUMMARY The water resources of the lower Fitzroy River catchment in the Kimberley region of north-west Western Australia are continuing to present both opportunities and impediments for future irrigation development, mining activities and municipal water supply to southern parts of the State. The recent CSIRO Northern Australia Sustainable Yields (NASY) project revealed that the groundwater and surface water resources of this catchment, and many others across northern Australia, lack the historical monitoring data and fundamental technical understanding required to undertake quantitative water assessments and therefore establish sustainable water management policies. In particular, there is a dearth of information and knowledge of groundwater controls on dry season flows in the Fitzroy River. This report presents a synthesis of preliminary research projects that have aimed at starting to address these knowledge gaps. It includes work undertaken by CSIRO as part of the Tropical Rivers and Coastal Knowledge (TRaCK) program, as well as a project in which CSIRO collaborated with WA Department of Water under the Raising National Water Standards program of the National Water Commission, and finally work undertaken by CSIRO as an extension to NASY. This suite of projects has used contemporary hydrogeological mapping techniques and water bore drilling, in combination with groundwater and river sampling for both routine and novel environmental chemistry analyses. A transect of nine new monitoring bores was installed on Noonkanbah Station in October 2009 to facilitate near-river groundwater sampling and enable monitoring of groundwater level responses to wet season flood flows and recession. Groundwater samples from these shallow bores, and nine other regional bores completed in the different geologies of the Canning Basin, were analysed for major ion chemistry, stable hydrogen and oxygen isotopes of water, radon-222, noble gases (particularly helium-4), chlorofluorocarbons, carbon-14 and stable strontium isotopes. Longitudinal sampling of surface water from different reaches of the Fitzroy River was undertaken on two occasions (May 2008 and May 2010) by helicopter, and samples were analysed for a similar suite of chemical and isotopic constituents. The main reach of the Fitzroy River on which these projects have focussed is between Jubilee Downs Station (i.e. downstream of Fitzroy Crossing) and the eastern boundary of Liveringa Station. We have identified two major zones of groundwater discharge along this reach: the first is around the confluence of the Fitzroy River with Cunningham Anabranch, and the second is between a well-known waterfall and Yungngora Community on Noonkanbah Station. Two complex discharge mechanisms have been invoked to explain chemical and isotopic data in the context of recently revised geology for these areas. In the first zone, old regional groundwater in the Liveringa Group is thought to flow westwards towards the river before being forced upwards into the alluvial aquifer, or directly into the river, as it meets the low permeability mudstones of the Noonkanbah Formation. In the second zone, even older regional groundwater from the deep Poole Sandstone aquifer is thought to discharge into the river, possibly via the alluvial aquifer, through a series of faults that transect the river. Modelling of the river chemistry profiles from May 2010 suggests the total rate of groundwater discharge over the 100 kilometre study reach is about 102 ML/day, comprising about 3.7 ML/day for the regional aquifers. The remaining discharge is sourced from local groundwater flow systems in the alluvial aquifer. The results demonstrate a high dependence of dry season flows in the Fitzroy River on discharge from both local and regional groundwater flow systems. It is likely that future groundwater pumping adjacent the Fitzroy River will result in a reduction to dry season flows, which in turn will have an impact on the water level of permanent pools. The distance at which future extractive industries should be placed away from the River in order to minimise impacts to dry season flows and permanent pools requires further research; however, it will be site specific—that is, it will depend upon the size and pumping regime of the proposed extraction, the hydrogeological properties of the aquifers between the river and the proposed development, and the proximity of the proposed extraction to the various groundwater discharge mechanisms identified above.
Introduction Groundwater in the Middle East and North Africa region is a critical component of the water supply budget due to a (semi-)arid climate and hence limited surface water resources. Despite the significance, factors affecting the groundwater balance and overall sustainability of the resource are often poorly understood. This often includes recharge and discharge characteristics, groundwater extraction and impacts of climate change. The present study investigates the groundwater balance in the Dead Sea Basin aquifer in Jordan using a groundwater flow model developed using the MODFLOW. Methods The study aimed to simulate groundwater balance components and their effect on estimation of the aquifer's safe yield, and to also undertake a preliminary analysis of the impact of climate change on groundwater levels in the aquifer. Model calibration and predictive analysis was undertaken using a probabilistic modeling workflow. Spatially heterogeneous groundwater recharge for the historical period was estimated as a function of rainfall by simultaneously calibrating the recharge and aquifer hydraulic property parameters. Results and discussion The model indicated that annual average recharge constituted 5.1% of the precipitation over a simulation period of 6 years. The effect of groundwater recharge and discharge components were evaluated in the context of estimation of safe yield of the aquifer. The average annual safe yield is estimated as ~8.0 mm corresponding to the 80% of the calibrated recharge value. Simulated groundwater levels matched well with the declining trends in observed water levels which are indicative of unsustainable use. Long-term simulation of groundwater levels indicated that current conditions would result in large drawdown in groundwater levels by the end of the century. Simulation of climate change scenarios using projected estimates of rainfall and evaporation indicates that climate change scenarios would further exacerbate groundwater levels by relatively small amounts. These findings highlight the need to simulate the groundwater balance to better understand the water availability and future sustainability.
Integrity failure of wells in gas resource developments poses a potential risk to groundwater resource quality and quantity by enhancing the connectivity and fluid migration between a gas reservoir and overlying aquifers, which may support groundwater dependent ecosystems or be used as a water source. This study assessed the potential for impact on groundwater resources from flow pathways created by well integrity failure in decommissioned coal seam gas (CSG) wells, deep water bores or gas wells repurposed as water bores and legacy coal exploration drillholes using an example based on a proposed CSG development near Narrabri, Australia. The study only considered the flow of water. A multi-stage screening method for likelihood and consequence assessment was used, which included (i) a semi-quantitative risk prioritisation of potential pathways for inter-aquifer leakage and development of metrics for impact assessment, (ii) assessment of the consequences of each of these pathways through an analytical model, and (iii) numerical groundwater modelling of single and multiple leaky wells. All three approaches indicated that increases in inter-aquifer leakage, drawdown in upper aquifers are not likely to be significant for high flow leaky gas wells (effective well conductivity, Kw <10−1 m/d) based on conditions reported in previous studies and for the case study. It is theoretically possible that extremely high flow leaky wells (Kw >102 m/d) could have an impact where aquitard conductivity is 10−4 m/d or less, or well failure density is higher than 1 well per km2, however Kw values for compromised gas wells of >1 m/d have not been identified in previous studies. The most extreme case tested, open legacy coal exploration drillholes or petroleum bores repurposed into water bores across an aquitard, should it occur, has the potential to deplete or contaminate groundwater resources in connected aquifers, the magnitude of which will depend on aquifer and production zone transmissivity. However, current Australian regulations for petroleum exploration make this an extremely unlikely case. More effort is required to determine Kw and failure rates of gas wells, water bores and exploration drillholes in Australian conditions to better quantify the potential risks associated with leaking infrastructure.
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