Warrick Dawes

Point stratigraphic picks published in Mory (2010) were collated along with stratigraphic picks from groundwater bores available from the Western Australian government. These two data sets were combined and used to interpolate isopachs for the thickness and extent of stratigraphic units overlying the interconnected Grant Group and Poole Sandstone in the Fitzroy Trough Western Australia. The surface represents the depth to the top of the interconnected Grant Group and Poole Sandstone below the natural surface. The purpose of the data set was to derive a spatial understanding of the change in depth to the top of the interconnected Grant Group and Poole Sandstone aquifers. This was used to communicate the depth required to intersect the aquifers by drilling.

Woodlots are generally established on land previously used for agriculture, and following the harvest of trees, the land may be returned to agriculture. Land used for agriculture generally has more stored soil water and higher nutrient status. Thus, the initial productivity of a woodlot established on such land may be relatively high, particularly in the lower rainfall zones where water would otherwise be limiting. However, productivity may decline as the stand develops and consumes these resources, even to the point of tree mortality due to drought. This chapter explores the performance of woodlots in areas considered too dry for conventional forestry. It examines the implications of climate, soil, salt and groundwater for the length of rotation required to achieve a balance between groundwater control and tree productivity. And it suggests a strategy in which woodlots can be moved around the farm to 'mine' soil water, thereby increasing the impact on recharge.

... MooRE, I. D., MACKAY, SM, WALLBRINK, P. J~ BURCH"GJ, and O'LoUGHLIN, EM, 1986, Hydrological characteristics and modelling of a small forested catchment in ... RYAN, PJ, 1991, Soil formation in the Wallagaraugh Adamellite, southeastern NSW~ Australia Catena, in press ...

In this paper, the long-term dynamics of water balance components in two different contrasting ecosystems in Australia were simulated with an ecohydrological model (WAter Vegetation Energy and Solute modelling (WAVES)) over the period 1950–2015. The selected two ecosystems are woodland savanna in Daly River and eucalyptus forest in Tumbarumba. The WAVES model was first manually calibrated and validated against soil water content measured by cosmic-ray probe and evapotranspiration measured with eddy flux techniques. The calibrated model was then used to simulate long-term water balance components with observed climate data at two sites. Analyzing the trends and variabilities of potential evapotranspiration and precipitation is used to interpret the climate change impacts on ecosystem water balance. The results showed that the WAVES model can accurately simulate soil water content and evapotranspiration at two study sites. Over the period of 1950–2015, annual evapotranspiration at bot...

The Australian Water Resource Assessment (AWRA) modelling system is developed to enable the Australian Bureau of Meteorology to meet its legislated role in providing an annual National Water Account (NWA) and regular Australian Water Resource Assessment Reports. The system uses available observations and an integrated landscape – river water balance model to estimate the stores and fluxes of the water balance required for reporting purposes (Figure 1). The National Landscape model (AWRA-L) provides gridded estimates of landscape runoff, evapotranspiration, soil moisture, and groundwater recharge/storage/lateral flow, and has been calibrated towards reproduction of a nationwide streamflow dataset. The gridded model structure provides an option of incorporating spatial variability of climate, land cover and soil properties. The model can be constrained only against observed streamflow or a combination of streamflow and remotely sensed soil moisture and evapotranspiration. The water balance fluxes from AWRA-L are used as inputs to the regulated river system model (AWRA-R) to undertake basin scale water balance modelling. The AWRA-R model includes river routing, irrigation diversions, reservoir storage, floodplain inundation and river to groundwater interaction components. All the AWRA modelling components are built within a software architecture which allows seamless interactions between the components at the appropriate spatial and temporal scales. The AWRA modelling system has been implemented across Australia and it provides estimates of water balance fluxes and stores which are substantially better than those from continental scale land surface models and similar to or better than those from widely used conceptual rainfall-runoff models. The system is currently being used for hydrological modelling in a number of large scale projects including the Bioregional Assessments and the Northern Australian Central northern rivers and dams. The AWRA modelling system provides consistent, robust and repeatable water assessments at catchment, regional and continental scale which can be used to guide future water planning and policy development as well as water resources development across Australia and globally.

A challenge for whole of river system calibration techniques is to maximise the model's calibration and validation (predictive) performance while still maintaining the model's hydrological integrity. Hydrological integrity is required to explain system behaviour according to hydrological principles. However, the predictive performance is obviously essential to justify practical use of the model for planning purposes. Good agreement between modelled and observed flow data is particularly important in multi-gauged river systems as otherwise upstream calibration errors will propagate to downstream reaches. To overcome this in river systems with no additional data other than gauged flow, river system modellers have used a traditional method to 'overfit' models by increasing the gains of a system by arbitrary factors and then fit monotonically increasing loss vs flow curves in order to more closely resemble observed flow data. Although monotonically increasing loss vs flow curves make hydrological sense in terms of physical river processes such as groundwater losses and overbank flood events, the increasing of the gains (i.e. rainfall-runoff) in order to do so, disregards system mass balance. This paper compares the calibration and validation results in river reaches using five different approaches: (1) using no loss/gain accounting method; (2) applying a loss/gain function based on flow; (3) applying a loss/gain function based on the rainfall-runoff model; (4) scaling the rainfall-runoff model contributions and applying a loss/gain function; and (5) fitting the Monod model (monotonically increasing function) to unaccounted losses. The comparison is undertaken for 19 river reaches sampled from different sub-catchments in the Murray-Darling Basin of Australia to represent a range of environmental conditions. In most sampled reaches, methods 2 and 4 worked the best during both calibration and validation. The paper discusses assumptions made about losses and gains of simplified lumped river reaches.

ABSTRACT About three – quarters of all water used in the south-western Australia is from groundwater. A decline in rainfall since about 1975 and increased abstraction has resulted in some groundwater levels declining and groundwater dependent ecosystems decreasing in health and extent. Levels are rising under some areas used for dryland (rainfed) agriculture because crops and pastures are shallow rooted. Almost all global climate models (GCMs) project a drier and hotter climate for the region by 2030. In this project, five climate scenarios were applied to groundwater models to estimate groundwater levels in the region in 2030. The climate scenarios were (i) a continuation of the historical climate of 1975–2007; (ii) a continuation of the more recent climate of 1997–2007 until 2030; and (iii–v) three climate scenarios derived by applying the GCM projected climate under three global warming scenarios of 0.7, 1.0 and 1.3 �C by 2030. A sixth scenario considered increasing abstraction levels to maximum allowed levels under a median future climate (1.0 �C warming). Groundwater levels were found to be much less affected than surface water resources by a future drier climate as well as for a continuation of the climate experienced since 1975. For a fixed rainfall, recharge was highest where soils were sandy, there was little or no perennial vegetation and the watertable was neither very shallow nor very deep. A feature of the project area is that about half has a watertable within 10 m of the soil surface, and about a quarter within 3 m. Levels were not as affected by a decline in rainfall when reduced groundwater drainage and evapotranspiration losses offset the reduced rainfall amounts. However once a threshold groundwater level is exceeded, the rainfall fails to refill the available seasonal storage and groundwater levels decline. Projected watertables declined in all areas under a drier climate where perennial vegetation was present and able to intercept recharge or use groundwater directly. In areas under dryland agriculture, projected groundwater levels continue to rise even under a drier future climate. The climate change effects on confined groundwater systems are expected to be modest. This is due to the longer times required for the changed recharge and water level conditions in the overlying aquifers to propagate to the confined aquifers. All water balance components are projected to be impacted by climate change to a greater or lesser extent. This has consequences for the amount of extractable water from both the unconfined and confined aquifers, changes the risk of seawater intrusion, and has implications for the groundwater dependent ecosystems.

A comprehensive framework for the assessment of water and salt balance for large catchments affected by dryland salinity is applied to the Boorowa River catchment (1550 km2), located in south‐eastern Australia. The framework comprised two models, each focusing on a different aspect and operating on a different scale. A quasi‐physical semi‐distributed model CATSALT was used to estimate runoff and salt fluxes from different source areas within the catchment. The effects of land use, climate, topography, soils and geology are included. A groundwater model FLOWTUBE was used to estimate the long‐term effects of land‐use change on groundwater discharge. Unlike conventional salinity studies that focus on groundwater alone, this study makes use of a new approach to explore surface and groundwater interactions with salt stores and the stream.Land‐use change scenarios based on increased perennial pasture and tree‐cover content of the vegetation, aimed at high leakage and saline discharge areas, are investigated. Likely downstream impacts of the reduction in flow and salt export are estimated.The water balance model was able to simulate both the daily observed stream flow and salt load at the catchment outlet for high and low flow conditions satisfactorily. Mean leakage rate of about 23·2 mm year−1 under current land use for the Boorowa catchment was estimated. The corresponding mean runoff and salt export from the catchment were 89 382 ML year−1 and 38 938 t year−1, respectively.Investigation of various land‐use change scenarios indicates that changing annual pastures and cropping areas to perennial pastures is not likely to result in substantial improvement of water quality in the Boorowa River. A land‐use change of about 20% tree‐cover, specifically targeting high recharge and the saline discharge areas, would be needed to decrease stream salinity by 150 µS cm−1 from its current level. Stream salinity reductions of about 20 µS cm−1 in the main Lachlan River downstream of the confluence of the Boorowa River is predicted.The FLOWTUBE modelling within the Boorowa River catchment indicated that discharge areas under increased recharge conditions could re‐equilibrate in around 20 years for the catchment, and around 15 years for individual hillslopes. Copyright © 2004 John Wiley & Sons, Ltd.

ABSTRACT This study assesses the impacts of several subcatchment and regional scale artificial drainage on on-site groundwater levels and salinity, and off-site streamflows, salt loads and lake discharge rates using a hydrological model LASCAM. The model is applied to the 21,147 km2 Blackwood Basin in southwestern Australia, much of which has been experiencing long-term rises in groundwater levels in response to large-scale clearing of native vegetation over the past 160 years. These rises in groundwater levels have led to substantial increases in stream salinity, waterlogging and land salinisation.The model predicts that under the baseline scenario (that is, without artificial drainage or any other salinity management strategy) most of the subcatchments of the Blackwood Basin are likely to experience rises in both future average groundwater levels and groundwater salinity, but at a slower rate than is currently occurring. Streamflows and stream salinity are also projected to increase over time under the baseline scenario. Artificial drainage is likely to lower both the groundwater levels and groundwater salinities. Mean annual and peak streamflows are expected to be considerably larger under the drainage scenarios than under the baseline scenario. All strategies assessed for the management of artificial drainage water are projected to further degrade the lower Blackwood River from higher salinity levels than are expected under the baseline scenario, with the exception of one strategy where drainage discharge is managed via subcatchment scale evaporation basins.

A system to overcome dry land salinization of farming systems in medium to low (300-600 mm) rainfall areas of southern Australia is proposed. Phase farming with trees (PFT) is designed to use trees grown in very short term rotations (3-5 years) to rapidly de-water farming catchments at risk of salinity, by depleting soil water while producing utilizable products such as wood fibre and biomass. The tree phase is followed by an agricultural phase of a length defined by the persistence of the hydrological buffer created by the trees. The system thus utilizes a resource (groundwater recharge) that is contributing to environmental problems while building more sustainable agricultural systems. Potential benefits include decreased salinization, improved soil structure and acting as a disease and weed break. Production of large amounts of biomass suitable for "green" electricity will decrease Australia's emissions of Greenhouse gases. The biophysical feasibility of PFT was ass...

<p>Setting groundwater allocation limits requires an understanding of recharge fluxes to the aquifer system. Very often rainfall percolation through the subsurface represents the critical recharge flux. In this groundwater limit setting context, recharge estimates are often established as a component of the groundwater flow model history matching process. Typically, there are many recharge models available, and the basis for selecting any particular model is often confusing.</p><p>Some of these recharge models are numerical solutions of variably saturated pressure head and flow and represent the full complexity of the soil-vegetation-atmosphere transfer of water. Such models require many parameters that may not be measured or verified, and/or are computationally expensive. This can make the history matching process and predictive uncertainty analyses difficult.</p><p>Simpler model representations of the recharge processes are also available, either through upscaling (e.g., by lumping together different soil profiles, with different vegetation) and/or by simplification of the recharge estimation method. Such simplifications may involve empirical equations to derive gross recharge, single bucket-type root zone water balance calculations, or solving net recharge with the help of analytical solutions of flow or pressure heads and linear approximations of gross recharge or evapotranspiration from groundwater as function of the groundwater head. These simpler models often have a greater utility (i.e., they are quicker to run and are more numerically stable) but may be accompanied by additional ‘simplification’ induced uncertainty.</p><p>Regardless of the method used, the uncertainty and bias of these recharge predictions can be high.  The uncertainty of groundwater model predictions underpinning the setting of allocation limits can also be high. However, the performance of a recharge model in terms of how it impacts the reliability of the predicted impacts relevant to the groundwater allocation limit, is currently not considered. This study addresses this issue, exploring the costs and benefits of recharge models of varying complexity, in the context of setting groundwater abstraction limits. This is demonstrated using a synthetic, but realistic case study in Western Australia.</p><p>We adopt a paired complex-simple model analysis workflow, and implement it using the Flopy-PyEMU Python-based scripting framework. This workflow is then used to explore the performance of more complex and simpler models within the groundwater allocation management context by measuring each model’s bias and uncertainty. We compare a cell-by-cell Richards’ equation-based recharge model, with a series of simpler recharge contender models. This scripted workflow supports the efficient deployment of the paired complex-simple model stochastic analysis and interpretation of its outputs.</p>

Executive Summary Groundwater aquifers impose time-lags between changing recharge and a subsequent change in groundwater discharge to the land surface and to streams. This groundwater response time varies depending on several factors, including length, ...

The Australian Water Resource Assessment (AWRA) modelling system is developed to enable the Australian Bureau of Meteorology to meet its legislated role in providing an annual National Water Account (NWA) and regular Australian Water Resource Assessment Reports. The system uses available observations and an integrated landscape - river water balance model to estimate the stores and fluxes of the water balance required for reporting purposes. The National Landscape model (AWRA-L) provides gridded estimates of landscape runoff, evapotranspiration, soil moisture, and groundwater recharge/storage/lateral flow, and has been calibrated towards reproduction of a nationwide streamflow dataset. The gridded model structure provides an option of incorporating spatial variability of climate, land cover and soil properties. The water balance fluxes from AWRA-L are used as inputs to the regulated river system model (AWRA-R) to undertake basin scale water balance modelling. The AWRA-R model includ...

The Australian Water Resource Assessment (AWRA) modelling system is developed to enable the Australian Bureau of Meteorology to meet its legislated role in providing an annual National Water Account (NWA) and regular Australian Water Resource Assessment Reports. The system uses available observations and an integrated landscape – river water balance model to estimate the stores and fluxes of the water balance required for reporting purposes (Figure 1). The National Landscape model (AWRA-L) provides gridded estimates of landscape runoff, evapotranspiration, soil moisture, and groundwater recharge/storage/lateral flow, and has been calibrated towards reproduction of a nationwide streamflow dataset. The gridded model structure provides an option of incorporating spatial variability of climate, land cover and soil properties. The model can be constrained only against observed streamflow or a combination of streamflow and remotely sensed soil moisture and evapotranspiration. The water ba...