The aim of this study was to develop a bio-economic model to estimate the feasibility and net profit (or net costs) of achieving set water quality targets (sediment, nitrogen, phosphorus and herbicide load reductions) in the Burnett-Mary region within the southern portion of the Great Barrier Reef (GBR), southern Queensland, Australia. Two sets of targets were evaluated, namely (1) Reef Plan Targets (RPTs) representing currently agreed targets, and (2) the more ambitious Ecologically Relevant Targets (ERTs) designed to halt the decline and improve the condition of the GBR. This paper describes the construction of a bio-economic optimisation framework linking field and catchment scale biophysical model results and farm economic analysis to solve for RPTs or ERTs assigned either regionally or within discrete basins. Key outcomes from the study were that RPTs could be achieved whereas ERTs required significant additional investment and were infeasible if individual basins must meet the targets.

This paper describes the construction of a bio-economic optimisation framework to evaluate the feasibility and net profit (or net costs) of achieving water quality targets in the Burnett-Mary region within the southern portion of the Great Barrier Reef (GBR), southern Queensland, Australia. Key outcomes from the study were that current sediment, nitrogen and phosphorus load reduction targets could be achieved whereas more ambitious ecologically relevant targets required significant additional investment and were not feasible based on the model if individual basins must meet the targets.

Assessment of nitrogen (N) loss forms and pathways from farming systems is important for improved understanding of potential off-farm impacts on high value environmental assets. The objective of this study was to estimate N losses in different pathways in dairy systems across the range of climate, soil and farm management by using west Gippsland (Victoria, Australia) as case study area, and to characterise the sensitivity of the adopted model parameters. We combined the point scale models DairyMod and Howleaky to estimate dissolved N (DN) and particulate N (PN) loads in runoff, and N leaching (LN) in deep drainage from representative dairy farms in west Gippsland. Monte Carlo error propagation with Latin hypercube sampling was performed to identify sensitive model parameters and assess potential uncertainty in N load predictions. The combined model was capable of simulating climate-soil-animal pasture management interactions and estimating DN, PN and LN at an annual scale; which were estimated at up to 18 kg-N ha(-1),15 kg-N ha(-1) and 312 kg-N ha(-1), respectively. The combined model demonstrated that more intensive feeding as mixed ration, and nutrient budgeting that takes into account the fertiliser equivalent of recycled nutrients can achieve an increase in milk production by up to 13% and a decrease in N loads by up to 31% compared to the intensive system in the case study catchment. Soil type and farm management explained much of the variability (up to 76%) observed in LN and DN loads, whereas climate and soil type had significant influence on PN loads (62-77%). Year-to-year variation, particularly under dry conditions had a marked influence on N loads. Soil N, vegetation cover, rooting depth and soil maximum drainage rate must be well characterised in order to reduce potentially high uncertainty in the estimation of N losses in heterogeneous catchments. (C) 2016 Elsevier B.V. All rights reserved.

The horticultural industry in Victoria is currently experiencing significant structural pressures due to a range of issues, including water constraints through the introduction of Sustainable Diversion Limits (SDL's), access to productive land and infrastructure, climate change and competition with overseas imports. Bio-economic models such as the Victorian Water Policy Model enable policy makers to explore scenarios which aim to optimize agricultural productivity and the trade-offs between various agricultural industries and regions under a series of water availability and physical constraints. However, the current data-sets which populate these models such as land-use, irrigation demand and production estimates are often sparse and not frequently updated. This paper discusses the design and implementation of an automated process to provide enhanced estimates of irrigated water use across the horticultural industries of northern Victoria. The service derives regional crop coefficient relationships for the horticultural industries using SEBAL-METRIC estimates of Evapotranspiration, Penman-Monteith estimates of potential evaporation and calculated Normalized Difference Vegetation Index (NDVI) from the Landsat-8 satellite. Application of the crop coefficient relationships provides estimates of crop evapotranspiration rates and irrigation water use over time. Automated reports for each horticultural industry within the water-trading-zones of the northern Victoria irrigation districts provide information on the distribution of crop coefficient curves, irrigation area, estimated evapotranspiration and water application. This information is critical for water resource management and to support physically-based biophysical models. It is anticipated that over time the service will also provide information on land-use transition and the adaptation of irrigation practices to changes in water availability.

Setting limits for consumptive water extraction from the Murray-Darling Basin, known as Sustainable Diversion Limits (SDLs), is a key feature of recent water reforms. The ecological and socioeconomic impacts of SDLs have been assessed for the entire Murray-Darling Basin. However, there is still little understanding of how these limits will play out at the catchment scale and at more localised levels. To build this understanding, the SDLs (estimates and rules) need to be examined using a multidisciplinary framework that includes water management policies, climate change projections, the nature of surface water-groundwater systems, and water-dependent economic and ecological systems. This paper presents an ongoing collaborative project between the research team in the National Centre for Groundwater Research and Training (NCGRT), Victorian Department of Environment and Primary Industries, North Central Catchment Management Authority and Goulburn-Murray Water. It examines the effects of implementing the SDLs for the Lower Campaspe catchment in Victoria in terms of tradeoffs between the profitability of agricultural production and ecosystem response, especially groundwater dependent ecosystems. The model under development is also intended to be flexible enough to investigate adaptation options for landholders and water policy initiatives. In undertaking such an integrated assessment project, the research team brings together researchers from multiple disciplines, including hydrology, hydrogeology, ecology, resource economics, social science and systems science. The project has applied an integrated modelling approach which focuses on working closely with project stakeholders to identify modelling questions, share results and seek feedback. Our aim is to develop an integrated modelling framework that can be reapplied in other catchments to address stakeholders' questions and concerns with regard to the implementation of the SDLs at the local level. In this paper, we give a brief overview of the design of the integrated model under development, and its key components and interactions.

The Corner Inlet and Nooramunga Coastal Hotspot and Ramsar site is one of Victoria's important environmental assets. The seagrass beds are critically important to the ecosystem and these are under threat due to sediment and nutrient (nitrogen, N and phosphorus, P) export from agricultural land management (mostly dairy and beef). The West Gippsland Catchment Management Authority (CMA), along with the Victorian and Australian governments, have responsibilities balancing the needs of local communities, including the economic viability of agricultural and fishing industries, and protecting the environmental values of the site through developing and implementing a Water Quality Improvement Plan (WQIP).This study used science and local expert knowledge to develop a bioeconomic optimisation framework (using the General Algebraic Modelling System, GAMS) which informed a stakeholder panel overseeing the WQIP about the costs of achieving pollutant reduction targets under different land use and management options. These included traditionally funded activities (gully, stream and waterway fencing), agricultural 'best-management practices' (BMPs) and land use change. A previously calibrated catchment model provided sub-catchment load estimates of total N (TN), total P (TP) and total suspended sediments (TSS). Development of a new land use layer allowed the proportions of dairy, beef and forestry to be ascribed. BMP effectiveness was assessed by expert opinion and the contribution of gully and waterways were estimated by extrapolating nearby modelling and mapping information based on similar soils. The change in operating profit was calculated assuming single representative dairy and beef systems and practices.A stakeholder and technical panel comprising the CMA, Victorian and Australian governments, farming, fluvial ecology, hydrodynamics, seagrass ecology and catchment modelling expertise oversaw development of the WQIP. Choices about TN, TP and TSS reduction targets to be assessed were made based not only on estimated ecological outcomes, but also considering costs and political acceptability of implied land use and management changes. Three scenarios are presented: 'ideal at least cost' (best estimate of load reduction targets required to maintain seagrass); 'revised at least cost' which was half of the ideal target; 'revised with traditional activities only' (gully, stream and waterway fencing).Achieving 'ideal' targets at least cost was estimated to result in an average loss in profit (cost) of $458/ha over the grazed area (757 km(2)) and involved large scale retirement of agricultural land (over 96% dairy area and over 30% beef area). The 'revised' targets were estimated to cost $157/ha and still required significant land retirement (75% dairy land). Restricting land use activities to those traditionally funded and excluding land use change/retirement options increased costs from $157 to $292/ha. Overall these results imply that achieving large environmental gains involves major politically, socially and economically unacceptable impacts on grazing industries. The premise of 'win: win' outcomes, the basis of most publicly funded programs in Australia, is significantly challenged.The results have been actively and adaptively used by the CMA to inform a realistic WQIP. Stakeholders recognised that the information base is imperfect and that refinement (finer scale catchment modelling and inclusion of heterogeneity in dairy and beef systems) could substantially reduce the estimated costs in achieving environmental outcomes. Bioeconomic modelling and active participation helped people understand the need for a more informed discussion about potential trade-offs between protecting environmental ecosystems and maintaining agricultural profitability. Policy choices involving targeted regulation to protect valuable ecosystems are likely to be needed, as is occurring elsewhere in the world.

Intensification of grazing industry management is a cause of concern as a potential source of nitrogen (N) pollution at the catchment scale. To explore the impact of grazing industry and its management on N loads, a point-to-catchment approach was developed in this study. Point-scale N losses in leaching and runoff were estimated with two models, DairyMod and HowLeaky, for unique combinations of management, soil type, and climate (i.e. Hydrological Response Units, HRU). HRU N losses were divided in dissolved N (nitrate) in runoff, particulate N in runoff, and dissolved N in leached below the root-zone. The Catchment Scale Management of Distributed Sources Model (CatchMODS) was used to assess annual average nutrient budgets at the catchment scale. The spatial units were subcatchments, which comprised a river reach and the area (of about 20-60 km(2)) delivering water, sediment and nutrients to it. River reaches were connected to upstream and downstream reaches in a node-link system. Subcatchment annual average N loads in runoff were assigned proportionally to HRU area in each subcatchment, and adjusted for topography. N loads from leaching were estimated from subcatchment average monthly N concentration in the soil water below the root zone and the monthly volume of subsurface water reaching the stream; monthly loads were summed over the simulation period and divided by the number of years to get the annual average leached N load. Total N loads generated by streambank and gully erosion were estimated from erosion rates and N content of gully and streambank eroding walls. In-stream attenuation of total N was modeled as a first order decay exponential function, assuming an inverse relationship between in-stream removal and stream size. The model was applied to the Moe River catchment in West Gippsland to assess the impact of grazing management intensification on TN loads at the catchment outlet. The uncertainty in TN load predictions due to catchment model parameters was assessed with a Bayesian inference method, following the Flexible Model Environment (FME) procedure implemented in R. Sensitivity and identifiability analyses were conducted to screen sensitive parameters and identify parameter sets that could be concurrently assessed. A Markov-Chain Monte-Carlo (MCMC) analysis was conducted to obtain parameter sets conditioned on mean annual flow and average annual sediment and nutrient loads observed at the outlet. These conditioned model parameter sets were then used in Monte Carlo Simulations (MCS) to propagate model uncertainty in land use scenario analysis. Of the 15 initial catchment model parameters, four upscaling parameters that regulated transfer of water, sediment and nutrients from HRUs to the subcatchment could be successfully conditioned using water quantity and quality data observed at the outlet: the fraction of water surplus to stream discharge F; the hillslope sediment delivery ratio SDR, and the in-stream nutrient attenuation parameters. Of 5000 MCMC simulations, 3431 were accepted. The best posterior parameter set resulted in a TN load of about 440 t TN y(-1) at the outlet, which was very close to TN load estimated from monitoring station data (430 t TN y(-1)); TN sources largely coincided with areas dominated by dairy land use. The MCS runs showed that intensity of grazing management had a significant impact on TN loads: intensification of the dairy industry based on increasing use of N fertiliser could triple current TN loads, up to about 1350 t TN y(-1).Conversely, extensification (little or no use of N fertilizer) could reduce TN loads to about 30% (i.e. 110-140 t TN y(-1)). Other sources of uncertainty, most notably uncertainties in point-scale model inputs and uncertainties in model structure, could also impact model predictions, but they could not be assessed because of insufficient data. However, because of their upscaling function, the four parameters that were assessed are believed to characterize most of model uncertainty, and may help buffer propagation of uncertainty from point-scale inputs. Notwithstanding the uncertainty in model results, grazing management intensity was identified as having a major impact on TN loads reaching the Moe River catchment outlet.

This paper describes a proposed approach to enhance potential GDE mapping to likely GDE extent by the application of a physically-based groundwater model. The paper also compares the estimated change in shallow watertable area and, by association, the change in GDE extent under pre-European conditions and under 2030 climate change conditions.The objectives of this paper are to (1) describe the groundwater model used which accounts for land use recharge and evapotranspiration plus surface water/groundwater interactions (2) analyse the simulated depth to watertable surface with pre-existing potential GDE mapping and (3) to present a supplementary methodology for better defining GDE map units. The impact on GDE extent under climate change and pre-European vegetation conditions are also considered.The paper presents a linked surface-water/groundwater catchment model (Catchment Analysis Tool, CAT) to describe the temporal soil moisture profile and groundwater dynamics within the Loddon Catchment of North Central Victoria. Results indicate that the current potential GDE mapping techniques have a high correlation with vegetation transpiration from the unsaturated zone and soil moisture status within the root zone, but poorly correlate with simulated depth to watertable. This paper concludes that the extent of existing potential GDE mapping is more than double the likely GDE extent based on estimates derived using a distributed groundwater model.The application of a distributed groundwater model is shown to provide a more robust representation of the likely locations of a GDE when used in conjunction with the existing potential GDE layer. The reduction in the area of likely GDE assuming a dry period (2030 climate change) and pre-European landuse relative to current environmental conditions is estimated to be a factor of 1.4 and 2.2 respectively.

The soil erodibility factor (K) is used in empirical erosion models based on the Universal Soil Loss Equation to account for soil susceptibility to detachment and transport by rainfall and runoff. Whilst soil erodibility is ideally measured from long-term standard plots, in catchment-scale modelling it is more often estimated by applying pedo-transfer functions. These are either based on soil properties reported in soil databases, or attributed by experts on the basis of soil characteristics. The aim of this study was to evaluate the impact of the soil erodibility factor on the amount and distribution of suspended sediment loads generated by hillslope erosion within the LaTrobe River catchment, in Victoria (south-east Australia).Two soil erodibility factor sets were developed for hydrologic soil groups in the LaTrobe catchment. The first ('local') set was based on a Victorian soil database; soil erodibility was attributed by an expert soil scientist on the basis of topsoil texture, soil structure, geology, hydrological properties of the profile, and local knowledge. The second ('global') set was derived from a global soil erodibility dataset using the probabilistic distribution of K based on climatic conditions, skeleton (i.e. fraction > 2mm), organic matter content, and topsoil texture. The K factor in the 'local' set ranged from 0.015 to 0.055 Mg ha h ha(-1) MJ(-1) mm(-1), whereas soil erodibility in the 'global' set had higher absolute values but a smaller range (0.044-0.067 Mg ha h ha-1 MJ-1 mm-1). Importantly, the two sets differed in ranking soils from the most to the least erodible. A catchment scale model based on CatchMODS was used to assess suspended sediment loads from three erosion processes: hillslope erosion (which depended on soil erodibility), gully, and streambank erosion. The model estimated deposition of suspended sediment on hillslopes, floodplains and in reservoirs. Hillslope deposition was calculated using a hillslope sediment delivery ratio (HSDR), which is a calibration parameter. The two model configurations (i.e. informed by the two erodibility factor sets) were calibrated independently using annual suspended sediment load estimates at ten water quality monitoring stations of the catchment for the period 1990-2005. The model performance was assessed in terms of model efficiency of specific sediment yield predictions.The calibration of HSDR did reduce the impact of absolute values of soil erodibility estimates on hillslope net erosion; with higher HSDR calibrated for the local K configuration. However, the two model configurations resulted in different contribution of hillslope net erosion to suspended sediment loads: in the local K dataset configuration, hillslope net erosion contribution was estimated at 3.6 kt/y in the local K configuration (11% of a total of 34 kt/y estimated to reach Lake Wellington). In the global dataset configuration, hillslope net erosion was estimated at 9 kt/y (23% of an estimated total of 40 kt/y at the lake).The spatial distribution of the soil erodibility factor (K) resulted in a measurable impact on model performance; the global K configuration better matched specific sediment load observations across the catchment (efficiency of 0.32). The main difference in the attribution of K by the two approaches was due to the influence of climatic conditions. Analysis of the global dataset indicated that, other conditions being equal, soil erodibility in warm climates is lower than in temperate climates (Salvador Sanchis et al., 2008). Apparently, the local dataset underestimated the climatic effect on soil erodibility, and resulted in an overall underestimation of net hillslope erosion in the study catchment. These exploratory results will need to be further explored in future research.

Terrain analysis based on digital elevation models is being routinely used in hydrological modelling.However, landscape connectivity enabling the routing of flow and nutrients from upslope landscape units to adjacent downslope landscape units within a sub watershed is not commonly incorporated into catchment scale models.This paper describes a process of generating connected landscape units within sub watersheds based on a threshold area and evaluates the impact of landscape connectivity on catchment water balance and groundwater response.Digital elevation models (DEMs) are commonly used for the automatic delineation of flow paths, sub watersheds and flow networks for hydrologic modelling.The capacity to define a flow path network describing how flow is routed to a drainage feature is fundamental to distributed hydrologic models.There is a variety of approaches for delineating flow networks using different flow direction algorithms, for example drainage to a single neighbouring cell or the partitioning of flow between multiple neighbouring cells.The resultant flow network underpins the watershed delineation based on upstream drainage area.This paper comments on each approach for representing the networks of rivers and streams and describes an approach using the watershed delineation to define landscape units using elevation intersects and flow paths connecting boundary nodes to drainage lines.This approach results in the generation of connected landscape units of variable size.Catchment scale models typically adopt an aggregated or lumped spatial unit within which land use, soil and climate are proportionally assigned with limited spatial reference.This paper reports on the integration of connected topographic landscape units into a catchment modelling framework (Catchment Analysis Tool, CAT) with application to the Loddon catchment in central Victoria.Comparative results derived using the CAT under historical climate conditions show a 12% improvement in streamflow prediction compared to observed when accounting for landscape connectivity relative to the lumped approach.Comparative results also show significant variation in the recharge patterning and up to 30% variation in recharge rates depending on landscape position as estimated when using landscape connectivity relative to the lumped approach.Incorporating landscape connectivity into a catchment modelling framework is shown to improve the predictive capacity of catchment models to estimate streamflow and groundwater recharge with associated improvement in water resource evaluation and flow and transport modelling

This paper describes (1) the development and validation of a native pasture model that accounts for species abundance, (2) the integration of the native pasture model into a catchment framework and (3) the likely biophysical trade-offs associated with increasing the proportion of native perennial pasture species within a pilot catchment. The rationale for developing the model was to build on the conceptualisation of contemporary pasture models and include new algorithms that better represent native grass species commonly found in temperate climate regions of Australia. The native pasture model is phenologically based and simulates both daily pasture growth and soil water dynamics. It was developed and validated against data from field experiments conducted at Wagga Wagga in NSW, Australia, for two native grass species, Austrodanthonia spp. (winter dominant C-3) and Bothriochloa macra (summer dominant C-4). The model predicted seasonal pattern and inter-annual variation of soil moisture contents and green leaf area index (GLAI) for various planting densities. There was a high correlation between the simulated and measured soil moisture contents (r(2) = 0.81, p < 0.0001 for Austrodanthonia spp; r(2) = 0.73, p < 0.0001 for Bothriochloa macra) and GLAI (r(2) = 0.66, p < 0.0001 for Austrodanthonia spp; r(2) = 0.83, p < 0.0001 for Bothriochloa macra) at actual measurement dates.The native pasture model was integrated into a physically-based catchment modelling framework (Catchment Analysis Tool, CAT) to provide a flexible platform for simulating the environmental impacts of various pasture management options and the likely consequences of land use changes on catchment dynamics. This catchment model comprises numerous vegetation modules (including cropping, forestry and alternative pasture models) of varying complexity. An example of how the native pasture model can be used within the CAT framework is described by the application to the Bet Bet catchment which has been identified as a high salt exporting catchment within the Murray Darling Basin of Australia. The Bet Bet catchment currently yields and exports annually approximately 36,056 ML and 20,000 tonnes of salt respectively. The grazing of unimproved pastures is the dominant land use within the catchment such that economically viable options for increasing perenniality in the catchment are limited to working with the native perennial grasses already present and targeted tree planting. The study evaluated the water yield, saturated area and salt load trade-offs associated with increasing the proportion of native perennial pasture species. Scenarios considered varying proportions of summer or winter dominant native pastures across the catchment in comparison to reafforestation. Results indicate that complete reafforestation of the grazing area would reduce both stream flow and salt exports, by 6,299 ML yr(-1) and 10,486 tonnes salt yr(-1) respectively. Complete catchment coverage of Bothriochloa macra was estimated to increase stream flow by 3,987 ML yr(-1) as well as to reduce groundwater inflows by 1,429 ML yr(-1)(2,745 tonnes salt yr(-1)). In contrast, Austrodanthonia spp. pasture was estimated to increase stream flow by 4,378 ML yr(-1) and increase salt export by 714 tonnes salt yr(-1). Targeted restoration of either summer or winter dominant native pastures within the steeper regions of the catchment with slopes greater than 5% (representing 11% of the catchment area) was considered. Results show that restoration of Bothriochloa macra in the upper catchment increased stream flow by 132 ML yr(-1) and reduced salt loads by 472 tonnes salt yr(-1), whereas restoration of Austrodanthonia spp. increased stream flow by 409 ML yr(-1) and reduced salt loads by 109 tonnes salt yr(-1). In contrast, reafforestation in the upper catchment reduced stream flow by 5,650 ML yr(-1) and salt loads by 8,689 tonnes salt yr(-1). Overall, results suggest that increasing the proportion of summer active native perennial grasses across large parts of the catchment may be an effective salinity management option for reducing recharge and salt loads to rivers.Integration of a validated native pasture model into the CAT framework is shown to provide the capability to simulate the long-term effects of land use changes in the landscape on catchment dynamics.

This paper considers the problem of integrating projected future climate change predictions into a catchment modelling framework to determine future impacts on the groundwater resource. Catchment hydrology will also be altered as land managers alter management and land use regimes in response to a changing climate. The response of the groundwater system is further complicated in water-limited environments as plant systems will not respond linearly to changing rainfall, temperature and CO(2) inputs. There is a need to separate the effects on hydrology due to land use change, and those resulting from climate change, to enable adaptation strategies to be proposed that help best manage our groundwater resource.Presented are results from the Catchment Analysis Tool (CAT), a modelling framework which links the daily surface water balance from actual land use management to a calibrated fully-distributed MODFLOW groundwater model. The MODFLOW model, calibrated against historical climate conditions, has been used to assess the groundwater impact under projected changes in rainfall, temperature and solar radiation due to climate change, for the Corangamite catchment in Victoria. Monthly climate change projections provided by the CSIRO climate change model for regional Australia have been converted to daily data using a modified downscaling method. The historic and projected climate data have been used as inputs to a suite of daily biophysical simulation models (CAT) that account for multiple agricultural landscapes, generating mean-annual groundwater recharge estimates which are fed into a steady-state MODFLOW groundwater model. A method proposed to separate the localised groundwater impact of changing land use from the more regional impacts due to climate change is also presented.The following conclusions are drawn from our modelling analyses:The A1F1 climate change scenario resulted in mean annual rainfall for the catchment decreasing by 73 mm and average annual temperature increasing by 1.6 degrees C. Using the current practice scenario, the model predicted that mean annual evapotranspiration would decrease by 7% (39 mm/year) and recharge by 21% (24 mm/year) under climate change;The groundwater resource will be affected by the impact of climate change in Corangamite, especially in the upper reaches;Based on the results shown, a 100 ha tree plantation had a decreased impact on potentiometric head, within 5 km of the plantation due to climate change. The impact, however, was greater between 5 and 10 km;The potential impact of climate change on potentiometric surface can exceed the impact on a tree plantation; andThe combined effect of land use and climate change will be large although the response across the landscape is variable.

This paper presents three modelling approaches commonly used to estimate the nutrient balance within large catchments and outlines the rationale of the different model constructs. Each model is evaluated by application to a catchment in north central Victoria, Australia, that has an area of 371,000 ha and comprises mixed landuse enterprises. The catchment is also in connection with a groundwater system that contributes on average 20% of streamflow. Model results are shown to compare favourably with available nitrate observation data. However results indicate that the lumped and extrapolated approaches, whilst easily calibrated to stream flow data, do not adequately describe the within-catchment processes. The physics-based model is the only approach capable of representing spatially explicit surface water, leached water and groundwater concentrations across the catchment. This modelling approach identified the importance of transport of nitrate within overland flow events and groundwater discharge to stream, a hitherto undocumented process within the study catchment. The objectives of this paper are to (i) contrast the development rationale and basic assumptions currently embedded into existing modelling approaches to estimate catchment nutrient balances, (ii) evaluate and compare the capacity of the different models to account for land management changes by application to a focus catchment and (iii) present the strengths and weaknesses of each of the modelling approaches. Presented results suggest that the physics-based catchment modelling approach has superior predictive capability to account for the impacts of land management change than the process-based and generation rate-based approaches. However until the landscape attenuation and transformation processes are generalised with confidence for inclusion into the more physics-based catchment models it is recommended that the generation rate-based approach linked to a catchment model capable of predicting hydrologic pathways at the land management scale be adopted. This paper concluded that all of the modelling approaches evaluated require further development.

Natural resource managers are becoming increasingly interested in incorporating into policy and investment frameworks the likely lag between land use change and groundwater response time. Until recently, predicting the response times of groundwater systems to a range of investment strategies (eg. agronomic changes and recharge management options) has relied on bounded analytical solutions or empirical observations from limited transect monitoring trials. This paper describes and evaluates an approach to estimate spatial groundwater response times to changes in groundwater recharge from land use and/or climate change. The approach is based on linking an unsaturated catchment model to a multi-layered distributed groundwater model and was applied to the upper Loddon Catchment (6113 km(2)) in southwestern Victoria, Australia. The objectives of this paper are to (i) present spatial and temporal variation estimates in groundwater response times and (ii) identify locations in the landscape which have the greatest impact on watertable level. The modelling approach presented in this paper demonstrates the capacity to link a suite of farming system models into a catchment framework to derive spatially explicit recharge estimates which are integrated into a distributed groundwater model. In combination with the catchment depth to watertable impact mapping, the response time predictions derived using this modelling approach offer robust estimates of storage-discharge characteristics of catchments in contrast to idealised groundwater analogues which were found not to adequately capture complex groundwater interactions and within-catchment dynamics.

This paper reports on the application and enhancement of a catchment-wide biophysical modelling framework to support an evidence-based approach for the procurement of environmental goods.A biophysical modelling framework known as the Catchment Analysis Tool (CAT) is been used in this exercise to estimate on-site impacts of land management changes with off-site environmental outcomes. The framework comprises a suite of one-dimensional farming systems models capable of simulating a range of farming enterprises with modifications to account for lateral flow and groundwater recharge and is integrated into a fully distributed 3D-groundwater model.This paper reports on the application to the Upper Wimmera catchment (310 326 ha) in western Victoria, Australia. The model is used to assess likely environmental outcomes due to farm scale revegetation. Additional information derived included the mapping of aquifer response times to land use/management change. This information is then used to prioritise catchment investment. The objectives of this paper are to;(i) Describe the construct of the modelling framework,(ii) Detail the modifications to the 3D-groundwater model to account for landuse, evapotranspiration and surface water/groundwater interactions, and(iii) Present the application results. The paper concludes that spatially explicit, physically-based models can provide robust information to support evidence-based approaches to the procurement of environmental outcomes.

This paper is an extension of previous work completed in the development and application of an evidence-based approach to the procurement of environmental improvement (Eigenraam et al 2007). Additional modelling results are presented supporting the economic principle of joint production as well as demonstrating environmental outcomes are both spatially and temporally correlated. The modelling framework, known as the Catchment Modelling Framework (CMF), explicitly links biophysical and catchment scale processes and was used to estimate multiple environmental outcomes. The CMF model was used to support a project piloting a market-based approach to procure multiple environmental outcomes. Whereas market-based approaches have been used in the past to distribute environmental funds, this is the first time a market-based policy has been fully integrated from desk to field with a biophysical modelling framework for the purchase of multiple outcomes. This paper reports on the application of the CMF to the Avon-Richardson sub-catchment (371,000 ha) in north central Victoria. The catchment model was used to undertake an a priori assessment of environmental outcomes. The CMF operates at both the farm scale (< 1 ha) and the catchment scale; explicitly links surface and groundwater interactions; accounts for land management and practice; and estimates water balance, erosion, carbon and vegetation dynamics on a daily basis. The paper concludes that spatially explicit, physically-based biophysical models are capable of providing robust and transparent information to support evidence-based approaches to the procurement of environmental outcomes.

assumptions of 4 catchment modelling approaches representing different generic classes of predictive models. These models are commonly used to estimate the impacts of land use and management change on stream flow and salinity regimes within a target region. Three approaches are based on a simple conceptual framework that assumes a single layer groundwater aquifer and requires minimal information and calibration (Zhang-BC2C, CAT1D-BC2C and LUCICAT), whereas the fourth approach (CAT3D) adopts a fully distributed highly parameterised catchment model capable of simulating complex multi-layered groundwater aquifer systems. All models were applied to the Gardiner subcatchment within the Goulburn - Broken region of Victoria, identified as a National Action Plan for Salinity priority subcatchment. Current condition simulation results were compared with observed stream flow and groundwater hydrograph data. Results show that the simple frameworks predicted whole-of-catchment mean annual salt and water yield with minimum parameterisation. The fully distributed framework produced similar catchment-scale responses to the simple approaches, but required more intensive input data and solution times. However, the fully distributed framework provides finer temporal and spatial scale information within the catchment. The more detailed models ( such as CAT3D) also have the predictive capacity to assess the within-catchment dynamics at a range of scales and account for landscape position and complex surface/ groundwater interactions. This paper concludes that the simple frameworks are useful for judging the whole-of-catchment impacts of broad-scale land use change on catchment water yields and salinity and therefore provide valuable tools for community engagement. However, the within-catchment dynamics are not well represented and particular care must be taken when applying such models in those catchments where the interaction between groundwater and surface features result in saturated areas that are disconnected from streams. Adoption of a distributed groundwater modelling environment similar to that of CAT3D provides higher spatial resolution relative to the lumped broad scale groundwater glow system (GFS) based parameterisation adopted by the BC2C rapid assessment approaches. The developers of the BC2C model acknowledge that such models are currently limited to upland local and intermediate groundwater flow systems. Given that the majority of land salinisation is located in regions dominated by intermediate and regional groundwater systems, this tool is not well suited to adequately model regional processes. In contrast, the CAT3D distributed groundwater models are likely to be applicable across a range of scales and provide the capacity to assess the trade offs between salinity recharge and discharge intervention strategies. We conclude that more complex models ( e. g. CAT3D) are needed to identify at the land management scale (paddock/farm) cost effective land use and land management changes within the catchment to improve catchment health.

Management of dryland salinity in Australia will require changes in the design and utilisation of plant systems in agriculture. These changes will provide new opportunities for livestock agriculture. In areas already affected by salt, a range of plants can be grown from high feeding value legumes with moderate salt tolerance through to highly salt tolerant shrubs. A hectare of these plants may support between 500 and 2000 sheep grazing days per year. The type of plants that can be grown and the subsequent animal production potential depend on a range of factors that contribute to the ‘salinity stress index’ of a site, including soil and groundwater salinity, the extent and duration of waterlogging and inundation, the pattern and quantity of annual rainfall, soil texture and chemistry, site topography and other site parameters. Where the salinity stress index is high, plant options will usually include a halophytic shrub that accumulates salt. High salt intakes by grazing ruminants depress feed intake and production. Where high and low salt feeds are available together, ruminants will endeavour to select a diet that optimises the overall feeding value of the ingested diet. In areas that are not yet salt affected but contribute to groundwater recharge, perennial pasture species offer an opportunity for improved water and salt management both on-farm and at the catchments. If perennial pasture systems are to be adopted on a broad scale, they will need to be more profitable than current annual systems. In the high rainfall zones in Victoria and Western Australia, integrated bioeconomic and hydrological modelling indicates that selection of perennial pasture plants to match requirements of a highly productive livestock system significantly improves farm profit and reduces groundwater recharge. In the low to medium rainfall zones, fewer perennial plant options are available. However, studies aiming to use a palette of plant species that collectively provide resilience to the environment while maintaining profitable livestock production may also lead to new options for livestock in the traditional cropping zone.

The need for a consistent Statewide approach to the modelling of water and salt export across the Murray-Darling Basin has led to the conceptualisation of the 2CSalt model. The model was developed by State agencies and associated partners of the CRCCH and Murray-Darling Basin Commission. It provides consistent and transparent predictions of salt movement under current practice and is capable of predicting the likely impact of land-use change on catchment yield and salt export.The 2CSalt model has been designed for application to upland catchments dominated by local-to-intermediate Groundwater Flow Systems (GFS). The model operates on monthly time-steps and builds on the existing understanding of the GFS (Coram et al., 2000) to estimate the partitioning of surface, lateral and groundwater pathways of water within a catchment. The surface hydrology and partitioned vertical to lateral water pathways are generated a priori and are required as an input to the 2CSalt model.The 2CSalt model simulates end-of-catchment stream flow and salt export from catchments up to 200,000 ha in area. The catchment landscape must be topographically and climatically variable to meet criteria associated with GFS modelling approaches. The catchment must also be unregulated and gauged so as to provide continuous stream and salt load data to underpin model calibration and validation. Surface terrain modelling is used to define the catchment groundwater response units, and as such, the surface topographical features are reflected in the hydrological processes.This paper presents results from the application of the 2CSalt model to the Bet Bet catchment that covers an area of 64342 ha within the south-west region of the North Central catchment of Victoria. The Bet Bet pilot region has an estimated mean annual salt export of 20,020 tonnes and has been targeted as a priority catchment by the North Central Catchment Management Authority (NCCMA, 2003). Results incorporate recent improvements to the modelled salt pathways and a discussion is included on the impact of these changes.Four land-use scenarios were tested in the Bet Bet catchment to demonstrate the use of the 2CSalt model to determine the impact of land-use change on salt and water yield. These scenarios were:Upland alluvial: the planting of trees in upland alluvial areas.Biodiversity: biodiversity enhancement rules developed by Wilson et al (2003).Break-of-slope: connection between hillslope and alluvial areas buffered by trees.Upland break-of-slope: break-of-slope scenario applied to upland areas only.The impact of each land-use change on stream flow and salt load per hectare of trees planted is summarised in Table 1. The results show that the 2CSalt model can predict differences in streamflow and salt load between different configurations of planted trees. The optimum outcome in terms of salinity management is to decrease salt load while maintaining stream flow for potential use downstream. Of the four scenarios tested the biodiversity scenario had the greatest impact in terms of reducing end-of-catchment stream salt concentration.[GRAPHICS]Results presented in this paper show that the 2CSalt model is capable of representing the primary pathways of the end-of-catchment water and salt export. As such, this model is capable of providing stakeholders with information on the optimum land-use implementation strategy to mitigate the impact of stream salinity in upland catchments.

One-dimensional simulation models of farming systems have been used to evaluate production and environmental aspects of farming systems, including the amount of deep drainage lost under crops and pastures. Most of this deep drainage is assumed to contribute recharge to groundwater. In addition, previous studies, most notably in the Liverpool Plains, have identified large anomalies between estimates derived using one-dimensional models of deep drainage lost below the plant root zone and recharge estimates based on hydrograph responses. In this paper we report the integration and application of a one-dimensional farming systems model (GrassGro TM ) into a catchment framework based on the USDA soil and water assessment tool (SWAT model) with enhanced allowance for lateral flows. The catchment framework was applied to the Hughes Creek sub-catchment of the Goulburn-Broken catchment, which has been identified by the National Action Plan for Salinity as a Victorian priority catchment. Simulation results were validated against three independent approaches: 1) predicted transpiration compared with estimates derived using the broad scale Zhang approach; 2) catchment averaged recharge estimates compared with recharge data embedded in the ABARE model based on the Catchment Characterisation groundwater conceptualisation project; and 3) observed stream flow data. Derived simulation results show good agreement between deep drainage estimates, observed stream flow and available experimental data. Reported results suggest that this framework can be used to assess the off-site impacts of land management decisions in a catchment context and can therefore extend the application of one-dimensional farming systems simulation models for assessing the potential impacts of salinity from agricultural land management.