Namoi Catchment Research Articles

Precipitation Data Retrieval and Quality Assurance from Different Data Sources for the Namoi Catchment in Australia

Within the Horizon 2020 Project WaterSENSE a modular approach was developed to provide different stakeholders with the required precipitation information. An operational high-quality rainfall grid was set up for the Namoi catchment in Australia based on rain gauge adjusted radar data. Data availability and processing considerations make it necessary to explore alternative precipitation approaches. The gauge adjusted radar data will serve as a benchmark for the alternative precipitation data. The two well established satellite-based precipitation datasets IMERG and GSMaP will be analyzed with the temporal and spatial requirements of the applications envisioned in WaterSENSE in mind. While first results appear promising, these datasets will need further refinements to meet the criteria of WaterSENSE, especially with respect to the spatial resolution. Inferring information from soil moisture-derived from EO observations to increase the spatial detail of the existing satellite-based datasets is a promising approach that will be investigated along with other alternatives.

Long-term surface water trends and relationship with open water evaporation losses in the Namoi catchment, Australia

Economic pressures on natural resources have led to a modification of natural surface water patterns. This has affected the hydrologic cycle at a global scale with multiple environmental and socioeconomic implications. This study evaluates long-term trends in surface water occurrence and related climate variables in a large agricultural catchment of Australia to understand trends in evaporative water losses from open water bodies. Surface water detection was based on a supervised classification of Landsat images between 1988 and 2018 to obtain inundation and surface water frequencies across the catchment, which were compared with other surface water products. Climate trends were based on monthly SILO gridded datasets. Open water evaporation was estimated using the FAO56 methodology and compared with the Penman-Monteith-Leuning Evapotranspiration V2 (PML_V2) product. Evaporation trends were analysed using the Mann Kendall (MK) test and the Sen’s slope (SS). Generally, open water frequencies showed significant negative trends, though these varied spatially. The number of dams, on the other hand, had an increasing trend. Temperatures are increasing in the catchment, while rainfall and relative humidity are decreasing, resulting in an overall positive trend for reference evapotranspiration (ETr) across 90% of the catchment. Even though ETr and evaporation per unit area of water show positive trends, lumped open water evaporation showed a negative trend, possibly associated with an average decrease in surface water frequencies. Annual evaporative losses averaged 201.9 GL, exceeding annual total account usage of surface water in the catchment. All the studied changes imply a loss of blue and green water in the catchment, and provide evidence of an overall intensification of the hydrologic cycle as predicted under climate change.

Site suitability and water availability for a managed aquifer recharge project in the Namoi basin, Australia

Study regionThis study was conducted in the Namoi catchment, Australia. Study focusManaged aquifer recharge (MAR) site suitability has been widely studied through multicriteria decision analysis (MCDA). However, the selection of areas for MAR project implementation can be a vague process with different validation approaches. The aim of this study was to create a site suitability map for MAR projects and conduct a sensitivity analysis for the selection of an area of interest (AOI) by combining highly suitable and low sensitive areas. Ten hydrologic and hydrogeologic criteria were chosen for the selection of sites for the MAR project. All criteria were reclassified and used in a MCDA that combined Analytic Hierarchy Processes (AHP) and pairwise comparisons to construct a site suitability map. Validation of the map and the AOI selected was performed using hydrograph data. Based on the AOI map, water availability and frequency were analysed using gauging station data. New Hydrological Insights for the RegionThe selected AOI represents high spatio-temporal variability in natural recharge rates, highly dependent on the Namoi River streamflow. Moreover, all recharge rates in the AOI are high, particularly in the paleochannel surrounding the current Namoi River. The selected AOI coincides with an area of thick coarse sediments underlying the riverbed and demonstrates the usefulness of the proposed methodology.

Non-stationarity of low flows and their relevance to river modelling during drought periods

Changes in groundwater storage lead to a reduction in groundwater contribution to river flow and present as non-stationarity, especially during low-flow conditions. Conventional river models typically ignore this non-stationarity, and, hence, their predictions of declines in low flows during drought periods are likely to be compromised. The present study assesses non-stationarity and highlights its implications for river modelling. A quantile regression analysis showed non-stationarity of low flows in the Namoi catchment (Australia), with statistically significant downward trends in the 10th percentile of log-transformed baseflow (10-LTB). This highlighted the usefulness of the 10-LTB metric to identify non-stationarity and, hence, alert modellers to the importance of adopting models that explicitly account for groundwater processes when modelling such river systems.

Culture, climate change and farm-level groundwater management: An Australian case study

Summary Cultural factors – values, beliefs, and norms – provide important insights into the environmental attitudes, risk perceptions, and behaviors of the general population. Little is known, however, about the ostensibly complex relationships linking those elements of culture to climate change risk perceptions, especially in the context of farm level decision in the ground water context. This paper addresses that gap through an analysis of survey data provided by irrigators in the Namoi catchment of Australia’s Murray–Darling Basin. We use Values–Beliefs–Norms theory to construct multivariate models of the relationship between ground water irrigators’ interpretations of climate change risks and their implementation of adaptive water conservation practices. Results indicate that these cultural factors are important explanations of irrigators’ climate change risk perceptions, and these risk perceptions are related to adaptive ground water management strategies at the farm level. The implications of the findings are discussed for research on the culture-environment nexus and for outreach designed to encourage agricultural adaptations to climate change.

Can existing practices expected to lead to improved on-farm water use efficiency enable irrigators to effectively respond to reduced water entitlements in the Murray–Darling Basin?

Summary Australia is the driest continent and there is increasing competition for scarce fresh water resources between agriculture and the environment. In the Murray–Darling Basin (MDB) that conflict has largely been resolved by reallocating water from agriculture to the environment. As part of the water reform process both governments and industry are focussed on improving on-property water use efficiency (WUE), particularly of irrigated agriculture. This paper examines the potential for WUE to enable MDB irrigators to adapt to cuts in their irrigation entitlements. The paper draws on data from a case study in the Namoi Valley of New South Wales. The distinctive contribution of this paper is that we draw on survey data of the existing and intended adoption of a limited suite of currently available WUE practices. That is, we have not simply assumed that all irrigators, or a specific proportion of irrigators, will adopt each WUE option. Given survey respondents’ intended level of adoption, we calculated the potential water savings for each property and then the catchment, without extrapolating beyond the survey respondents. Those calculations suggest that water savings of up to 100.9 GL could be achieved across the Namoi catchment if those interested in doing so were to convert to existing improved WUE practices. Those savings represented 82% of the reduction in irrigator entitlements under the draft MDB Plan, and exceed the 10 GL/yr reductions required under the revised MDB Plan. These results suggest that those adopting existing WUE practices will have additional water for irrigation. To the extent that this is the case, there seems to be less justification for government support for irrigators during the adjustment process.

Riparian vegetation NDVI dynamics and its relationship with climate, surface water and groundwater

Maintaining the integrity of riparian ecosystems whilst continuing to reserve and extract water for other purposes necessitates a greater understanding of relationships between riparian vegetation and water availability. The Normalised Difference Vegetation Index (NDVI) is a good indicator for identifying long-term changes in vegetated areas and their condition. In this study, we use regression tree analysis to investigate long term NDVI data (23 years) at semi-arid riparian areas in the Namoi catchment, Australia. Climatic factors (temperature and rainfall), surface water (flow and flooding) and groundwater levels are analysed collectively. We find that in general maximum temperature is the variable that primarily splits NDVI values, followed by antecedent 28-day rainfall and then inter-flood dry period and groundwater levels. More rain is required in the warmer months compared to cooler months to achieve similar mean NDVI values in tree patches or areas of high NDVI in riparian zones, presumably because of higher evaporation. Inter-flood dry period is shown to be important for maintenance of NDVI levels, particularly when rainfall is limited. Shallower groundwater levels sustain the NDVI and hence vegetation greenness when conditions are cooler and wetter.

Marrying Hydrological Modelling and Integrated Assessment for the needs of Water Resource Management

Abstract. This paper discusses the integration of hydrology with other disciplines using an Integrated Assessment (IA) and modelling approach to the management and allocation of water resources. Recent developments in the field of socio-hydrology aim to develop stronger relationships between hydrology and the human dimensions of Water Resource Management (WRM). This should build on an existing wealth of knowledge and experience of coupled human–water systems. To further strengthen this relationship and contribute to this broad body of knowledge, we propose a strong and durable "marriage" between IA and hydrology. The foundation of this marriage requires engagement with appropriate concepts, model structures, scales of analyses, performance evaluation and communication – and the associated tools and models that are needed for pragmatic deployment or operation. To gain insight into how this can be achieved, an IA case study in water allocation in the Lower Namoi catchment, NSW, Australia is presented.

Can NRM agencies rely on capable and effective staff to build trust in the agency?

Trust is recognised as an important component of agency–community relations, influencing the social acceptability of resource access and natural resource management (NRM). It is not clear if perceptions of the trustworthiness of agency staff members can lead to trust in an agency. This is an important question for agencies working in contentious policy arenas such as water reform in Australia's Murray-Darling Basin. This research addressed that gap and developed a set of survey items that can be employed to benchmark trust and trustworthiness by exploring groundwater irrigator's trust in the New South Wales Office of Water (NoW). A survey was mailed to all farming properties with a groundwater licence in the Namoi catchment. As might be expected, licence holders were more likely to trust agency staff than NoW itself. Perceptions of agency and staff trustworthiness influenced landholder trust in NoW. Agency trustworthiness partially mediated the relationship between staff trustworthiness and agency trust. These findings suggest that trust should be viewed as a multi-level phenomenon. To the extent that these findings are replicated, a key implication is that community engagement strategies attempting to build trust in an agency should set out to influence how the agency itself is perceived as an organisation.

A reassessment of the Lower Namoi Catchment aquifer architecture and hydraulic connectivity with reference to climate drivers

We demonstrate the need for better representations of aquifer architecture to understand hydraulic connectivity and manage groundwater allocations for the ∼140 m-thick alluvial sequences in the Lower Namoi Catchment, Australia. In the 1980s, an analysis of palynological and groundwater hydrograph data resulted in a simple three-layer stratigraphic/hydrostratigraphic representation for the aquifer system, consisting of an unconfined aquifer overlying two semi-confined aquifers. We present an analysis of 278 borehole lithological logs within the catchment and show that the stratigraphy is far more complex. The architectural features and the net-to-gross line-plot of the valley-filling sequence are best represented by a distributive fluvial system, where the avulsion frequency increases at a slower rate than the aggradation rate.We also show that an improved understanding of past climates contextualises the architectural features observable in the valley-filling sequence, and that the lithofacies distribution captures information about the impact of climate change during the Neogene and Quaternary. We demonstrate the correlation between climate and the vertical lithological succession by correlating the sediment net-to-gross ratio line-plot with the marine benthic oxygen isotope line-plot – a climate change proxy. Pollens indicate that there was a transition from a relatively wet climate in the mid–late Miocene to a drier climate in the Pleistocene, with a continuing drying trend until present. Groundwater is currently extracted from the sand and gravel belts associated with the high-energy wetter climate. However, some of these channel belts are disconnected from the modern river and flood zone. We show that the cutoff between the hydraulically well- and poorly connected portions of the valley-filling sequence matches the connectivity threshold expected from a fluvial system.

Training Images from Process-Imitating Methods

The lack of a suitable training image is one of the main limitations of the application of multiple-point statistics (MPS) for the characterization of heterogeneity in real case studies. Process-imitating facies modeling techniques can potentially provide training images. However, the parameterization of these process-imitating techniques is not straightforward. Moreover, reproducing the resulting heterogeneous patterns with standard MPS can be challenging. Here the statistical properties of the paleoclimatic data set are used to select the best parameter sets for the process-imitating methods. The data set is composed of 278 lithological logs drilled in the lower Namoi catchment, New South Wales, Australia. A good understanding of the hydrogeological connectivity of this aquifer is needed to tackle groundwater management issues. The spatial variability of the facies within the lithological logs and calculated models is measured using fractal dimension, transition probability, and vertical facies proportion. To accommodate the vertical proportions trend of the data set, four different training images are simulated. The grain size is simulated alongside the lithological codes and used as an auxiliary variable in the direct sampling implementation of MPS. In this way, one can obtain conditional MPS simulations that preserve the quality and the realism of the training images simulated with the process-imitating method. The main outcome of this study is the possibility of obtaining MPS simulations that respect the statistical properties observed in the real data set and honor the observed conditioning data, while preserving the complex heterogeneity generated by the process-imitating method. In addition, it is demonstrated that an equilibrium of good fit among all the statistical properties of the data set should be considered when selecting a suitable set of parameters for the process-imitating simulations.

Upland wetlands in the Namoi Catchment: mapping distribution and disturbance classes of fens, bogs and lagoons.

To assist with planning and conservation strategies, mapping of wetlands above 700 m elevation across the Namoi Catchment (east of Tamworth) was undertaken. The number of hectares of each type within this high-elevation region, the area currently in conservation reserves and the status of these remnants was assessed. 1 001 wetlands were mapped and allocated to three wetland types (fens, bogs and lagoons) and six disturbance groups (based on agricultural clearing and presence of dams). Total wetlands cover was 4 490 ha, of which fens were the most common, followed by bogs and a single lagoon. The smallest wetland was 0.12 ha in size, the largest 113 ha and the average 5 ha. Only 10% of all wetlands were considered to be in near natural state with only 5.5% of all wetland area protected within conservation reserves. Cunninghamia (2013) 13: 331-335 doi: 10.7751/cunninghamia2013.009

Variations in Soil Carbon Stocks with Texture and Previous Landuse in North-western NSW, Australia

<p>Australia’s land managers will need specific information about the best locations at which to sequester carbon if they are to take advantage of the recent Carbon Farming Initiative of the Australian Government under which carbon offsets can be created through sequestration of carbon in soil and trees. The literature indicates that soil texture and previous landuse are important determinants of soil carbon content. This paper describes the results of work to assess the current levels of soil carbon and the extent to which they vary with previous landuse and soil texture in the Namoi Catchment Management Authority in North West NSW, Australia. Soil samples were taken at 74 sites for determination of soil carbon concentration and stocks as well as soil texture and landuse in the last 10 years. There was wide variation between sites in soil carbon concentration and stocks which were greatest in those soils which had not been disturbed by cultivation and in soils with higher clay content. Thus, the greatest potential for carbon sequestration is in soils with the lowest carbon concentration, those which have been previously disturbed, and with higher clay content. Maintaining any increased carbon concentration will depend on minimizing disturbance, increased carbon input and minimizing loss of carbon through soil erosion. As these factors all vary significantly on a regional and landscape basis it will be important for land managers to have access to information which allows them to choose the sites at which potential for sequestration of soil carbon is greatest.</p>

Aquifer heterogeneity and response time: the challenge for groundwater management

Groundwater is an important contributor to irrigation water supplies. The time lag between withdrawal and the subsequent impacts on the river corridor presents a challenge for water management. We highlight aspects of this challenge by examining trends in the groundwater levels and changes in groundwater management goals for the Namoi Catchment, which is within the Murray–Darling Basin, Australia. The first high-volume irrigation bore was installed in the cotton-growing districts in the Namoi Catchment in 1966. The development of high-yielding bores made accessible a vast new water supply, enabling cotton growers to buffer the droughts. Prior to the development of a groundwater resource it is difficult to accurately predict how the water at the point of withdrawal is hydraulically connected to recharge zones and nearby surface-water features. This is due to the heterogeneity of the sediments from which the water is withdrawn. It can take years or decades for the impact of groundwater withdrawal to be transmitted kilometres through the aquifer system. We present the analysis of both historical and new groundwater level and streamflow data to quantify the impacts of extensive groundwater withdrawals on the watertable, hydraulic gradients within the semi-confined aquifers, and the movement of water between rivers and aquifers. The results highlight the need to monitor the impacts of irrigated agriculture at both the regional and local scales, and the need for additional research on how to optimise the conjunctive use of both surface-water and groundwater to sustain irrigated agriculture while minimising the impact on groundwater-dependent ecosystems.

Carbon sequestration under subtropical perennial pastures I: Overall trends

The use of subtropical perennial grasses in temperate grazing systems is increasingly being promoted for production and environmental benefits. This study employed a combination of elemental and stable isotope analyses to explore whether pastures sown to either kikuyu (Pennisetum clandestinum) or a combination of panic (Panicum maximum) and Rhodes grass (Chloris gayana) could increase soil organic carbon (SOC) levels in five regions across southern Australia. Carbon was sequestered under kikuyu at a rate of 0.90 ± 0.25 Mg C ha–1 year–1 along the south coast of Western Australia. Lower but still significant sequestration rates were found for kikuyu in South Australia (0.26 ± 0.13 Mg C ha–1 year–1). No changes in SOC were found for panic–Rhodes grass pasture systems in the northern district of Western Australia. Additionally, we found no changes in SOC when kikuyu-based pastures were established on formerly cropped paddocks in the Namoi Catchment of New South Wales. Stable isotope results corroborated these findings and suggested that, where SOC has accumulated, the gains have been dominated by SOC derived from the perennial vegetation and have been concentrated in the upper 10 cm of soil.

Assessing environmental protection investments in New South Wales catchments

In this study we analyse the benefits and costs of investing in environmental protection in regional New South Wales. We do so by generating cost-benefit analyses for three projects which aim to protect native species: the regent honeyeater in the Hawkesbury-Nepean Catchment; the malleefowl in the Lachlan Catchment; and the booroolong frog in the Namoi Catchment. By generating benefit-cost ratios for these three cases, we demonstrate the use of choice modelling as a means to estimate the often difficult-to-determine benefits associated with environmental investment. The use of choice modelling estimates strengthens the analysis by including ‘non-monetary’ values which are often excluded from such analyses. We conclude by indicating how the benefit-cost ratios can be tabulated to offer a comparison of investments, thus demonstrating how this approach gives policy makers a useful quantitative decision support tool when considering investments. Access to such information allows for the funding of only those investments that cause an improvement in the well-being of society and the prioritisation of competing proposals.

Implications of deep drainage through saline clay for groundwater recharge and sustainable cropping in a semi-arid catchment, Australia

Abstract. The magnitude and timing of deep drainage and salt leaching through clay soils is a critical issue for dryland agriculture in semi-arid regions (<500 mm yr−1 rainfall, potential evapotranspiration >2000 mm yr−1) such as parts of Australia's Murray-Darling Basin (MDB). In this rare study, hydrogeological measurements and estimations of the historic water balance of crops grown on overlying Grey Vertosols were combined to estimate the contribution of deep drainage below crop roots to recharge and salinization of shallow groundwater. Soil sampling at two sites on the alluvial flood plain of the Lower Namoi catchment revealed significant peaks in chloride concentrations at 0.8–1.2 m depth under perennial vegetation and at 2.0–2.5 m depth under continuous cropping indicating deep drainage and salt leaching since conversion to cropping. Total salt loads of 91–229 t ha−1 NaCl equivalent were measured for perennial vegetation and cropping, with salinity to ≥ 10 m depth that was not detected by shallow soil surveys. Groundwater salinity varied spatially from 910 to 2430 mS m−1 at 21 to 37 m depth (N = 5), whereas deeper groundwater was less saline (290 mS m−1) with use restricted to livestock and rural domestic supplies in this area. The Agricultural Production Systems Simulator (APSIM) software package predicted deep drainage of 3.3–9.5 mm yr−1 (0.7–2.1% rainfall) based on site records of grain yields, rainfall, salt leaching and soil properties. Predicted deep drainage was highly episodic, dependent on rainfall and antecedent soil water content, and over a 39 yr period was restricted mainly to the record wet winter of 1998. During the study period, groundwater levels were unresponsive to major rainfall events (70 and 190 mm total), and most piezometers at about 18 m depth remained dry. In this area, at this time, recharge appears to be negligible due to low rainfall and large potential evapotranspiration, transient hydrological conditions after changes in land use and a thick clay dominated vadose zone. This is in contrast to regional groundwater modelling that assumes annual recharge of 0.5% of rainfall. Importantly, it was found that leaching from episodic deep drainage could not cause discharge of saline groundwater in the area, since the water table was several meters below the incised river bed.

Protecting the Booroolong Frog in the Namoi Catchment: A Cost-Benefit Analysis

The Booroolong frog project in the Namoi Catchment represents an environmental investment to protect the species and around 10.7 kilometres of its habitat in the catchment. The project’s benefit-cost ratio (BCR) of 8.6 indicates that the benefits outweigh the costs by a significant margin. The measures introduced by landholders, at relatively low cost, should therefore result in a significant return on investment upon project completion in 10 years time. The benefits are estimated using a choice modelling study which was recently developed for the valuation of investment in natural resource management in the Namoi Catchment. As this is a largely ex ante cost-benefit analysis, the BCR is subject to uncertainty associated with assumptions which had to be made for some variables. However, sensitivity analysis indicates that the project benefits outweigh the costs by a significant margin even under conservative conditions.

Estimating water yield response to land use in the Namoi catchment of the Murray-Darling Basin, Australia

The Namoi catchment is an intensively developed irrigation area in the Murray-Darling Basin (MDB) and has a mixture of land use types including cropping, pasture and forests. It is yet to implement an integrated groundwater and surface water management system. The Soil Water Assessment Tool was applied for the Namoi to estimate surface runoff and groundwater contribution to streams. SWAT estimates showed that the water yield is substantially lower in areas where grazing natural vegetation and plantations are located. Areas where modified pastures and natural and conservation forests are located have generated higher water yield. The variation of water yield in relation to climatic factors and different types of land use can be used to identify areas where water saving can be made through adopting better management practices in an integrated groundwater and surface water management system.

Multisite seasonal forecast of arid river flows using a dynamic model combination approach

This paper dynamically combines three independent forecasts of multiple river flow volumes a season in advance for arid catchments. The case study considers five inflow locations in the upper Namoi Catchment of eastern Australia. The seasonal flows are predicted on the basis of concurrent sea surface temperature anomalies (SSTAs), which are predicted a season forward using a dynamic combination of three SSTA forecasts. The river flows are predicted using three statistical forecasting models: (1) a mixture of generalized lognormal and multinomial logit models, (2) the local regression of independent components of five inflows, and (3) the weighted nearest neighbor method, where each of these models use the forecasted SSTA along with prior lags of the flow as the main driving variables. The study demonstrates that improved SSTA forecast (due to dynamic combination) in turn improves all three flow forecasts, while the dynamic combination of the three flow forecasts results in further, although smaller, improvements.