Long-term trends in the annual groundwater recharge estimates using the water table fluctuation method

Groundwater recharge is critical for sustainable water resource planning and modelling fluid and contaminant transport within th e subsurface. Unfortunately, direct groundwater measurements are often too short to investigate long-term trends for many regions in Australia. Over the past, a number of methods have been developed to estimate groundwater recharge over different temporal and spatial scales. Among the most widely used techniques for estimating recharge, the water table fluctuation (WTF) method has been applied in numerous studies. In this study, we use the WTF method to estimate annual groundwater recharge at 438 groundwater monitoring bores in South Australia and analyse long-term annu al groundwater recharge trends using the nonparametric Mann -Kendall trend test. The results indi cate that the spatially averaged annual groundwater recharge has declined significantly with a trend of -0.92 mm/year for the period 1970- 2012. Similar trend tests for the 237 groundwater monitoring bores with longer data records exhibit that 161 bores have downward trends of which 103 bores are statistically significant, whereas 44 bores have upward trends and 15 of them are statistically significant. Moreover, a linear extrapolation of annual groundwater recharge trend suggests that the m ean will reach the lowest recorded annual recharge in history (2006 drought) by 2058 if the recent clima tic trends continue over a longer peri od, indicating a potential threat to the hydrological and ecological regimes. Furthermor e, the correlation analysis demonstrates that the dominating downward trends in annual groundwater rech arge are affected by the large-scale hydroclimate variables (e.g. rainfall) in South Australia

Multi-decadal trends in global terrestrial evapotranspiration and its components

Evapotranspiration (ET) is the process by which liquid water becomes water vapor and energetically this accounts for much of incoming solar radiation. If this ET did not occur temperatures would be higher, so understanding ET trends is crucial to predict future temperatures. Recent studies have reported prolonged declines in ET in recent decades, although these declines may relate to climate variability. Here, we used a well-validated diagnostic model to estimate daily ET during 1981–2012, and its three components: transpiration from vegetation (Et), direct evaporation from the soil (Es) and vaporization of intercepted rainfall from vegetation (Ei). During this period, ET over land has increased significantly (p < 0.01), caused by increases in Et and Ei, which are partially counteracted by Es decreasing. These contrasting trends are primarily driven by increases in vegetation leaf area index, dominated by greening. The overall increase in Et over land is about twofold of the decrease in Es. These opposing trends are not simulated by most Coupled Model Intercomparison Project phase 5 (CMIP5) models, and highlight the importance of realistically representing vegetation changes in earth system models for predicting future changes in the energy and water cycle

Pollutant buildup and washoff in urban areas and the modelling of stormwater pollutant load

© 2001 Dr. Jai VazeUrban stormwater is a major contributor of non-point source pollution. Estimates of diffuse source pollution loads are required to evaluate the severity of the pollution problems and to determine appropriate management measures. The main problems in modelling stormwater pollution loads are the lack of event water quality data and the large variability in the data that are available. As such, the errors in the estimates derived using existing models are often very large. The lack of data has also led to a diversity of opinions about the pollutant buildup-washoff mechanisms. A better understanding of the governing physical processes is essential to improve the load estimates. The best way to gain an understanding of the physical processes involved is to single out the contribution of each process and the explanatory variable(s) involved. To investigate the physical process of buildup, field experiments are carried out on an urban road surface in Melbourne. The data indicate that buildup over the dry days occurs relatively quickly after a rain event, but slows down after several days as redistribution occurs. The surface pollutant also becomes finer over the dry days as it is disintegrated. Washoff of the surface pollutant is dependent on the rainfall and runoff characteristics, but the results here show that common storms only remove a small proportion of the total surface pollutant load. The data also show that street sweeping may have an adverse impact on pollutant washoff because the street sweeper releases the finer material but only removes some of them, making the fine sediment available for washoff by the next storm. A series of field and laboratory washoff experiments are carried out to investigate the relative contribution of raindrop impact energy and overland flow shear stress to pollutant washoff from impervious surfaces. The experiments are carried out under simulated rainfall on a concrete surface, where half the surface is covered with insect screens to absorb most of the rainfall energy. The results show that both the turbulence created by falling raindrops and the shear stress imparted by runoff are important in loosening the surface particles and suspending them in water, making them available for washoff. The energy of falling raindrops in detaching the surface pollutants appear to be more important at the start of an event but is less dominant as the surface pollutant availability decreases over the storm. To investigate the nutrient loads associated with different particle size ranges of sediments, dry pollutant samples collected as part of the field accumulation study and stormwater washoff samples for natural storm events are analysed in the laboratory. The dry pollutant analyses indicate that although more than half of the surface pollutant are coarser than 300 µm, less than 15% of the total TP and TN are attached to particle sizes greater than 300 µm. The stormwater sample analysis results are similar to the results from the dry pollutant analysis. These results indicate that in stormwater runoff, less than 10% of the total TP and TN is associated with particle sizes greater than 300 µm. This suggests that to effectively reduce nutrient loads in particulates, treatment facilities should be designed to be able to remove the finer particles down to 50 µm for TP and down to 10 µm for TN and not just the total sediment or suspended solid load. A modelling study is also carried out to investigate the relative merits of using process-based water quality models as compared to simple empirical equations. Comparison of the predictive ability of the process-based model and the simple regression equations showed that they are both equally able to simulate measured event pollutant washoff loads. Given this conclusion, when only the estimates of event loads are required, regression models are preferable to the process-based model as they produce comparable results with a far smaller input of resources

Field Estimates of Recharge Across Australia. Bureau of Meteorology Metadata

No abstract available

The controlling factors in the daily and monthly groundwater recharge estimation using the water table fluctuation method

Understanding groundwater recharge is essential for sustainable management of water resources and modelling fluid and contaminant transport within the subsurface. Over the past, a number of methods have been developed to estimate groundwater recharge because it cannot be measured directly. However, it is still unclear what are the primary factors controlling groundwater recharge estimation at the daily and monthly temporal scales. In this paper, we examine multiple correlations between the possible controlling factors and their corresponding daily and monthly groundwater recharge estimates using the water table fluctuation (WTF) method within the Tomago sand beds, New South Wales, to identify the primary factors controlling recharge. The results show that the most important factor controlling the daily and monthly WTF recharge is rainfall, rather than the depth to the water table or groundwater level, although both of them are important parameters in the WTF groundwater recharge estimation

Flood inundation modelling: A review of methods, recent advances and uncertainty analysis

This paper reviews state-of-the-art empirical, hydrodynamic and simple conceptual models for determining flood inundation. It explores their advantages and limitations, highlights the most recent advances and discusses future directions. It addresses how uncertainty is analysed in this field with the various approaches and identifies opportunities for handling it better. The aim is to inform scientists new to the field, and help emergency response agencies, water resources managers, insurance companies and other decision makers keep up-to-date with the latest developments. Guidance is provided for selecting the most suitable method/model for solving practical flood related problems, taking into account the specific outputs required for the modelling purpose, the data available and computational demands. Multi-model, multi-discipline approaches are recommended in order to further advance this research field.This work was carried out as part of a PhD research. The authors thank the CSIRO Land and Water (the Water Resource Management Program) and the Murray-Darling Basin Authority for funding and supporting this research

Enhancing the Capability of a Simple, Computationally Efficient, Conceptual Flood Inundation Model in Hydrologically Complex Terrain

The simple conceptual flood inundation model TVD (Teng-Vaze-Dutta) is more computationally efficient and cost-effective than traditional hydrodynamic models. It is especially useful for applications that do not require velocity output and have low demands on flood dynamic representation. In this study, we have addressed the main inherent limitations of the original TVD model including: the assumption that all the floodplain depressions connected to the river are instantly filled up to the in-stream water level at each time step; the lack of information sharing at the boundary of two modelling reaches; and insufficient soil moisture processes. All of these can affect the model’s applicability and accuracy, especially in very flat and hydrologically complex floodplains. A number of improvements to the model structure have been implemented to address mass conservation, reach connectivity and water balance issues. The revised model was set up to simulate a number of flood events in Australia’s lower Balonne River and Darling River to test for its enhanced capability. The modelled inundation extents before and after the improvements were assessed against remote sensing water maps. The model developments have improved the accuracy of modelled flood extent. Nevertheless, there are still remaining issues that require the model to be used with caution when simulating flood inundation in difficult-to-model topographies, largely, the demand for reliable input of overbank flow volume and the extrapolating issue with weighting schemes