Brunner, Philip

2014-5-18, Xie, Y. Q., Cook, Peter G., Brunner, Philip, Irvine, Dylan J., Simmons, Craig Trevor

Decline in regional water tables (RWT) can cause losing streams to disconnect from underlying aquifers. When this occurs, an inverted water table (IWT) will develop beneath the stream, and an unsaturated zone will be present between the IWT and the RWT. The IWT marks the base of the saturated zone beneath the stream. Although a few prior studies have suggested the likelihood of an IWT without a clogging layer, most of them have assumed that a low-permeability streambed is required to reduce infiltration from surface water to groundwater, and that the IWT only occurs at the bottom of the low-permeability layer. In this study, we use numerical simulations to show that the development of an IWT beneath an unclogged stream is theoretically possible under steady-state conditions. For a stream width of 1m above a homogeneous and isotropic sand aquifer with a 47m deep RWT (measured in an observation point 20m away from the center of the stream), an IWT will occur provided that the stream depth is less than a critical value of 4.1m. This critical stream depth is the maximum water depth in the stream to maintain the occurrence of an IWT. The critical stream depth decreases with stream width. For a stream width of 6 m, the critical stream depth is only 1mm. Thus while theoretically possible, an IWT is unlikely to occur at steady state without a clogging layer, unless a stream is very narrow or shallow and the RWT is very deep.

2008-5-26, Cook, Peter G., Wood, Cameron, White, Troy, Simmons, Craig Trevor, Fass, T., Brunner, Philip

Radon activity within a shallow wetland in southern Australia has been measured on three occasions between May and October 2006. Measured activities within the surface water display a similar pattern of spatial variability on each occasion, suggesting that it is related to the locations of groundwater inflow and mixing processes. The mean groundwater inflow rate has been estimated from the mean radon activity using a mass balance approach. The components of the radon budget are (i) contribution from groundwater inflow, (ii) diffusive flux from wetland bottom sediments (iii) loss due to gas exchange, (iv) loss due to radioactive decay, (v) toss due to groundwater or surface water outflow. Also required to complete the water balance are the surface water inflow rate, direct precipitation on the wetland, and evaporation rate. The radon diffusive flux has been estimated from measurements of radon production within the sediments and a diffusive transport model., calibrated by measurements of radon activity in seated chambers that can receive radon only from diffusion and lose it only by radioactive decay. Radon loss due to gas exchange is inferred from the loss rate of SF6, following its injection into isolated areas of the wetland, while the rate of radioactive decay is known. The radon activity in groundwater inflow is measured from sampling piezometers surrounding the wetland. Steady state and transient mass balance approaches yield similar results, with groundwater inflow rates varying between 12 and 18 m(3)/day. Estimated groundwater inflow rates are most sensitive to the radon activity of groundwater inflow, the gas exchange velocity, surface water area and the accuracy with which the mean radon activity in the wetland can be, measured. Importantly, it is relatively insensitive to the surface water inflow rate, which is poorly known. Crown Copyright (c) 2008 Published by Elsevier B.V. All rights reserved.

2014-5-18, Lamontagne, S., Taylor, A. R., Cook, Peter G., Crosbie, R. S., Brownbill, R., Williams, R. M., Brunner, Philip

In semi-arid and arid river basins, understanding the connectivity between rivers and alluvial aquifers is one of the key challenges for the management of groundwater resources. The type of connection present (gaining, losing-connected, transitional and losing-disconnected) was assessed at 12 sites along six Murray-Darling Basin river reaches. The assessments were made by measuring the hydraulic head in the riparian zone near the rivers to evaluate if the water tables intersected the riverbeds and by measuring fluid pressure () in the riverbeds. The rationale for the latter was that will always be greater than or equal to zero under connected conditions (either losing or gaining) and always lesser than or equal to zero under losing-disconnected conditions. A mixture of losing-disconnected, losing-connected and gaining conditions was found among the 12 sites. The losing-disconnected sites all had a riverbed with a lower hydraulic conductivity than the underlying aquifer, usually in the form of a silty clay or clay unit 0.5-2m in thickness. The riparian water tables were 6 to 25m below riverbed level at the losing-disconnected sites but never lower than 1m below riverbed level at the losing-connected ones. The contrast in water table depth between connected and disconnected sites was attributed to the conditions at the time of the study, when a severe regional drought had generated a widespread decline in regional water tables. This decline was apparently compensated near losing-connected rivers by increased infiltration rates, while the decline could not be compensated at the losing-disconnected rivers because the infiltration rates were already maximal there. Copyright (c) 2012 John Wiley & Sons, Ltd.

, Lamontagne, Sébastien, Taylor, A. R, Cook, Peter G, Crosbie, R. S, Brownbill, R, Williams, R. M, Brunner, Philip

In semi-arid and arid river basins, understanding the connectivity between rivers and alluvial aquifers is one of the key challenges for the management of groundwater resources. The type of connection present (gaining, losing-connected, transitional and losing-disconnected) was assessed at 12 sites along six Murray-Darling Basin river reaches. The assessments were made by measuring the hydraulic head in the riparian zone near the rivers to evaluate if the water tables intersected the riverbeds and by measuring fluid pressure (Ψ) in the riverbeds. The rationale for the latter was that will always be greater than or equal to zero under connected conditions (either losing or gaining) and always lesser than or equal to zero under losing-disconnected conditions. A mixture of losing-disconnected, losing-connected and gaining conditions was found among the 12 sites. The losing-disconnected sites all had a riverbed with a lower hydraulic conductivity than the underlying aquifer, usually in the form of a silty clay or clay unit 0.5-2m in thickness. The riparian water tables were 6 to 25m below riverbed level at the losing-disconnected sites but never lower than 1m below riverbed level at the losing-connected ones. The contrast in water table depth between connected and disconnected sites was attributed to the conditions at the time of the study, when a severe regional drought had generated a widespread decline in regional water tables. This decline was apparently compensated near losing-connected rivers by increased infiltration rates, while the decline could not be compensated at the losing-disconnected rivers because the infiltration rates were already maximal there. Copyright (c) 2012 John Wiley & Sons, Ltd.

2009-5-26, Li, H. T., Brunner, Philip, Kinzelbach, Wolfgang, Li, W. P., Dong, X. G.

Due to the chronic lack of verification data, hydrologic models are notoriously over-parameterized. If a large number of parameters are estimated, while few verification data are available, the calibrated model may have little predictive value. However, recent development in remote sensing (RS) techniques allows generation of spatially distributed data that can be used to construct and verify hydrological models. These additional data reduce the ambiguity of the calibration process and thus increase the predictive value of the model. An example for such remotely sensed data is the spatial distribution of phreatic evaporation. In this modeling approach, we use the spatial distribution of phreatic evaporation obtained by remote sensing images as verification data Compared to the usual limited amount of head data, the spatial distribution of evaporation data provides a complete areal coverage. However, the absolute values of the evaporation data are uncertain and therefore three ways of using the spatial distribution pattern of evaporation were tested and compared. The first way is to directly use the evaporation pattern defined in a relative manner by dividing the evaporation rate in a pixel by the total evaporation of a selected rectangular area of interest. Alternatively, the discrete fourier transform (DFT) or the discrete wavelet transform (DWT) are applied to the relative evaporation pattern in the space domain defined before. Seven different combinations of using hydraulic head data and/or evaporation pattern data as conditioning information have been tested. The code PEST, based on the least-squares method, was used as an automatic calibration tool. From the calibration results, we can conclude that the evaporation pattern can replace the head data in the model calibration process, independently of the way the evaporation pattern is introduced into the calibration procedure. (C) 2009 Elsevier B.V All rights reserved.