No abstract

Groundwater responses to barometric pressure fluctuations are characterized using the concept of barometric efficiency (BE). For semiconfined and confined aquifers, BE values can be used to provide efficient, low‐cost estimates of specific storage. This study compares, for the first time, eight existing methods of BE estimation. Comparisons were undertaken using data from the Peel region of Western Australia. Fourier analysis and regression deconvolution methods were used to estimate aquifer confinement status. The former approach was found to be robust and provided a quantitative basis for spatial comparisons of the degree of confinement. The latter approach was confounded by the presence of diurnal and/or semidiurnal signals. For wells at which semiconfined or confined responses were identified, frequency and time domain methods were used to estimate BE values. Most BE estimation methods were similarly confounded by diurnal and/or semidiurnal signals, with the exception of the Acworth et al. (2016) method. Specific storage values calculated from BE values were order‐of‐magnitude consistent with the results of four historical pumping tests. The methods implemented in this research provide efficient, low‐cost alternatives to hydraulic testing for estimating aquifer confinement, as well as the BE and specific storage of semiconfined and confined aquifers. The frequency and duration of observations required by these methods are minimal; for example, typically requiring a minimum of four observations per day over a four month period. In some locations they may allow additional insights to be derived from existing groundwater hydrograph data.

The water table fluctuation method of estimating recharge is widely used because it is conceptually simple and easy to implement. The major source of uncertainty in the recharge estimates come from the specific yield. The apparent specific yield has a dependence on the depth to water table that makes its measurement difficult (if not impossible) for appropriate use in the water table fluctuation method. This study has treated the specific yield as a conceptual parameter that cannot be measured and has constrained it using a rejection sampling approach using probabilistic estimates of net recharge from the chloride mass balance method and excess water derived from the difference between precipitation and remotely sensed actual evapotranspiration. The method developed here provided probabilistic estimates of the ultimate specific yield and a probabilistic time series of gross recharge, both important in shallow water table environments. An additional benefit of the method is that by jointly constraining the three different recharge types (i.e., excess water, gross, and net recharge) they are assured of being internally consistent. The method was implemented for 58 bores across four catchments in Northern Australia that may see increased development in coming years.

No abstract

No abstract