Comparing Methods of Barometric Efficiency Characterization for Specific Storage Estimation

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.

Hydrogeological Characterization of Coastal Aquifer on the Basis of Observed Sea Level and Groundwater Level Fluctuations: Neretva Valley Aquifer, Croatia

“…Following Figure 3, time series were detrended to eliminate present trends. The usual frequency upper limit to eliminate for trends ranges from 0.5 cycles per day [56] to 0.8 cycles per day [46,50]. Hereby, we did not limit the cutoff threshold, since the sixth order polynomial fit was applied to minimize RMSE when fitting the observed signal, and thus the cutoff was not same for different time series.…”

“…Long-term periodicity in barometric pressure is usually explained as the consequence of the spatial displacement of air mass [42,46,56], whereas p A captures diurnal and semidiurnal barometric changes due to the effects of air heating and cooling following the transition from day to night and opposite, as well as the all changes, except for the trends [45,50]. In this manner, detrended groundwater head signal was defined as temporally dependent:…”

“…The difference h OBSERVED (t) − h TIDAL (t) was actually the residual found within the detrended observed signal relative to tidally induced change in groundwater head, and corresponded to the influence of barometric changes. This was the main premise in terms of defining barometric efficiency, BE, by applying different methods ranging from the spectral to the temporal domain [45,50].…”

“…If the external stress represented by barometric pressure is transmitted to the aquifer, reaction stress can be divided between the sediments that the aquifer is made of and water contained within the aquifer pore volume. Because BE represents the percentage of stress that is accommodated by the sediment matrix [43,44,50], a zero BE value corresponds to no response case, whereas a unity BE value respresents a fully efficient response to barometric changes. In case of a zero BE value, total barometric pressure-induced stress is accommodated by the pore water, whereas for a unity BE value, total stress is accommodated purely by sediment matrix.…”

“…Because some of the tidal methods imply the knowledge of loading efficiency [9,14,26], barometric efficiency, BE, has to be determined to characterize tidally induced changes inland from the shoreline. The topic of excluding the effects of barometric pressure from observed groundwater level was of interest in several publications [41][42][43][44][45][46][47][48][49][50][51], whereas BE determination can be approached by time domain or frequency domain analysis [50].…”