Determination of porosity and storage capacity of a calcareous aquifer (France) by correlation and spectral analyses of time series

Time-series analyses were used to investigate the relationships between barometric pressure changes, earth tides, and water-level fluctuations in a confined aquifer. The method was applied to data from the fractured aquifer at the Hydrogeological Experimental Site in Poitiers (France) and used to yield estimates of the aquifer’s storage capacity, porosity and barometric efficiency. The aim is to address relevance of these analyses for an aquifer showing both fracture draining and confined karstic flow in thin strata. Cross-correlation and spectral analysis are used to compare water-level head and atmospheric-pressure fluctuations. Porosity and storage capacity are calculated using this method and compared to results from petrophysical measurements and hydraulic pumping tests, respectively. The storage coefficients calculated by the time-series analyses are in agreement with those obtained by interpretation of the interference pumping tests. Conversely, porosity values calculated by time-series analyses are underestimated compared to those obtained by other methods.