Waterhead data

The original data used in this study come from the control network of the aquifer, carried out by the Instituto Geologico y Minero de Espafia (IGME) and Confederation Hidrografica del Guadalquivir (Ministry of Environment). The piezometric series expand up to 35 years with the oldest data from 1968. The number of piezometric series used in this work was 53, scattered all over the aquifer. Observations were made on a monthly basis for most parts, and sometimes every two months. Thus, the series average nearly 150 measurements, which is sufficient for studies of this nature. The data are measured almost monthly, but not on the same day of the month. The sampling with a constant step of one month does not introduce any considerable distortion of the spectral content. The database was checked for errors and, afterwards, the time series were sampled with a constant step of one month using linear interpolation. Figure 3 shows the time series at four piezometers, located in different sectors of the aquifer. These series can be considered representative of the water level variations (Luque-Espinar 2001). Piezometer A (Fig. 3) is situated at the western end, in a sector of the aquifer where fine-grained sediments predominate. The piezometric time series presents a cyclical aspect of long periods with minor piezometric variations; no monthly fluctuations are seen. Piezometer B (Fig. 3) is near the eastern border, in the main recharge area. In this area, gravel-size sediments are abundant, and permeability values are very high. Evolution over time shows long cycles with monthly fluctuations. Piezometer C (Fig. 3) is located in the central part of the aquifer, near the main river, which contains water all year round. The high permeability values are due to the abundance of gravel and sand. The series is characterized by distinctive annual cycles within the longrange variations. Finally, piezometer D (Fig. 3) is located between A and C, in the aquifer's discharge area. The sand-sized detritic fraction predominates, with intercalating gravel and lime parcels. Monthly oscillations are very pronounced, while long-term ones are scarcely observed.

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