No abstract

Groundwater recharge (GWR) is analyzed and evaluated within the Aguascalientes Valley by means of a modified linearized Boussinesq equation and the Water Table Fluctuations (WTF) technique. These techniques use the specific yield, water table variations and the subsurface drainage of groundwater. The methodology is applied to the semiarid Aguascalientes valley, which contains a thick vadose zone. The combination of the analytical solution based on the Boussinesq equation and the WTF technique, allows the method to be applied in areas with deep groundwater levels, such as the Aguascalientes valley, without the need for high temporal resolution data. The data for the application of the method were provided by various government agencies and includes information on 145 wells positioned within the valley during the period 1985-2015. The specific yield and the transmissivity were integrated from the results of two previous investigations. Results indicate that the variation of recharge ranges from 0.86 to 525.69 mm/year in the analyzed period, with the highest recharge rates occurring in the north and center parts of the valley and is likely attributed to high specific yield and vertical hydraulic conductivity due to the presence of coarse permeable soils present in the area. Conversely, the lowest recharge rates were found to occur near the north and south borders of the valley. RESUMENEn la presente investigación, la recarga de agua subterránea (GWR) se analiza y evalúa dentro del Valle de Aguascalientes mediante el ajuste a la ecuación linealizada de Boussinesq y la técnica Water Table Fluctuation (WTF), que involucra el rendimiento específico, la variación del nivel freático y el drenaje subsuperficial de aguas subterráneas. La metodología se aplica al semiárido valle de Aguascalientes que contiene una zona vadosa espesa. La combinación de la solución analítica basada en la ecuación de Boussinesq y la técnica WTF permite que el método se aplique en áreas con niveles profundos de aguas subterráneas, como el valle de Aguascalientes, sin la necesidad de datos de alta resolución temporal. Los datos para la aplicación del método fueron provistos por varias agencias gubernamentales a través de la información de 145 pozos ubicados a lo largo del valle durante el período 1985-2015. El rendimiento específico se integró a partir de los resultados de dos trabajos anteriores, así como la transmisividad. Como resultado, la variación de la altura de recarga se obtuvo de 0.86 a 525.69 mm/año en el período analizado, las tasas de recarga más altas se presentan al norte y al centro del valle, probablemente atribuidas a un alto rendimiento específico y conductividad hidráulica debido a la presencia de suelos permeables gruesos presentes en el área, por otro lado, las fronteras norte y sur del valle tienen las tasas de recarga más bajas.Palabras clave: recarga de agua subterránea; valle de Aguascalientes;

Abstract. In the Aguascalientes valley, middle Mexico, the demand of groundwater from the local aquifer system was suddenly increased after the late 1970s. Since then, several related problems have been occurring or become critical such as land subsidence, ground fissuring, and low-magnitude earthquakes. The most recent data of vertical deformation from PSInSAR, groundwater levels, and earthquakes, has provided critical information regarding the relationship amongst all these processes. In particular, that related to land subsidence, earth fissuring and seismicity. Regarding this, more satellite imagery and data from GPS stations are being revised as a possibility of a more generalized vertical deformation derived with low-magnitude seismicity. A particular seismic event recorded on 6 April 2019 has revealed critical information on the close association between vertical displacements occurred in active faults and low-magnitude seismic events.

The impact of faults and fissures (discontinuities) on the groundwater flow has become important in several parts of the world because the heterogeneous and anisotropic distribution of permeability in fault zones is difficult to characterize. Based on this, we propose an analysis of patterns of parameters measured in groundwater, under the premise that the observed anomalies can be indicators of the hydraulic behavior of the flow in the direction perpendicular to the fault plane. In this context, if the discontinuities are sealed, they behave as hydraulic barriers, causing variation in the continuity of the parameters across the fault plane. Conversely, when faults are a conduit, they appear to have a small or null variation in the distribution of the parameter measurements. The impact of discontinuities in groundwater flow in a zone with a large number of faults and fissures such as that of the Aguascalientes valley is being studied using a graphical-correlation analysis with the revision of 230 wells, through the measurement of parameters such as temperature and static levels across discontinuities, in order to determine the hydraulic behavior of the faults. This investigation considered values over 4 • C for geothermal variations and 10 m for hydraulic-head changes to define fault behavior. Results show three zones through mapping analysis, where the fault presents barrier behavior and where the hanging block represents high values; these anomalies are much higher than the average across the valley and indicate the propensity for the fault to restrict horizontal flow. In conclusion, the Oriente fault presents complex behavior of a barrier-conduct system along the fault. This analysis gives a robust way to describe fault behavior without referring to elaborate and invasive hydrological investigations.