Morphometric and hypsometric analysis in the Tierra Nueva Basin, San Luis Potosí, México

"In areas with long periods of drought, it is essential to implement strategies to manage the available water resource. Tierra Nueva Basin is affected by this situation, consequently the farm production and livestock holdings are affected and the people don’t have access to enough water. In this paper, we propose an integrative methodology based on mathematical tools such as hypsometric and morphometric analysis applying geographic information systems. The proposal is strengthened with the aggregation of geological-structural, morphometrical, hypsometrical parameters and climatological information through a precipitation analysis provided by the National Water Commission from 1962 to 2010. According to the available data and the results obtained through the implemented proposal, an acceptable level of reliability is inferred allowing to determine areas structurally suitable for the use of surface water and its uptake. The methodology that we propose facilitates and simplifies the processes of searching and exploring locations suitable for surface water capture in arid and semi-arid zones, identifying in a qualitative and quantitative manner the optimal zone. For the case study, test-and-validation of the methodology the Tierra Nueva Basin in San Luis Potosí, México was selected. Tierra Nueva is a semi-arid site where “La Muñeca” dam is located. The results obtained in this work confirm the location of the “La Muñeca” dam as one of the most suitable areas for water collection. The methodology that we propose is a useful tool for the studies of water capturing purposes in arid and semi-arid zones.

Hydrogeological Investigations in Northwestern Yucatan, Mexico, Using Resistivity Surveys

Eight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground‐water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh‐water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben‐Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal‐to‐vertical permeability anisotropy

Determination of flow characteristics in the aquifer of the Northwestern Peninsula of Yucatan, Mexico

Flow characteristics were studied in the Northwestern Peninsula of Yucatan, Mexico. The Yucatan aquifer is a mature karst system, influenced by the Ring of Cenotes (sinkholes). This zone of aligned sinkholes is a high-permeability zone with respect to its surroundings. The aquifer is unconfined within the study area. Water-level measurements at 48 locations were made in June and October 1994; they were measured up to four times in October. Water levels in a limited group of wells showed variations up to 60% during October 1994 whereas others had variations of the order of 5% in the same period. By studying the resulting equipotential regimes, a highly variable zone (HVZ) was identified. Drain characteristics are significantly different from the rest of the study area, which leads to the hypothesis that the HVZ represents an independent subsystem of interconnected fractures. To determine directions of high permeability within the study area, azimuthal resistivity surveys were conducted at 22 locations. Resistivity curves particularly in the HVZ show two or more peaks, each indicating a direction of high permeability. Directions of high permeability are interpreted to be preferential directions of aligned fractures. Comparison with the two different equipotential regimes in October 1994 shows that in the majority of the cases the direction of the hydraulic gradient coincides with the direction of one fracture system. The hydraulic gradient can be considered to be the major control in the dissolution process at least in the HVZ, resulting in the selective opening of the fractures. Peaks in the resistivity curves are of the same order of magnitude. This shows that both regimes of equipotential lines and the corresponding changes of the hydraulic gradients are sufficiently frequent to be able to create different fracture systems with a comparable fracture density. The variations of the equipotential regime in time may have severe consequences in terms of the risk of aquifer contamination in the highly variable zone.

Basement topography and fresh-water resources of the coastal aquifer at Acapetahua, Chiapas, Mexico

El acuífero costero de Acapetahua, Chiapas, en el sureste de México, consiste en una unidad hidroestratigráfica compuesta de sedimentos continentales con un basamento cristalino. Se realizaron veinticuatro sondeos de resistividad y se tomaron cincuenta y una muestras de agua con el fin de determinar las características básicas del acuífero, como son la geometría del acuífero y sus reservas de agua dulce. La topografía del basamento se caracteriza por cumbres y valles profundos. La profundidad al basamento varía entre unos pocos metros y varios cientos de metros. Los altos del basamento se encuentran a lo largo de la línea costera, a distancias entre 4 y 15 km de la costa, reduciendo considerablemente el espesor del acuífero. La zona de transición entre agua salada y agua dulce coincide en el espacio con los altos del basamento, que representan actualmente el límite del acuífero de agua dulce hacia la costa. Con base en la geometría del acuífero de Acapetahua determinada con los modelos de resistividad, y considerando los valores de sólidos totales disueltos de las muestras de agua, el volumen máximo de poros saturados de agua dulce fue estimado en 75 km3. doi: https://doi.org/10.22201/igeof.00167169p.1999.38.2.38

Hydrogeology of a contaminated sole-source karst aquifer, Mérida, Yucatán, Mexico

La ciudad de Mérida, Yucatán obtiene su agua potable principalmente de tres campos de pozos localizados en los alrededores de la ciudad. Adicionalmente, existen pozos del sistema de agua potable dentro de la ciudad. Se ha reportado la presencia de plomo, cadmio y cromo excediendo el límite de la Norma de Agua Potable Mexicana en agua del sistema de agua potable. Los siguientes contaminantes orgánicos también han sido detectado en el agua subterránea de la porción sur de la ciudad: TCA, PCE, TCE y CTET. Mérida obtiene aproximadamente 65% de su agua potable del campo de pozos JAPAY-I, el cual extrae el agua de la sección sureste de la ciudad de Mérida. Es en esta zona donde se concentra la actividad industrial. No se cuenta con información de la calidad del agua de este campo de pozos, pero es probable que se encuentre bastante contaminada. Sugerimos que se implemente un sistema de monitoreo del agua subterránea. Una zona de reserva hidrogeológica también debería de ser establecida para permitirles a los habitantes de Mérida contar con una fuente sustentable de agua potable. doi: https://doi.org/10.22201/igeof.00167169p.2000.39.4.24

Geophysical investigations of the vadose zone in the Valley of Hermosillo aquifer, Sonora, Mexico

En el Valle de Hermosillo, Sonora, Mexico, siete sondeos tipo Schlumberger y tres sondeos azimutales fueron realizados con el fin de investigar la zona vadosa del acuífero del Valle de Hermosillo. Este acuífero costero consiste de material aluvial y es considerado como libre en su parte superior. El estudio de los sondeos muestra que los cambios laterales de las resistividades pueden ser interpretados relativos a un 'valor de fondo' de 100 Ωm. Los valores de la resistividad menores de 50 Ωm fueron encontrados cerca de la costa y de los centros urbanos e industriales de Hermosillo y Miguel Alemán. Estos valores relativamente bajos pueden estar reflejando la presencia de agua de mala calidad en los poros por la irrigación con aguas subterráneas afectadas por intrusión salina, con aguas negras no tratadas, y/o con aguas subterráneas contaminadas con aguas negras de procedencia industrial y doméstica. Basado en la Ley de Archie, la porosidad se estimó en un valor aproximado de 25%. Los sondeos azimutales muestran que existe anisotropía de la resistividad en la superficie; sin embargo, esta disminuye con la profundidad, por lo que se propone que se debe al arreglo de los granos del suelo relacionado con la infiltración del agua de irrigación