Antonio Hernández-Espriú

The DRASTIC-Sg model: an extension to the DRASTIC approach for mapping groundwater vulnerability in aquifers subject to differential land subsidence, with application to Mexico City

Mexico City relies on groundwater for most of its domestic supply. Over the years, intensive pumping has led to significant drawdowns and, subsequently, to severe land subsidence. Tensile cracks have also developed or reactivated as a result. All such processes cause damage to urban infrastructure, increasing the risk of spills and favoring contaminant propagation into the aquifer. The effects of ground deformation are frequently ignored in groundwater vulnerability studies, but can be relevant in subsiding cities. This report presents an extension to the DRASTIC methodology, named DRASTIC-Sg, which focuses on evaluating groundwater vulnerability in urban aquifers affected by differential subsidence. A subsidence parameter is developed to represent the ground deformation gradient (Sg), and then used to depict areas where damage risk to urban infrastructure is higher due to fracture propagation. Space-geodetic SqueeSAR data and global positioning system (GPS) validation were used to evaluate subsidence rates and gradients, integrating hydrogeological and geomechanical variables into a GIS environment. Results show that classic DRASTIC approaches may underestimate groundwater vulnerability in settings such as the one at hand. Hence, it is concluded that the Sg parameter is a welcome contribution to develop reliable vulnerability assessments in subsiding basins.RésuméLa ville de Mexico est dépendante de l’eau souterraine pour l’essentiel de son usage domestique. Au fil des années, les pompages intensifs ont conduit à des abaissements importants du niveau piézométrique et par conséquence à d’important affaissement de terrain. Des fissures de tension se sont développées ou ont été réactivées. Tous ces processus causent des dommages sur les infrastructures urbaines augmentant le risque de fuites favorisant la propagation de contaminants dans l’aquifère. Les effets des déformations du sol sont souvent ignorés dans les études de vulnérabilité des eaux souterraines, mais peuvent être pertinents pour les villes soumises à des affaissements de terrain. Cet article présente un développement de la méthodologie DRASTIC, nommée DRASTIC-Sg, ciblant l’évaluation de la vulnérabilité des eaux souterraines pour des aquifères en milieu urbain impactés par un affaissement différentiel des terrains. Un paramètre affaissement est développé pour représenter le gradient de déformation du sol, et ensuite utilisé pour décrire les zones où les risques de dommage des infrastructures urbaines sont plus élevés dus à la propagation des fractures. Les données spatiales et de géodésie (SqueeSAR) et les données de validation du système global de positionnement (GPS) ont été utilisées pour évaluer les vitesses d’affaissement des terrains et les gradients, intégrant les variables hydrogéologiques et géomécaniques dans un système d’information géographique. Les résultats montrent que les approches classiques DRASTIC sous-estiment la vulnérabilité des eaux souterraines dans des environnements tels que celui de la ville de Mexico. Par conséquence, on conclut que l’ajout du paramètre Sg contribue à élaborer des évaluations fiables de la vulnérabilité dans des bassins subsidents.ResumenLa ciudad de México depende del agua subterránea para la mayoría de sus abastecimientos domésticos. A través de los años, el bombeo intensivo ha llevado a depresiones significativas y, subsecuentemente, a una severa subsidencia del terreno. Como resultado también se han desarrollado o reactivado fracturas de tensión. Tales fenómenos han causado daños a la infraestructura urbana, incrementando el riesgo de vertidos y favoreciendo la propagación de contaminantes en el acuífero. Los efectos de la deformación del terreno son frecuentemente ignorados en los estudios de vulnerabilidad del agua subterránea, pero pueden ser relevantes en las ciudades subsidentes. Este trabajo presenta una extensión de la metodología DRASTIC, denominada DRASTIC-Sg, que se enfoca para evaluar la vulnerabilidad del agua subterránea en acuíferos afectados por subsidencia diferencial. Se desarrolla un parámetro de subsidencia para representar el gradiente de deformación del terreno (Sg), y luego se usa para delinear áreas donde el riesgo al daño para la infraestructura urbana es mayor debido a la propagación de las fracturas. Se usaron datos de espacio geodético SqueeSAR y la validación por el sistema de posicionamiento global (GPS) para evaluar las tasas y gradientes de subsidencia, integrando variables hidrogeológicas y geomecánicas en un ambiente GIS. Los resultados muestran que el enfoque DRASTIC clásico puede subestimar la vulnerabilidad del agua subterránea en configuraciones como la que nos ocupa. Por lo tanto, se concluye que el parámetro Sg es una contribución bienvenida para desarrollar evaluaciones confiables de vulnerabilidad en cuencas subsidentes.摘要墨西哥城大部分家庭用水依赖地下水。多年以来,强烈开采地下水 导致地下水水位大幅下降低,并由此造成严重的地面沉降。还使拉伸缝进 一步发育或使原来的拉伸缝再度激活。所有这些过程对城市基础设施造成 损坏,增加泄漏物和污染物进入含水层的风险。地面变形的影响在地下水 脆弱性研究中经常受到忽略,但在沉降的城市中有重要意义。本文介绍了 DRASTIC 方法的延伸,即DRASTIC-Sg。这个方法聚焦于评价受不同沉 降影响的城市含水层中地下水的脆弱性。找到了代表地面变形梯度(Sg)的 沉降参数,用来描述由于断裂蔓延造成对城市基础设施损害风险较高的地 区。太空大地测量SqueeSAR 资料和全球定验证用来评价沉降速度和梯 度,把水文地质变量和岩土力学变量整合在地理信息系统环境中。结果显 示,传统的DRASTIC 方法可能低估所研究的环境中地下水的脆弱性。因 此,结论就是,在进行沉降盆地可靠的脆弱性评价中,Sg 参数是一个积 极贡献。ResumoA Cidade do México depende de águas subterrâneas para a maior parte do seu abastecimento doméstico. Ao longo dos anos, bombeamentos intensivos levaram a significativos decréscimos do nível freático e, subsequentemente, a severa subsidência de terrenos. Como resultado, foram desenvolvidas ou reativadas fendas de tração. Todos estes processos causam danos nas infraestruturas urbanas, aumentando o risco de derramamentos e favorecendo a propagação da contaminação no aquífero. Os efeitos da deformação dos terrenos são frequentemente ignorados nos estudos de vulnerabilidade das águas subterrâneas, mas podem ser significativos em cidades sob subsidência. Este artigo apresenta uma extensão à metodologia DRASTIC, denominada DRASTIC-Sg, que se foca na avaliação da vulnerabilidade da água subterrânea em aquíferos urbanos afetados por subsidência diferencial. É desenvolvido um parâmetro de subsidência para representar o gradiente de deformação do solo (Sg), sendo depois usado para descrever áreas onde o risco de danos às infraestruturas urbanas é maior devido à propagação de fraturas. Foi usada validação com dados espaço-geodésicos SqueeSAR e sistemas de posicionamento global (GPS) para avaliar as taxas de subsidência e os gradientes, integrando variáveis hidrogeológicas e geomecânicas num ambiente SIG. Os resultados mostram que a abordagem DRASTIC clássica pode subestimar a vulnerabilidade da água subterrânea em ambientes como este. Conclui-se portanto que o parâmetro Sg é uma contribuição bem-vinda para o desenvolvimento de avaliações de vulnerabilidade em bacias em subsidência.

A B-Spline Framework for Smooth Derivative Computation in Well Test Analysis Using Diagnostic Plots

In the oil and gas industry, well test analysis using derivative plots, has been the core technique in examining reservoir and well behavior over the last three decades. Recently, diagnostics plots have gained recognition in the field of hydrogeology; however, this tool is still underused by groundwater professionals. The foremost drawback is that the derivative function must be computed from noisy field measurements, usually based on finite-difference schemes, which complicates the analysis. We propose a B-spline framework for smooth derivative computation, referred to as Constrained Quartic B-Splines with Free Knots. The approach presents the following novelties in relation to methodological precedents: (1) the use of automatic equality derivative constraints, (2) a knot removal strategy and (3) the introduction of a Boolean shape parameter that defines the number of initial knots to choose. These can lead to evaluate both simple (manually recorded drawdown measurements) and complex (transducer measured records) datasets. Furthermore, we propose an additional shape preserving smoothing preprocess procedure, as a simple, fast and robust method to deal with extremely noisy signals. Our framework was tested in four pumping tests by comparing the spline derivative with regards to the Bourdet algorithm, and we found that the latter is rather noisy (even for large differentiation intervals) and the second derivative response is basically unreadable. In contrast, the spline first and second derivative led to smoother responses, which are more suitable for interpretation. We concluded that the proposed framework is a welcome contribution to evaluate reliable aquifer tests using derivative-diagnostic plots.

Conservation status assessment of the endangered Mexican Blindcat, Prietella phreatophila

content from an oral presentation July 15, 2017 at the annual Joint Meeting of Ichthyologists and Herpetologists in Austin, Texas, USA (http://conferences.k-state.edu/JMIH-Austin-2017/)

Discovery of Endangered Mexican Blindcat, Prietella phreatophila, in Texas: Implications for International Groundwater Management and Evolution of the Regional Karst Aquifer Biota

Paper presented July 15, 2017 at the annual Joint Meeting of Ichthyologists and Herpetologists in Austin, Texas, USA (http://conferences.k-state.edu/JMIH-Austin-2017/). The oral presentation of this content mentioned questions about the taxonomy and phylogenetic position of Prietella lundbergi and the only specimens attributed to P. lundbergi apart from the holotype. Since the presentation, we obtained high resolution CT scans of both the holotype and a specimen (TNHC 25767) from Cueva del Nacimiento del Rio Frio, not far north of the type locality. The anatomy revealed in those CT scans suggests that these specimens represent a single species, and that P. lundbergi is only remotely related to Prietella phreatophila, which would be consistent with results of Wilcox, T.P., F.J. Garcia de Leon, Dean A. Hendrickson, and D.M. Hillis. 2004. “Convergence among Cave Catfishes: Long-Branch Attraction and a Bayesian Relative Rates Test.” Molecular Phylogenetics and Evolution 31 (3): 1101–13. doi:10.1016/j.ympev.2003.11.006). Thus, further research is in progress by Hendrickson, Lundberg, Luckenbill and Arce that may result in taxonomic revision removing P. lundbergi from Prietella.