ABSTRACT:Hydrogeochemistry is an essential tool for the verification of conceptual models, especially of groundwater flow models. This is even more relevant when dealing with complex hydrogeological models that have intercalating layers with different degrees of permeability, and regional flows contributing to the system. The hydrogeochemical characteristics of the Urabá-Colombia Aquifer and geological cross-sections were studied to establish possible processes that explain the groundwater flow evolution and the recharge zones. 4 flow lines were considered to show the groundwater evolution from Ca 2+ -HCO 3 -facies and a TDS concentration of approximately 400 mg/L, trough Ca 2+ -Mg 2+ -HCO 3 -and Na + -Mg 2+ -HCO 3 -facies, ending with Na + -HCO 3 -facies close to discharge area, with TDS=1,550 mg/L. Data on stable isotopes confirmed the groundwater flow directions. It is also clear that evolution orders correspond to the possible flow rates in areas with a homogeneous gradient, but with higher hydraulic conductivity conditions to the south and center, compared to the north. RESUMEN:La hidrogeoquímica constituye una herramienta fundamental para la verificación de los modelos conceptuales, en particular los modelos de flujo de aguas subterráneas, esto se hace aún más relevante cuando se tienen modelos hidrogeológicos complejos en los que se intercalan capas de distinta permeabilidad e intervienen flujos regionales. Analizando las características del Acuífero del Golfo de Urabá y secciones geológicas, fue posible establecer procesos que explican la evolución del flujo del agua subterránea y las zonas de recarga del acuífero. Se utilizaron 4 líneas de flujo para mostrar la evolución del agua subterránea de facies Ca 2+ -HCO 3 -y una concentración de STD de 400 mg/L aproximadamente, pasando por facies Ca 2+ -Mg 2+ -HCO 3 -y Na + -Mg 2+ -HCO 3 -, y finalizando con una facies Na + -HCO 3 -, cerca de la zona de descarga, con STD=1,550 mg/L aproximadamente. Algunos datos de isotopos estables sustentan la verificación de los sentidos de flujo hidrogeológico. También es claro que los ordines de evolución se corresponden con las posibles velocidades de flujo en zona con gradiente homogéneo pero condiciones de conductividad hidráulica más altas en el sur y centro que en el norte.

Understanding the physical, chemical and biological system is an indispensable precondition to addressing groundwater management. This understanding is based on Conceptual Hydrogeological Models, which contain different interpretations and their validity is checked through the application of specific research techniques (numerical modelling, hydrochemistry, isotope hydrology,process evaluation and biological functions). This paper describes the experience carried out by an academic team that, together with entities responsible for the protection of waterresources, established strategic alliances to improve the knowledge of the hydrogeological system,providing new elements for governance. This study was carried out in the Urabá antioqueño zone, located north-west of Colombia. A complex aquifer system is located in the region,characterized by a series of permeable, semi-permeable and impermeable layers. In such alayered aquifer the determination of the physical, chemical and biological characteristics of the layers and their management are a challenge for researchers because groundwater represents a strategic resource for supplying the population and developing economic activities. Starting from the conceptual hydrogeological model, multiscale numerical modelling exercises have been carried out, enabling the characterization of local, intermediate and regional flow systems. In addition,by determining the natural background level, the concentration ranges of chemical compounds from natural sources were obtained, in order to detect future changes in water quality. It was also possible to examine the stygofauna, which allowed the recognition of different types of organisms (stygobits, stygophiles and stygoxens) associated with underground ecosystems.These scientific elements serve as a support for the management instruments such as the groundwater management plan that is important for water governance, ensuring its future sustainability.

From the end of 2020 until July 2021, the first phase of a study that evaluated the hydrogeological potential in tropical dry forest (TDF) areas took place in the bosque seco tropical (BS-T), which was associated with the Cauca River Canyon in the jurisdiction of Corantioquia. Based on the litho-structural evaluation of the area, hypotheses were established by which conditions of greater or lesser aquifer potential were assigned according to the different types of geological materials present. The first step to confirm these hypotheses was an inventory of groundwater points. The results indicated the existence of more than 1172 points, including springs, hand-dug wells, galleries and wells.Relating the occurrence of these water points with the lithological units, approximately 560 points in Quaternary deposits and rocks of the Amagá Formation and the Urrao Member of the Penderisco Formation were found; 146 were located in volcano-sedimentary deposits of the Combia Formation, and more than 466 were associated with hard rocks. It is thus concluded that in the study area, the igneous and metamorphic rocks, intensely affected by tectonic effects, have gained permeability conditions, which was evidenced by field observations, which confer aquifer conditions. This finding provides new research perspectives toward fractured environments and presents groundwater as a main and alternative source to meet the needs of the population, in addition to playing a fundamental role in terms of the ecosystem sustainability of the tropical dry forest.

La recarga potencial de aguas subterráneas se estima comúnmente mediante balances hídricos por unidad  hidrogeológica. La mayoría de los estudios en Antioquia  (Colombia) se refieren a la recarga en depósitos aluviales o  unidades de rocas sedimentarias. En 2020 se inició la  evaluación del potencial hidrogeológico en zona de  influencia del bosque seco tropical en el cañón del río  Cauca, en jurisdicción de Corantioquia, incluyendo estimaciones regionales de recarga potencial por  precipitación. La estimación de la recarga se realizó a través  de un modelo distribuido de balance de humedad en el  suelo a escala diaria, en el que se incorporó de manera  eficiente la variabilidad espaciotemporal de las condiciones  meteorológicas de la región, así como la variabilidad  espacial de las propiedades de superficie, como suelos,  coberturas terrestres y topografía. Entre 2013 y 2020 se estimaron tasas de recarga anual que  varían espacialmente entre 5 mm/año y 2000 mm/año, lo  que representa entre 0,4 % y 45 % de la precipitación, con promedio espacial y multianual de 342 mm/año (17 % de la  precipitación). Los acuíferos de la Formación Penderisco se  caracterizan por recarga potencial media anual entre 284  mm (al noroeste) y 756 mm (al suroeste); los acuíferos de la  Formación Combia presentan tasas de recarga media anual  de 456 mm; el Acuífero Libre del Occidente Antioqueño y otros asociados a depósitos cuaternarios registran tasas de  recarga media anual de 36 mm. El comportamiento evidenciado de recarga en la zona favorece la condición de  flujos regionales entre unidades hidrogeológicas y ratifica el potencial hidrogeológico significativo de diversas unidades de rocas duras fracturadas.