Hydrogeochemical Characterization and Speleogenesis of Sistema Huautla in Oaxaca, Mexico

Sierra Mazateca, Mexico is home to Sistema Huautla, the deepest cave in the Western hemisphere with 1,560 meters of depth and 90 kilometers of passage, including 26 entrances distributed in a high-relief, karstified terrain, within the Sistema Huautla Karst Groundwater Basin. Exploration of the cave has generated research questions about its evolution and geomorphology given the different vadose and phreatic zones impacted by tectonic and incision processes. Dye traces during this study of Cueva de La Peña Colorada confirmed it is a fossil resurgence of the cave system. An additional cave, Cueva Elysium, was connected hydrologically in 2019, expanding the basin and recharge area for the cave system. Four springs were monitored at high-resolution along the Rio Santo Doming for water level, temperature, and specific conductivity in 2019. The dye trace results indicate connection between the springs and that primary dissolution likely occurs at the water table and phreatic zone, due to the extreme verticality of the cave system, while flood responses are rapid and short-lived, despite seasonal storms. Results from this study also help aid in understanding and managing water resources in the region, further exploration of the cave system and potential connections, and the future evolution of Sistema Huautla under a changing climate as exploration continues

Dye Tracing and the Effects of Infrastructure in Hidden River Cave, Horse Cave, KY

Hidden River Cave is a stream cave system found in Horse Cave, KY with continuous water flow of its two branches, Wheet River and East River. The infrastructure of the city of Hose Cave, KY was originally designed to utilize natural sinkholes for drainage of all wastewaters. The city uses many of these, now modified, sinkholes for wastewater disposal and storm water drainage. Historically, Hidden River Cave has been severely impacted by unmonitored dumping of contamination. To better understand and identify specific flow paths from sinkholes and infrastructure into Hidden River Cave, this study documented various sinkholes and other infrastructure, such as storm drains, sewer systems, and other undocumented pipes, that could send water from the surface to Hidden River Cave. The study focused on using fluorescent dyes injected into four sites in order to document how the water carrying these dyes moved through the cave system. These dyes were identified using charcoal dye receptors placed at six locations within Hidden River Cave. Additionally, passage cross-sections of two major branches of the cave were measured, while depth and velocity measurements were taken to calculate the discharge of the river in these branches of the cave. Dye trace results identified two flow paths and hypothesized a small groundwater basin based on the detection of various dyes within the cave from multiple injection sites. Discharge results appear to agree with the flow path interpretation derived from the dye traces. The most significant findings of this research include: 1) identifying multiple flow paths from various injection points, 2) determining the relationship between discharge of the Wheet River and East River in Hidden River Cave, and 3) hypothesizing a flow route based on a lack of detection from a previously unidentified injection point. These findings improve the understanding of the relationship between surface water catchment in the city of Horse Cave and the flow into Hidden River Cave

Land-use changes and precipitation cycles to understand hydrodynamic responses in semiarid Mediterranean karstic watersheds

This research was funded partially by the Central University of Ecuador and by the projects RESERVOIR (PRIMA programme supported by the European Union under grant agreement no. 1924) and BBVA2021-Leonardo2 along with local companies (projects Comunidad Regantes 220-I and Comunidad Regantes 1-20T). Antonio Jodar-Abellan acknowledges financial support received from the project BBVA2021-Leonardo2. In the same way, this work has been conducted within the Catedra del Agua of the University of Alicante (catedradelaguaua.org). Moreover, authors acknowledge the reviewers of the manuscript whose comments contributed greatly to improve this paper.Non-planned agricultural land abandonment is affecting natural hydrological processes. This is especially relevant in vulnerable arid karstic watersheds, where water resources are scarce but vital for sustaining natural ecosystems and human settlements.However, studies assessing the spatiotemporal evolution of the hydrological responses considering land-use changes and precipitation cycles for long periods are rare in karstic environments. In this research, we selected a representative karstic watershed in a Mediterranean semiarid domain, since in this belt, karst environments are prone to land degradation processes due to human impacts. Geographic Information Systems-based tools and hydrological modeling considering daily time steps were combined with temporal analysis of climate variables (wavelet analysis) to demonstrate possible interactions and vulnerable responses. Observed daily flow data were used to calibrate/ validate these hydrological models by applying statistic indicators such as the NSE efficiency and a selfdeveloped index (the ANSE index). This new index could enhance goodness-of-fit measurements obtained with traditional statistics during the model optimization. We hypothesize that this is key to adding new inputs to this research line. Our results revealed that: i) changes in the type of sclerophyllous vegetation (Quercus calliprinos, ilex, rotundifolia, suber, etc.) from 81.5% during the initial stage (1990) to natural grasslands by 81.6% (2018); and, ii) decreases in agricultural areas (crops) by approximately 60% and their transformation into coniferous forests, rock outcrops, sparsely natural grasslands, etc. in the same period. Consequently, increases in the curve number (CN) rateswere identified as a result of land abandonment. As a result, an increase in peak flow events jointlywith a relevant decrease of the average flow rates (water scarcity) in the watershed was predicted by the HEC-HMS model and verified through the observed data. This research provides useful information about the effects of anthropogenic changes in the hydrodynamic behaviour of karstic watersheds andwater resource impacts, especially key in water-scarce areas that depict important hazards for the water supply of related populations and natural ecosystems.Central University of EcuadorEuropean Commission 1924Comunidad de Madrid 220-ICatedra del Agua of the University of Alicant

Potential of natural groundwater recharge in the Chennai Basin with a special emphasis on the urban area

Groundwater is the primary source of drinking water in India, and the Chennai River Basin (CRB) is no exception. However, available resources of both groundwater and surface water, are constantly decreasing because of overexploitation and contamination. Well fields in the northern part of the CRB control the water supply for the region, including the Chennai Metropolitan Area (CMA), the capital of the state of Tamil Nadu. Thus, any changes in groundwater storage and availability in the basin directly affect the 11-million people who live in the CMA. So, even though the focus of this study is on the CMA, the entire basin must be considered in order to understand the hydrogeological condition and groundwater situation. This research aims to provide a holistic study of the topographic condition of the basin, the amount of water stress, the identification and mapping of the groundwater potential zones, a review of the groundwater recharge estimation techniques on national scale, and most importantly, the creation of an estimate of the natural groundwater recharge in the CRB and how climate and landuse patterns affect the recharge process. A critical review has been made of popular groundwater recharge estimation practices. The suitability of each method is found to be dependent on time-space, hydrogeological condition, and data availability. Considering the hydrogeological and climatic conditions, the Water Table Fluctuation (WTF) method is the most appropriate method of recharge estimation. Groundwater recharge is largely controlled by topographical factors such as morphometric and hypsometric analysis and understanding these factors is necessary in water resource development planning. Shuttle Radar Topographic Mission (SRTM) and Digital Elevation Model (DEM) data were used in the Geographical Information System (GIS) platform to derive the morphometry and hypsometry. The CRB is an elongated basin of the 7th order and has been classified into 11 sub-basins. Major linear, areal and relief aspects were calculated and discussed based on their hydrologic significance. Steep slopes in the basin may affect the infiltration rate and, subsequently, recharge. Hypsometric curves show the concave type for most of the sub-basins, indicating an old stage. These results provide vital information about the hydrological conditions of the basin. Protecting the resource from depletion and identifying potential zones is essential for sustainable development. Remote Sensing (RS) and GIS technologies with field data were used to map groundwater potential zones in the CRB. For the most accurate results, a total of 11 controlling factors were brought into the GIS platform and a multi-criteria decision making (MCDM) tool, Analytical Hierarchal Process (AHP), was also used. Based on this analysis, groundwater potential zones were classified into five categories- very poor, poor, moderate, good, and very good. The final groundwater potential map showed that 35% of the total area has good to very good groundwater potential, 27% has moderate potential, and 38% has poor to very poor potential. Comparison of the specific capacity obtained from borehole data with these results showed that the predicted groundwater potential identified in this study matches 80% of the area. Groundwater potential depends on climatic conditions such as droughts, atmospheric temperatures, and monsoonal patterns. Using long-term temperature and rainfall data, meteorological drought has been calculated and agricultural drought has been determined using NDVI, NDWI and VCI indices. Agricultural drought indices showed that the vegetation is healthy in the northern and southern regions. However, more than 40% of the area was found to be water stressed. The calculation was made on a decadal scale and the highest water stress was observed in the year 2010. Agricultural drought is more prominent than meteorological drought in the CRB. Chennai faces a severe water shortage in the summer season and flooding in the rainy seasons. The groundwater recharge rate for the Chennai River Basin has been estimated using the empirical method, the rainfall infiltration (RIF) technique, a GIS based distributed model, and the Water Table Fluctuation (WTF) method. The average groundwater recharge rates for different methods vary, with results of 196mm/ year (Empirical formula), 127mm/year (WTF method) and 122mm/year (RIF method). The ratio of effective recharge to rainfall is found as 10% for RIF and WTF methods and 16% using the empirical formula. Considering the conditions in India, as recommended by the Groundwater Estimation Committee (GEC), the WTF method was found to be the most reliable. Still, using multiple methods is suggested for a more fully accurate estimate. This is one of the first extensive studies that covers aspects such as terrain characteristics, proposing the most suitable groundwater recharge estimating methods, groundwater potential zone identification, water stress analysis and natural groundwater recharge estimations in the Chennai River Basin. During this study, large amount of field data on water level, atmospheric temperature, rainfall, and aquifer parameters was collected from different institutions and brought into a single scale. All this data has been brought into the GIS platform and created maps. Thus, a baseline has been created for future groundwater studies. After considering variable recharge estimates and the effective recharge ratio (approx. 10%), it is suggested that groundwater recharge be improved either by repairing existing structures or implementing artificial recharge structures based on the groundwater potential identified. This thesis contains both basic and advanced levels of scientific information, all that is necessary for policymakers to begin improvements, and even provides a number of recommendations for the most effective approach to groundwater management.Das Grundwasser stellt in Indien die wichtigste Quelle zur Gewinnung des Trinkwassers dar. Das Flusseinzugsgebiet Chennai (CRB) bildet dabei keine Ausnahme. Durch Übernutzung und Verunreinigung schwinden jedoch verfügbare Wasserressourcen, sowohl Grundwasser als auch Oberflächenwasser, stetig. Die sich im nördlichen Teil des Flussbeckens befindenden Brunnenfelder kontrollieren die Wasserversorgung der Region, einschließlich der Metropolregion Chennai (CMA) und somit der Hauptstadt des Bundesstaats Tamil Nadu. Aus diesem Grund haben jegliche Änderungen des Grundwasserspeichers und -verfügbarkeit im Flussbecken direkte Auswirkungen auf die 11 Millionen Einwohner der Metropolregion. Obwohl der Fokus dieser Arbeit auf der Metropolregion Chennai liegt, muss zum Verständnis der hydrogeologischen Verhältnisse und der Grundwassersituation das ganze Flussbeckens berücksichtigt werden. In dieser Arbeit wird eine ganzheitliche Betrachtung der topografischen Verhältnisse des Flussbeckens, der Stärke des Wasserstresses, der Bestimmung und Abbildung der möglichen Grundwasserzone, einer Überprüfung der Ermittlungsverfahren zur Grundwasserneubildung auf nationaler Ebene und, am wichtigsten, der Ermittlung der natürlichen Grundwassererneuerung im Flussbecken Chennai sowie der Weise, wie Klima- und Bodennutzungsmuster diesen Erneuerungsprozess beeinflussen, durchgeführt. Die gängigsten Praktiken zur Ermittlung der Grundwassererneuerung wurden kritisch untersucht. Es wurde festgestellt, dass die Eignung der einzelnen Methoden von den Raum- Zeit-Bedingungen, hydrogeologischen Umständen und der Datenverfügbarkeit abhängt. Bei Berücksichtigung der hydrogeologischen und klimatischen Bedingungen stellt die WTF-Methode (Water Table Fluctuation) die passendste Methode zur Ermittlung der Grundwassererneuerung dar. Die Grundwassererneuerung wird größtenteils von den topografischen Faktoren, wie der morphometrischen und hypsometrischen Analyse, bestimmt. Das Verstehen dieser Faktoren ist für die Planung der Wasserressourcenentwicklung unerlässlich. Für die Durchführung der Merphometrie und der Hypsometrie wurden SRTM- und DHM-Daten in geografische Informationssysteme (GIS) eingesetzt. Das Flusseinzugsgebiet Chennai ist ein längliches Becken der 7. Ordnung und wird in 11 Unterbecken unterteilt. Die wichtigsten Linear-, Areal- und Reliefaspekte wurden anhand ihrer hydrologischen Bedeutung berechnet und überprüft. Steilhänge in Becken können die Infiltrationsrate und somit die Grundwassererneuerung beeinflussen. Die hypsografischen Kurven der meisten Unterbecken weisen eine konkave Form vor und geben somit ihre Altersstufe an. Diese Ergebnisse bieten entscheidende Informationen über die hydrologischen Verhältnisse des Beckens. Der Schutz vor der Erschöpfung der Ressource und die Bestimmung der möglichen Zonen ist für eine nachhaltige Entwicklung unumgänglich. Die Felddaten der Fernerkundung und GIS-Technologien wurden zur Abbildung der möglichen Grundwasserzonen im FlusseinzugsgebietChennai eingesetzt. Um ein genaues Ergebnis erzielen zu können, wurden in die GIS-Plattform insgesamt 11 Kontrollfaktoren eingebracht und ein Hilfsmittel für mehrkriterielle Entscheidungen, ein analytischer Hierarchieprozess (AHP), genutzt. Aufgrund dieser Analyse wurden die möglichen Grundwasserzonen in fünf Kategorien eingeteilt: sehr schwach, schwach, mittel, gut und sehr gut. Die endgültige Karte der möglichen Grundwasserzonen zeigt, dass 35 % des Gesamtbereichs über ein gutes bis sehr gutes Grundwasserpotential, 27 % über ein mittleres Potential und 38 % über ein schwaches bis sehr schwaches Grundwasserpotential verfügen. Vergleiche der spezifischen Kapazität, die aus dem Bohrlochdaten gewonnen wurden, mit diesen Ergebnissen zeigen, dass das in dieser Arbeit vorhergesagte Grundwasserpotential zu 80% des Gebiets passt. Das Grundwasserpotential hängt von den Klimabedingungen wie Dürren, Atmosphärentemperaturen und Monsunmustern ab. Durch den Einsatz der Langzeitdaten über Temperatur und Regenfällen wurde die meteorologische Dürre berechnet, die landwirtschaftliche Dürre wurde mittels der Indexe NDVI, NDWI und VCI bestimmt. Die Indexe für die landwirtschaftliche Dürre zeigen, dass sich die Vegetation in den nördlichen und südlichen Gebieten im guten Zustand befindet. Eine Fläche von 40% des Gebiets erlebt jedoch Wasserstress. Die Berechnung erfolgte auf der dekadischen Skala, wobei der höchste Wasserstress im Jahr 2010 zu beobachten war. Im Flusseinzugsgebiet Chennai ist die landwirtschaftliche Dürre starker als die meteorologische Dürre zu spüren. In Chennai herrscht im Sommer gravierender Wassermangel, während der Regenzeit sind jedoch starke Überflutungen vorhanden. Die Grundwasserneubildungsrate für das Flussbecken Chennai wurde anhand der empirischen Methode, des Modells der Regeninfiltration (RIF), eines auf dem GIS-basierten verteilten Modells und der WTF-Methode ermittelt. Die durchschnittliche Grundwasserneubildungsrate variiert je nach Methode/Modell und zeigt die Ergebnisse von 196mm/Jahr (empirische Formel), 127mm/Jahr (WTF-Methode)und122mm/Jahr(RIF-Methode) vor. Der auf den Regen zurückgehender Anteil der effektiven Erneuerung liegt bei den Methoden RIF und WTF bei 10%, bei dem Einsatz der empirischen Formel erreicht dieser Anteil 16%. In Anbetracht der in Indien herrschenden Verhältnisse wurde die WTF-Methode, wie vom indischen Komitee für Grundwasserermittlung (GEC) empfohlen, als die zuverlässigste Methode bestimmt. Für eine möglichst genaue Ermittlung wird jedoch empfohlen, mehrere Methoden zu nutzen. Diese Arbeit gehört zu den ersten ausführlichen Studien, die sich mit Aspekten wie den Geländeeigenschaften, einer Empfehlung der geeignetsten Methoden zur Ermittlung der Grundwasserneubildung, der Bestimmung der möglichen Grundwasserzonen, der Wasserstressanalyse und der Ermittlung der natürlichen Grundwasserneubildung im Flussbecken Chennai beschäftigen. In dieser Arbeit wurde von diversen Einrichtungen eine hohe Zahl an Felddaten über den Wasserstand, Atmosphärentemperatur, Regenfälle und aquiferspezifische Parameter erworben und in einer Skala zusammengeführt. Alle diese gesammelten Daten wurden in die GIS-Plattform eingetragen und es wurden Karten erstellt. Somit wurde eine Ausgangsbasis für zukünftige Grundwasserstudien geschaffen. In Anbetracht der variablen Ermittlungswerte und des effektiven Erneuerungsanteils (etwa 10%) wird empfohlen, die Grundwasserneubildung entweder durch die Sanierung vorhandener Strukturen oder durch den Einsatz künstlicher Anreicherungsstrukturen auf der Grundlage des bestimmten Grundwasserpotentials zu verstärken. Es werden wissenschaftliche Basisinformationen vorgelegt, welche den Entscheidungsträgern zur Optimierung einer angepassten und nachhaltigen Wasserbewirtschaftung dienen können

Assessment of Climate Change Impacts on Water Quantity and Quality at Small Scale Watersheds

This book was inspired by the Hydrology–H030 Session of the 2019 AGU (America Geophysical Union) Fall Meeting. In recent years, simulating potential future vulnerability and sustainability of water resources due to climate change are mainly focused on global and regional scale watersheds by using climate change scenarios. These scenarios may have low resolution and may not be accurate for local watersheds. This book addresses the impacts of climate change upon water quantity and quality at small scale watersheds. Emphases are on climate-induced water resource vulnerabilities (e.g., flood, drought, groundwater depletion, evapotranspiration, and water pollution) and methodologies (e.g., computer modeling, field measurement, and management practice) employed to mitigation and adapt climate change impacts on water resources. Application implications to local water resource management are also discussed in this book

Runoff characteristics and the influence of land cover in drylands of western Texas

In dryland regions, where water is a limited resource, land use/land cover has undergone and continues to undergo significant change mainly due to human activities. The nature of runoff from dryland regions and the influence of land use/land cover change are largely not quantified. The objective of this study is to examine runoff dynamics and the influence of land cover in drylands of western Texas across multiple spatial and temporal scales. The study consists of four major components: (1) an experimental study at Honey Creek upland catchment (19 ha) to assess vegetation treatment effects on runoff by hydrometric and isotopic methods; (2) a hydrochemical evaluation of hydrologic linkage between the upland and bottomland at the second-order Honey Creek watershed; (3) a detailed precipitation-streamflow analysis at North Concho River basin to assess long-term and large-scale precipitation-streamflowvegetation dynamics; and (4) a comparison of streamflow in North, Middle, and South Concho River basins and a regional streamflow trend analysis for the entire western Texas. The study indicates runoff production in the drylands of western Texas is dominated by a few large runoff-producing events. The small catchment experiment indicated that runoff increased about 40 mm per year when 60% of woody plants were removed. This effect may relate to the presence of a baseflow component, but was not verified in regional trend analysis for the Edwards Plateau region where most rivers are spring-fed. The decrease in streamflow in North Concho River basin after the 1950's is in large part related to the enhanced infiltration capacity from reduced grazing pressure and improved vegetation cover. Regional streamflow trend analysis suggests some headwater areas outside the Edwards Plateau region experienced patterns of streamflow change similar to those in North Concho River basin, although artificial impoundments complicated the analysis. The study has broader application in ecohydrological research beyond specific geographic areas and specific vegetation types when evaluating the impact of ecosystem structure change on hydrology and water resources