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Since the evolution of any cave system is largely deterministic, in theory the processes responsible for this development could be described mathematically. In a practical sense, we will never have such a model to realistically describe the evolution of the Mammoth Cave System in detail. However, the search itself can provide a framework within which to understand what processes are important. This can guide the design of rate process studies that would eventually be coupled to provide a comprehensive understanding of the cave's evolution. Data gaps, as well, are identified during this process.
The geometry of a cave system depends on the individual growth rates of sequential sets of passage cross-sections. The growth of each of these cross-sections is determined by a set of coupled processes, the rates of which are related to well-defined variables. Major processes include limestone dissolution and precipitation (dependent on water and rock chemistry, flow characteristics, wetted passage perimeter, and temperature), sediment entrainment, deposition, and abrasion (dependent on flow velocity distributions and properties of the sediment supply), and breakdown processes (dependent on fracture characteristics). Our ability to model the complete picture depends on our grasp of these individual behaviors, as well as their interactions.
A long-term study of the behaviors of two single active passage cross-sections is underway in the Right and Left forks of Hawkins River of Mammoth Cave, where continuous water quality data are being obtained through two 145 m deep wells. Experiments are currently underway to determine storm- and seasonal-scale changes in limestone dissolution rates. Planned studies will explore sediment dynamics and the impact of sediment masking on dissolution rates, as well as potential impacts of sediment abrasion on passage growth. Complete understanding of a single cave slice is an important step to understanding cave evolution in general.
The conservation and protection of caves requires suitable management tools that are based on a detailed knowledge of the environmental parameters of karst areas. The main tool for karst management is the definition and delimitation of protected areas and, in the case of tourist caves, an estimation of the visitor carrying capacity. This doctoral thesis deals with the most important methodologies related to the monitoring of cave microclimates, and focuses on show caves. The use of a great quantity of environmental data derived from different caves in southern Spain has required the use of several statistical techniques to meet the objective of simplifying and revaluating this environmental information. It is expected that the main focus of interest of this research thesis to managers of these geo-heritage sites lies in the possibility of incorporating the results of cave environmental monitoring into an integrated model of management, which also contemplates socio-economic aspects. The analysis of microclimates in each of the caves under study is dealt with in different ways depending on the type of data recorded within each one of them. Caves such as the 'Cueva del Agua' and 'Cueva de las Ventanas' are typified by the spatiotemporal behavior of the main microclimatic variables, such as the temperature and carbon dioxide content of the air. This information about the 'zero state' of the cave is complemented by an analysis of the infiltration processes and a study of the air-mass exchange phenomena. In the Sorbas karst, the design and installation of an intelligent environmental control system inside one of the potential tourist caves (System Covadura) allowed an extensive time series database to be assembled, which together with information about the spatial microclimate, comprises the base knowledge of the initial state of the cave before any tourist activities are authorized. The Giant Geode of Pulpí (Almería, Spain) represents an exceptional case with characteristics that are distinct from show caves as defined in the strictest sense of the term. The uniqueness of this site in terms of its fragility and dimension, together with the imminent need to adopt measures for its protection, resulted in the execution of an exhaustive microclimatic study in order to evaluate the possibility of opening the geode to tourists.
The conservation and protection of caves requires suitable management tools that are based on a detailed knowledge of the environmental parameters of karst areas. The main tool for karst management is the definition and delimitation of protected areas and, in the case of tourist caves, an estimation of the visitor carrying capacity. This doctoral thesis deals with the most important methodologies related to the monitoring of cave microclimates, and focuses on show caves. The use of a great quantity of environmental data derived from different caves in southern Spain has required the use of several statistical techniques to meet the objective of simplifying and revaluating this environmental information. It is expected that the main focus of interest of this research thesis to managers of these geo-heritage sites lies in the possibility of incorporating the results of cave environmental monitoring into an integrated model of management, which also contemplates socio-economic aspects. The analysis of microclimates in each of the caves under study is dealt with in different ways depending on the type of data recorded within each one of them. Caves such as the 'Cueva del Agua' and 'Cueva de las Ventanas' are typified by the spatiotemporal behavior of the main microclimatic variables, such as the temperature and carbon dioxide content of the air. This information about the 'zero state' of the cave is complemented by an analysis of the infiltration processes and a study of the air-mass exchange phenomena. In the Sorbas karst, the design and installation of an intelligent environmental control system inside one of the potential tourist caves (System Covadura) allowed an extensive time series database to be assembled, which together with information about the spatial microclimate, comprises the base knowledge of the initial state of the cave before any tourist activities are authorized. The Giant Geode of Pulpí (Almería, Spain) represents an exceptional case with characteristics that are distinct from show caves as defined in the strictest sense of the term. The uniqueness of this site in terms of its fragility and dimension, together with the imminent need to adopt measures for its protection, resulted in the execution of an exhaustive microclimatic study in order to evaluate the possibility of opening the geode to tourists.
Modelling seawater intrusion (SWI) has evolved from a tool for understanding to a water management need. Yet, it remains a challenge. Difficulties arise from the assessment of dispersion coefficients and the complexity of natural systems that results in complicated aquifer geometries and heterogeneity in the hydraulic parameters. Addressing such difficulties is the objective of this thesis. Specifically, factors that may affect the flow and transport in coastal aquifers and produce heterogeneous salinity distributions are studied.
First, a new paradigm for seawater intrusion is proposed since the current paradigm (the Henry problem) fails to properly reproduce observed SWI wedges. Mixing is represented by means of a velocity dependent dispersion tensor in the new proposed problem. Thereby, we denote it as "dispersive Henry problem". SWI is characterized in terms of the wedge penetration, width of the mixing zone and influx of seawater. We find that the width of the mixing zone depends basically on dispersion, with longitudinal and transverse dispersion controlling different parts of the mixing zone but displaying similar overall effects. The wedge penetration is mainly controlled by the horizontal permeability and by the geometric mean of the dispersivities. Transverse dispersivity and the geometric mean of the hydraulic conductivity are the leading parameters controlling the amount of salt that enters the aquifer.
Second, the effect of heterogeneity was studied by incorporating heterogeneity in the hydraulic permeability into the modified Henry problem. Results show that heterogeneity causes the toe to recede while increases both the width and slope of the mixing zone. The shape of the interface and the saltwater flux depends on the distribution of the permeability in each realization. However, the toe penetration and the width of the mixing zone do not show large fluctuations. Both variables are satisfactorily reproduced, in cases of moderate heterogeneity, by homogeneous media with equivalent permeability and either local or effective dispersivities.
Third, the effect of aquifer geometry in horizontally large confined aquifers was analyzed. Lateral slope turned out to be a critical factor. Lateral slopes in the seaside boundary of more than 3% cause the development of horizontal convection cells. The deepest zones act as preferential zones for seawater to enter the aquifer and preferential discharging zones are developed in the upwards lateral margins. A dimensionless number, Nby, has been defined to estimate the relative importance of this effect.
All these factors can be determinant to explain the evolution of salinity in aquifers such as the Main aquifer of the Llobregat delta. Finally, a management model of this aquifer is developed to optimally design corrective measures to restore the water quality of the aquifer. The application of two different optimization methodologies, a linear and a non-linear optimization method, allowed (1) to quantify the hydraulic efficiency of two potential corrective measures: two recharge ponds and a seawater intrusion barrier; (2) to determine the water necessary to be injected in each of these measures to restore the water quality of the aquifer while minimizing changes in the pumping regime and (3) to assess the sustainable pumping regime (with and without the implementation of additional measures) once the water quality has been restored. Shadow prices obtained from linear programming become a valuable tool to quantify the hydraulic efficiency of potential corrective measures to restore water quality in the aquifer
Vulnerability maps illustrate the potential threat of contaminants to groundwater and can be considered as important tools for land-use planning and related legislation. For karst areas with characteristic preferential infiltration conditions, vulnerability maps are also excellent tools for source and resource protection. However, the resulting qualitative maps are often inconsistent and even contradictive and thus might lead to inconclusive vulnerability assessments. The results of a validation of vulnerability maps produced using four different methods, DRASTIC, GLA, PI and EPIK, are reported for a karst area in southwest Germany. By means of measured hydraulic and transport parameters of the geological sequence, numerical simulations were used based on a conceptual model for the area under study. The mean transit time through the unsaturated zone (resource protection) was used as the validation parameter. The study demonstrates that the highest level of accuracy is achieved with the GLA- and PI methods. Both DRASTIC and EPIK are not able to incorporate highly variable distributions and thickness of cover sediments and their protective properties in the respective mapping procedure. Thus, vulnerability maps produced with DRASTIC, EPIK, and related methods should be used with care when employed in vulnerability assessments for land use planning and related decision-making.
Les cartes de vulnerabilite illustrent la menace potentielle des contaminants envers les eaux souterraines, et peuvent etre considerees comme des outils importants en matiere d'amenagement foncier et de reglementation associee. Sur les domaines karstiques, caracterises par des conditions d'infiltration preferentielle, ces cartes sont egalement d'excellents outils de protection des sources et des ressources. Cependant, les cartes qualitatives resultantes sont generalement incoherentes voire contradictoires, et peuvent par la-meme mener a des evaluations de vulnerabilite peu concluantes. La presente etude expose les resultats de validation de cartes de vulnerabilite produites selon quatre methodes differentes (DRASTIC, GLA, PI et EPIK), dans le cas d'un domaine karstique du sud-est de l'Allemagne. Par le biais des parametres de transport et hydrauliques mesures sur la sequence geologique, des simulations numeriques basees sur un modele conceptuel du secteur d'etude ont ete utilisees. Les temps de transit moyens a travers la zone non saturee (protection de la ressource) ont ete utilises comme parametres de validation. L'etude demontre que le niveau maximum de precision est obtenu par les methodes GLA et PI. Dans la phase de cartographie, les methodes EPIK et DRASTIC sont incapables d'integrer une forte variabilite dans les distributions et les epaisseurs de sediments de couverture, ainsi que dans leurs potentiels de protection. Aussi, les cartes de vulnerabilite produites par les methodes DRASTIC et EPIK doivent etre utilisees avec precaution dans le cadre des evaluations de vulnerabilite a but decisionnaire pour les amenagements fonciers.
Los mapas de vulnerabilidad ilustran la amenaza potencial de contaminantes para el agua subterranea y pueden ser considerados herramientas importantes para planeamiento del uso de la tierra y legislacion relacionada. Para areas carsticas con sus caracteristicas condiciones de infiltracion preferencial, los mapas de vulnerabilidad son tambien excelentes herramientas para proteccion de fuentes y recursos. Sin embargo, los mapas cualitativos resultantes son frecuentemente inconsistentes y hasta contradictorios y por lo tanto podrian conducir a evaluaciones de vulnerabilidad no concluyentes. Los resultados de una validacion de mapas de vulnerabilidad producidos usando cuatro metodos diferentes, DRASTIC, GLA, PI y EPIK, son presentados aqui para un area carstica en Alemania suroccidental. Se usaron simulaciones numericas usando parametros hidraulicos y de transporte medidos de la secuencia geologica y basandose en un modelo conceptual del area en estudio. El tiempo promedio de transito a traves de la zona no saturada (proteccion del recurso) fue utilizado como el parametro de validacion. El estudio demuestra que el maximo nivel de precision es alcanzado con los metodos GLA y PI. DRASTIC y EPIK no fueron capaces de incorporar distribuciones altamente variables ni espesor de sedimentos de cubierta y sus propiedades protectivas en el respectivo procedimiento de elaboracion de mapas. Por lo tanto los mapas de vulnerabilidad producidos con DRASTIC, EPIK y metodos relacionados deberian ser usados con cuidado cuando se usen en evaluaciones de vulnerabilidad para planeamiento del uso de tierra
This work presents a methodology for elaborating sinkhole hazard models that incorporate the magnitude and frequency relationships of the subsidence process. The proposed approach has been tested in a sector of the Ebro valley mantled evaporite karst, where sinkholes, largely induced by irrigation practices, have a very high occurrence rate (>50 sinkholes/km2/yr). In this area, covering 10 km2, a total of 943 new cover collapse sinkholes were inventoried in 2005 and 2006. Multiple susceptibility models have been generated analyzing the statistical relationships between the 2005 sinkholes and different sets of variables, including the nearest sinkhole distance. The quantitative evaluation of the prediction capability of these models using the 2006 sinkhole population has allowed the identification of the method and variables that produce the most reliable predictions. The incorporation of the indirect variable nearest sinkhole distance has contributed significantly to increase the quality of the models, despite simplifying the modeling process by using categorical rather than continuous variables. The best susceptibility model, generated with the total sinkhole population and the selected method and variables, has been transformed into a hazard model that provides minimum estimates of the spatial–temporal probability of each pixel to be affected by sinkholes of different diameter ranges. This transformation has been carried out combining two equations derived from the more complete 2006 sinkhole population; one of them expressing the expected spatial–temporal probability of sinkhole occurrence and the other the empirical magnitude and frequency relationships generated for two different types of land surfaces, which control the strength of the surface layer and the size of the sinkholes. The presented method could be applied to predict the spatial–temporal probability of events with different magnitudes related to other geomorphic processes (e.g. landslides).
This article focuses on the natures, origins, and significances of clastic sediments in caves. Clastic sediments are fragments of preexisting rocks that have been transported and redeposited. Streams transport large quantities of clastic sediments through caves, including stream gravels and mud, but clastic sediments also move as gravity flows by slumping and sliding. Sedimentology and stratigraphy offer the means to understand the origins and transport mechanisms behind individual clastic deposits. Together, the two methodologies consider layering within deposits and grain sizes, sorting, mineralogies, and sedimentary structures within individual beds. Facies are recognized where those variables include diagnostic properties tied to particular depositional processes or driving forces. As is shown using examples, stratigraphy and facies analysis make it possible to reconstruct cave or landscape histories, including system responses to disturbances such as climate change and land use. Notably, system responses typically reflect changes in sediment supply, hydraulic gradients, or obstructions. These factors are recorded in passage morphologies, which should always be considered when studying clastic sediments in caves, and examples are cited.
Cave cricket abundance is used as an indicator of integrity of cave ecosystems. One means of monitoring cave cricket abundance is counting crickets as they emerge from cave entrances for two hours after sunset. The influence of cloud cover, relative humidity, and surface temperature on counts is unknown and there might be few cave crickets that emerge during the first hour of the survey. Using mixed effects models, I assessed the influence of these environmental variables on exit counts and estimated when cave crickets emerged within the two-hour survey period. Exit-count surveys were conducted in eleven caves over four years in central Texas, and caves were surveyed up to four times a year across the four calendar seasons. Cloud cover, relative humidity, and temperature influenced counts, but the greatest influence was from temperature. Peaks in cave cricket counts occurred 80 to 90 minutes after the start of a survey and declined thereafter. Cave cricket exit count surveys should record surface temperature, cloud cover, and relative humidity at the start of surveys so that counts can be adjusted for these environmental influences. Also, surveys can be shortened to 1 or 1.5 hours in length. Cave cricket abundance is used as an indicator of integrity of cave ecosystems. One means of monitoring cave cricket abundance is counting crickets as they emerge from cave entrances for two hours after sunset. The influence of cloud cover, relative humidity, and surface temperature on counts is unknown and there might be few cave crickets that emerge during the first hour of the survey. Using mixed effects models, I assessed the influence of these environmental variables on exit counts and estimated when cave crickets emerged within the two-hour survey period. Exit-count surveys were conducted in eleven caves over four years in central Texas, and caves were surveyed up to four times a year across the four calendar seasons. Cloud cover, relative humidity, and temperature influenced counts, but the greatest influence was from temperature. Peaks in cave cricket counts occurred 80 to 90 minutes after the start of a survey and declined thereafter. Cave cricket exit count surveys should record surface temperature, cloud cover, and relative humidity at the start of surveys so that counts can be adjusted for these environmental influences. Also, surveys can be shortened to 1 or 1.5 hours in length.
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