Maintaining a safe water supply is particularly crucial for karst islands such as Barbados. In order to take proper measures to prevent and reduce saltwater intrusion and to safely extract the right fraction of recharge, karst characteristics must first be fully understood. Geomorphologic investigations of karst surface features of the Porters & Trents groundwater catchments (Barbados) employed GIS technologies to explore the development and distribution of sinkhole features. Contour-based digital elevation models, surface geology, lithology, and remote sensing images were incorporated in this investigation. Seventy-six sinkholes were investigated and occupied approximately 1% (0.16 km2) of the total area (16.41 km2) under study. It was found that age of karstification is not related to age of a terrace. The middle terrace was the one found to be most karstified. Yet, degree of karstification within a terrace is age related. Also, cluster density increases with age of coral within the middle terrace. Density of sinkholes within a cluster also increases with age of coral within the middle terrace. / Finally, this study shows that sinkhole long axis, cluster elongation direction, sinkhole alignment and karst lineament all have a tendency to a northeast alignment. This supports the idea that underlying coral rock fracture and conduits have a northeast orientation.

Heavy wheeled and tracked vehicle training has been conducted on portions of the landscape of Fort Knox, Kentucky for approximately 60 years. Fort Knox is located on the Kentucky Karst Plain and sinkholes are dominant features of this area. Sinkholes and karst terrain present an atypical problem in combination with this unique land use, potentially impacting downstream and local terrestrial environment. A study of the training area sinkhole complex was conducted as a first step toward mitigating the impact of military activities and reduces potential problems of sedimentation and water quality degradation. A total of 20 sinkholes within Training Areas 9 and 10 at the Fort Knox Military Reservation were randomly selected to represent the study area. The objective of this study was to determine the relationship between stand structural characteristics, understory light availability and understory vegetation in sinkhole riparian buffers and concentrated flow paths and with the amount of sediment entering sinkholes in the study area. Vegetation data were collected during the growing months of May and June in 2009. All regressions analyses for vegetative structures have r2 values between 0.000 to 0.308 indicating weak to no correlation among the variables. Light availability and percent herbaceous cover showed moderate and weak relationship in buffers (r = 0.547, p = 0.003) and flow paths (r = 0.164, p = 0.245). Sediment gained in splay areas showed no significant relationship to vegetation structure (r = 0.039 to -0.335). The relationship between sediment gained and mean percent herbaceous cover was not significant in flow paths (r = -0.172, p = 0.2341) or buffers (r = 0.130, p = 0.292). While the results of this study suggest the amount of the sediment depositing in the sinkholes was unrelated to observe variation in sinkhole vegetation, the relationship between overstory vegetation and understory vegetation within sinkholes was more noticeable. On site observations strongly suggest that concentrated flow paths were the primary conduits for sedimentation into splay areas. Therefore, management considerations pertaining to training areas should minimize flow paths leading to sinkholes. Best management practices for Fort Knox training areas should integrate these research findings, in addition to current knowledge of riparian buffers and training areas' management requirements.

El estudio se enmarca en un análisis numérico orientado a determinar la distribución de tensiones efectivas que se generan en un medio poroso cuando el gradiente hidráulico se aproxima al gradiente hidráulico crítico, condición que gatilla la migración de finos en medios porosos de estructura inestable. Este fenómeno ha sido crítico en los suelos de transición y núcleo pertenecientes a la presa W.A.C. Bennet, la cual presentó serias anomalías con manifestaciones de “sinkholes” en varios puntos del coronamiento, luego de 30 años de funcionamiento. Para estos efectos, se ha desarrollado un modelo numérico que utiliza el programa computacional que resuelve las ecuaciones de un medio continuo vía diferencias finitas, para reproducir las trayectorias de esfuerzos verticales obtenidas en probetas de suelos durante la etapa de flujo, i.e., los ensayos efectuados en el permeámetro de grandes dimensiones del laboratorio de UBC. Un aspecto relevante que requiere la solución del fenómeno, se refiere a modelar la pérdida de esfuerzos verticales en el suelo, producto del roce generado en el contacto suelo – permeámetro. Se contempla la implementación de dos alternativas que permiten evaluar por separado dicha pérdida. Éstas corresponden a una interfaz, con propiedades de fricción y rigidez y a la distribución del módulo de deformación, expresada en función del nivel de confinamiento del suelo. La primera solución establece que la interfaz es capaz de provocar la pérdida de los esfuerzos verticales, independiente del módulo de deformación del suelo utilizado. La segunda, que no usa interfaz, requiere del ajuste del parámetro que controla la expansión lateral en el modelo (Modulo de Poisson), en cuanto permite que el suelo se “cuelgue” de las paredes del permeámetro para provocar la pérdida deseada. Debido a que ambas aproximaciones corresponden a diferentes formas de modelar el mismo problema, se establece que la mejor solución corresponde a la alternativa que considera la distribución del módulo de deformación en la probeta. El presente estudio incluye conceptos como línea de falla hidromecánica que, en definitiva, entrega el marco geotécnico requerido para generar una solución que se aproxime al problema de inestabilidad interna, por lo que el programa computacional desarrollado en esta tesis es una útil herramienta práctica en el análisis de estabilidad interna de presas de tierra.

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Dynamic forces in the hydrologic cycle move underground water through Florida's carbonate rocks dissolving chemical components of the rocks, leaving behind caves, solution pipes, and other voids that result in a karst terrain. Ravelling is the common subsidence mechanism throughout most of Florida where unconsolidated materials filter downward into voids in the underlying limestone. A cavity in the overburden develops and enlarges over a period of many years. The enlarged cavity is also known as sinkhole. The investigations of sinkhole characteristics and potential involve studying the regional geology, hydrology and mapping historic sinkholes that have occurred in the area. Use of Cone Penetration Test (CPT) soundings, in conjunction with conventional soil borings are becoming more common in the assessment of subsurface soil conditions in the vicinity of sinkhole-related ground surface. The penetration resistance data by CPT can determine the presence and extent of raveled soil zones characteristic of sinkhole features, and the penetration pore water pressure data can be used to determine the integrity of the clay confining unit at each test sounding location. The objective of this study is to identify the possible location of the confining breach at a sinkhole in Seminole County. The methods used in the assessment of the sinkhole's subsurface conditions were Standard Penetration Test (SPT), which provided information that helped to identify the location of the ravelled zones within the soil profile, and Cone Penetration Test that gave information of the piezometric water levels obtained from the pore pressure dissipation curves. The total head was calculated from the piezometric water levels corresponding to the different elevations. The data were found to exhibit a downward behavior of the total head, starting at around elevation 50 feet, NGVD that extended towards lower elevations. The SPT boring log identified a ravelled zone starting at 31 feet approximately. From both information it was possible to establish that the hydraulic head was influenced by the proximity of the ravelled zones, where the head precipitated rapidly as the elevation decreased. From the result of this study, it was concluded that the location of the breach in the confining layer started at 61.8 feet deep below the ground surface. Potentiometric contour lines at elevation 24.40 feet denoted flow patterns of water from the surroundings of the depression towards the approximate location of the center, which is the existing of subsurface cavity.

In the United States, karst ecosystems cover approximately 20 percent of the country and karst aquifers provide 40 percent of the water used for drinking. In karst-influenced watersheds, karst features such as sinkholes and sinking streams act as rapid pathways for carrying water and pollutants into streams and groundwater. Human activities on karst landscapes can present some special problems such as alterations to hydrologic regime, contamination of groundwater, ground subsidence, and damage to cave ecosystems. Modeling a karst-influenced watershed can provide a better understanding of the interactions between surface and ground water and how water quality is affected by human activities. Several models were evaluated to determine their ability to model both discharge and nutrient transport in karst watersheds. The Soil Water Assessment Tool (SWAT) model was found to be appropriate due to its capability to represent almost all of the hydrological processes, its user-friendliness, and its ability to generate most of the parameters from available data. Moreover, SWAT can represent nitrogen transformations and transport processes and calculate nitrogen loadings, which is critical for karst watersheds. While it has been widely used and found to be an appropriate prediction tool, it does not explicitly include the capacity to represent specific features characteristic of karst-influenced basins. Baffaut and Benson (2008) modified the SWAT 2005 code to simulate faster aquifer recharge in karst environments, and this version was further modified here in the SWAT-Karst to represent karst environments at the HRU scale. A new parameter sink allows simulating the hydrology and nitrate transport in a sinkhole representing its unique landuse and soil characteristics, and a new parameter ss partitions nitrate transported with water that is lost from sinking streams. The SWAT-KARST model was used to simulate discharge and nitrogen loadings within the Opequon Creek karst-influenced watershed, located in the Potomac and Shenandoah River basin in Virginia and West Virginia. In the Opequon Creek watershed, SWAT-karst using the HRU to represent sinkholes had a more notable impact in the watershed hydrology than SWAT-B&B using a pond to represent sinkholes. Results of statistical evaluation show that SWAT-karst and the Baffaut and Benson (2008) version performed better than SWAT in predicting streamflow in a karst-influenced watershed. Although SWAT-karst showed almost the same performance as SWAT-B&B, SWAT-karst model offers the flexibility to represent the unique relationship between surface and ground water in karst features in an HRU. Using an HRU to represent sinkholes can depict the associated variability of a karst landscape. The new variables sink and ss provide a mechanism to represent the nutrient transport through sinkholes and sinking streams. Sensitivity analysis showed that SWAT-karst was sensitive to the new parameter sink which can be used for model calibration and to represent water recharge and nutrient transport to aquifers outside the watershed boundary. / Master of Science

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Master of Science in Engineering, 2016 / Previously undermined areas pose a significant challenge to mining by opencast due to the risk of sinkhole occurrence. In order to optimise reserve utilisation as well as safeguard personnel and equipment there was need to develop a “Sinkhole Prediction Model” to assist in the prediction of areas prone to sinkhole formation. The aim of this research therefore was to develop a “Sinkhole prediction tool” with a view to pre-identifying areas of potential sinkhole hazard to inform better controls to assist in mining these areas safely. This was done utilising the current Hill (1996) caving height method culminating in the development of a hazard index model dividing the mining zones into high and low hazard. These areas were colour coded Red (High hazard) and Green (Low Hazard). The “Sinkhole Prediction Model” evolved to include over hundred sinkhole incidences that were statistically analysed to firm up on the robustness of the Prediction Model capabilities. The Hill (1996) caving height formula was discounted after the statistical analysis indicated that a good prediction model lies in the interrogation of site specific data. The outcome of the work conducted in this research report indicated a 97% correlation between the refined “Sinkhole Prediction Model” and the actual sinkhole occurrence at the Anglo American case study area (Mine X). Various refinements inclusive of lithological assessments, blast and drilling reconciliations as well as the implementation of the roughening up quality audits led to the implementation of a robust sinkhole management process that has managed to consistently assist in safeguarding equipment and personnel thus allowing for coal extraction optimisation in areas that could have been written off due to the sinkhole hazard. This risk can only be eliminated by mining the areas with the sinkhole risk. Currently the method is being impacted by significant roughening up cost incurred in a drive to make the areas safe to allow for coal extraction. The roughening up process on average costs R3.5 million per sinkhole and is a function of the number of sinkholes found, which translates to an equivalent cost of R7 / sales tonne. The current sinkhole prediction model being employed in deficient in that it cannot pinpoint the actual location of the void in the area previously undermined by bord and pillar and this is a great limitation of this report. Various geophysical techniques were pursued to assist in the precise identification of the actual sinkhole spatially. This process was aimed to reduce the roughening up cost (entire block stabilisation) as opposed to targeted sinkhole excavation and stabilisation. This process proved futile as the void identification systems are highly incapable of identifying the voids / iv sinkholes spatially (x, y and z coordinates) to assist targeted sinkhole treatment as a result of the following:  System inability to penetrate areas comprised of highly conductive strata such as clays.  Inability to distinguish between the underground voids and geological anomalies such as dykes.  Not suitable for penetrating wet strata.  Impacted by noise interference from mining machinery. The major result of this research is the establishment of a site specific “Sinkhole Prediction Model” that can generate hazard plans in real time thus informing the management on areas associated with a potential sinkhole hazard. The hazard plans can be generated timely and decisions made to facilitate safe coal extraction in areas of high sinkhole hazard. This has culminated in a robust sinkhole management process within the group that has managed to eliminate the risk of personnel and equipment exposure at Mine X. The roughening up process is accepted as the primary sinkhole mitigation or rehabilitation process with the need to work towards reducing the roughening up costs through development of the tool capable of precisely identifying the voids routinely to facilitate targeted rehabilitation. Significant research is required in this area as the mining environment is comprised of strata that currently cannot support the use of real time void identification to facilitate targeted void identification and rehabilitation. There is also merit in the future to formulate the database capable of assisting in the prediction of sinkholes in the Witbank coalfield as well as assist in robust management of mining boundaries across the different mining houses. The system implemented at Mine X is currently being deployed to other operations in the group where modification will be made to match the site specific conditions. Future research into understanding the sinkhole occurrence dynamics is quite crucial if targeted rehabilitation is to be achieved for cost reduction and mining sustainability. A combination of the understanding of the sinkhole occurrence driving mechanisms in conjunction with use of modelling packages such as ELFEN (a hybrid Modelling) tool will go a long way in enhancing the development of precise sinkhole prediction point in space.

Beaches can provide a natural barrier between the ocean and inland communities, ecosystems, and resources. These environments can move and change in response to winds, waves, and currents. When a hurricane occurs, these changes can be rather large and possibly catastrophic. The high waves and storm surge act together to erode beaches and inundate low-lying lands, putting inland communities at risk. There are thousands of buoys in the Atlantic Basin that record and update data to help predict climate conditions in the state of Florida. The data that was compiled and used into a larger data set came from two different sources. First, the hurricane data for the years 1992 – 2014 came from Unisys Weather site (Atlantic Basin Hurricanes data, last 40 years) and the buoy data has been available from the national buoy center. Using various statistical methods, we will analyze the probability of a storm being present, given conditions at the buoy; determine the probability of a storm being present categorically. There are four different types of sinkholes that exist in Florida and they are: Collapse Sinkholes, Solution Sinkholes, Alluvial Sinkholes, and Raveling Sinkholes. In Florida there are sinkholes that occur, because of the different soil types that are prevalent in certain areas. The data that was used in this study came from the Florida Department of Environmental Protection, Subsidence Incident Reports. The size of the data was 926 with 15 variables. We will present a statistical analysis of a sinkholes length and width relationship, determine the average size of the diameter of a sinkhole, discuss the relationship of sinkhole size depending upon their soil types, and acknowledge the best probable occurrence of when a sinkhole occurs. There will be five research chapters in this dissertation. In Chapter 2, the concept of Exploratory Factor Analysis and Non-Response Analysis will be introduced, in accordance of analyzing hurricanes. Chapter 3 will also address the topic of hurricanes that have formed from the Atlantic Basin from 1992 – 2014. The discussion of the probability of a storm being present (also categorically) will be addressed. In Chapter 4 a study of sinkholes in Florida will be addressed. In Chapter 5 we will continue our discussion on sinkholes in Florida, but focus on the time to event between the occurrences of the sinkholes. In the last chapter, Chapter 6, we will conclude with a future works and projects that can be created from the foundations of this dissertation.