GIS-based spatial analysis coupled with geophysical imaging to identify and evaluate factors that control the formation of karst sinkholes in southwestern Missouri

Sinkholes are inherent features of the karst terrain underlying much of Greene County, Missouri. These features present hazards and engineering challenges to existing infrastructure unknowingly constructed on a seemingly benign ground surface. The primary objective of this research was to investigate the physical processes chiefly responsible for triggering the seemingly random distribution of sinkholes in the study area. This research employed an integrated approach encompassing regional scale GIS-based spatial analyses and site-specific geophysical data. GIS-based spatial analysis was employed to identify significant physical factors that appeared to influence the formation and distribution of sinkholes. Seven out of the twelve most cited factors influencing sinkhole development were identified in the study area. These factors were: overburden thickness, depth-to-groundwater, slope of the ground surface, distance to the nearest water course, distance to the nearest geologic structures, distance to nearest springs, and distance to the nearest roads. In the site-specific geophysical investigations, two dimensional (2D) and pseudo three dimensional (3D) - ERT, MASW, and borehole data were used to characterize the subsurface morphology of the karstified soil-bedrock interface in five selected sinkholes. From the interpretation of the 2D and pseudo 3D-ERT profiles, it was determined that four of the five sinkholes occurred at the intersections of regional systematic joint sets. The joint sets are characterized by a linear, visually prominent zones of low resistivity. The relatively low resistivity values are attributed to vertical seepage and the associated piping of fine-grained soils through preexisting fractures (often widened by solutioning) --Abstract, page iv

Hydrogeologic Investigation of a Covered Karst Terrain

Increasing demand for water for agricultural use within the Dougherty Plain of the Southeastern United States has depleted surface water bodies. In karstic landscapes, such as the Dougherty Plain in southwest Georgia where the linkages between surface and ground waters are close, there is a need to understand the physical characteristics of the subsurface that allow these close linkages. Having a better understanding of the subsurface characteristics will aid numerical modeling efforts that underpin policy decisions and economic analyses. Two common features on this karstic landscape are draws and geographically isolated wetlands. Using LiDAR, aerial imagery, and ground-penetrating radar, this study investigates the subsurface characteristics of a draw and a series of geographically isolated wetlands. GPR reflections indicative of karst features are laterally-continuous and connect the landscape to nearby Ichawaynochaway Creek. The identification of the size and scale of the laterally continuous karstic features will guide the implementation of groundwater models used to determine irrigation and forest restoration programs while minimizing the impacts of water use on surface streams and the ecosystems

Investigation of the Flow and Fate of Nitrate in Epikarst at the Savoy Experimental Watershed, Northwest Arkansas

Many karst aquifers are at high risk of nitrate contamination due to a combination of vulnerable geology characterized by thin soils and conduit flow, and excess inputs of nutrients from animal feeding operations. One zone that is present in many karst regions and could play an important role in nitrate attenuation due to properties such as increased residence time and matrix-water contact is the upper, weathered portion of karst, the epikarst. However, the understanding of this role is lacking, and the objective of this dissertation was to elucidate it. The fate of nitrate in the epikarst was traced along a hydrologic gradient using a multi-faceted geochemical approach based primarily on concentration and stable isotope composition of the reactants and products of denitrification. In addition, dye-tracing tests were conducted to assess the flow, solute transport and aquifer characteristics of the epikarst system. The study found multiple lines of evidence for denitrification which is spatially and temporally highly variable and can remove up to 33% of nitrate along the studied flowpaths. Dissolved organic carbon and dissolved oxygen appear to control denitrification levels, and both in turn appear to be controlled by hydrologic conditions (saturation). However, the most significant agent of nitrate attenuation is dilution, decreasing nitrate concentration by upwards of 50%. Transport of water and solutes in the epikarst can be relatively fast (up to 2.2 m/h) and involves preferential flowpaths. However, transport of a point-source solute located in the upper epikarst depends on saturation, and the transported mass is likely to be negligible in the short term (weeks-months) under the normal weather pattern. Overall, the results indicate that the epikarst can be an important buffer against potential groundwater contaminants

Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom‐up control hypothesis using high‐resolution topographic data

The depth to bedrock controls a myriad of processes by influencing subsurface flow paths, erosion rates, soil moisture, and water uptake by plant roots. As hillslope interiors are very difficult and costly to illuminate and access, the topography of the bedrock surface is largely unknown. This essay is concerned with the prediction of spatial patterns in the depth to bedrock (DTB) using high‐resolution topographic data, numerical modeling, and Bayesian analysis. Our DTB model builds on the bottom‐up control on fresh‐bedrock topography hypothesis of Rempe and Dietrich (2014) and includes a mass movement and bedrock‐valley morphology term to extent the usefulness and general applicability of the model. We reconcile the DTB model with field observations using Bayesian analysis with the DREAM algorithm. We investigate explicitly the benefits of using spatially distributed parameter values to account implicitly, and in a relatively simple way, for rock mass heterogeneities that are very difficult, if not impossible, to characterize adequately in the field. We illustrate our method using an artificial data set of bedrock depth observations and then evaluate our DTB model with real‐world data collected at the Papagaio river basin in Rio de Janeiro, Brazil. Our results demonstrate that the DTB model predicts accurately the observed bedrock depth data. The posterior mean DTB simulation is shown to be in good agreement with the measured data. The posterior prediction uncertainty of the DTB model can be propagated forward through hydromechanical models to derive probabilistic estimates of factors of safety.Key Points:We introduce an analytic formulation for the spatial distribution of the bedrock depthBayesian analysis reconciles our model with field data and quantifies prediction and parameter uncertaintyThe use of a distributed parameterization recognizes geologic heterogeneitiesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137555/1/wrcr22005.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137555/2/wrcr22005_am.pd

Non-invasive imaging and assessment of pavements

Eight electrical resistivity tomography (ERT) and multi-channel analysis of surface wave (MASW) case studies are presented. The objective is to assess the condition of pavement, base, native soil, and rock all the way down to the top of the bedrock. Each segment of road way is approximately 1000 ft. long. The cases include US 63 north of Rolla, US 54 in Camden County, Rte. 179 in Jefferson City, HWY AT in Franklin County, I-55 in Pemiscot County, I-55 in Perry County, HWY U in Dent County, I-35 in Daviess County. In addition, there are only three types of pavement in these sites portland cement concrete (PCC), asphalt concrete overlaying portland cement concrete (AC/PCC), and full-depth asphalt concrete (AC) pavements. Accordingly, the geophysical tools examined different types of pavements with different distress conditions. Based on the analyses of the acquired ERT and MASW data, the data of both tools correlate reasonably well and generate reliable and comprehensive information about variations in soil and rock rigidity, variations in rock lithology, pattern, placement and density of solution-widened joints and offset of faults, locations of air-filled voids, distribution of dry and moist soil, distribution of clayey soil, and mapping variable depth to top of bedrock. Therefore these technologies can be routinely used by not only the Missouri Department of Transportation but also worldwide agencies in support of its pavement management process. The research demonstrated that the ERT and MASW methods were effective tools for assessing the condition of pavement. This is the first comprehensive assessment of paved sections of roadway to the best of the author knowledge --Abstract, page iii

Some evolutionary patterns of palaeokarst developed in Pleistocene deposits (Ebro Basin, NE Spain): Improving geohazard awareness in present-day karst

Pleistocene detrital deposits in the central Ebro Basin frequently show deformation features due mainly to karstification in the underlying Neogene evaporites. In 123 cases, estimation of parameters of shape and minimum volume of materials involved was accomplished. Six of them were analysed in more detail to establish the main processes involved in their genesis and the succession of events. All the deformation features in the selected sites are synsedimentary. To achieve the objectives, intense fieldwork was made applying methods of sedimentology and structural geology. Usually, a complex evolutionary pattern was observed, with evidences of dissolution, sagging, collapse, gravity flow, suffosion, and plastic flow. In a schematic way, three main situations, independent of the age of the analysed deposits, can be distinguished: (a) slow subsidence, (b) collapse, and (c) temporal overlapping of both processes. In the first 2 scenarios, basins with smooth or abrupt borders, respectively, were generated on the land surface. In the third one, slow subsidence was followed by a collapse, located in the area of maximum flexure. These patterns are also observed in present-day dolines. Comparison of direct and indirect parameters between paleodolines and present-day dolines indicates a bigger size of the latter, probably caused by the different conditions of observation. This study helps to know the possibilities in the evolution of mantled karst features, to estimate the volume of material affected by karstification and to improve the knowledge of present-day dolines behaviour. Consequently, study of paleodolines must be considered to achieve a better urban planning in active karstic areas

Groundwater flow controls on coastal water quality and global groundwater ages

Humanity relies on groundwater. But, current consumption may be outpacing groundwater renewal rates, and anthropogenic activities are altering its quality. This dissertation advances the state of knowledge of how local and regional groundwater dynamics affect its quality and quantity. First, I investigate groundwater discharge patterns and fluxes in three lakes in the Nebraska Sand Hills region and on the island of Rarotonga, Cook Islands, to understand the hydrologic connection between groundwater and surface water in these lacustrine and coastal settings. In Nebraska, I use electrical geophysical methods to characterize the spatial signature of groundwater recharge and discharge to and from the lakes using groundwater salinity patterns. On Rarotonga, a detailed field study of groundwater flow at the intertidal zone shows how groundwater flow influences the thermal regimes of nearshore environments, affecting the biota that live and chemical processes that occur near and below this dynamic interface. Next, a dense network of geophysical surveys across the coastal plain and into the lagoon on Rarotonga constrains multiple features of the larger-scale hydrologic system that are primarily controlled by the local carbonate and volcanic geology on the island. Finally, I give the first estimate of the global storage and spatial distribution of groundwater with a mean age since recharge of less than fifty years. I use several thousand two-dimensional groundwater flow and age-as-mass transport simulations parameterized by the best available hydrologic and geologic datasets. This global analysis suggested that ~6% of the groundwater stored in the upper 2 km of the Earth’s crust is younger than 50 years. Comparing this young groundwater storage to current groundwater depletion rates indicates that more than half of the irrigated areas depending significantly on groundwater could have already used up all of the young groundwater and are using groundwater more quickly than the storage is replenished. Together, these studies advance how to quantify groundwater as a renewable resource through the global estimation of groundwater storage associated with certain timespans and by analyzing the implications of groundwater flow on water quantity and quality in field settings.Geological Science

Integrated geophysical approach using electrical resistivity tomography and multichannel analysis of surface wave in assessing Wilson Spring development

This research investigated fractured zones leading to preferential flow paths of Wilson Spring. In this context, electrical resistivity tomography (ERT) data and multi-channel analyses of surface waves (MASW) data were acquired at studied site with the purpose of mapping a variable depth to top of bedrock and geological structures. Interpretation of the boreholes, MASW, and ERT data indicated that a depth to top of rock does vary significantly at the studied site due to many solution-widened fractures. Multiple near-vertical solution-widened fractures were mapped in the studied site based on the interpretation of the ERT data. The mapped solution-widened fractures appear to be trending north-south, almost perpendicular to the ERT traverses (west-east), and however it is possible they extend at oblique angle to the ERT traverses. The conducted geophysical survey is the first attempt to map geological structures and karst features that might be possible access of underground water. The underground water expose on land surface through fractures to develop Wilson Spring. Thus the seepage pathway near or beneath Wilson Creek is interpreted as through a solution-widened fractures. ERT method has proven to be effective in mapping variable depth to bedrock and solution-widened fractures. The MASW method and boreholes data were able to map variable depth to top of bedrock --Abstract, page iii

Assessment and Conceptualization of Groundwater Flow in the Edwards Aquifer Through the Knippa Gap in Uvalde County, Texas

The Edwards aquifer is one of the major regional karst aquifers in the United States, with an average withdrawal of 950 million liters per day (L/d). This investigation focuses on the connection between the Uvalde pool and the San Antonio pool of the Edwards aquifer, known as the Knippa Gap, west of the San Antonio metropolitan area in Uvalde County. This is a major zone of recharge to the Edwards aquifer and is approximately 6.4 km wide. The Knippa Gap is bounded by northeast trending faults of the Balcones Fault Zone (BFZ) on the north (specifically the Cooks and Trio Faults), and uplift from the Uvalde salient and igneous intrusive plugs to the south. Aspects of the hydrogeology in the Knippa Gap have been a topic of major interest among researchers in this area for numerous years, however, the exact location and nature of boundaries are undefined, and the discharge through this area is not accurately known. The input data from this investigation will allow for assessments of discharge, better water budget approximations for the San Antonio pool, and determination of accurate flow boundaries and budgets for Uvalde County. This investigation was limited to the transmissive (karstified) portion of the Edwards aquifer within the study area, and is based on previous studies, and newly collected data. The newly collected data include: 1) compilation of a complete table of wells within the study area; 2) redefined placement of flow boundaries (faults) most of which appear to be structurally controlled; 3) hydrostratigraphic analysis of the Knippa Gap area based on drilling and wireline logs; 4) characterization of the depth of karstification within the Knippa Gap; and 5) analyses of water quality within and contiguous to the study area. These data constrain a revised conceptual model of the flow and karstification in this critical area of recharge to the Edwards aquifer, and provide specific lateral boundaries and vertical karstification zones which can be tested quantitatively. Although current interpretations are tentative, it appears this conceptual model will be readily convertible into a digital model that can test hypotheses relating to water levels and spring discharges