Processing of Outcrop-Based Lidar Imagery to Characterize Heterogeneity for Groundwater Models
Elizabeth M. Nichols, Gary S. Weissmann, Timothy F. Wawrzyniec, Jedediah D. Frechette, Katherine A. Klise, 2011. "Processing of Outcrop-Based Lidar Imagery to Characterize Heterogeneity for Groundwater Models", Outcrops Revitalized: Tools, Techniques and Applications, Ole J. Martinsen, Andrew J. Pulham, Peter D.W. Haughton, Morgan D. Sullivan
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Accurate representation of heterogeneity at varying scales is vital for modeling solute dispersion in groundwater aquifers and petroleum reservoirs. Dispersion, the result of varying velocities in a flow field, is, in part, due to material heterogeneity. In order to represent the influence of heterogeneity at the outcrop scale, a series of terrestrial LIDAR scans at millimeter-scale point spacing were recorded in sediments located in braided stream exposures west of Albuquerque, New Mexico, and outside the Hanford Site in Washington. Scans are projected onto a vertical plane and converted to a high-resolution TIFF image. Using the mean and standard deviation of the ‘‘stacked’’ images, the data are processed through a series of filters to enhance textural information and distinguish between lithologies. The product is converted to a grid with numerical color values for each lithology (e.g., sandstone, gravel). Each lithologic class is assigned reasonable values of hydraulic conductivity. Groundwater flow and transport time are simulated using MODFLOW and MODPATH, respectively. Simulations show that flow and solute transport are focused in the coarser-grained laminae of cross-bedded units. Flow may be focused into some areas in finer-grained beds as well, if the adjacent gravel bed has been cut. Thus, most of the flow may be focused into a smaller volume of the material making up the aquifer. This result shows that terrestrial LIDAR can be successfully applied to produce synthetic stratigraphy for use in fluid flow models.
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Outcrops are fundamental to everything we hope to achieve in geological understanding. They are gateways to geological processes, earth history and they help ground-truth remote sensing applications. With increasing resolution of subsurface tools and techniques, one could be forgiven in believing that outcrops have had their day and their utility is less than in the past great eras of field mapping and the development of facies models. This premise is far from the truth and this new SEPM volume illustrates how new analytical techniques are revitalizing outcrops and in the process creating a wealth of new data and fresh geological understandings. In this book you will find a compilation of the growing arsenal of outcrop tools and techniques and a consideration of future developments. This collection of papers, delivered at a SEPM Research Conference on the West coast of Ireland in the summer of 2008, is a smorgasbord of case studies, workflows, modeling, and applications which spans clastic and carbonate settings. Whatever your interest in outcrop geology and its application there is something in this volume for you. If you are seeking guidance for using new outcrop tools, looking for efficiencies in data collection or desiring new insights for old and favorite outcrops, this volume is a must have. This volume also makes an excellent reference or textbook for any group of professionals or students working or studying the new technologies that have allowed new insights from outcrops. We also consider this a superbly timed publication because many new outcrop tools are now becoming mainstream via reduced purchase and operating costs. Once you read this volume, and there are reduced prices for SEPM members and students, please share your new experiences with the authors and editors and help continue the revitalization of our shared and continually surprising outcrop library of the earth.