Airborne electromagnetic imaging of discontinuous permafrost

The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to stream flow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ~1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ~4 million years and the configuration of permafrost to depths of ~100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface – groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past 1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments

Airborne Electromagnetic Surveys For 3d Geological Mapping

The U.S. Geological Survey and its partners have collaborated to create 3D geologic maps for areas of the North and South Platte River valleys, including Lodgepole Creek, in western Nebraska using airborne electromagnetic surveys. The objective of the surveys is to map the 3D configuration of aquifers and bedrock topography created by the paleochannels of the ancestral Platte River. The ultimate goal is to gain a new understanding of groundwater–surface-water relationships to improve water management decisions through the use of groundwater management models. This goal was not achievable using traditional mapping methodologies, including surface geologic maps and borehole drilling logs. Airborne electromagnetic surveys provided nearly continuous information (data is collected every 3 to 20 meters along a flight path) of the subsurface electrical-resistivity variations (immediately below the sensor) at a depth range of 2 to 300 m below ground surface. To make the geophysical data useful for 3D geologic mapping, numerical inversion is necessary to convert the measured data into a depth-dependent subsurface electrical-resistivity model. The electrical-resistivity model, combined with sensitivity analysis, geological ground truth (boreholes), and geologic interpretation, is used to characterize geologic features. The 3D map provides the groundwater modeler with a high-resolution geologic framework and a quantitative estimate of framework uncertainty. This method of creating geologic frameworks improves the understanding of the actual flow-path orientation by redefining the location of the paleochannels and associated base of aquifer highs. The improved models depict the hydrogeology at a level of accuracy not achievable using previous data sets

Cooperative Hydrology Study COHYST Hydrostratigraphic Units and Aquifer Characterization Report

The Cooperative Hydrology Study (COHYST) is a geohydrologic study of surface and groundwater resources in the Platte River Basin of Nebraska upstream from Columbus, Nebraska. Information relating to COHYST and the products produced by it are found at the website http://cohyst.dnr.state.ne.us/ . COHYST was started in early 1998 to develop scientifically supportable hydrologic databases, analyses, models, and other information which, when completed, will: 1. Assist Nebraska to meet obligation under a separate three-state Cooperative Agreement (CA). (Governors of Wyoming, Colorado, and Nebraska, and the Secretary of the Interior, 1997) 2. Assist Nebraska\u27s Natural Resources Districts along the Platte River in providing appropriate regulation and management. 3. Provide Nebraskans with a basis to develop policy and procedures related to groundwater and surface water. 4. Help Nebraskans analyze proposed activities of the CA and/or other water management programs in Nebraska

Geophysical Log Analysis of Selected Test Holes and Wells in the High Plains Aquifer, Central Platte River Basin, Nebraska

The U.S. Geological Survey in cooperation with the Central Platte Natural Resources District is investigating the hydrostratigraphic framework of the High Plains aquifer in the Central Platte River basin. As part of this investigation, a comprehensive set of geophysical logs was collected from six test holes at three sites and analyzed to delineate the penetrated stratigraphic units and characterize their lithology and physical properties. Flow and fluid-property logs were collected from two wells at one of the sites and analyzed along with the other geophysical logs to determine the relative transmissivity of the High Plains aquifer units. The integrated log analysis indicated that the coarse-grained deposits of the alluvium and the upper part of the Ogallala Formation contributed more than 70 percent of the total transmissivity at this site. The lower part of the Ogallala with its moderately permeable sands and silts contributed some measureable transmissivity, as did the fine-grained sandstone of the underlying Arikaree Group, likely as a result of fractures and bedding-plane partings. Neither the lower nor the upper part of the siltstone- and claystone-dominated White River Group exhibited measurable transmissivity. The integrated analysis of the geophysical logs illustrated the utility of these methods in the detailed characterization of the hydrostratigraphy of the High Plains aquifer

Subsurface Mapping with Airborne Electromagnetics in the Central Valley of California

Extensive pumping of groundwater has led to subsidence in parts of the Central Valley of California. Airborne electromagnetic data were acquired to assess the ability of the method to assist in understanding the spatial variation of the observed subsidence. A total of 104 km of data were acquired and the derived resistivity model related to subsurface lithology using 12 lithology logs from near-by wells. We were able to map the clay layers, within and between aquifers, that are the likely geologic controls on the observed subsidence

Reconnaissance of surface-water quality in the North Platte Natural Resources District, western Nebraska, 1993 /

Shipping list no.: 97-0313-P.Includes bibliographical references (p. 14-15).Mode of access: Internet

Use of NMR logging to obtain estimates of hydraulic conductivity in the High Plains aquifer, Nebraska, USA

Hydraulic conductivity (K) is one of the most important parameters of interest in groundwater applications because it quantifies the ease with which water can flow through an aquifer material. Hydraulic conductivity is typically measured by conducting aquifer tests or wellbore flow (WBF) logging. Of interest in our research is the use of proton nuclear magnetic resonance (NMR) logging to obtain information about water-filled porosity and pore space geometry, the combination of which can be used to estimate K. In this study, we acquired a suite of advanced geophysical logs, aquifer tests, WBF logs, and sidewall cores at the field site in Lexington, Nebraska, which is underlain by the High Plains aquifer. We first used two empirical equations developed for petroleum applications to predict K from NMR logging data: the Schlumberger Doll Research equation (KSDR) and the Timur-Coates equation (KT-C), with the standard empirical constants determined for consolidated materials. We upscaled our NMR-derived K estimates to the scale of the WBF-logging K(KWBF-logging) estimates for comparison. All the upscaled KT-C estimates were within an order of magnitude of KWBF-logging and all of the upscaled KSDR estimates were within 2 orders of magnitude of KWBF-logging. We optimized the fit between the upscaled NMR-derived K and KWBF-logging estimates to determine a set of site-specific empirical constants for the unconsolidated materials at our field site. We conclude that reliable estimates of K can be obtained from NMR logging data, thus providing an alternate method for obtaining estimates of K at high levels of vertical resolution

The state of the science and vision of the future: Report from the Hydrogeophysics Workshop

peer reviewedIn July 2012, 72 hydrogeophysicists from around the world gathered at the Hydrogeophysics Workshop in Boise, Idaho, USA. This was the first workshop to be jointly sponsored by the Society of Exploration Geophysicists (SEG) and the American Geophysical Union (AGU), and brought together members from both societies, primarily from the Near-Surface Geophysics Section of SEG and the Near-Surface Focus Group and Hydrology Section of AGU. The intent of the workshop was to address current hydrogeophysical approaches for determining, predicting, and studying hydrologic properties and processes in both the saturated and unsaturated zones, at scales ranging from centimeters to watersheds