Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey, in collaboration with the U.S. Army Corps of Engineers, at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Eleven ERT profiles were acquired along the right (west) abutment, and immediately downstream, of the concrete, fixed-crest spillway located west of the lock to map geologic structure at depths up to 50 meters (m) using the Advanced Geosciences, Inc. SuperSting R8 resistivity meter. Frequency-domain electromagnetic induction data were acquired along approximately 9 line-kilometers with the Geophex GEM-2 system to map variations in structure up to about 10 m in depth. Self-potential data were acquired at 384 unique stations with Borin Stelth 3 copper-copper sulfate porous-pot electrodes and Keysight U1253B high-impedance multimeter to identify variations in subsurface hydrologic flow. This data release includes raw data for all methods as well as processed data and/or inverted resistivity models. Digital data from all methods are provided, and data fields are defined in respective data dictionaries. Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment.

Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey, in collaboration with the U.S. Army Corps of Engineers, at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Frequency-domain electromagnetic induction data were acquired along approximately 9 line-kilometers with the Geophex GEM-2 system to map variations in structure up to about 10 m in depth. This data release includes the raw and processed frequency-dependent in-phase and quadrature data. They are provided as digital data, and data fields are defined in the data dictionary (https://www.sciencebase.gov/catalog/item/5e101094e4b0b207aa163768). Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment. REFERENCE Abraham, J.D., Deszcz-Pan, M., Fitterman, D.V., and Burton, B.L., 2006, Use of a handheld broadband EM induction system for deriving resistivity depth images, in 19th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Seattle, Washington, April 2–6, 2006, 18 p.

Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey, in collaboration with the U.S. Army Corps of Engineers, at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Frequency-domain electromagnetic induction data were acquired along approximately 9 line-kilometers with the Geophex GEM-2 system to map variations in structure up to about 10 m in depth. This data release includes the raw and processed frequency-dependent in-phase and quadrature data. They are provided as digital data, and data fields are defined in the data dictionary (https://www.sciencebase.gov/catalog/item/5e101094e4b0b207aa163768). Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment. REFERENCE Abraham, J.D., Deszcz-Pan, M., Fitterman, D.V., and Burton, B.L., 2006, Use of a handheld broadband EM induction system for deriving resistivity depth images, in 19th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Seattle, Washington, April 2–6, 2006, 18 p.

Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey (USGS), in collaboration with the U.S. Army Corps of Engineers (USACE), at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Eleven ERT profiles were acquired along the right (west) abutment, and immediately downstream, of the concrete, fixed-crest spillway located west of the lock to map geologic structure at depths up to 50 meters (m) using the Advanced Geosciences, Inc. SuperSting R8 resistivity meter. This data release includes the raw and processed resistivity data as well as inverted resistivity models. All are provided as digital data, and data fields for each file type are defined in the respective data dictionary (https://www.sciencebase.gov/catalog/item/5e101068e4b0b207aa163765). Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment. REFERENCE Abraham, J.D., Deszcz-Pan, M., Fitterman, D.V., and Burton, B.L., 2006, Use of a handheld broadband EM induction system for deriving resistivity depth images, in 19th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Seattle, Washington, April 2–6, 2006, 18 p.

Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey (USGS), in collaboration with the U.S. Army Corps of Engineers (USACE), at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Eleven ERT profiles were acquired along the right (west) abutment, and immediately downstream, of the concrete, fixed-crest spillway located west of the lock to map geologic structure at depths up to 50 meters (m) using the Advanced Geosciences, Inc. SuperSting R8 resistivity meter. This data release includes the raw and processed resistivity data as well as inverted resistivity models. All are provided as digital data, and data fields for each file type are defined in the respective data dictionary (https://www.sciencebase.gov/catalog/item/5e101068e4b0b207aa163765). Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment. REFERENCE Abraham, J.D., Deszcz-Pan, M., Fitterman, D.V., and Burton, B.L., 2006, Use of a handheld broadband EM induction system for deriving resistivity depth images, in 19th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Seattle, Washington, April 2–6, 2006, 18 p.

Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey, in collaboration with the U.S. Army Corps of Engineers, at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Self-potential (SP) data were acquired at 384 unique stations with Borin Stelth 3 copper-copper sulfate porous-pot electrodes and Keysight U1253B high-impedance multimeter to identify variations in subsurface hydrologic flow. This data release includes the raw and processed self-potential data. They are provided as digital data, and data fields are defined in the data dictionary (https://www.sciencebase.gov/catalog/item/5e1011dae4b0b207aa16376c). Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment.

This data release consists of three different types of data: including direct current (DC) resistivity profiles, frequency domain electromagnetic (FDEM) survey data, and global navigation satellite system (GNSS) coordinate data of the geophysical measurement locations. A data dictionary is included along with the data and defines all of the table headings, definitions, and units. Earthen dams are common on lakes and ponds, but characteristics of these structures such as construction history, composition, and integrity are often unknown for older dams. Geophysical surveying techniques provide a non-invasive method of mapping their lithology and structure. In particular, DC resistivity and FDEM methods can, when properly processed, provide the information necessary to construct a lithologic model of an earthen dam without having to trench or core through the shell of the dam itself. In September, 2016 the U.S. Geological Survey (USGS) conducted geophysical surveys at Bob Kidd Lake, an 81-hectare lake, in northwestern Arkansas to help determine the composition of the earthen dam and guide any potential geotechnical investigations. A series of DC resistivity surveys were conducted along, parallel, and perpendicular to the axis of the crest of the dam to identify the soil-bedrock interface and any variations in the composition of the earthen dam. A dense survey using a multi-frequency electromagnetic sensor was used to map the shallow materials comprising the dam at a higher resolution. Resistivity measurements were made by transmitting a known current through two electrodes (transmitter) and measuring the voltage potential across two other electrodes (receiver). The multiple channels on the resistivity meter allow for voltage measurements to be made at 10 receivers simultaneously following a current injection. The configuration of the transmitter relative to the receiver(s) is referred to as an array. For these surveys, a Reciprocal Schlumberger array was used, which positions the transmitting pair of electrodes toward the center of the array and the receiving pairs extending away from the transmitter (Loke, 2000; Zonge and others, 2005). The electrical resistance was calculated by dividing the measured voltage by the applied current. The apparent resistivity was determined by multiplying the electrical resistance by a geometric factor. Apparent resistivity is not the true resistivity, but rather a volume-averaged estimate of the true resistivity distribution, because a homogeneous, isotropic subsurface is assumed. To estimate the true resistivity of the heterogeneous and/or anisotropic subsurface, the apparent resistivity data were processed using an inverse modeling software program. The FDEM method complements the two-dimensional (2-D) DC resistivity method and was used to extend the depth of subsurface characterization obtained with resistivity profiles. The FDEM method uses multiple current frequencies to measure bulk electric conductivity values (the inverse of resistivity values) of the earth at different depths (Lucius and others, 2007). For this project FDEM data were collected with a GEM-2, a broadband, multifrequency, fixed-coil electromagnetic induction unit (Geophex, 2015). In addition to the geophysical surveys a concurrent Global Navigation Satellite System (GNSS) survey was conducted using a Real Time Kinematic system (RTK). All electrode locations on the DC resistivity profiles, all measurement locations in the FDEM survey, as well as a point-cloud survey were collected and are included in the dataset. These data were used to geo-reference the geophysical data and may be used to create a Digital Elevation Model (DEM) of the dam surface.

This data release consists of three different types of data: including direct current (DC) resistivity profiles, frequency domain electromagnetic (FDEM) survey data, and global navigation satellite system (GNSS) coordinate data of the geophysical measurement locations. A data dictionary is included along with the data and defines all of the table headings, definitions, and units. Earthen dams are common on lakes and ponds, but characteristics of these structures such as construction history, composition, and integrity are often unknown for older dams. Geophysical surveying techniques provide a non-invasive method of mapping their lithology and structure. In particular, DC resistivity and FDEM methods can, when properly processed, provide the information necessary to construct a lithologic model of an earthen dam without having to trench or core through the shell of the dam itself. In September, 2016 the U.S. Geological Survey (USGS) conducted geophysical surveys at Bob Kidd Lake, an 81-hectare lake, in northwestern Arkansas to help determine the composition of the earthen dam and guide any potential geotechnical investigations. A series of DC resistivity surveys were conducted along, parallel, and perpendicular to the axis of the crest of the dam to identify the soil-bedrock interface and any variations in the composition of the earthen dam. A dense survey using a multi-frequency electromagnetic sensor was used to map the shallow materials comprising the dam at a higher resolution. Resistivity measurements were made by transmitting a known current through two electrodes (transmitter) and measuring the voltage potential across two other electrodes (receiver). The multiple channels on the resistivity meter allow for voltage measurements to be made at 10 receivers simultaneously following a current injection. The configuration of the transmitter relative to the receiver(s) is referred to as an array. For these surveys, a Reciprocal Schlumberger array was used, which positions the transmitting pair of electrodes toward the center of the array and the receiving pairs extending away from the transmitter (Loke, 2000; Zonge and others, 2005). The electrical resistance was calculated by dividing the measured voltage by the applied current. The apparent resistivity was determined by multiplying the electrical resistance by a geometric factor. Apparent resistivity is not the true resistivity, but rather a volume-averaged estimate of the true resistivity distribution, because a homogeneous, isotropic subsurface is assumed. To estimate the true resistivity of the heterogeneous and/or anisotropic subsurface, the apparent resistivity data were processed using an inverse modeling software program. The FDEM method complements the two-dimensional (2-D) DC resistivity method and was used to extend the depth of subsurface characterization obtained with resistivity profiles. The FDEM method uses multiple current frequencies to measure bulk electric conductivity values (the inverse of resistivity values) of the earth at different depths (Lucius and others, 2007). For this project FDEM data were collected with a GEM-2, a broadband, multifrequency, fixed-coil electromagnetic induction unit (Geophex, 2015). In addition to the geophysical surveys a concurrent Global Navigation Satellite System (GNSS) survey was conducted using a Real Time Kinematic system (RTK). All electrode locations on the DC resistivity profiles, all measurement locations in the FDEM survey, as well as a point-cloud survey were collected and are included in the dataset. These data were used to geo-reference the geophysical data and may be used to create a Digital Elevation Model (DEM) of the dam surface.

This data release consists of three different types of data: including direct current (DC) resistivity profiles, frequency domain electromagnetic (FDEM) survey data, and global navigation satellite system (GNSS) coordinate data of the geophysical measurement locations. A data dictionary is included along with the data and defines all of the table headings, definitions, and units. Earthen dams are common on lakes and ponds, but characteristics of these structures such as construction history, composition, and integrity are often unknown for older dams. Geophysical surveying techniques provide a non-invasive method of mapping their lithology and structure. In particular, DC resistivity and FDEM methods can, when properly processed, provide the information necessary to construct a lithologic model of an earthen dam without having to trench or core through the shell of the dam itself. In September, 2016 the U.S. Geological Survey (USGS) conducted geophysical surveys at Bob Kidd Lake, an 81-hectare lake, in northwestern Arkansas to help determine the composition of the earthen dam and guide any potential geotechnical investigations. A series of DC resistivity surveys were conducted along, parallel, and perpendicular to the axis of the crest of the dam to identify the soil-bedrock interface and any variations in the composition of the earthen dam. A dense survey using a multi-frequency electromagnetic sensor was used to map the shallow materials comprising the dam at a higher resolution. Resistivity measurements were made by transmitting a known current through two electrodes (transmitter) and measuring the voltage potential across two other electrodes (receiver). The multiple channels on the resistivity meter allow for voltage measurements to be made at 10 receivers simultaneously following a current injection. The configuration of the transmitter relative to the receiver(s) is referred to as an array. For these surveys, a Reciprocal Schlumberger array was used, which positions the transmitting pair of electrodes toward the center of the array and the receiving pairs extending away from the transmitter (Loke, 2000; Zonge and others, 2005). The electrical resistance was calculated by dividing the measured voltage by the applied current. The apparent resistivity was determined by multiplying the electrical resistance by a geometric factor. Apparent resistivity is not the true resistivity, but rather a volume-averaged estimate of the true resistivity distribution, because a homogeneous, isotropic subsurface is assumed. To estimate the true resistivity of the heterogeneous and/or anisotropic subsurface, the apparent resistivity data were processed using an inverse modeling software program. The FDEM method complements the two-dimensional (2-D) DC resistivity method and was used to extend the depth of subsurface characterization obtained with resistivity profiles. The FDEM method uses multiple current frequencies to measure bulk electric conductivity values (the inverse of resistivity values) of the earth at different depths (Lucius and others, 2007). For this project FDEM data were collected with a GEM-2, a broadband, multifrequency, fixed-coil electromagnetic induction unit (Geophex, 2015). In addition to the geophysical surveys a concurrent Global Navigation Satellite System (GNSS) survey was conducted using a Real Time Kinematic system (RTK). All electrode locations on the DC resistivity profiles, all measurement locations in the FDEM survey, as well as a point-cloud survey were collected and are included in the dataset. These data were used to geo-reference the geophysical data and may be used to create a Digital Elevation Model (DEM) of the dam surface.

This data release consists of three different types of data: including direct current (DC) resistivity profiles, frequency domain electromagnetic (FDEM) survey data, and global navigation satellite system (GNSS) coordinate data of the geophysical measurement locations. A data dictionary is included along with the data and defines all of the table headings, definitions, and units. Earthen dams are common on lakes and ponds, but characteristics of these structures such as construction history, composition, and integrity are often unknown for older dams. Geophysical surveying techniques provide a non-invasive method of mapping their lithology and structure. In particular, DC resistivity and FDEM methods can, when properly processed, provide the information necessary to construct a lithologic model of an earthen dam without having to trench or core through the shell of the dam itself. In September, 2016 the U.S. Geological Survey (USGS) conducted geophysical surveys at Bob Kidd Lake, an 81-hectare lake, in northwestern Arkansas to help determine the composition of the earthen dam and guide any potential geotechnical investigations. A series of DC resistivity surveys were conducted along, parallel, and perpendicular to the axis of the crest of the dam to identify the soil-bedrock interface and any variations in the composition of the earthen dam. A dense survey using a multi-frequency electromagnetic sensor was used to map the shallow materials comprising the dam at a higher resolution. Resistivity measurements were made by transmitting a known current through two electrodes (transmitter) and measuring the voltage potential across two other electrodes (receiver). The multiple channels on the resistivity meter allow for voltage measurements to be made at 10 receivers simultaneously following a current injection. The configuration of the transmitter relative to the receiver(s) is referred to as an array. For these surveys, a Reciprocal Schlumberger array was used, which positions the transmitting pair of electrodes toward the center of the array and the receiving pairs extending away from the transmitter (Loke, 2000; Zonge and others, 2005). The electrical resistance was calculated by dividing the measured voltage by the applied current. The apparent resistivity was determined by multiplying the electrical resistance by a geometric factor. Apparent resistivity is not the true resistivity, but rather a volume-averaged estimate of the true resistivity distribution, because a homogeneous, isotropic subsurface is assumed. To estimate the true resistivity of the heterogeneous and/or anisotropic subsurface, the apparent resistivity data were processed using an inverse modeling software program. The FDEM method complements the two-dimensional (2-D) DC resistivity method and was used to extend the depth of subsurface characterization obtained with resistivity profiles. The FDEM method uses multiple current frequencies to measure bulk electric conductivity values (the inverse of resistivity values) of the earth at different depths (Lucius and others, 2007). For this project FDEM data were collected with a GEM-2, a broadband, multifrequency, fixed-coil electromagnetic induction unit (Geophex, 2015). In addition to the geophysical surveys a concurrent Global Navigation Satellite System (GNSS) survey was conducted using a Real Time Kinematic system (RTK). All electrode locations on the DC resistivity profiles, all measurement locations in the FDEM survey, as well as a point-cloud survey were collected and are included in the dataset. These data were used to geo-reference the geophysical data and may be used to create a Digital Elevation Model (DEM) of the dam surface.