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DC Resitivity Methodology Direct current (DC) resistivity transects were surveyed using an IRIS Syscal Pro Switch 96 instrument (IRIS Instruments, Inc., Orléans, France). Steel electrodes were hammered into the ground at a fixed distance along the profile. These were connected to the instrument using copper wires and junction boxes. The number of electrodes on each profile and their spacing is shown below: Line 1: 180 electrodes, 5 meter spacing Line 2: 48 electrodes, 2 meter spacing Line 3: 48 electrodes, 2 meter spacing Line 4: 24 electrodes, 2 meter spacing Line 5: 36 electrodes, 2 meter spacing On Line 1, the roll-along method was used to extend the line to its full extent. In this method, 48 electrodes...
Categories: Data
Lake Poinsett is a 260-hectare (640 acres) lake located on Crowley’s Ridge in northeastern Arkansas, approximately 6 km southeast of Harrisburg, Arkansas within Poinsett County. The lake was built for recreation by the Arkansas Highway Department in 1960 by constructing a roughly 800-meter dam across the southern boundary of the Distress Creek watershed. The dam is currently operated by the Arkansas Game and Fish Commission (AGFC). AGFC and Arkansas Natural Resources Commission (ANRC) plan to drain the lake to allow access for a series of bank stabilization and dam safety improvements. Because none of the original blueprints exist, AGFC asked the U.S. Geological Survey (USGS) to conduct a series of differential...
Categories: Data;
Tags: Arkansas,
Crowley's Ridge,
Electrical Resistivity,
Frequency Domain Electromagnetics,
GNSS Survey,
FDEM Methodology For this project frequency domain electromagnetic (FDEM) data were collected with a GEM-2, a broadband, multifrequency, fixed-coil electromagnetic induction unit (Geophex, 2015). Both in-phase and quadrature data were collected on 15 channels from a frequency of 810 Hz to 66,090 Hz. This system was carried along profiles that followed the axis of the dam and along tie lines that were perpendicular to the axis of the dam. Each data point was located using a backpack mounted GPS. To correct the drift of the instrument, a base station was established on the east side of the dam. Each survey started and ended with an occupation of the base station. These occupations occur as even line numbers...
Categories: Data
GNSS Method A benchmark monument was set at each end of the earthen dam in accordance with (U.S. Army Corps of Engineers, 2002). A level II survey (Rydlund & Densmore 2012) was conducted on each monument to establish control. Two 4-hour observations were conducted with a staggered approach for each monument, with one 4-hour session in the morning of the first day and one 4-hour session in the afternoon of the second day. Once elevational control was established, a Real Time Kinematic (RTK) system was set up with base on the monument that had the best observations. Using this system, a point cloud survey was conducted along the top and face of the dam using both a monopod and an All-Terrain Vehicle. A Global...
Categories: Data
FDEM Processing The frequency domain electromagnetic (FDEM) data were downloaded from the GEM-2 instrument and aggregated into a single data file. The data were manually despiked and smoothed to remove negative values and the effects of metallic objects. A drift correction was applied by finding the average in-phase and average quadrature values for each frequency transmitted each time the base station was occupied. This average value was then used to calculate a linear trend of the data in time and the linear trend was subtracted from the data set. After the data were drift corrected, the data was leveled by calculating the arithmetic mean of the survey data subtracting that value from the dataset to level...
Categories: Data
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,...
Categories: Data;
Tags: Arkansas,
Bob Kidd Lake,
Direct current resistivity,
Earthen dam,
Earthen structure,
FDEM Methodology For this project frequency domain electromagnetic (FDEM) data were collected with a GEM-2, a broadband, multifrequency, fixed-coil electromagnetic induction unit (Geophex, 2015). Both in-phase and quadrature data were collected on 15 channels from a frequency of 810 Hz to 66,090 Hz. This system was carried along profiles that followed the axis of the dam and along tie lines that were perpendicular to the axis of the dam. Each data point was located using a backpack mounted GPS. To correct the drift of the instrument, a base station was established on the east side of the dam. Each survey started and ended with an occupation of the base station. These occupations occur as even line numbers...
Categories: Data
DC Resitivity Methodology Direct current (DC) resistivity transects were surveyed using an IRIS Syscal Pro Switch 96 instrument (IRIS Instruments, Inc., Orléans, France). Steel electrodes were hammered into the ground at a fixed distance along the profile. These were connected to the instrument using copper wires and junction boxes. The number of electrodes on each profile and their spacing is shown below: Line 1: 180 electrodes, 5 meter spacing Line 2: 48 electrodes, 2 meter spacing Line 3: 48 electrodes, 2 meter spacing Line 4: 24 electrodes, 2 meter spacing Line 5: 36 electrodes, 2 meter spacing On Line 1, the roll-along method was used to extend the line to its full extent. In this method, 48 electrodes...
Categories: Data
DC Resistivity Processing Data were imported into the Workbench Electrical Resistivity Tomography Module (Aarhus Geophysical, Inc.; version 5.5.0.0) using the “Syscal” data import options. The data were then manually despiked and any negative resistivity values were removed. The data were subsequently inverted using “Aarhus 2D” inversion option. The “Smooth” Inversion setting was chosen with model converging to the L2 norm. The number of layers of the starting model was set to 20. The vertical model discretization was set to the default for each given combination of line length and electrode spacing. The starting value was set to “Auto”. The lateral and vertical constraints were set to the “Medium” settings....
Categories: Data
FDEM Processing The frequency domain electromagnetic (FDEM) data were downloaded from the GEM-2 instrument and aggregated into a single data file. The data were manually despiked and smoothed to remove negative values and the effects of metallic objects. A drift correction was applied by finding the average in-phase and average quadrature values for each frequency transmitted each time the base station was occupied. This average value was then used to calculate a linear trend of the data in time and the linear trend was subtracted from the data set. After the data were drift corrected, the data was leveled by calculating the arithmetic mean of the survey data subtracting that value from the dataset to level...
Categories: Data
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