Electrical Resistivity Tomography Data

Dates

Publication Date: 2020-03-25
Start Date: 2018-08-20
End Date: 2018-09-05

Citation

Ely, C.P., Groover, K.D., Christensen, A.H., and Kohel, C.A., 2020, Electrical Resistivity Tomography in the Anza-Terwilliger Valley, Riverside County, California 2018: U.S. Geological Survey data release, https://doi.org/10.5066/P9LCEHD7.

Summary

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments [...]

Summary

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

Electrical resistivity tomography data were collected using an 8-channel SuperSting R8 resistivity/induced polarization meter (Advanced Geosciences, Inc., Austin, Tex., U.S.A.) with a maximum of 56 electrodes. 18-inch stainless steel stakes, with approximately 0.5-inch diameters were buried to a depth of approximately 12 inches. Stakes were positioned every 5 m along transect 1 (L1NS0821) and every 7 m along transect 2 (L2IS0820). For each profile, a linear array of electrodes spaced at regular intervals was placed in the ground, and many different combinations of current and potential electrode pairs were used to take resistance measurements. Information about lateral resistivity variability in the subsurface was gained as the measuring electrodes were translated across the array, whereas information about greater depths is obtained by increasing the separation between the electrode pairs. The 8-channel resistivity meter used a command file to acquire measurements from predetermined current electrode and potential electrode configurations. Measurements were made for a period of 1.2 seconds, equivalent to 0.83 Hertz (Hz), during which the polarity of the current electrodes was reversed (number of cycles set to 2) in order to minimize electrode polarization effects. The resistivity meter was powered by two 12- volt batteries and capable of injecting up to 2,000 milliamperes (mA) of current into the ground. An inverse Schlumberger array geometry was used in this study for its measurement efficiency and good contrast between lateral and vertical resolution (Minsley and others, 2010).

Contacts

Point of Contact :: Christopher P Ely, U.S. Geological Survey, SOUTHWEST REGION
Originator :: Ely, C.P., Groover, K.D., Christensen, A. H., Kohel, C. A.
Metadata Contact :: Christopher P Ely, U.S. Geological Survey, SOUTHWEST REGION
Distributor :: U.S. Geological Survey - ScienceBase

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ElectricalResistivityTomographyDataAtAnzaCA_metadata.xml Original FGDC Metadata	View	16.75 KB	application/fgdc+xml
ElectricalResitivityTomography_Data.zip		42.72 KB	application/zip
TerrainFiles.zip		2.06 KB	application/zip

Purpose

Data on this page provide electrical resistivity and terrain data collected in August 2018.

Electrical Resistivity Tomography Data

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