In April 2015, approximately 19 miles of continuous resistivity profiling (CRP) surveys were collected on the Cedar River in Cedar Rapids, Iowa. The CRP method was used to characterize the resistivity of the water column and subbottom materials. Five CRP profiles were collected concurrently with the continuous seismic methods. For this investigation, 11 electrodes spaced 10 m apart and mounted in a streamer were towed behind the boat and data were collected using the dipole-dipole array type. The first two electrodes, closest to the boat, were used to inject current into the water and subbottom materials, and eight electrical potential measurements were made using the remaining nine electrodes. With this system, a complete suite of measurements is collected every 2.8 seconds. Because the boat is moving at a slow rate of speed, a complete measurement is taken while the boat has moved about 3-5 m. In general, voltage measurements taken with larger electrode spacings extend deeper into the subsurface. The exact depth and resistivity are determined through a process of inversion. The raw CRP data are shared in this data release.

Electrical resistivity tomography (ERT) surveys were collected in April 2015 to support hydrogeologic characterization of the alluvial aquifer and to assess the suitability of larger-scale airborne geophysics. For this investigation, five sites were surveyed with ERT methods. At each site three surveys were collected, including: dipole-dipole, Schlumberger, and inverse Schlumberger configurations. For each survey a total of 56 electrodes spaced 5-meters (m) apart were used. During the ERT measurement, current is injected through two current electrodes and voltage is measured sequentially across multiple pairs of potential electrodes, which is used to determine the apparent resistivity of the subsurface. Results were combined into a merged dataset. ERT surveys can be inverted to obtain resistivity profiles that can be interpreted for subsurface layers. This data release provides only the raw ERT data.

Electrical resistivity tomography (ERT) surveys were collected in April 2015 to support hydrogeologic characterization of the alluvial aquifer and to assess the suitability of larger-scale airborne geophysics. For this investigation, five sites were surveyed with ERT methods. At each site three surveys were collected, including: dipole-dipole, Schlumberger, and inverse Schlumberger configurations. For each survey a total of 56 electrodes spaced 5-meters (m) apart were used. During the ERT measurement, current is injected through two current electrodes and voltage is measured sequentially across multiple pairs of potential electrodes, which is used to determine the apparent resistivity of the subsurface. Results were combined into a merged dataset. ERT surveys can be inverted to obtain resistivity profiles that can be interpreted for subsurface layers. This data release provides only the raw ERT data.

In April 2015, approximately 22 miles of continuous seismic profiling (CSP) surveys were collected on the Cedar River in Iowa. The swept frequency (chirp) CSP subbottom profiler was used to characterize the unconsolidated materials above the bedrock. The CSP subbottom profiler is an acoustic sound source that travels through the water column and reflects off the bottom and sub-bottom layers and is received at the transducer. (see Collecting resistivity and seismic data Cedar River IA 2.JPG. Applying a water column velocity, the two-way travel time can be converted to distance. CSP methods provide the depth to water bottom, and when sufficient signal penetration is achieved, CSP can be used to delineate the depth of subbottom layers and topography of the bedrock surface.

In April 2015, approximately 22 miles of continuous seismic profiling (CSP) surveys were collected on the Cedar River in Iowa. The swept frequency (chirp) CSP subbottom profiler was used to characterize the unconsolidated materials above the bedrock. The CSP subbottom profiler is an acoustic sound source that travels through the water column and reflects off the bottom and sub-bottom layers and is received at the transducer. (see Collecting resistivity and seismic data Cedar River IA 2.JPG. Applying a water column velocity, the two-way travel time can be converted to distance. CSP methods provide the depth to water bottom, and when sufficient signal penetration is achieved, CSP can be used to delineate the depth of subbottom layers and topography of the bedrock surface.

In September 2018, approximately 13 miles of continuous resistivity profiling (CRP) surveys were collected on the Des Moines River and Beaver Creek in Des Moines, Iowa. The CRP method was used to characterize the resistivity of the water column and the underlying geologic materials. Three CRP line profiles were collected during one day of field work and were collected concurrently with continuous seismic profiling (CSP) methods. For this investigation, 11 electrodes spaced 10 m apart and mounted in a streamer were towed behind a manned boat and data were collected using the dipole-dipole array type. The first two electrodes, closest to the boat were used to inject current into the water and river bottom, and eight electrical potential measurements were made using the remaining nine electrodes. With this system, a complete suite of measurements is collected every 2.8 seconds. Considering the boats slow rate of speed a complete measurement is taken about every 3-5 meters of boat movement. In general, voltage measurements taken with larger electrode spacings extend deeper into the subsurface. The exact depth and resistivity are determined through a process of inversion. Data were collected concurrently with CSP methods. Both methods used the same .gps files for georeferencing. Starting and ending coordinates for each line are specified in readme_CRP. This data release contains a notes file for archiving surface-geophysical data (CRP_Archive_Notes_DesMoinesIA.csv), a text file (Readme_CRP.txt) explaining the data files and processing references, and a color scale file (CRP_colorscale.png) relating colors to resistivity values. This data release also contains compressed zip folders (one for each survey line) that contain the original instrument files (windows command script, .crs, .stg, and .gps), two .xyz files (raw data culled and inverted data), and the inverted model output image for each survey line (.wmf). Field notes taken at the time of data collection are not included in this data release but are available upon request.

In September 2018, approximately 13 miles of continuous resistivity profiling (CRP) surveys were collected on the Des Moines River and Beaver Creek in Des Moines, Iowa. The CRP method was used to characterize the resistivity of the water column and the underlying geologic materials. Three CRP line profiles were collected during one day of field work and were collected concurrently with continuous seismic profiling (CSP) methods. For this investigation, 11 electrodes spaced 10 m apart and mounted in a streamer were towed behind a manned boat and data were collected using the dipole-dipole array type. The first two electrodes, closest to the boat were used to inject current into the water and river bottom, and eight electrical potential measurements were made using the remaining nine electrodes. With this system, a complete suite of measurements is collected every 2.8 seconds. Considering the boats slow rate of speed a complete measurement is taken about every 3-5 meters of boat movement. In general, voltage measurements taken with larger electrode spacings extend deeper into the subsurface. The exact depth and resistivity are determined through a process of inversion. Data were collected concurrently with CSP methods. Both methods used the same .gps files for georeferencing. Starting and ending coordinates for each line are specified in readme_CRP. This data release contains a notes file for archiving surface-geophysical data (CRP_Archive_Notes_DesMoinesIA.csv), a text file (Readme_CRP.txt) explaining the data files and processing references, and a color scale file (CRP_colorscale.png) relating colors to resistivity values. This data release also contains compressed zip folders (one for each survey line) that contain the original instrument files (windows command script, .crs, .stg, and .gps), two .xyz files (raw data culled and inverted data), and the inverted model output image for each survey line (.wmf). Field notes taken at the time of data collection are not included in this data release but are available upon request.

A suite of geophysical methods was used along the Cedar River in Cedar Rapids, Iowa to support the hydrogeologic characterization of the alluvial aquifer associated with the river and to assess the area for suitability for larger-scale airborne geophysics. The aquifer is comprised of sand and gravel, interbedded with finer sediments, and underlain by carbonate-dominated bedrock. The aquifer is the principal source of municipal drinking water for the City of Cedar Rapids. The raw data files provided here include waterborne continuous resistivity profiling (CRP) and continuous seismic profiling (CSP) data, which were collected concurrently in April 2015, electrical resistivity tomography (ERT) profiles from April 2015, horizontal to vertical spectral ratio (HVSR) seismic from April 2015 and several borehole geophysical logs including nuclear magnetic resonance (NMR), gamma, and electromagnetic induction (EMI) from nine wells, collected in June, 2017. The CRP, ERT, and borehole logs measure the electrical properties of the subsurface, which can be related to stratigraphic layers. The HVSR, CSP, CRP and some of the borehole logs characterize the depth to bedrock. Collectively the suite of methods can help characterize the subsurface and map the extent of the sand and gravel aquifer. In addition, these geophysical measurements can be used to plan and to ground truth air-borne electromagnetic surveys.

A suite of geophysical methods was used along the Cedar River in Cedar Rapids, Iowa to support the hydrogeologic characterization of the alluvial aquifer associated with the river and to assess the area for suitability for larger-scale airborne geophysics. The aquifer is comprised of sand and gravel, interbedded with finer sediments, and underlain by carbonate-dominated bedrock. The aquifer is the principal source of municipal drinking water for the City of Cedar Rapids. The raw data files provided here include waterborne continuous resistivity profiling (CRP) and continuous seismic profiling (CSP) data, which were collected concurrently in April 2015, electrical resistivity tomography (ERT) profiles from April 2015, horizontal to vertical spectral ratio (HVSR) seismic from April 2015 and several borehole geophysical logs including nuclear magnetic resonance (NMR), gamma, and electromagnetic induction (EMI) from nine wells, collected in June, 2017. The CRP, ERT, and borehole logs measure the electrical properties of the subsurface, which can be related to stratigraphic layers. The HVSR, CSP, CRP and some of the borehole logs characterize the depth to bedrock. Collectively the suite of methods can help characterize the subsurface and map the extent of the sand and gravel aquifer. In addition, these geophysical measurements can be used to plan and to ground truth air-borne electromagnetic surveys.

Airborne electromagnetic (AEM) and magnetic survey data were collected by CGG Canada Services Ltd. in collaboration with the US Geological Survey (USGS) for the City of Cedar Rapids in a 53-square-kilometer area of the Cedar River Basin to the west of Cedar Rapids, Iowa. The survey was flown between May 4 and May 5, 2017 along 347 line kilometers. Electromagnetic data were acquired using RESOLVE frequency-domain helicopter-borne electromagnetic system. Magnetic data were collected with 1-Scintres Cesium Vapour (CS-3) magnetometer. Sensor elevation above ground was measured with Optech G-150 laser. The nominal elevation of the sensor was 30 m. This data release includes processed AEM and magnetic data and inverted resistivity depth sections.