In September 2018, approximately 13 miles of continuous seismic profiling (CSP) surveys were collected on the Des Moines River and Beaver Creek in Des Moines, 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. 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. Data were collected concurrently with CRP methods. Both methods used the same .gps files for georeferencing. Starting and ending coordinates for each line are specified in the file "readme_CSP.txt". This data release contains the raw instrument files for each survey line converted to open-source files (.SGY), a comma separated values notes file (CSP_Archive_Notes_DesMoinesIA.csv), and a text file (readme_CSP.txt) file that explains data files and contains the processing references. Field notes taken at the time of data collection are not included in this data release but are available upon request.

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 Des Moines River, Beaver Creek, and in the Des Moines River floodplain in Des Moines, Iowa to support the hydrogeologic characterization of the alluvial aquifer associated with the river. The aquifer consists of sands and gravels underlain by weathered shale bedrock. Groundwater from the aquifer along with surface water sources are used for municipal drinking water for the City of Des Moines and surrounding communities. The raw data provided in this data release are minimally processed to filter out erroneous measurements. Data provided in this data release includes continuous resistivity profiling (CRP) and continuous seismic profiling (CSP) that were collected concurrently, electrical resistivity tomography (ERT) profiles, and horizontal-to-vertical spectral ratio (HVSR) passive seismic measurements. The CRP and ERT measure the electrical properties of the subsurface, which can be related to stratigraphic layers. The CRP, ERT, CSP, and HVSR can be used to estimate depth to bedrock. Collectively, the suite of methods can help characterize the subsurface by mapping the extent of the sand and gravel aquifer and bedrock topography.

A suite of geophysical methods was used along the Des Moines River, Beaver Creek, and in the Des Moines River floodplain in Des Moines, Iowa to support the hydrogeologic characterization of the alluvial aquifer associated with the river. The aquifer consists of sands and gravels underlain by weathered shale bedrock. Groundwater from the aquifer along with surface water sources are used for municipal drinking water for the City of Des Moines and surrounding communities. The raw data provided in this data release are minimally processed to filter out erroneous measurements. Data provided in this data release includes continuous resistivity profiling (CRP) and continuous seismic profiling (CSP) that were collected concurrently, electrical resistivity tomography (ERT) profiles, and horizontal-to-vertical spectral ratio (HVSR) passive seismic measurements. The CRP and ERT measure the electrical properties of the subsurface, which can be related to stratigraphic layers. The CRP, ERT, CSP, and HVSR can be used to estimate depth to bedrock. Collectively, the suite of methods can help characterize the subsurface by mapping the extent of the sand and gravel aquifer and bedrock topography.

In summer 2018, a total of 43 passive seismic surveys were conducted in the Des Moines River floodplain. The horizontal-to-vertical spectral ratio (HVSR) method is a passive seismic technique that uses a three-component seismometer to measure the vertical and horizontal components of ambient seismic noise. A resonance frequency (f0) is induced in the unconsolidated deposits when there is a substantial contrast (greater than 2:1) in shear-wave acoustic impedance between the overburden and the bedrock. The f0 is determined from the analysis of the spectral ratio of the horizontal and vertical components of the seismic data. The thickness of the overburden can be related to the f0. In general, lower f0 relates to thicker sediments, and higher f0 relates to relatively thinner overburden. This data release contains a text file (Readme_HVSR.txt) that explains data files and processing references, 6 .zip folders 5 related to survey line(s) on a given date and one for individual measurements not related to survey lines with each zip folder containing measurement site folders and original data files and resultant measurement report (.trc, .saf or .dat, and .doc) , a notes file for archiving surface-geophysical data (HVSR_Archive_Notes_DesMoinesIA.csv), and another comma-separated values file (HVSR_Index_DesMoinesIA.csv) that can be used to help navigate the data files. Field notes taken at the time of data collection are not included in this data release but are available upon request.

In summer 2018, a total of 43 passive seismic surveys were conducted in the Des Moines River floodplain. The horizontal-to-vertical spectral ratio (HVSR) method is a passive seismic technique that uses a three-component seismometer to measure the vertical and horizontal components of ambient seismic noise. A resonance frequency (f0) is induced in the unconsolidated deposits when there is a substantial contrast (greater than 2:1) in shear-wave acoustic impedance between the overburden and the bedrock. The f0 is determined from the analysis of the spectral ratio of the horizontal and vertical components of the seismic data. The thickness of the overburden can be related to the f0. In general, lower f0 relates to thicker sediments, and higher f0 relates to relatively thinner overburden. This data release contains a text file (Readme_HVSR.txt) that explains data files and processing references, 6 .zip folders 5 related to survey line(s) on a given date and one for individual measurements not related to survey lines with each zip folder containing measurement site folders and original data files and resultant measurement report (.trc, .saf or .dat, and .doc) , a notes file for archiving surface-geophysical data (HVSR_Archive_Notes_DesMoinesIA.csv), and another comma-separated values file (HVSR_Index_DesMoinesIA.csv) that can be used to help navigate the data files. Field notes taken at the time of data collection are not included in this data release but are available upon request.

In May 2017 and July 2018, continuous seismic profiling (CSP) surveys were collected in Goose Pond at the Callahan Mine site. The chirp frequency CSP tool was used in the deep water. A tuned transducer (dual-echo sounder) was used in the shallow water, and the data are served separately but within this data release (See CSP-DSO). CSP methods use an acoustic sound source that travels through the water column, reflects off the bottom and sub-bottom layers and is received at the transducer. Using 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 can be achieved, CSP can be used to delineate the depth and topography of the subbottom layers and/or the bedrock surface. In a limited number of places, the bedrock surface was observed in the CSP record, creating a discontinuous and sporadic image of the bedrock surface. Some profiles exhibited multiple stratigraphic layers. The interpretation of subsurface in the seismic record generally matched depths to till or bedrock observed in core data (when/where the signal penetrated the subbottom). However, in many places, CSP surveys were adversely affected by a highly reflective water bottom, which caused strong multiples in the seismic record and limited to no depth of penetration. These multiples are attributed to the signal reflecting off of an acoustically hard layer caused by entrapped gas (methane) in the sediments, compacted sediments, or bedrock. The returning signal reflects off of the water/air interface, returns to the acoustic hard layer and reverberates between these two interfaces.