Surface and water-borne geophysical methods can provide information for the characterization of the subsurface structure of the earth for aquifer investigations. Floating and towed transient electromagnetic (FloaTEM and tTEM) surveys provide resistivity soundings of the subsurface, which can be related to lithology and hydrogeology. In the TEM method, electrical current is cycled through a wire in a transmitter loop (Tx), which in turn produces a static magnetic field. When the current is abruptly terminated, an instantaneous current is induced in the earth, and it moves downward and outward as the induced current decays with time. The decay is controlled by the resistivity of the earth. A receiver (Rx) pulled behind the Tx loop measures the secondary magnetic field as a function of time (dB/dt). Decaying voltage measurements at the receiver are converted to apparent resistivity, which can be inverted to recover the depth-dependent resistivity structure of the earth. FloatTEM surveys were conducted at four locations on the Eel River near Falmouth, Massachusetts,on the Rainbow Reservoir near Windsor, Connecticut, on the Upper Delaware River near Barryville, New York, and on the Tallahatchie River in Shellmound, Mississippi. A tTEM survey was collected adjacent to the Tallahatchie River in Shellmound, Mississippi. The data collected at each site are provided as separate datasets. This data release includes the averaged, culled and inverted TEM data showing resistivity (in ohm-meters) with depth for each of the survey sites.

Electromagnetic (EM) geophysical methods provide information about the bulk electrical conductivity of the subsurface. EM data has been widely used to investigate aquifers and geologic structures. In the following study, the United States Geological Survey conducted a boat-towed, waterborne transient electromagnetic (FloaTEM) survey to examine conductivity within the subsurface of the main Delaware River channel and the Leipsic River. The Leipsic River flows through an estuary into the Delaware Bay. Subsurface conductive zones, when viewed in the context of the regional conceptual model and other data, can help determine the likely groundwater location of the freshwater/saltwater interface within the Delaware River, as well as key hydrogeological layers such as the Lower Potomac-Raritan-Magothy Aquifer within the Northern Atlantic Coastal Plain Aquifer System, and their connectivity with the riverbed. Permeable aquifers could provide a hydraulic connection between surface water and inland groundwater. Therefore, changes to river water salinity could have an accelerated impact on water pumped from wells inland that are connected via these permeable aquifers. The FloaTEM system transmits a primary electrical current through a transmitter loop (Tx) wire. This creates a static primary magnetic field. Then, the current in the TX loop is subsequently turned off, resulting in secondary electrical currents being induced in the earth. These induced electrical currents decay with time, and this rate of decay in the secondary electrical field is a function of the bulk conductivity of the subsurface material. As the secondary electrical field decays, a secondary magnetic field is induced and measured at a receiver (Rx) loop towed behind the Tx loop. The Rx loop measures the decay of the secondary magnetic field as a function of time (dB/dt). Measured dB/dt decay curves can be inverted to recover the depth-dependent resistivity structure of the earth. FloaTEM surveys were conducted downstream from Wilmington, DE on 8/26/2020 and 8/27/2020. Data from 8/26/2020 were collected around the Augustine Wildlife Area boat ramp, and data on 8/27/2020 were collected near the Collins Landing boat ramp. FloaTEM surveys were again conducted downstream from Wilmington, DE on 8/25/2021 and 8/26/2021. Data from 8/25/2021 were collected upstream of the 2020 surveys around the Pennsville public boat ramp, while data on 8/26/2021 were collected near the Collins Landing boat ramp and covered a similar area as the 2020 data. Data collected in 2021 also included a section of the Delaware River further upstream near Philadelphia PA, collected on 8/24/2021 and made use of the Fort Mifflin boat ramp. A final back and forth profile in the Leipsic River within the Bombay Hook National Wildlife Refuge (estuary) was gathered on 8/27/21, and used the Port Mahon Boat Launch as the starting/ending point. Surface water specific conductance data were also collected during portions of the surveys.

Floating transient electromagnetic (FloaTEM) data were acquired on the Eel River during November 2018. During the survey, approximately 1.6 line-kilometers were collected in the Eel River, Falmouth, Massachusetts study area. Data were collected by members of the U.S. Geological Survey, Hydrogeophysics Branch, and New England Water Science Center. FloaTEM data acquired along the Eel River in Barnstable County, in Massachusetts, were collected to test a new continuous water-borne transient electromagnetic data collection platform, and to characterize the subsurface resistivity structure in support of a U.S. Geological Survey groundwater investigation of the Falmouth, Massachusetts area. FloaTEM data were collected using an Aarhus University HydroGeophysics Group FloaTEM unit using a transmitter loop (Tx) size, 4 by 2 meter square (m^2), in an offset-loop receiver (Rx) configuration utilizing a receiver coil that is 0.5 by 0.5 m^2 in size (with an effective area of 35 m^2) towed about 7 meters behind the Tx loop. The Tx outputs dual currents of about 3 and 30 amperes (A) for dual-moment transmission. The measurement cycles take approximately 0.5 seconds to complete and are comprised of several hundred individual transients that are averaged into 1D soundings along the profile. This data release includes the averaged, culled, and inverted FloaTEM data along the survey line that were used to produce the final resistivity models. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed.Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-impacted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and comma-delimited ASCII files containing the inversion model results. Model locations are provided as UTM Zone 15 N projection and datum of WGS-84. (4) Files with *WATER-DEPTH_DATA.xyz and *WATER-DEPTH_DATA.csv are space- and comma-delimited ASCII files containing the water-depth data as measured from the bottom of the transducer. Water-depth measurement locations are provided as UTM Zone 15 N, WGS-84. (5) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.

High-resolution multichannel boomer seismic-reflection data were collected by the U.S. Geological Survey and the University of Washington in February of 2017 east of Seattle in Lake Washington, Washington. Data were collected aboard University of Washington’s R/V Clifford A. Barnes during USGS field activity 2017-612-FA using an Applied Acoustics triple plate S-Boom sound source and recorded on a 24 channel Geometrics digital hydrophone streamer. Sub-bottom acoustic penetration spans several hundreds of meters and is variable by location.

Towed transient electromagnetic (tTEM) data were acquired adjacent to the Tallahatchie River during March 2018. During the survey, approximately 35 line-kilometers were collected in the Shellmound, Mississippi study area. Data were collected by members of the U.S. Geological Survey, Hydrogeophysics Branch, and the Aarhus University HydroGeophysics Group. FloaTEM data acquired near the Tallahatchie River in Leflore County, in Mississippi, were collected to characterize the subsurface resistivity structure in support of a U.S. Geological Survey groundwater investigation of the Mississippi Alluvial Plain. tTEM data were collected using an Aarhus University HydroGeophysics Group tTEM unit using a transmitter loop (Tx) size, 4 by 2 meter square (m^2), in an offset-loop receiver (Rx) configuration utilizing a receiver coil that is 0.5 by 0.5 m^2 in size (with an effective area of 35 m^2) towed about 7 meters behind the Tx loop. The Tx loop was towed about 2.8m behind the all-terrain vehicle (ATV) The Tx outputs dual currents of about 3 and 30 amperes (A) for dual-moment transmission. The measurement cycles take approximately 0.5 seconds to complete and are comprised of several hundred individual transients that are averaged into 1D soundings along the profile. This data release includes the averaged, culled, and inverted tTEM data along the survey line that were used to produce the final resistivity models. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-impacted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and comma-delimited ASCII files containing the inversion model results. Model locations are provided as UTM Zone 15 N projection and datum of WGS-84. (4) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.

Hourly maps of surface currents were made using SeaSonde HF systems deployed in northern Oregon and southern Washington on the Columbia River from June 2004 to December 2006. The instruments were operated near 5 MHz, which allowed long-range measurements of radial currents from each station. Where data from different stations overlapped, two-dimensional currents were produced by mapping to a fixed grid. Data quality measures including GDOP (geometric dilution of precision), are also included.

Lagrangian surface currents were measured using drifters equipped with global navigation satellite system (GNSS) receivers. A total of 8 drifter deployments were performed between May 25 and June 8, 2013. For each deployment, drifters were released within the MCR and their positions were recorded until the drifters were recovered. The average duration of the drifter deployments varied between 1.6 h and 17.2 h and the number of drifters released in a deployment ranged between 11 and 84. The initial positions and timing of the release of the drifters relative to the tidal cycle varied throughout the drifter deployments. Digital files containing the drifter data from each deployment are available in NetCDF format.

Single-beam bathymetry, gravity, and magnetic data along with DGPS navigation data was collected as part of field activity L-3-76-WO in Washington to Vancouver Island, British Columbia from 06/11/1976 to 06/20/1976, http://walrus.wr.usgs.gov/infobank/l/l376wo/html/l-3-76-wo.meta.html These data are reformatted from space-delimited ASCII text files located in the Coastal and Marine Geology Program (CMGP) InfoBank field activity catalog at http://walrus.wr.usgs.gov/infobank/l/l376wo/html/l-3-76-wo.bath.html, http://walrus.wr.usgs.gov/infobank/l/l376wo/html/l-3-76-wo.grav.html, and http://walrus.wr.usgs.gov/infobank/l/l376wo/html/l-3-76-wo.mag.html into MGD77T format provided by the NOAA's National Geophysical Data Center(NGDC). The MGD77T format includes a header (documentation) file (.h77t) and a data file (.m77t). More information regarding this format can be found in the publication listed in the Cross_reference section of this metadata file.