Waterborne resistivity surveys for streams in the Mississippi Alluvial Plain, 2017

This data release has three components for each of the eight stream lengths: 1) a geospatial dataset of the processed data; 2) tabular data of the processed waterborne resistivity profiling data and associated water-quality data; 3) tabular data of the raw waterborne resistivity data and associated water-quality data. In fresh water aquifers, the geoelectric resistivity of earth materials commonly has a positive correlation with hydraulic conductivity (Faye and Smith, 1994). Throughout 2017, continuous resistivity profiling data were collected, as a proxy for streambed hydraulic conductivity, along reaches of eight streams in the Mississippi Alluvial Plain of Mississippi, Arkansas, and Missouri. A total of 879 kilometers (km) of continuous resistivity profiles were collected during several field excursions in 2017. Individual lengths of surveyed profiles per river include; 203 km on the Yazoo River, 197 km on the Floodway near Kennett, Missouri, 165 km on the Sunflower River, 97 km on the Black River, 83 km on the Bogue Phalia, 55 km on the Tallahatchie River, 42 km on the St. Francis River, and 37 km on the Yalobusha River. These river reaches were selected to aid in calibration of a regional groundwater model, specifically with regards to surface water-groundwater interaction. Resistivity profiling was done using a ten-channel, direct-current resistivity meter and a floating, multi-electrode cable with 13 electrodes spaced 5 meters (m) apart. Resistivity measurements are made by transmitting a known current through two electrodes (transmitter) and measuring the voltage potential across two other electrodes (receiver). The multiple channels on the resistivity meter allows for voltage measurements to be made at 10 receivers simultaneously following a current injection. The configuration of the transmitter relative to the receiver(s) is referred to as an array. For these surveys, a reciprocal Schlumberger array was used, which positions the transmitting pair of electrodes toward the center of the array and the receiving pairs radiating away from the transmitter. The electrical resistance is calculated by dividing the measured voltage by the applied current. The apparent resistivity is determined by multiplying the electrical resistance by a geometric factor. Apparent resistivity is not the true resistivity because a homogeneous, isotropic subsurface is assumed. To estimate the true resistivity or the resistivity structure where the subsurface is heterogeneous and/or anisotropic, the apparent resistivity data were processed using an inverse modeling software program. Since these data have not been modeled they should only be used qualitatively. The resistivity meter used an external global positioning system (GPS) and echosounder to determine the spatial location of the array and the thickness of the water column. The resistivity of the water in the river was continuously measured every 30 seconds using a field conductivity meter which included a GPS location for each measurement. Data collected within each river include: Latitude, longitude, altitude of the water surface, water depth, water resistivity, injected current, voltage, resistance, apparent resistivity, and electrode location (referenced to the position of the GPS). Faye, R.E., and Smith, W.G., 1994, Relations of borehole resistivity to the horizontal hydraulic conductivity and dissolved-solids concentration in water of clastic coastal plain aquifers in the southeastern United States., U.S. Geological Survey Water Supply Paper 2414, 33 p.