14.86 km Profiles of the Electric and Self-potential Fields Measured in the Lower Guadalupe River Channel, Texas Interior Gulf Coastal Plain, September 2016

This data release consists of three geophysical data sets measured in the lower Guadalupe River channel, south-central Texas, and one supplementary geophysical data set measured in a laboratory. The lower Guadalupe River is incised into the outcrop of the Carrizo-Wilcox aquifer in south-central Texas. The river and the aquifer are hydraulically connected across the outcrop, although the connectivity is obscured by alluvium and surface-water and groundwater exchange dynamics are currently poorly understood. The data sets were therefore produced to investigate surface-water and groundwater exchange dynamics between the lower Guadalupe River and the Carrizo-Wilcox aquifer, and consist of (1) a 14.86 kilometer (km) profile of waterborne gradient self-potential (SP) data; (2) a 20 km profile of waterborne resistivity tomography data; and (3) discrete profiles of water temperature and electric conductivity in the channel, acquired with a handheld conductivity probe. The shorter gradient SP profile overlaps the longer waterborne resistivity tomography profile. Gradient SP profile data were measured with floating 2 meter dipole by logging potential differences between the dipole electrodes at a frequency of one sample per second while the dipole floated in a downstream direction in the channel. Resistivity tomography profile data were measured using the IRIS Syscal Pro direct-current resistivity meter connected to an 80 m long floating, multi-electrode cable containing 13 stainless-steel electrodes. The resistivity meter incorporated an echo sounder to determine the depth of the water column along the resistivity profile, and the data along each respective profile were geospatially located with a differential global positioning system. The laboratory data set contains approximately 4.5 hours of logged measurements of the potential difference between the electrodes of the dipole used for gradient SP profiling in the lower Guadalupe River. This data set was used to correct the gradient SP field measurements for their transient drift characteristics based upon the drift-characteristics that were observed in the laboratory. The companion journal paper to this data release explores the utility of these water-borne geoelectric methods in delineating gaining and losing channel reaches, and demonstrates that geoelectric signals in the form of total electric field strength can be logged with an electric dipole and decomposed into component SP signals and interpreted with respect to regional and local groundwater flow patterns, net gaining and losing segments of a surface channel, and localized gains and losses distributed throughout a channel that are attributable to bed-form induced hyporheic exchange flows.