Techniques and Methods report from the USGS Arizona Water Science Center: Procedures for Field Data Collection, Processing, Quality Assurance and Quality Control, and Archiving of Relative- and Absolute-Gravity Surveys
This particular report has additional meaning as an Arizona product. The use of microgravity for hydrologic purposes was pioneered as a collaboration between the University of Arizona and USGS Arizona Water Science Center. The original publication was a 1971 dissertation by Errol Montgomery, and in the time since that dissertation was completed, the technique has been continually refined, improved, and operationalized into a unique approach to analysis of groundwater and aquifers. Until now, the method has not been published as a USGS Techniques and Methods report. Doing so helps establish the method as a standard approach to hydrologic data collection. The report also presents two new software packages for data collection and analysis—a Windows GUI and an Excel spreadsheet.
What are gravity measurements good for? Changes in mass underlying a point on the Earth result in tiny but measurable changes in the pull of gravity. Aquifer storage changes are a change in mass, so measuring microgravity repeatedly through time allows for direct monitoring of changes in subsurface water storage. The usual approach to groundwater monitoring, measuring water levels in wells, provides an indication of change in stored groundwater, but because aquifer storage properties are widely variable, water level monitoring does not directly indicate the amount of water-storage change. Gravity monitoring solves that problem!
Should you have any questions or comments, feel free to reach out to me or to the lead author, Jeff Kennedy (jkennedy@usgs.gov).
The full citation for the report is:
Kennedy, J.R., Pool, D.R., and Carruth, R.L., 2021, Procedures for field data collection, processing, quality assurance and quality control, and archiving of relative- and absolute-gravity surveys: U.S. Geological Survey Techniques and Methods, book 2, chap. D4, 50 p., https://doi.org/10.3133/tm2D4.