GPS Determination of Groundwater Withdrawal Subsidence

Abstract

Global Positioning System (GPS) surveys were undertaken in 1984 and repeated in 1985 along level lines in southeastern Arizona where subsidence induced by groundwater withdrawal was occurring. The objective of these surveys was to determine the accuracy with which subsidence could be determined both from comparison of repeat GPS measurements and from comparison of GPS measurements with existing leveling. Repeatability of GPS determinations of differential ellipsoid height during a single survey was at the 1–2‐cm level. Differencing results of repeat GPS surveys performed 15 months apart gave subsidence values that agreed at the 2–4‐cm level with those obtained from leveling. Also, it was found that, after using gravimetric geoid heights to convert GPS‐derived ellipsoid heights to orthometric heights, agreement between the GPS/geoid orthofnetric heights and leveling orthometric heights was in the 3–7‐cm range. These results show that repeated GPS measurements can be used to monitor future subsidence in southeastern Arizona and that comparison of GPS results with existing leveling can give valuable information on past subsidence in the area.