By Michelle Sneed, Marti E. Ikehara, Sylvia V. Stork, Falk Amelung, and Devin L. Galloway
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 03-4015
Sacramento, California 2003
Prepared in cooperation with the Mojave Water Agency
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A Global Positioning System (GPS) survey of a geodetic network was used to determine the location, extent, and magnitude of vertical land-surface changes in Lucerne Valley in the Morongo ground-water basin. The GPS survey was conducted in 1998 to estimate historical elevation changes by comparing GPS-derived elevations with historical elevations (which were available for some of the monuments in the network as early as 1944) and to establish baseline values that can be used for comparisons with future GPS surveys. The GPS measurements indicated that about 600 millimeters (2 feet) [plus or minus 1,500 millimeters (5 feet)] of subsidence occurred at three of the monuments between 1969 and 1998 but that very little to no vertical change in position occurred at seven other monuments in the network. Water levels in the area of subsidence in Lucerne Valley declined about 15 meters (50 feet) during 1970-98.
Interferometric synthetic aperture radar (InSAR) methods were used to characterize vertical land-surface changes in the Mojave River and Morongo ground-water basins during various intervals of time between 1992 and 1999. Interferograms, InSAR-generated displacement maps, show that subsidence ranging from 45 to 90 mm (0.15 to 0.3 ft) occurred in four areas of these two ground-water basins--the El Mirage, Lockhart-Harper Lake (dry), Newberry Springs, and Lucerne Valley areas. Some of the InSAR measurements were affected by the earthquakes at Landers and Hector Mine, California, and by atmospheric artifacts.
Water-level data were examined for areas undergoing vertical land-surface changes to determine whether the vertical land-surface changes may be related to aquifer-system compaction caused by ground-water-level changes. Temporally relevant water-level data were sparse for some areas, particularly the El Mirage and Lockhart-Harper Lake (dry) areas. Water levels in wells proximate to the subsiding areas generally declined between 1992 and 1999; water levels in some wells proximate to the subsiding areas experienced seasonal periods of declines and recoveries.
Description of Study Area
Mojave River Ground-Water Basin
Morongo Ground-Water Basin
Mechanics of Land Subsidence
Global Positioning System (GPS) Survey of Lucerne Valley Area
Land-Subsidence Monitoring Network
Determination of Ellipsoid Heights and Orthometric Heights (Elevations)
GPS Results and Ground-Water Levels in Nearby Wells
Interferometric Synathetic Aperture Radar (InSAR)
Mojave River Ground-Water Basin
El Mirage Area
Lockhart-Harper Lake (Dry) Area
Newberry Springs Area
Morongo Ground-Water Basin--Lucerne Valley Area
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