Arizona Water Science Center
U.S. Geological Survey
Scientific Investigations Report 2007-5190
Prepared in cooperation with the Arizona Department of Water Resources, City of Tucson Water Department, Pima County, the Town of Oro Valley, the Town of Marana, and the Metropolitan Domestic Water Improvement District
The U.S. Geological Survey monitors land subsidence and aquifer-system compaction caused by ground-water depletion in Tucson Basin and Avra Valley—two of the three alluvial basins within the Tucson Active Management Area. In spring 1987, the Global Positioning System was used to measure horizontal and vertical positions for bench marks at 43 sites to establish a network for monitoring land subsidence in Tucson Basin and Avra Valley. Between 1987 and 2005, the original number of subsidence monitoring stations was gradually increased to more than 100 stations to meet the need for information in the growing metropolitan area. Data from approximately 60 stations common to the Global Positioning System surveys done after an initial survey in 1987 are used to document land subsidence. For the periods of comparison, average land-surface deformation generally is less than the maximum subsidence at an individual station and takes into account land-surface recovery from elastic aquifer-system compaction. Between 1987 and 1998, as much as 3.2 inches of subsidence occurred in Tucson Basin and as much as 4 inches of subsidence occurred in Avra Valley. For the 31 stations that are common to both the 1987 and 1998 Global Positioning System surveys, the average subsidence during the 11-year period was about 0.5 inch in Tucson Basin and about 1.2 inches in Avra Valley.
For the approximately 60 stations that are common to both the 1998 and 2002 Global Positioning System surveys, the data indicate that as much as 3.5 inches of subsidence occurred in Tucson Basin and as much as 1.1 inches of subsidence occurred in Avra Valley. The average subsidence for the 4-year period is about 0.4 inch in Tucson Basin and 0.6 inch in Avra Valley. Between the 2002 and the 2005 Global Positioning System surveys, the data indicate that as much as 0.2 inch of subsidence occurred in Tucson Basin and as much as 2.2 inches of subsidence occurred in Avra Valley. The average subsidence for the 3-year period is about 0.7 inch in Avra Valley.
Between 1987 and 2004-05, land subsidence was greater in Avra Valley than in Tucson Basin on the basis of the average cumulative subsidence for the stations that were common to the original Global Positioning System survey in 1987. The average total subsidence during the 17- to 18-year period was about 1.3 inches in Tucson Basin and about 2.8 inches in Avra Valley. Three stations in Tucson Basin showed subsidence greater than 4 inches for the period—5 inches at stations C45 and X419 and 4.1 inches at station PA4. In Avra Valley, two stations showed subsidence for the 17- to 18-year period greater than 4 inches—4.3 inches at station AV25 and 4.8 inches at station SA105.
In 1983, fourteen wells were fitted with borehole extensometers to monitor water-level fluctuations and aquifer-system compaction. Continuous records of water level and aquifer-system compaction indicate that as much as 45 feet of water-level decline and 4 inches of aquifer-system compaction occurred in Tucson Basin from January 1989 through December, 2005. In Avra Valley, extensometer data indicate that as much as 55 feet of water-level decline and 1.7 inches of aquifer-system compaction occurred during the same time period. Rates of compaction vary throughout the extensometer network, with the greater rates of compaction being associated with areas of greater water-level decline and more compressible sediments. In Avra Valley, data from the Global Positioning System surveys indicate that more than half of the total subsidence of the land surface may be the result of aquifer-system compaction below the portion of the aquifer instrumented with the vertical extensometers.
For the area in the northern part of Tucson Basin between the Rillito and Santa Cruz rivers, an Interferometric Synthetic Aperture Radar interferogram indicates that about 1.65 inches of subsidence occurred between 2003 and 2006. Between 2002 and 2004, the Global Positioning System station at C45, in the same northern area of Tucson basin, shows subsidence of 1.2 inches, indicating a good correlation between the Global Positioning System data and the Interferometric Synthetic Aperture Radar data.
Introduction
Background
Purpose and Scope
Previous Investigations
Acknowledgments
Description of the Study Area
Methods of Data Collection
Hydrogeology
Potential for Land Subsidence
Land Subsidence and Aquifer-System Compaction
Summary
References Cited
1. Tucson Active Management Area in south-central Arizona
2. Long-term elevation-change monitoring stations in the Tucson Active Management Area
3. Photograph of a typical setup of a geodetic GPS receiver in the Tucson Active Management Area
4. Tucson Active Management Area borehole extensometer stations
5. Diagrammatic sketch of a borehole extensometer in the Tucson Active Management Area
6. Generalized geology of the Tucson Active Management Area
7. Water level and compaction readings at extensometers in the Tucson Basin, 1989 to 2005
8. Water level and compaction readings at extensometers in the Avra Valley, 1989 to 2005
9. Land-surface elevation change in the Tucson Active Management Area from 1987 to 1998
10. Land-surface elevation change in the Tucson Active Management Area from 1998 to 2002
11. Land-surface elevation change in the Tucson Active Management Area from 2002 to 2005
12. Land-surface elevation change in the Tucson Active Management Area from 1987 to 2004 and 2005
13. Land-surface elevation change in the Tucson Active Management Area based on a 3-year, 8-month interferogram, February 2003 to October 2006
1. Positions and elevations of monitoring stations in the Tucson Active Management Area and changes in vertical position from 1987 to 2005
2. Aquifer-system compaction and water-level data for the Tucson Active Management Area, 1989-2005
Carruth, R.L., Pool, D.R., Anderson, C.E., 2007, Land subsidence and aquifer-system compaction in the Tucso Active Management Area, south-central Arizona, 1987–2005: U.S. Geological Survey Scientific Investigations Report 2007-5190, 27 p.
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Send questions or comments about this report to the author, Robert L. Carruth , (520) 670-6671.
For more information about water activities in Arizona, visit the ARIZONA DEPARTMENT OF WATER RESOURCES home page.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2007/5190/
Page Contact Information: Michael Diggles
Page Last Modified: October 19, 2007
