The Arizona Water Science Center is monitoring aquifer-storage changes at an artificial recharge facility operated by Tucson Water in southeast Tucson. Aquifer-storage change is monitored by measuring changes in gravity over time at the same network of benchmarks. As water is added or removed from the aquifer, there is a change in mass and a corresponding measurable change in gravity.
Tucson Water currently operates several artificial recharge projects in the Tucson Active Management Area, recharging both Colorado River water delivered via the Central Arizona Project (CAP) canal, and reclaimed wastewater. A new recharge facility, the Southeast Houghton Area Recharge Project (SHARP) has been constructed to permit storage of an additional 4,000 acre-feet per year of reclaimed water by the utility. Tracking the movement of recharged water is necessary to assess the dispersal of that water within specific target boundaries, and to enable resource managers to plan and develop locations of water supply wells that will utilize the recharged water.
The SHARP facility is located in a largely undeveloped area currently used for recreation, with relatively few wells nearby (figure 1). Installing additional monitoring wells would be expensive, and previous studies in the Southwest have shown that water levels in wells alone do not always provide a complete estimate of aquifer-storage change due to aquifer heterogeneity, well construction, and proximity to recharge sources (Pool, 2008). Repeat microgravity is the only geophysical method that overcomes the limitations of groundwater-level monitoring by providing a direct, quantitative measurement of changes in aquifer storage.
The repeat microgravity method, developed primarily at the University of Arizona and the U.S. Geological Survey (USGS) Arizona Water Science Center, is an established method for monitoring aquifer-storage changes in alluvial basins. The method has successfully been used to track the dispersal of water recharged through the channel of an ephemeral stream in Tucson, Arizona (Pool, 1997). Gravity monitoring of a spreading-basin artificial recharge facility in Avra Valley, Arizona, showed preferential groundwater flow, as storage accumulated to the west of three recharge basins but not to the east (Kennedy and Ferré, 2016). Also, at that facility, gravity data proved useful for identifying hydraulic conductivity and storage parameters in a MODFLOW groundwater model (Kennedy and others, 2016). The method is presently in use by the USGS Southwest Gravity Program for several projects across New Mexico, Arizona, and California. Maps of storage change from microgravity measurements can help water managers track the storage, movement and dispersal of recharged water in time. The spatial and temporal resolution of the mapped storage changes can be largely controlled by monitoring station density/distribution, and by the timing of repeat measurements.
This project is designed to provide information about the magnitude and location of aquifer-storage changes associated with artificial recharge at Tucson Water's SHARP facility. The proposed monitoring network and timing of surveys is designed to identify storage changes occurring during active recharge cycles and over several years of seasonal recharge within the focus area (figure 2).This project will provide Tucson Water managers with an improved temporal and spatial understanding of aquifer-storage changes occurring near the SHARP facility. This information is useful for quantifying movement of recharged water, and for evaluating the performance of the SHARP facility.
Additional Resources
- Carruth, R.L., Kahler, L.M., and Conway, B.D., 2018, Groundwater-storage change and landsurface elevation change in Tucson Basin and Avra Valley, south-central Arizona—2003– 2016: U.S. Geological Survey Scientific Investigations Report 2018–5154, 34 p.
- Evenson, E.J., Orndorff, R.C., Blome, C.D., Böhlke, J.K., Hershberger, P.K., Langenheim, V.E., McCabe, G.J., Morlock, S.E., Reeves, H.W., Verdin, J.P., Weyers, H.S., and Wood, T.M., 2013, U.S. Geological Survey water science strategy—Observing, understanding, predicting, and delivering water science to the Nation: U.S. Geological Survey Circular 1383–G, 49 p.
- Kennedy, J.R., 2018, Changes in Earth’s gravity reveal changes in groundwater storage: U.S. Geological Survey Fact Sheet 2018–3032, 4 p.
- Kennedy, J. R., and Ferré, T. P. A., 2016, Accounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data. Geophysical Journal International, vol. 204 no. 2, 892–906
- Kennedy, J. R., Ferré, T. P. A., and Creutzfeldt, B., 2016, Time-lapse gravity data for monitoring and modeling artificial recharge through a thick unsaturated zone. Water Resources Research, vol. 52 no. 9, 7244–7261
- Pool, D.R., and Schmidt, W., 1997, Measurements of ground-water storage change and specific yield using the temporal-gravity method near Rillito Creek, Tucson, Arizona: U.S. Geological Survey Water-Resources Investigations Report 97–4125, 30 p.
- Pool, D. R., 2008, The utility of gravity and water-level monitoring at alluvial aquifer wells in southern Arizona: Geophysics, vol. 73 no. 6, WA49-WA59
- Pool, Donald R., and Anderson, Mark T., 2008, Ground-water storage change and land subsidence in Tucson Basin and Avra Valley, southeastern Arizona, 1998-2002: U.S. Geological Survey Scientific Investigations Report 2007-5275, 34 p
- More information on this and other projects by the U.S. Geological Survey Southwest Gravity Program (including complete bibliography).
Below are publications associated with this project.
Aquifer storage change and storage properties, 2010–2017, in the Big Chino Subbasin, Yavapai County, Arizona
Groundwater-storage change and land-surface elevation change in Tucson Basin and Avra Valley, south-central Arizona--2003-2016
Changes in Earth’s gravity reveal changes in groundwater storage
Time-lapse gravity data for monitoring and modeling artificial recharge through a thick unsaturated zone
Accounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data
Ground-Water Storage Change and Land Subsidence in Tucson Basin and Avra Valley, Southeastern Arizona, 1998-2002
The utility of gravity and water-level monitoring at alluvial aquifer wells in southern Arizona
Measurement of ground-water storage change and specific yield using the temporal-gravity method near Rillito Creek, Tucson, Arizona
Below are partners associated with this project.
- Overview
The Arizona Water Science Center is monitoring aquifer-storage changes at an artificial recharge facility operated by Tucson Water in southeast Tucson. Aquifer-storage change is monitored by measuring changes in gravity over time at the same network of benchmarks. As water is added or removed from the aquifer, there is a change in mass and a corresponding measurable change in gravity.
Tucson Water currently operates several artificial recharge projects in the Tucson Active Management Area, recharging both Colorado River water delivered via the Central Arizona Project (CAP) canal, and reclaimed wastewater. A new recharge facility, the Southeast Houghton Area Recharge Project (SHARP) has been constructed to permit storage of an additional 4,000 acre-feet per year of reclaimed water by the utility. Tracking the movement of recharged water is necessary to assess the dispersal of that water within specific target boundaries, and to enable resource managers to plan and develop locations of water supply wells that will utilize the recharged water.
The SHARP facility is located in a largely undeveloped area currently used for recreation, with relatively few wells nearby (figure 1). Installing additional monitoring wells would be expensive, and previous studies in the Southwest have shown that water levels in wells alone do not always provide a complete estimate of aquifer-storage change due to aquifer heterogeneity, well construction, and proximity to recharge sources (Pool, 2008). Repeat microgravity is the only geophysical method that overcomes the limitations of groundwater-level monitoring by providing a direct, quantitative measurement of changes in aquifer storage.
Figure 1. Location of the Southeast Houghton Area Recharge Project (SHARP) facility and surrounding area within the Tucson Active Management Area, Arizona. The repeat microgravity method, developed primarily at the University of Arizona and the U.S. Geological Survey (USGS) Arizona Water Science Center, is an established method for monitoring aquifer-storage changes in alluvial basins. The method has successfully been used to track the dispersal of water recharged through the channel of an ephemeral stream in Tucson, Arizona (Pool, 1997). Gravity monitoring of a spreading-basin artificial recharge facility in Avra Valley, Arizona, showed preferential groundwater flow, as storage accumulated to the west of three recharge basins but not to the east (Kennedy and Ferré, 2016). Also, at that facility, gravity data proved useful for identifying hydraulic conductivity and storage parameters in a MODFLOW groundwater model (Kennedy and others, 2016). The method is presently in use by the USGS Southwest Gravity Program for several projects across New Mexico, Arizona, and California. Maps of storage change from microgravity measurements can help water managers track the storage, movement and dispersal of recharged water in time. The spatial and temporal resolution of the mapped storage changes can be largely controlled by monitoring station density/distribution, and by the timing of repeat measurements.
This project is designed to provide information about the magnitude and location of aquifer-storage changes associated with artificial recharge at Tucson Water's SHARP facility. The proposed monitoring network and timing of surveys is designed to identify storage changes occurring during active recharge cycles and over several years of seasonal recharge within the focus area (figure 2).This project will provide Tucson Water managers with an improved temporal and spatial understanding of aquifer-storage changes occurring near the SHARP facility. This information is useful for quantifying movement of recharged water, and for evaluating the performance of the SHARP facility.
Figure 2. Proposed gravity network within focus/study area. Final locations dependent on existing infrastructure and access to undeveloped areas. Proposed gravity locations that partially overlap wells would be located on well pads, where possible. Two of the wells within the facility (NW and SE corners) would be located on the well pads of existing monitoring wells. Additional Resources
- Carruth, R.L., Kahler, L.M., and Conway, B.D., 2018, Groundwater-storage change and landsurface elevation change in Tucson Basin and Avra Valley, south-central Arizona—2003– 2016: U.S. Geological Survey Scientific Investigations Report 2018–5154, 34 p.
- Evenson, E.J., Orndorff, R.C., Blome, C.D., Böhlke, J.K., Hershberger, P.K., Langenheim, V.E., McCabe, G.J., Morlock, S.E., Reeves, H.W., Verdin, J.P., Weyers, H.S., and Wood, T.M., 2013, U.S. Geological Survey water science strategy—Observing, understanding, predicting, and delivering water science to the Nation: U.S. Geological Survey Circular 1383–G, 49 p.
- Kennedy, J.R., 2018, Changes in Earth’s gravity reveal changes in groundwater storage: U.S. Geological Survey Fact Sheet 2018–3032, 4 p.
- Kennedy, J. R., and Ferré, T. P. A., 2016, Accounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data. Geophysical Journal International, vol. 204 no. 2, 892–906
- Kennedy, J. R., Ferré, T. P. A., and Creutzfeldt, B., 2016, Time-lapse gravity data for monitoring and modeling artificial recharge through a thick unsaturated zone. Water Resources Research, vol. 52 no. 9, 7244–7261
- Pool, D.R., and Schmidt, W., 1997, Measurements of ground-water storage change and specific yield using the temporal-gravity method near Rillito Creek, Tucson, Arizona: U.S. Geological Survey Water-Resources Investigations Report 97–4125, 30 p.
- Pool, D. R., 2008, The utility of gravity and water-level monitoring at alluvial aquifer wells in southern Arizona: Geophysics, vol. 73 no. 6, WA49-WA59
- Pool, Donald R., and Anderson, Mark T., 2008, Ground-water storage change and land subsidence in Tucson Basin and Avra Valley, southeastern Arizona, 1998-2002: U.S. Geological Survey Scientific Investigations Report 2007-5275, 34 p
- More information on this and other projects by the U.S. Geological Survey Southwest Gravity Program (including complete bibliography).
- Publications
Below are publications associated with this project.
Aquifer storage change and storage properties, 2010–2017, in the Big Chino Subbasin, Yavapai County, Arizona
The Big Chino Subbasin is a groundwater basin that includes the Verde River headwaters in Yavapai County in north-central Arizona. Groundwater in the southern part of the subbasin is found primarily in the Big Chino and Williamson Valleys. The former is a potential municipal water source for growing communities in Yavapai County, particularly groundwater from the Big Chino Water Ranch, about 15 miAuthorsJeffrey R. Kennedy, Libby M. Kahler, Amy L. ReadGroundwater-storage change and land-surface elevation change in Tucson Basin and Avra Valley, south-central Arizona--2003-2016
The U.S. Geological Survey monitors groundwater-storage change and land-surface elevation change caused by groundwater withdrawal in Tucson Basin and Avra Valley—the two most populated alluvial basins within the Tucson Active Management Area. The Tucson Active Management Area is one of five active management areas in Arizona established by the 1980 Groundwater Management Act and governed by the ArAuthorsRobert L. Carruth, Libby M. Kahler, Brian D. ConwayChanges in Earth’s gravity reveal changes in groundwater storage
Changes in the amount of water stored in underground aquifers cause small changes in Earth’s gravitational field. The U.S. Geological Survey’s Southwest Gravity Program has developed methods for measuring terrestrial gravity changes with part-per-billion precision. The measurements allow scientists to map changes in groundwater storage and to improve models that simulate groundwater flow.AuthorsJeffrey R. KennedyTime-lapse gravity data for monitoring and modeling artificial recharge through a thick unsaturated zone
Groundwater-level measurements in monitoring wells or piezometers are the most common, and often the only, hydrologic measurements made at artificial recharge facilities. Measurements of gravity change over time provide an additional source of information about changes in groundwater storage, infiltration, and for model calibration. We demonstrate that for an artificial recharge facility with a deAuthorsJeffrey R. Kennedy, Ty P.A. Ferre, Benjamin CreutzfeldtAccounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data
The relative gravimeter is the primary terrestrial instrument for measuring spatially and temporally varying gravitational fields. The background noise of the instrument—that is, non-linear drift and random tares—typically requires some form of least-squares network adjustment to integrate data collected during a campaign that may take several days to weeks. Here, we present an approach to removeAuthorsJeffrey R. Kennedy, Ty P.A. FerreGround-Water Storage Change and Land Subsidence in Tucson Basin and Avra Valley, Southeastern Arizona, 1998-2002
Gravity and land subsidence were measured annually at wells and benchmarks within two networks in Tucson Basin and Avra Valley from 1998 to 2002. Both networks are within the Tucson Active Management Area. Annual estimates of ground-water storage change, ground-water budgets, and land subsidence were made based on the data. Additionally, estimates of specific yield were made at wells within the moAuthorsDonald R. Pool, Mark T. AndersonThe utility of gravity and water-level monitoring at alluvial aquifer wells in southern Arizona
Coincident monitoring of gravity and water levels at 39 wells in southern Arizona indicate that water-level change might not be a reliable indicator of aquifer-storage change for alluvial aquifer systems. One reason is that water levels in wells that are screened across single or multiple aquifers might not represent the hydraulic head and storage change in a local unconfined aquifer. Gravity estiAuthorsD. R. PoolMeasurement of ground-water storage change and specific yield using the temporal-gravity method near Rillito Creek, Tucson, Arizona
The temporal-gravity method was used to estimate ground-water storage change and specific -yield values at wells near Rillito Creek, Tucson, Arizona, between early December 1992 and early January 1994. The method applies Newton's Law of Gravitation to measure changes in the local gravitational field of the Earth that are caused by changes in the mass and volume of ground water. Gravity at 50 statiAuthorsDonald R. Pool, Werner Schmidt - Partners
Below are partners associated with this project.