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Groundwater Response to Managed Aquifer Recharge at the Southeast Houghton Artificial Recharge Project in Tucson, Arizona

Scientific Investigations Report 2025-5017
Water Availability and Use Program
Prepared in cooperation with Tucson Water
By: , , and 
https://doi.org/10.3133/sir20255017

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Abstract

Managed aquifer recharge is a widespread practice for storing water in the subsurface as groundwater. At a managed aquifer recharge facility in southern Arizona, groundwater-level and repeat microgravity data were collected to monitor aquifer response. These data were used to inform parameter identification for an unsaturated-zone flow model used to simulate the recharge process. The facility, the Southeast Houghton Artificial Recharge Project (SHARP), consists of 3 surface basins (about 27,600 square meters [6.8 acres] total surface area) where recycled water is distributed in recharge cycles lasting several months, with dry periods in between. During the study period, December 2020–December 2022, Tucson Water (the City of Tucson’s water utility) reported 6.56×106 cubic meters of water (5,320 acre-feet) recharged.

Monitoring included groundwater-level observations at 3 monitoring wells and repeat microgravity measurements at as many as 22 locations (some stations were destroyed between surveys). Six gravity surveys were carried out using absolute- and relative-gravity meters. Large gravity increases, more than 250 microgals, were observed during the first repeat survey, 3.5 months after the start of recharge, but only in the immediate vicinity of the recharge basins. Data show that water moved downward to the water table, and storage changes in the unsaturated zone away from the facility were likely minimal. Gravity decreased at stations more than 1 kilometer from the facility, consistent with regional groundwater-level changes. Groundwater-level increases in wells adjacent to the recharge basins began 2 months after the second repeat gravity survey, and 5.5 months after recharge began.

Unsaturated-zone flow modeling was carried out using software that simulates water movement and parameter estimation. Model calibration was carried out by minimizing an objective function calculated from the differences between simulated and observed groundwater levels, and between simulated and observed repeat microgravity data. Including repeat microgravity data in the objective function reduced the uncertainty in estimated parameter values for saturated hydraulic conductivity and saturated water content. Modeling indicated that the unsaturated zone between the recharge basins and the water table does not become saturated even after 685 days of simulated infiltration. This gradual wetting may account for increasing infiltration rates over time, as hydraulic conductivity increases with increasing water content. Unsaturated-zone water content decreased rapidly between recharge cycles. Model-simulated groundwater mounding extended about 1 kilometer from the center of SHARP after the 685-day period following the onset of recharge.

Suggested Citation

Wildermuth, L.M., Kennedy, J.R., and Conrad, J.L., 2025, Groundwater response to managed aquifer recharge at the Southeast Houghton Artificial Recharge Project in Tucson, Arizona: U.S. Geological Survey Scientific Investigations Report 2025–5017, 38 p., https://doi.org/10.3133/sir20255017.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Setting
  • Methods
  • Results
  • Summary
  • References Cited
  • Appendix 1
  • Appendix 2
Publication type Report
Publication Subtype USGS Numbered Series
Title Groundwater response to managed aquifer recharge at the Southeast Houghton Artificial Recharge Project in Tucson, Arizona
Series title Scientific Investigations Report
Series number 2025-5017
DOI 10.3133/sir20255017
Publication Date November 19, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Arizona Water Science Center
Description Report: v, 38 p.; Data Release
Country United States
State Arizona
City Tucson
Other Geospatial Southeast Houghton Artificial Recharge Project
Online Only (Y/N) Y
Additional publication details