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Water Resources

CAP recharge/groundwater mixing studies

Since 1997, PAG has evaluated stable isotope data for water withdrawn from the City of Tucson’s storage and recovery projects located in Avra Valley. The Pima Mine Road Recharge Project was added to the program in 2009.  These facilities are used to recharge Central Arizona Project (CAP) water, which is delivered to Tucson from the Colorado River. The purpose is to use the stable isotope composition of the pumped water to determine the proportion of CAP water vs. groundwater in the subsurface aquifer. As recharge continues over time, there is a higher percentage of CAP water mixed with the aquifer’s groundwater.

In 2008, PAG stopped working on the Central Avra Valley Storage and Recovery Project (CAVSARP) to make room for collection of Southern Avra Valley Storage and Recovery Project (SAVSARP) samples.  Isotope sampling at the CAVSARP site was restarted in 2010.

PAG is currently evaluating isotope data from CAVSARP, SAVSARP and Pima Mine Road.

Well studies in shallow groundwater area

As our region’s population expands and groundwater aquifers become developed, it becomes increasingly important to understand pumping trends for sensitive areas, such as shallow groundwater areas, so that riparian habitats and private well owners are not compromised. Shallow groundwater areas have water tables that lie less than 50 feet below ground surface, and they are often demarcated by indicator vegetation, such as mesquite and cottonwood trees. PAG released the updated and expanded report, Shallow Groundwater Areas in Eastern Pima County, Water Well Inventory and Pumping Trend Analysis, in 2012. The study identifies 32 shallow groundwater areas, grouped into 10 regions and uses ADWR and PAG well data to describe water level changes, water use trends, well densities and drilling histories. The report includes a series of trend analyses on pumping data from non-exempt wells, but it also provides a general summary of data collected from the exempt wells*. The trend analysis helps identify those areas that have experienced increased or decreased groundwater withdrawals from non-exempt wells over the last two decades. *Exempt wells are permitted to withdraw up to 35 gallons per minute (gpm), but no pumping data is available for these wells. Non-exempt wells, may pump more than 35gpm and are required to report pumping volumes to the state.

Because riparian trees depend on groundwater, they become vulnerable if groundwater levels decline. While habitat supported in shallow groundwater areas is critical to the region's wildlife, the water resources in these basins also provide water to numerous private well owners and public water systems.  With continued warming and drought, there will undoubtedly be increased competition for water resources in these delicately balanced systems. Monitoring water levels and improving education to private well owners are two important future steps to ensure that riparian areas associated with shallow groundwater areas are not adversely impacted in the future. 


Central Arizona Groundwater Replenishment District (CAGRD) Report & Map

In September 2011, Pima Association of Governments released the "Central Arizona Groundwater Replenishment District Membership in the Tucson Active Management Area" report. The report contains data current to 2009. The purpose of the report is to provide regional managers and the public with updated information on Central Arizona Groundwater Replenishment District (CAGRD) membership in the context of its impact on Assured Water Supply (AWS).

Analysis includes calculations of obligated replenishment for members, membership growth trends and location of recharge facilities. The Central Arizona Project (CAP) also has used this report to address boundary reconciliation issues. Several concerns arise when considering the widespread dependence on the GRD to meet AWS requirements.

These concerns include the dependence of CAGRD on excess CAP supplies, which are decreasingly available, and that the recharge will not benefit areas where groundwater is actually pumped, which has impacts on subsidence and localized water availability. PAG's analysis is available in the report and maps linked below, in addition to accompanying datasets in raw format from PAG and on the Pima County Map Guide website for interactive viewing.

Regional Water Assessment

In 2010, the Regional Water Assessment Task Force was convened to help the region shape its efforts to achieve a sustainable water future.

As an initial step, the Task Force held a series of computer network-based ThinkTank sessions to gain input and guidance from stakeholders throughout the Tucson Active Management Area. The sixty four participants included elected officials, municipal managers, public and private utility managers, water attorneys, representatives from Central Arizona Project, state and federal agencies, Indian nations, University of Arizona, and people that represented economic, environmental, agricultural, and mining interests. In response to the following questions, participants generated nearly 900 responses, each of which they ranked as high, medium or low importance or priority.

  1. What regional water issues need to be addressed?
  2. What could our water use priorities be at a regional level?
  3. How can water resources be managed at a regional level? 
  4. How can water use be managed at a regional level? 
  5. How can water infrastructure for the region be funded?

In August 2011, Task Force members completed analysis of the ThinkTank responses and generated a report that includes tables showing the responses and analysis results. The Task Force focused on those ideas that gained the highest level of consensus to identify several ThinkTank themes, which are described in the report. In addition, several regional priorities emerged out of the ideas and the Task Force went one step further to conceptualize how Regional Solution/Strategy Groups might be used to help the region follow up on the ideas generated through the sessions.

Think Tank Report

ThinkTank Session Transcripts

Regional Water Assessment Task Force Members

  • Madeline Kiser
  • Sharon Megdal, Water Resources Research Center
  • Mark Stratton, Southern Arizona Water Users Association
  • Vince Vasquez, Tucson Regional Water Coalition
  • Claire Zucker, Pima Association of Governments



Cienega Creek Projects

Cienega Creek, located 20 miles southeast of Tucson, contains remnants of a historically extensive cienega system, defined by springs and marsh areas. Designated as an “Outstanding Water” by the State of Arizona, Cienega Creek contains critical habitat for many wildlife and plant species, including threatened and endangered species.
Since 1989, PAG has conducted monthly and quarterly hydrologic monitoring and research in Cienega Creek and Davidson Canyon in coordination with the Pima County Regional Flood Control District and Pima County Natural Resources Parks and Recreation.
PAG’s hydrologic monitoring includes:

  •     Calculating the quantity of streamflow
  •     Sampling the water quality to serve baseline data, should the creek become impacted by mining or development
  •     Conducting repeat photography
  •     Assessing the depths to groundwater at wells located throughout the preserve
  •     Measuring and mapping the lengths of the intermittent, ephemeral and flowing segments of the creek
  •     Monitoring erosion
  •     Evaluating the impact of drought

Drought impacts can be seen in the variation of flow extent measured during PAG’s wet/dry monitoring.

Cienega Creek Projects Part 2


Take a 3D look at Marsh Station, to get a feeling for Cienega Creek’s lush perennial flow.


Mining Issues
Cienega Creek and Davidson Canyon are downstream from various mining interests, including the potential Rosemont Copper Mine in the Santa Rita Mountains and other limestone and gravel mineral leases along the creek.

Cienega Creek Watershed Map
The map below shows a birds-eye view from above Cienega Creek looking across the greater Santa Cruz Watershed. The location of the proposed Rosemont Valley open pit copper mine is shown where it could be located within the Cienega watershed, if approved by state and federal agencies. The map also includes symbology for locations of Arizona Outstanding Waters, perennial flows, the Tucson Active Management Area, etc.

Water Level and Water Consumption Studies in the Cienega Watershed

In 2012, PAG completed a report on groundwater use near shallow groundwater areas in eastern Pima County. The report includes totals of the number of exempt and non-exempt wells, drilling histories and water production estimates.  We found that a one mile buffer around the Cienega-Davidson shallow groundwater system contains 29 non-exempt wells and 355 exempt (private low-water use) wells.  PAG defined this system to contain upper and lower Cienega Creek, Davidson Canyon, Barrel Canyon, Gardner Canyon, and Agua Verde-Posta Quemada.  Each area has unique well histories and groundwater level trends. Overall, the total number of exempt wells drilled in the buffered areas has steadily increased since 1990.  PAG, in coordination with Pima County, has monitored groundwater and surface water in the Cienega Creek Natural Preserve (lower Cienega Creek) since 1989, thereby providing over three decades of water resource information.  As a result, the quantity and quality of water resource data for lower Cienega Creek is dramatically better than that available for many other parts of the Cienega Valley. Riparian habitat and well owners, alike, rely on shallow groundwater resources.

Pima County conducted a 2013 analysis of long term water level trends by Pima County using PAG data among additional sources.  This report shows a decline of most water-related parameters monitored in the Preserve.   From 1993-2011, precipitation showed a declining trend in the winter, but no trend in the summer.  During the same period, streamflow declined by approximately 50% with the most significant decline during June, which is a critical period for aquatic plants and animals each year.  The extent of surface flow declined from a high of 9.5 miles (1984-1996), to a low of 1.24 miles in June of 2012.  These trends cause researchers in the region to be concerned about the prospects for long term health of the aquatic and riparian system of Cienega Creek. 

Collaborative presentation from the Science in the Sonoita Plains Symposium in June 2013 regarding both of the above topics.

Cienega Creek Hydrologic Research and Findings

The Pima County Regional Flood Control District has provided support over the years for PAG's monitoring program, in recognition that this unique perennial stream, with its pristine native riparian habitat, is a critical resource in southern Arizona.

Portions of both Cienega Creek and its tributary, Davidson Canyon, are protected through their designation as Outstanding Arizona Waters by the State.

PAG's 20 years of hydrologic monitoring along Cienega Creek indicates that the region is in the midst of a long-term drought. A developing headcut, an erosion feature PAG began studying in 2002, surprised many who recognized the major successes of restoration, since the Pima County Natural Preserve was established in Lower Cienega Creek in 1986.

Annual Report
The most recent technical reports for the Cienega Creek Monitoring Project are shown below. This report summarizes PAG's groundwater and surface water monitoring between July and June each fiscal/monitoring year. The report contains monitoring methodology, comprehensive maps, and graphs of trends for surface flow volume, wet-dry flow lengths, groundwater levels and water chemistry. It also contains information on drought, erosion and repeat photography.

ADWR Water Protection Fund Award for Headcut Study
Interest in preserving Cienega Creek continues to drive monitoring, discussion and community engagement. In recent years, a large erosion feature (a headcut) developed, radically changing the stream habitat as it migrates upstream. Since 2002, the headcut has migrated over 1,200 feet and has grown to 12 feet deep and 20 feet wide. In 2007, PAG received a grant from the Arizona Department of Water Resources, under its Arizona Water Protection Fund program. This two-year project consists of habitat surveys, and groundwater and streamflow monitoring near a large erosional headcut feature that appeared on the creek in 2001. The resulting report discusses the findings on the changes of the water table slope, the increase in fish habitat diversity, loss of vegetation cover and change in vegetation composition. Many new discussions have resulted from recent field trips, presentations and meetings regarding needs for restoration, potential causes, and possible impacts on other aspects of habitat. PAG is participating in a Sky Island/Sonoran Desert Restoration Network which formed to share information and to engage scientists, land managers, citizen volunteers and landowners throughout the region.

Drought Findings
PAG’s hydrologic monitoring at Cienega Creek reveals that drought impacts have been noticeable since 2002.  Cienega Creek experienced record breaking drought conditions in for three consecutive years until we saw marginal improvements in 2015.  PAG conducts flow mapping in June in Davidson Canyon and Cienega Creek Outstanding Arizona Waters to determine the minimal length of flow in the during the driest part of the year, coordinated with other river mapping efforts across the region. June 2015 showed only 0.88 miles of flow, an increase of 0.02 miles from last year, but still just nine percent of the full 9.5 miles of flow extent observed in June of the mid-1980s. Current groundwater levels also remain significantly below pre-drought levels. 2015 records showed increases in average annual stream flow, volume not recorded since the wet 2008-2009 period, and a slight rise in average groundwater well levels.  Because surface water base flows and groundwater are strongly correlated, these trends parallel each other.

Drought Planning
PAG’s 2012 investigation of shallow groundwater areas revealed private wells tapping into this riparian area and other similar areas.  Drought conditions can be highly localized in the desert southwest so rural private well owners and the riparian habitat that they live in may experience unique conditions and risks as temperatures rise and precipitation becomes more variable in coming years.

Since  drought information is primarily disseminated by large municipal water providers in urban areas, PAG works with the Local Drought Impact Group to recommend that special consideration for drought stage triggers and outreach be given to vulnerable areas including riparian, shallow groundwater and areas with rural households dependent on private wells. We support a focused alert message to homeowners in these areas during the pre-monsoon season.

Take a virtual field trip to the headcut.

Davidson Canyon

The extent of streamflow in Upper Davidson Canyon has declined substantially since 2003. Since the channel and pools completely dried out during the summer of 2005, PAG has not seen native fish there. Lowland leopard frogs are still present along the reach. This reach of the creek is currently under stress from off-road vehicle and cattle use, but the county has made efforts to exclude these activities from the riparian area.

Highlights of PAG Studies on Cienega Creek

The PAG Watershed Planning library has additional publications on Cienega Creek from outside sources.

Additional Links

Drinking Water

The City of Tucson Water Department (Tucson Water) provides potable water and reclaimed water to much of the Tucson region. The Long-Range Water Plan includes projections about current and future water needs and the water supplies available to meet the growing demand.

Public and private water providers in the region include:

  • Tucson Water
  • Metropolitan Domestic Water Improvement District
  • Community Water Company of Green Valley
  • Marana Domestic Water Improvement District
  • Town of Oro Valley Water Utility
  • Flowing Wells Irrigation District
  • Davis-Monthan Air Force Base
  • Green Valley Domestic Water Improvement District
  • Town of Marana Water Utility
  • University of Arizona
  • Vail Water Co.
  • Davis-Monthan AFB

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