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Active Management Area Surface Water Hydrology

The U.S. Geological Survey (USGS) divides the United States into successively smaller hydrologic units based on hydrologic features.  These units are classified into four descending levels. From largest to smallest they are: regions, subregions, accounting units and cataloging units.  Each hydrologic unit is identified by a hydrologic unit code (HUC) consisting of two to eight digits depending on the unit level.  A 6-digit code corresponds to accounting units, which are used by the USGS for designing and managing the National Water Data Network.

The AMA planning area encompasses portions of six watersheds at the accounting unit level. From north to south they are: the Verde River, the Agua Fria River-Lower Gila River, the Salt River, the Middle Gila River, the Santa Cruz River and the Rio Asuncion (Figure 8.0-5).  More detailed information on stream flow gages, springs, reservoirs and general surface water characteristics are found in the individual AMA sections.  An additional and comprehensive source of information on watersheds is Arizona NEMO (Non-point Education for Municipal Officials), which has produced watershed based plans for a number of Arizona watersheds including the Middle Gila, Salt, Santa Cruz, Upper Agua Fria and Verde watersheds. These plans characterize and classify watershed features with a focus on mitigation nonpoint source pollution. (Plans are available at

Click to view Figure 8.0-5

Figure 8.0-5 USGS HUCs in the AMA Planning Area

Verde River Watershed

The 6,100 square mile Verde River Watershed is located in north-central Arizona. A large part of the watershed is located in the Verde River groundwater basin (See Volume 5, Figure 5.0-5). The northern portion of the watershed begins near Seligman with tributaries of Big Chino Wash. The Verde River is perennial and  almost 140 miles in length.  Starting below Sullivan Lake Dam just north of the Prescott AMA it flows eastward to Perkinsville and southeastward to Fossil Creek, then passes southward through two reservoirs (Horseshoe and Bartlett) before its confluence with the Salt River in the Fountain Hills Sub-basin of the Phoenix AMA. The last 25 miles of the river, and the southernmost part of the watershed are located in the Phoenix AMA.

The Verde River is impounded by Horseshoe Dam and Bartlett Dam outside the Phoenix AMA, both of which are part of the Salt River Project (SRP). SRP consists of two entities that provide water and power to the Phoenix metropolitan area. One of the entities, the Salt River Valley Water Users Association, is a private corporation that delivers nearly 1.0 maf of water annually to the Phoenix area through an extensive water delivery system that includes reservoirs, wells, canals and irrigation laterals.

Watson Lake

Watson Lake, Prescott AMA.

The Little Chino Sub-basin in the northwestern portion of the Prescott AMA is also part of the Verde River watershed. Granite and Willow creeks are the major tributaries draining the Little Chino Sub-basin into the Verde River. An estimated 14% of the base flow in the upper Verde River comes from the Little Chino Sub-basin (Wirt and others, 2005).  Dams constructed on Granite Creek and Willow Creek form Watson Lake and Willow Lake, respectively, and originally  stored water for the Chino Valley Irrigation District (CVID).  The lakes are now used by the City of Prescott for recreation and municipal water use.  During major flood events water discharged  from these lakes flows northward and joins the Verde River near Paulden outside the AMA (see Figure 8.3-4).  Little Chino Creek and Big Draw Creek drain the northwestern part of the Little Chino Sub-basin.  Little Chino Creek drains the CVID area and flows into the Del Rio Springs area where groundwater naturally discharges at the surface. 

Del Rio Springs, located in the northern part of the Prescott AMA, is the only large spring in the AMA with a discharge of 874 gpm measured in 1999 (Table 8.3-5). Spring discharge maintains baseflow below the springs.  The only other major spring in this part of the watershed is Camp Spring northeast of Carefree in the Phoenix AMA with a discharge of about 75 gpm.  Sycamore Creek, a tributary of the Verde River, and Camp Creek northeast of Carefree, both have reaches with perennial flow  (Figure 8.1-5).

Streamgages are located at Del Rio Springs, and along Granite and Willow creeks in the Prescott AMA, and on the Verde River in the Phoenix AMA. Mean flows measured at three Granite Creek streamgages have ranged between approximately 3,500 and 5,000 AFA. Flows on the Verde River in the Phoenix AMA are controlled by releases from Bartlett and Horseshoe dams.  The highest reported annual flow at two Verde River gages was approximately 1.8 maf in 1993, while the median annual flow measured at these gages is approximately 298,000 acre-feet (Table 8.1-2).

Agua Fria – Lower Gila River Watershed

The Agua Fria – Lower Gila River Watershed begins near Prescott and extends south of Gila Bend in the Lower Colorado River Planning Area. Its major drainages include the Agua Fria River, the Lower Hassayampa River and the Gila River. Within the AMA planning area, this watershed encompasses the southeastern portion of the Prescott AMA as well as the western half of the Phoenix AMA. 

In the Prescott AMA, the Agua Fria – Lower Gila River Watershed includes the Upper Agua Fria Sub-basin. Upper Lynx Creek, Lynx Creek and the Agua Fria River drain the sub-basin. Most of the runoff from Lynx Creek is impounded by a dam and used for recreation and industrial purposes.  A short reach of the Agua Fria River becomes perennial before leaving the AMA and a portion of this reach receives effluent discharged from the Prescott Valley Wastewater Treatment Facility (Figure 8.3-10). All other flows in the Upper Agua Fria Sub-basin are ephemeral.

All or portions of five Phoenix AMA sub-basins lie within the Agua Fria – Lower Gila River Watershed including Carefree, Lake Pleasant, Hassayampa, West Salt River Valley and Rainbow Valley.  The Agua Fria River enters the AMA approximately 20 miles north of Peoria, in the Lake Pleasant Sub-basin. The river is impounded by New Waddell Dam at the northern boundary of the sub-basin and only flows below the dam when water is released during major flood events. From there it flows south along the western edge of the Phoenix metropolitan area and joins the Gila River south of Avondale (Figure 8.1-4B). Downstream of the confluence of the Salt River, the Gila River flows year round due to effluent discharge from the City of Phoenix 23rd and 91st Avenue wastewater treatment plants into the Salt River, and from return flow from nearby agricultural areas.  Some of this water is diverted for agricultural and industrial uses. This reach of the Gila River has been designated as impaired by the Arizona Department of Environmental Quality (ADEQ) due to pesticide concentrations that exceed the use standard (Figure 8.1-10A and Table 8.1-8B). The Gila River exits the Phoenix AMA at Gillespie Dam.

The Hassayampa River originates in the Bradshaw Mountains and flows through the Hassayampa Sub-basin before its confluence with the Gila River west of Buckeye (Figure 8.1-4B).  It is an ephemeral stream within much of the AMA except for short perennial reaches where it enters the AMA and near its confluence with the Gila River. The Hassayampa River is impaired above the Gila River confluence due to elevated concentrations of selenium and boron (Table 8.1-8B and Figure 8.1-10A).

The only major spring in the watershed is Seven Springs north of Carefree with a discharge of about 75 gpm. Perennial reaches occur along Cave Creek and Seven Springs Wash northeast of Carefree (Figure 8.1-5).

 Flow records from streamgages in the watershed are included in Table 8.1-2 and 8.3-2. The annual median flow in the Agua Fria River near the Humboldt gage is about 3,400 acre-feet and the annual median flow on the Hassayampa River near Morristown is about 6,500 acre-feet. The highest annual flow measured in the watershed occurred at a gage on the Gila River (#9514100) where 6.1 maf  was reported for 1993.  The median flow at this gage is only about 12,000 AFA. (Table 8.1-2)

Salt River Watershed

Most of the Salt River Watershed is within the Salt River and Tonto Creek basins in the Central Highlands Planning Area. Its western edge extends into the Phoenix AMA and includes  the confluence of the Salt and Gila rivers. The Salt River originates in eastern Arizona and drains approximately 6,000 square miles of the Mogollon Rim area in the east-central part of the State.  Before entering the Phoenix AMA in the Fountain Hills Sub-basin, surface water from the Salt River Watershed passes through a series of four reservoirs: Roosevelt Lake, Apache Lake, Canyon Lake and Saguaro Lake. These reservoirs and associated dams are operated by SRP and used to supply water to the agricultural, municipal and industrial sectors in the Phoenix AMA.

The Salt River channel enters the AMA north of the Goldfield Mountains, flows southwest through the East Salt River Valley and West Salt River Valley sub-basins and the cities of Mesa, Tempe, Scottsdale and Phoenix, and then joins the Gila River near Laveen (Figure 8.1-4B).  Downstream from the Granite Reef Diversion Dam located four miles below the confluence of the Salt and Verde rivers, the Salt River is ephemeral and only flows in response to flooding or reservoir releases.  The Granite Reef Diversion Dam diverts flow to the Arizona Canal and the South Canal to serve municipal, agriculture and tribal uses.  The Salt River becomes perennial further downstream due to effluent discharges from the 23rd Avenue and 91st Avenue WWTPs (Figure 8.1-5).

Salt River near eagle nest

Salt River near Eagle's Nest

There are no major springs in the AMA portion of the watershed.  Flow records from streamgages in the watershed are found in Table 8.1-2. Annual median flow on the Salt River below Stewart Mountain Dam is about 585,700 acre- feet with a maximum annual flow of over 3.2 maf in 1993. Further downstream near its confluence with the Gila River and below the Granite Reef Diversion Dam, annual median flows in the Salt River at 51st  Avenue are about 4,300 acre-feet.

Middle Gila River Watershed

The Middle Gila River Watershed extends west from Coolidge Dam on the Gila River, located in the Southeastern Arizona Planning Area, to the confluence of the Gila and Salt rivers. The San Pedro and San Francisco rivers are major tributaries to the Gila River outside of the AMA Planning Area. Portions of the Phoenix AMA, Pinal AMA and Tucson AMA are located in this watershed. The Gila River enters the Pinal AMA in its northeastern corner and flows from east to west. Before development, the Gila River flowed year round through this area. Pre-development flows along the portion of the Gila River that passes through the Pinal AMA are estimated to have been about 500,000 AFA.  The first records of San Carlos Irrigation Project (SCIP) diversions of Gila River water begin in 1930, although diversions by non-Indian farmers began much earlier.  According to the Gila Water Commissioner’s report annual diversions by SCIP at the Ashurst-Hayden Diversion Dam northeast of Florence in the Pinal AMA averaged 253,100 AFA between 2005 to 2008.

There are no major springs in this portion of the Middle Gila River Watershed. Short reaches of Queen Creek and Arnett Creek near Superior are perennial (Figure 8.1-5).  Queen Creek has been designated as impaired from its headwaters to about nine miles downstream due to elevated copper concentrations from mining discharge (Table 8.1-8B and Figure 8.1-10A). Flow records from streamgages in the watershed are found in Table 8.1-2 and 8.2-2. The annual median flow measured at the gage on Queen Creek below Whitlow Dam near Superior is about 1,600 acre-feet. Gages on the Gila River have either been discontinued or have only recent data. The Gila River gage near Laveen has the longest period of record (55 years) but was discontinued in 1994. The annual median flow at that gage was 9,420 acre-feet with a maximum annual flow of almost 1.2 maf in 1993.

Fork of Santa Cruz River

Fork of the Santa Cruz River

Santa Cruz River Watershed

A large portion of the AMA Planning Area falls within the Santa Cruz River Watershed, including the Santa Cruz AMA and most of the Tucson and Pinal AMAs. The Santa Cruz River is the main surface water drainage in the Santa Cruz and Tucson AMAs. The river originates in the San Rafael Valley east of the planning area near the Mexican border and flows southward to Mexico before turning north and re-entering the U.S. east of Nogales. Within the planning area it flows from the international border northwestward to its confluence with the Gila River (where it is known as the Santa Cruz Wash) in the northern portion of the Pinal AMA. Major tributaries to the river in the Santa Cruz AMA are Nogales Wash, Sopori Wash and Sonoita Creek. Major tributaries to the Santa Cruz River in the Tucson AMA include Rillito Creek, Cañada del Oro Wash and Brawley Wash. Three smaller streams (Vekol Wash, Santa Rosa Wash and Aguirre Wash) drain the southern portion of the Pinal AMA and join Santa Cruz Wash upstream from its confluence with the Gila River.

Prior to development, the Santa Cruz River was locally perennial in its southernmost reach from its headwaters in the San Rafael Valley to near Tubac, forming a series of cienegas (marshes).  North of Tubac, a few relatively short perennial sections existed including reaches near the mission of San Xavier del Bac south of Tucson and at “A” Mountain near downtown Tucson. From the Nine-Mile water hole north of the confluence of the Santa Cruz River and the Rillito River in Tucson, to its confluence with the Gila River, the Santa Cruz River was historically dry except during floods. (Tellman and others, 1997)

Currently, two segments of the Santa Cruz River within the Tucson AMA and the Santa Cruz AMA flow year round downstream of  wastewater discharges (Figures 8.4-11 and 8.5-12).  In 2006, approximately 66,000 acre-feet was discharged at the Ina and Roger Road WWTPs by Pima County.  In 2004, approximately 16,200 acre-feet of sewage was treated at the Nogales International WWTP, which treats sewage from both Nogales, Sonora and Nogales, Arizona prior to discharge to the river. Approximately 11,500 acre-feet of the influent was from Mexico.  In the Pinal AMA, a portion of the Santa Cruz River currently receives wastewater discharge from the Casa Grande WWTP. 

Perennial flows in the watershed include portions of Sabino, Romero, Cienega and Rincon creeks in the east central part of the Tucson AMA and Sonoita Creek in the Santa Cruz AMA (Figures 8.4-5 and 8.5-5).  Nogales Wash, a tributary of the Santa Cruz River, originates about five miles south of the international border in Sonora and enters Arizona as a covered floodway.  It joins the Santa Cruz River about 8 miles north of the border.  Nogales Wash is the major drainage system for both Nogales, Arizona and Nogales, Sonora. (Varady and others, 1995) Springs create perennial flow in Nogales Wash near its headwaters in Mexico and below the springs, storm flows and uncontrolled sewage discharges also contribute to its flow (IBWC, 1998).  In the Santa Cruz AMA the Santa Cruz River and Nogales Wash have designated impaired reaches due to elevated levels of E. coli and other constituents.

There are ten major springs in the watershed with locations near Arivaca, in mountains east of Tucson, and west of Amado in the Santa Cruz AMA.  The spring with the largest discharge is Sopori, located west of Amado, with a discharge rate of 377 gpm measured in 1952 (see Tables 8.4-5 and 8.5-5).

Flow records from streamgages in the watershed are found in Tables 8.4-2 and 8.5-2.  The annual median flow at the Santa Cruz River near Nogales is 14,013 acre-feet with a maximum annual flow of over 88,000 acre-feet in 1983. Downstream in the Tucson AMA the annual median flow at the gage on the Santa Cruz River at Cortaro is 38,655 acre-feet with a maximum annual flow in 1993 of over 182,000 acre-feet.

Rio Asuncion Watershed

A small part of the Rio Asuncion Watershed is located at the base of the Tucson AMA along the international border. This watershed drains a large area of northwest Sonora, Mexico and discharges into the Sea of Cortez.  Sycamore Creek, a perennial stream located in this watershed, flows south-southwest into Mexico. Due to its rich biological diversity, a portion of Sycamore Canyon has been designated as the Gooding Research Natural Area. There are no major springs identified in the U.S. portion of the watershed.



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