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Hydrology of the Aravaipa Canyon Basin

Groundwater Hydrology

Western Portion

On the western side of the planning area are a group of basins that are tributary to the San Pedro and Gila rivers; Aravaipa Canyon, Donnelly Wash, Lower San Pedro and Upper San Pedro. Groundwater is found in stream alluvium and basin-fill sediments in these basins. 

Aravaipa Canyon Basin

The sparsely populated Aravaipa Canyon Basin is characterized by a relatively flat northwest-trending valley in the southern half of the basin and an incised valley, Aravaipa Canyon that cuts through the Galiuro Mountains, in the northern half. The principal aquifers are the unconfined stream alluvium, which is the major source of groundwater, and a confined basin fill aquifer. Water level records suggest that the confined aquifer leaks into the unconfined aquifer. The thickness of the younger alluvium decreases to the south. (Holmes, 2003) Groundwater flow is similar to the surface water runoff pattern; northwest along the central axis of the valley.  Groundwater flows towards the head of Aravaipa Canyon where its flow path is geologically restricted, resulting in the perennial portion of Aravaipa Creek (Holmes, 2003). Groundwater recharge is from infiltrating precipitation and runoff and is estimated to range from 7,000 to 16,700 AFA (Table 3.1-3).  Groundwater discharge is to Aravaipa Creek from springs and baseflow, with small discharge to wells. Freethey and Anderson (1986) estimated 5 maf of water in storage in the basin.  Depth to water within the basin fill varies from 25 feet bls where the younger alluvium is thin to over 500 feet bls in the uplands in the southern part of the basin (Holmes, 2003).  Two recent water level measurements in the central valley were 64 and 39 feet bls (Figure 3.1-6). Arsenic is the water quality parameter that most frequently exceeds drinking water standards in wells measured in the basin (Table 3.1-4), but groundwater is generally of good chemical quality (Holmes, 2003).

Surface Water Hydrology

The U.S. Geological Survey (USGS) divides and subdivides the United States into successively smaller hydrologic units based on hydrologic features.  These units are classified into four levels. From largest to smallest these are: regions, subregions, accounting units and cataloging units.  A hydrologic unit code (HUC) consisting of two digits for each level in the system is used to identify any hydrologic area (Seaber et al., 1987).  A 6-digit code corresponds to accounting units, which are used by the USGS for designing and managing the National Water Data Network.  There are portions of five watersheds in the planning area at the accounting unit level: Lower Colorado River below Lake Mead; Middle Gila River; Rio Bavispe; San Pedro River; Santa Cruz River; and the Upper Gila River (Figure 3.0-5).  More detailed information on stream flow, springs, reservoirs and general surface water characteristics are found in the individual basin sections.


Click to view Table 3.1-3

Click for Table 3.1-3 Groundwater Data for the Aravaipa Canyon Basin

Click to view Figure 3.1-6

Click for Figure 3.1-6 Aravaipa Canyon BasinGroundwater Conditions

Figure 3.0-10

USGS 6-Digit Hydrologic Unit Code (HUC) Boundaries in the Southeastern Arizona Planning Area

San Pedro-Willcox Watershed

The Arizona portion of the San Pedro River Watershed is contained entirely within the planning area.  Approximately 696 square miles of the Watershed extends into Mexico. In Arizona, the Watershed includes all of the Aravaipa Canyon and Upper San Pedro basins, most of the Lower San Pedro and Willcox basins and relatively small portions of the Cienega Creek, Douglas and San Rafael basins.  A few tributaries to the San Pedro River begin on the southwest slopes of the Huachuca Mountains in the San Rafael Basin and drain into Mexico. (ADWR, 2005a) The San Pedro River enters the U.S. from Mexico near Palominas (see Figure 3.13-1) and flows north to its confluence with the Gila River. Major tributaries are the Babocomari River and Aravaipa Creek.

With the exception of Whitewater Draw in the extreme southern end of the basin that drains into the Douglas Basin, most of the surface water drainage in the Willcox Basin is to the Willcox Playa.  The playa occupies about 50 square miles in the center of the basin and is a remnant of Pleistocene-age Lake Cochise. (Oram, 1993)


Some stretches of the San Pedro River are perennial, although recent drought and delay of the summer monsoon has affected some previously perennial stretches for short periods of time, most notably at Charleston in the Upper San Pedro Basin. The Babocomari River, in the Upper San Pedro Basin, is perennial in its upper reach. Aravaipa Creek is perennial within Aravaipa Canyon above its confluence with the San Pedro River as are three of its tributaries in the Aravaipa Canyon Basin (see Figures 3.1-5 and 3.8-6).  Other perennial streams are found in the Lower San Pedro, Upper San Pedro and Willcox basins (Figures 3.8-6, 3.13-5 and 3.14-5).

There are 12 active streamgages in the watershed; two in the Lower San Pedro Basin and 10 in the Upper San Pedro Basin. The gage on the San Pedro River at Charleston has been in operation since 1904. The largest annual flow ever measured in the watershed, (152,798 acre-feet), was recorded at this gage in 1914.  More recently, in 1984, a maximum annual flow of 102,107 acre-feet was measured at the gage on the San Pedro River near Tombstone.  Median annual flow at these gages is 33,203 acre-feet and 29,654 acre-feet, respectively.

The only major springs in the watershed are found in the Lower San Pedro and Upper San Pedro basins. There are 14 major springs in the Lower San Pedro Basin. The largest, Cooks Lake Spring, had a discharge rate of 1,000 gpm when last measured in 1951.  Twelve major springs have been identified in the Upper San Pedro Basin. The largest is Garden Canyon No.1 with a discharge of 134 gpm measured in 1963. Most of the spring measurements in both basins date from before 1980 and may not be indicative of current conditions (see Tables 3.8-5 and 3.13-5).

Fifteen miles of the San Pedro River in the Lower San Pedro Basin from Aravaipa Creek to the Gila River are impaired due to elevated concentrations of E. coli and selenium (Table 3.8-7). In the Upper San Pedro Basin, water quality standards were exceeded in three reaches of the San Pedro River for a total of 53 miles. These reaches are impaired due to elevated levels of E. coli, nitrate and copper (Table 3.13-6).



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