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Hydrology of the Donnelly Wash 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. 

Donnelly Wash Basin

Donnelly Wash Basin is a relatively small basin with few inhabitants. The principal aquifer is a strip of basin fill that covers about 30 percent of the basin.  The rest of the basin is composed of hardrock that surrounds and underlies the basin fill (Overby, 2000). A 16-mile reach of the Gila River flows east to west through the basin, which is also drained by Donnelly Wash and Box O Wash located on the south side of the Gila River. In general, groundwater flow follows surface water drainage patterns, flowing toward the Gila River. Aquifer recharge is from the mountain fronts and streambed infiltration.  Groundwater is discharged from the alluvium into the Gila River and from domestic and stock wells. Storage estimates for the basin range from 140,000 acre-feet to 2.0 maf. (Table 3.4-3.)  Depth to water in the basin fill varies from about 150 feet in the north, 256 feet in the center, and about 370 feet in the south. Water levels are more shallow in wells located in the hardrock areas (Overby, 2000).  Elevated fluoride concentrations were measured in two springs in the basin (Table 3.4-4).  Eleven water samples collected by the Department in 1996 and 1997 did not find elevated fluoride levels in groundwater in either the alluvium or the hardrock (Overby, 2000).

Click to view Table 3.4-2

Click for Table 3.4-3 Groundwater Data for the

Donnelly Wash Basin



Click to view Figure 3.0-5

Click to view Figure 3.0-5 USGS 6-Digit Hydrologic Unit Code Boundaries in the Southeastern Arizona Planning Area

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). 

Middle Gila

The Middle Gila Watershed extends west from Coolidge Dam to the confluence of the Gila and Salt rivers in the Phoenix AMA.  The San Pedro River is the major tributary to this watershed in the Southeastern Arizona Planning Area.  Dripping Springs Wash, Donnelly Wash and the northernmost part of the Lower San Pedro basins are included in the Watershed.  Below Coolidge Dam, flow in the Gila River is from releases from the San Carlos Reservoir and flood flow from the San Pedro River (ADWR, 1994). Perennial streams include the Gila River, and portions of the San Pedro River and Mineral Creek in the Lower San Pedro Basin, Box Canyon in the Donnelly Wash Basin and Mescal Creek in the Dripping Springs Wash Basin (see Figures 3.8-6, 3.5-5 and 3.6-5).

Since 1936, an average of 260,000 AFA of reservoir storage and inflows have been released to the river below Coolidge Dam (ADWR, 2006).  There are three streamgages in the watershed. The highest annual flow was recorded at the Kelvin gage where a flow of 2.375 maf was measured in 1993. Annual median flow at this gage is approximately 324,300 acre-feet (see Table 3.8-2). This gage is located downstream of the confluence of the San Pedro and Gila rivers.

There are two major (10 gpm or greater) springs in the watershed, both located in the Dripping Springs Wash Basin. Both are warm springs with measured discharges of 200 gpm (Mescal Warm Spring) and 165 gpm (Coolidge Dam Warm Spring). These measurements were taken during or prior to 1982 and may not be indicative of current conditions.

Ten miles of Mineral Creek, located northwest of Kearny, are impaired due to elevated concentration of copper and selenium.



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