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Hydrology of the Cienega Creek Basin

Groundwater Hydrology

Other Basins

Two basins, Cienega Creek and Willcox, have hydrogeologic conditions that are unique in the planning area.  The Cienega Creek Basin has three groundwater sections based on the presence of distinctive aquifers and groundwater flows to the north and to the southwest. Groundwater in the Willcox Basin is generally isolated from surrounding basins, with groundwater flow primarily to the center of the basin, the Willcox Playa.

Cienega Creek Basin

The Cienega Creek Basin consists of a narrow northeast trending alluvial valley, drained by Cienega and Sonoita creeks, and surrounded by fault-block mountains.  There is a surface water divide southwest of Sonoita, with Cienega Creek flowing northeast and Sonoita Creek flowing to the south and west.  Hydrogeologic conditions in the basin are complex. The basin has been divided into three subareas based on the presence of a distinctive aquifer or set of aquifers: upper Cienega Creek, lower Cienega Creek and Sonoita Creek. 

“The Narrows” (T18S, R18E, S6), where bedrock outcrops on both sides of the Cienega Creek channel, divides the lower and upper Cienega Creek subareas (Bota, 1997). The upper Cienega Creek subarea includes most of the basin’s central valley. The main aquifer is basin fill, which is deepest in the southern part of the subarea between Sonoita and Elgin.  To the north, the lower Cienega Creek subarea extends to the northern basin boundary. It contains three aquifers: stream alluvium, basin fill and the Pantano formation. The main aquifer in this subarea is stream alluvium. The basin-fill alluvium is a relatively poor aquifer in this subarea with relatively low well yields and interbedded clay layers that create leaky confined and artesian aquifer conditions. 

The southwestern part of the basin is the Sonoita Creek subarea where the main aquifer is stream alluvium that forms the floodplain of Sonoita Creek and its tributaries and may be up to 90-feet thick.  Wells drilled in the basin fill are generally low yielding. Groundwater flow follows the surface water flow direction with flow toward the northeast, north of Sonoita, and to the south, south of Sonoita.

Groundwater recharge comes from mountain front recharge and streambed infiltration along Cienega and Sonoita creeks and their tributaries.  Groundwater recharge estimates vary from 8,500 to 25,500 AFA, although this estimate does not include the Sonoita Creek subarea (Table 3.3-5). Estimates of groundwater in storage range from 5.1 to 11 maf.  Water level trends are generally stable with some declines noted near Patagonia and east of Sonoita (Figure 3.3-6).  Groundwater quality is generally good although cadmium and copper concentrations exceeding drinking water standards have been measured in several wells in the vicinity of Patagonia.

Click to view Table 3.3-5

Click for Table 3.3-5 Groundwater Data for the Cienega Creek Basin Geographic Features

Click to view Figure 3.3-6

Click for Figure 3.3-6 Cienega Creek Basin

Groundwater Conditions

Click to view Figure 3.0-5

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). 

Santa Cruz Watershed

The Santa Cruz Watershed includes most of the Cienega Creek and San Rafael basins and extends south into Mexico and west to include the Santa Cruz AMA and most of the Tucson and Pinal AMAs. The Santa Cruz River originates in the San Rafael Valley and flows southward to Mexico before turning north and reentering the U.S. east of Nogales, Arizona.  Surface water in the Cienega Creek Basin drains west to the Santa Cruz River from Sonoita Creek and north to tributaries of the Santa Cruz River from Cienega Creek.

The Santa Cruz River is perennial in the planning area.  In the Cienega Creek Basin there are perennial reaches of Cienega Creek, Sonoita Creek and Red Rock Canyon. The only streamgage on the Santa Cruz River is near Lochiel with a maximum annual flow of 12,600 acre-feet measured in 1955. Median annual flow at this gage is 1,410 acre-feet. The only other streamgage in the watershed is a gage on Cienega Creek near Sonoita (see Table 3.3-2).

Major springs are located only in the Cienega Creek Basin.  The largest of the seven major springs is Monkey Spring southwest of Sonoita with a discharge rate of 430 gpm.  A measurement date is lacking for this spring (Table 3.3-5). 

There are several impaired waters in the Santa Cruz Watershed. Parker Canyon Lake in the San Rafael Basin contains elevated levels of mercury.  In the Cienega Creek Basin, a total of 20 miles of impaired stream reaches occur on Alum Gulch, Harshaw Creek, Humboldt Canyon and on an unnamed tributary to Harshaw Creek. These waters contain concentrations of cadmium, copper, zinc or pH that exceed standards (Table 3.3-6).

 

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