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Hydrology of the Morenci Basin

Groundwater Hydrology

North/Northeastern Portion

Groundwater basins located in the north and northeastern portion of the planning area are Bonita Creek, Dripping Springs Wash, Duncan Valley, Morenci and Safford. The Safford Basin aquifers are primarily stream alluvium and basin fill, while the other basins also contain aquifers composed of volcanic rock or sedimentary rock (Gila Formation). Groundwater flow is toward the Gila River drainage and the Bonita Creek, Duncan Valley and Morenci basins contribute underflow to the Safford Basin. 

Morenci Basin

The Morenci Basin is characterized by steep canyons, mesas and mountains with numerous streams and washes. The basin consists mainly of volcanic rocks (rhyolite and agglomerates overlain by basalt flows). Groundwater is found primarily in alluvial deposits along major water courses and groundwater flow is to the south along the San Francisco River drainage. Groundwater recharge has been estimated at 15,000 AFA and groundwater in storage at 3 maf.  Water level change data in the Morenci Basin are available only for the area near Alpine where the measured depth to water is less than 80 feet bls and water levels rose over 15 feet in one well from 1990-1991 to 2003-2004 (Figure 3.9-7).   Water quality data shows metal contamination in the vicinity of the Morenci Mine.

Click to view Figure 3.9-7

Click to view Figure 3.9-7 Morenci Basin

Groundwater Conditions

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). 

Upper Gila Watershed

The Upper Gila Watershed drains about 7,400 square miles in the planning area above Coolidge Dam and contains the Bonita Creek, Duncan Valley, Morenci, and Safford basins.  Major tributaries include the San Francisco River, Eagle Creek, Bonita Creek, San Simon Creek and the San Carlos River.

An average of about 160,000 AFA of Gila River water flows into Arizona from New Mexico and over 40% of this flow typically occurs in the winter. Tributary inflows from the San Francisco River are significant, typically over 150,000 AFA.  Inflow to the San Carlos Reservoir from the Gila and San Carlos Rivers averages about 310,000 AFA (ADWR, 2006).  There are three active streamgages on the Gila River. The maximum annual flow recorded was at a gage near Solomon with a flow of 1.56 maf in 1993.  Median flow at this gage is approximately 273,000 AFA (see Table 3.10-2).

The San Francisco River is perennial with a number of hot springs located above Clifton. The Gila River has a 35-mile perennial stretch about 20 miles northwest of the New Mexico border. Flow in this stretch is maintained by tributary inflow and springs, including hot springs (ADWR, 1994). Flow in the Gila River becomes intermittent farther downstream due to irrigation diversions and seasonal variations in flow (ADWR, 2006).

The largest spring in the planning area is located in the Safford Basin.  Warm Springs, with a measured discharge of almost 3,400 gpm is located at the headwaters of the San Carlos River.  There are also a number of large springs downstream of Pima near the Gila River (USGS, 2006c). In total, there are 22 major springs in the Safford Basin. Other major springs are found in the Bonita Creek Basin (1 spring), Duncan Valley Basin (2), and Morenci Basin (9).  Most of the spring measurements shown on the springs tables in sections 3.2, 3.7, 3.9 and 3.10 were taken between 1940 and 1982 and may not be indicative of current conditions.

A 15-mile reach of the Gila River in the Duncan Valley Basin is impaired due to elevated selenium concentrations (Table 3.7-7).  In the Safford Basin, a 6-mile reach of the Gila River exceeded the water quality standard for E.coli and turbidity and a 8-mile reach of Cave Creek exceeded the standard for selenium (Table 3.10-7).  In the Morenci Basin, water quality standards were exceeded at Luna Lake and in a 13-mile reach of the San Francisco River near Alpine (Table 3.9-7).



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