Groundwater Hydrology

Southern Portion

Groundwater from three basins in the southern portion of the planning area flows south into Mexico. These basins are the Douglas and San Bernardino Valley basins in the southeastern part of the planning area and the San Rafael Basin in the southwest corner.

San Bernardino Valley

The San Bernardino Valley Basin is covered by volcanic flows and cinder cones with some relatively thin alluvial deposits. Groundwater is obtained from sand and gravel interbedded with basalt flows or from shallow alluvium. Springs and artesian wells support wetlands designated as the San Bernardino National Wildlife Refuge adjacent to the international border. Groundwater flow is from the mountains toward the valley center and south to Mexico. Estimated groundwater recharge is 9,000 AFA and groundwater storage estimates range from 1.6 to 2.0 maf (Table 3.11-3).  Most wells in the basin are located immediately north of the international border where water levels are generally less than 100 feet bls. The depth to water increases to the north and toward the mountains along the basin margins on the west, north and east. Little groundwater or water quality data are available for the basin.  Elevated nitrate levels were found in two wells measured in the basin (Table 3.11-4).

Click to view Table 3.11-3 Groundwater Data for the San Bernardino Valley Basin

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). 

Rio de Bavispe

The Rio de Bavispe Watershed drains south and extends into New Mexico and Mexico. Major drainages in Arizona are Whitewater Draw and Black Draw, which are tributary to the Rio de Bavispe in Mexico. The Rio de Bavispe joins the Rio Yaqui which discharges into the Gulf of California. The watershed includes most of the Douglas Basin, the southernmost portion of the Willcox Basin, and the entire San Bernardino Valley Basin. Whitewater Draw is the major drainage in the Douglas Basin. Black Draw is the main surface water drainage in the San Bernardino Valley Basin and becomes perennial just north of the international boundary.  In this basin, artesian wells and springs support wetlands near the border. In addition to Black Draw, perennial streams in the watershed include reaches of Rucker Canyon in the Willcox Basin, and Leslie Creek in the Douglas and Willcox basins  (see Figures 3.5-5 and 3.14-5).

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