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).