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Streamflow records obtained in the upper Santa Cruz River basin of southern Arizona, United States, and northern Sonora, Mexico, have been analyzed to aid in the appraisal of the surface-water resources of the area. Records are available for 15 sites, and the length of record ranges from 60 years for the gaging station on the Santa .Cruz River at Tucson to 6 years for Pantano Wash near Vail. The analysis provides information on flow duration, low-flow frequency magnitude, flood-volume frequency and magnitude, and storage requirements to maintain selected draft rates. Flood-peak information collected from the gaging stations has been projected on a regional basis from which estimates of flood magnitude and frequency may be made for any site in the basin.
Most streams in the 3,503-square-mile basin are ephemeral. Ground water sustains low flows only at Santa Cruz River near Nogales, Sonoita Creek near Patagonia, and Pantano Wash near Vail. Elsewhere, flow occurs only in direct response to precipitation. The median number of days per year in which there is no flow ranges from 4 at Sonoita Creek near Patagonia to 335 at Rillito Creek near Tomson. The streamflow is extremely variable from year to year, and annual flows have a coefficient of variation close to or exceeding unity at most stations.
Although the amount of flow in the basin is small most of the time, the area is subject to floods. Most floods result from high-intensity precipitation caused by thunderstorms during the period ,July to September. Occasionally, when snowfall at the lower altitudes is followed by rain, winter floods produce large volumes of flow.
Additional Publication Details
USGS Numbered Series
Streamflow in the upper Santa Cruz River basin, Santa Cruz and Pima Counties, Arizona