Whitespar Watersheds

Description and History

A pair of watersheds located about 8 mi southwest of Prescott, on the Prescott National Forest, were gaged in 1958. One watershed designated as Whitespar A was about 300 acres in size and an adjacent watershed designated as Whitespar B was 250 acres. The elevations of Whitespar A and B range from 5,900 to 7,200 ft. The climate is semi-arid with 26 inches of annual precipitation over 30 yr. About 90% of the streamflow from the untreated watershed occurred between December and April. Medium-dense chaparral composed of shrub live oak/hairy mountain mahogany (Quercus turbinella/Cercocarpus breviflorus) habitat type provided a crown cover of about 50%. Whitespar A was dominated by chaparral with isolated areas of Gambel oak and ponderosa pine along the upper ridges and north-facing slopes. Whitespar B was totally covered with chaparral.

The initial research emphasis on the Whitespar watersheds was on water yield responses, with sediment production as a secondary hydrological evaluation. The major input and output measurements were precipitation, stream discharge, and sediment production. There was also emphasis on developing methods for controlling chaparral and converting a shrub cover to grass. As the research program evolved, environmental and ecological issues became increasingly important. One of these issues was increased nitrate concentrations that had been detected earlier on the Three-Bar experimental watersheds. The need to convert chaparral in a mosaic pattern to enhance wildlife, reduce fire danger and nitrate release resulting from brush control, and improve esthetics strongly influenced later treatments.

The information in this section is excerpted from History of Watershed Research in the Central Arizona Highlands.