THE SIERRA ANCHA EXPERIMENTAL FOREST, ARIZONA: A BRIEF HISTORY

Abstract

The availability of adequate and reliable water supplies has always been a critical concern in central Arizona since prehistoric times. The early European settlers in 1868 initially utilized the ancient Hohokam Indian canal system which drew water from the Salt River. However, the river fluctuated with periods of drought and periods of high flows which destroyed the diversion structures. The settlers proposed a dam to store water and to regulate flows. In 1903, the Salt River Water Users Association was formed and an agreement was reached with the U.S. Government for the construction of a dam on the Salt River at its junction with Tonto Creek. The Salt River drains more than 4,306 square miles (mi2) from the White Mountains of eastern Arizona to the confluence with Tonto Creek. Tonto Creek drains a 1,000-mi2 watershed above the confluence. The agreement was authorized under the Reclamation Act of 1902. The Theodore Roosevelt Dam was started in 1905, completed in 1911, and dedicated in 1911 (Salt River Project 2002). The dam has the capacity to store 2.9 million acre-feet (af) of water. However, between 1909 and 1925, 101,000 af of sediment were accumulated behind Roosevelt Dam (Rich 1961). Much of it came from erosion on the granitic soils from the chaparral lands above the reservoir, and much of the erosion was blamed on overgrazing by domestic livestock. Water users were concerned that accelerated sedimentation would eventually compromise the capacity of the dam to hold sufficient water for downstream demands. The Tonto National Forest was originally created to manage the watershed above Roosevelt Dam and to prevent siltation. The Summit Plots, located between Globe, Arizona, and Lake Roosevelt were established in 1925 by the U.S. Department of Agriculture to study the effects of vegetation recovery, mechanical stabilization, and plant cover changes on stormflows and sediment yields from the lower chaparral zone (Rich 1961). The area initially was part of the Crook National Forest which was later added to the Tonto National Forest. The Summit Watersheds consisted of nine small watersheds ranging in size from 0.37 to 1.23 acres (ac). Elevations are between 3,636 and 3,905 feet (ft). The treatments included: exclusion of livestock and seeding grasses, winter grazing, hardware cloth check dams, grubbing brush, sloping gullies and grass seeding. Protection from grazing did not pro duce changes in runoff or sedimentation. Treatments that reduced surface runoff also reduced erosion. Hardware cloth check dams reduce total erosion, and mulch plus grass treatments checked erosion and sediment movement. Runoff was reduced by the combined treatments (Rich 1961). The Summit Watersheds were integrated into the Parker Creek Erosion-Streamflow Station in 1932.