Three-Bar Wildlife Area

Watershed D

AREA: 80.5 ac (32.6 ha)

SLOPE: Upper slopes are steep, often exceeding 60 %.

ASPECT: Northeast facing

ELEVATION: 3,700 to 5,250 ft (1,130 to 1,600 m)

VEGETATION: Chaparral—Dominant shrubs are shrub live oak, birchleaf mountainmahogany, sugar sumac, and Emory oak (crown cover averaged 60 to 75%).

PARENT MATERIAL: Course granite

GAGE: 90° V-notch

PERIOD OF RECORD: 1956 (partial) through 1983

HISTORY: This is one of the Three Bar watersheds located west of Lake Roosevelt in the Three Bar Wildlife Area, which is maintained cattle-free for game management studies. Stream and rain gages were installed in 1956. Streams were intermittent, flowing about one-third of the time during the first 3 years (1956-1959), and yielding less than 1 inch per year average flow (Hibbert et al 1974). The Boulder wildfire swept over the area in June 1959, topkilling all shrubs (Glendening et al 1961).

TREATMENT: None

OBJECTIVE: Watershed D was used as a hydrologic reference watershed. A paired watershed methodology was used to evaluate treatment response. Two watersheds with similar characteristics (e.g., size, vegetation, precipitation, and soil type) were selected and before any watershed manipulation was done, runoff from each watershed was measured for several years to determine streamflow variations under pretreatment conditions. The number of years required depends on year to year variability normally experienced. In the semi-arid southwestern United States, it usually take about 7 years of pretreatment calibration to define a pretreatment relationship. During this time, the quantity and quality of other natural resources were also inventoried (e.g., soil loss, forage production, animal types and populations).

With pretreatment measurements completed, one of the watersheds was designated to be the untreated or "control" watershed. It was shown to respond to environmental influences in a particular manner to the watershed where the experimental manipulation or treatment was to be applied.

Measurements continued on both the experimental and control watersheds for several years after a treatment was applied. Streamflow, sediment production, and water quality were monitored regularly, and other resources were reinventoried periodically. Changes caused by the management practice applied to the experimental unit were evaluated by comparing posttreatment values to the pretreatment data relationships.

SELECTED REFERENCES

Glendening, G. E., C. P. Pase, and P. Ingebo. 1961. Preliminary hydrologic effects of wildfire in chaparral. Arizona Watershed Symposium, Proceedings 5:12-15.

Hibbert, A.R.; Davis, E.A.; Scholl, D.G. 1974. Chaparral conversion. Part I: Water yield response and effects on other resources. USDA Forest Service Research Paper RM-17, 36 p. Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.