Historical Perspective on the Central
WaterToo Much or Too Little
Water has been recognized as an important resource in central Arizona
and the arid Southwest that has affected populations occupying the Salt
River Valley for centuries (Baker
1999b). Water related activities have been documented since about
200 BC, when Hohokam Indians settled the Valley and constructed canals
to irrigate their fields. Europeans began to settle in the Phoenix area
in the late 1860s and depended on irrigation water from the Salt River
for agriculture. However, water supplies fluctuated greatly because
the river often flooded in winter and dried up in the summer. There
were no impoundments to store water for the dry seasons.
Dams for Water Storage
In 1904, the Salt River Water Users Association signed an agreement
with the United States government under the National Reclamation Act to
build a dam on the Salt River below the confluence with Tonto Creek. The
Roosevelt or Theodore Roosevelt Dam, the first of six dams on the Salt
and Verde Rivers, was completed in 1911 and the Salt River Project was
In the early 20th century, watershed managers became concerned that erosion
on the adjacent and headwater watersheds of the Salt River would move
sediment into the newly constructed Roosevelt Reservoir and decrease its
capacity. Measurements indicated that 101,000 acre-ft of coarse granitic
sediments had accumulated behind Roosevelt Dam between 1909 and 1925.
The Summit Plots, located between Globe, Arizona and Lake Roosevelt, were
established in 1925 by the USDA Forest Service 15 mi upstream from Roosevelt
Dam to study the effects of vegetation recovery, mechanical stabilization,
and cover changes on stormflow and sediment yields from the lower chaparral
zone (Rich 1961).
Research Studies: Increase Water and Control Sediment
During the mid-1950s, the amount of water stored in project lakes was
very low and, as a consequence, apprehension arose among some residents
that a serious water shortage impended. Groundwater supplies in the Salt
River valley were also being rapidly depleted, and pumping costs were
Long-term studies at Sierra
Ancha Experimental Forest in central Arizona showed some potential
for increasing runoff by converting chaparral shrublands to grass. Based
on this, a belief existed that water yield from the Salt and Verde Watersheds
could be significantly increased by treatment of various vegetation types.
Suggestions for water-yield improvement included widespread burning of
chaparral, eradication of pinyon-juniper by burning and mechanical methods,
and prescribed burning in ponderosa pine.
Spring runoff at Sierra Ancha Weir
In the summer of 1955, several ranchers met with a USDA Forest Service
representative and an official with the Salt River Project on the Beaver
Creek watershed near Flagstaff. These people were concerned that increasing
densities of trees and shrubs on upland watersheds on the Salt and Verde
River basins were reducing the flow of streams and the supply of livestock
Barr ReportAs a result of this meeting, the University of
Arizona was commissioned to investigate the potential for increasing water
yield from the state's forests and ranges. The somewhat optimistic university
findings, titled Recovering rainfall (Barr 1956) and better known as the
Barr Report, suggested that surface-water runoff from mountain watersheds
might be increased by replacing high water-using plants, such as trees
and shrubs, with low water users such as grass. This 1956 report resulted
in demand for an immediate action program.
Cover of "Barr report"
Arizona Water Program
In responding to this demand, the Arizona Water Program of the USDA Forest
Service was initiated in the late 1950s to evaluate the usefulness of
selected vegetative management programs in increasing water yields and
other multiple resource benefits in the Salt River Basin (Arizona
State Land Department 1962). The Beaver Creek watershed became a significant
component of this program of experimental studies in the pinyon-juniper
and ponderosa pine types.
Experimental WatershedsTwenty pilot watersheds were established
between 1957 and 1962 to test the effects of vegetation management practices
on water yield and other resources (Brown, H.E. et al. 1974). Of the 20
watersheds, 18 were from 66 to 2,036 acres in size; 3 in the Utah juniper
type, 3 in the alligator juniper type, and 12 in the ponderosa pine type.
The other 2 catchments, encompassing 12,100 and 16,500 acres of ponderosa
pine forests, were set aside to demonstrate the effects of management
practices on areas that managers work with operationally.
Stream gauges were built at the outlets of all watersheds, while sediment-measuring
devices, in which suspended sediments and bedloads could be collected,
were constructed on some. A network of precipitation gauges was installed
throughout the study area (Baker
Timber, herbage, and wildlife resources were inventoried (the latter
by the Arizona Game and Fish Department) on a system of permanently-located
primary sampling units established on each pilot watershed (Brown, H.E.
et al. 1974, Clary et al. 1974). Point sampling techniques were used to
monitor stand structures, tree-stem form, and species composition over
time. These sampling points were also center-points for plots of varying
sizes on which regeneration success, herbaceous vegetation, wildlife populations
and habitat preferences, and hydrologic conditions were sampled.
Suspended sediment intake (A),
Beaver Creek flume (B),
sediment basin for bedload measurements(C)
Resource SamplingYields of water, timber, forage, and other natural
resource products from the pilot watersheds were determined before any
treatments were applied to provide the needed pre-treatment calibration
information. Using a paired-watershed approach,
one watershed was then altered through vegetative manipulation and the
other was held in its original condition as a control for evaluations
of potential changes in these yields. If a resource change was detected
after treatment, it was attributed to the treatment implemented.
To refine the findings from the studies on the pilot watersheds for use
over a wide range of conditions, 24 smaller watersheds, 12 to 40 acres
in size, with more uniform soil, plant life, and topography, were established
in the early 1970s to sample the range of diverse ecological characteristics
in the ponderosa pine forests (Brown,
H.E. et al. 1974). To compare the findings from watersheds with soils
developed on basalt and cinders (55% of the Salt-Verde River Basin) to
watersheds on soils formed from sedimentary rocks (45% of the Salt-Verde
River Basin), 3 of these smaller watersheds were established on limestone
soils at Rattle Burn (Campbell
et al. 1977) and 4 were established on sandstone and tertiary alluvium
soils near Heber (2 per each soil parent material) (Ffolliott
and Baker 1977).