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The dam undergoes safety modifications in the 1990’s, raising its height and re-skinning it with concrete.
Photo Courtesy SRP

Arizona’s Roosevelt Dam Celebrates Centennial

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On March 18, 1911, Theodore Roosevelt pressed a button, releasing the first flow of water from a dam bearing his name, deep within the Arizona Territory.

Photo Courtesy SRP
Dignataries witness laying of the corner stone for Theodore Roosevelt Dam.
Roosevelt Dam today, celebrating the centennial anniversary of its completion.
Photo by Scott Blair
Roosevelt Dam today, celebrating the centennial anniversary of its completion.
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“If there could be any monument which would appeal to any man, surely this is it,” Roosevelt told the crowd of 1,000 who had assembled in the remote Superstitions Wilderness, 76 miles northeast of Phoenix.

The former president had ardently campaigned for and signed the 1902 National Reclamation Act, making the dam, today’s Bureau of Reclamation and an irrigated West possible.

“Great things will take place in the Salt River Valley due to this project,” Roosevelt envisioned. A year later, Arizona became the 48th state.

Later this week, modern-day Arizonans will gather exactly 100 years later near the site that Roosevelt inaugurated the dam to celebrate its centennial.

Phoenix had begun in the decades following the Civil War as an agricultural community building on the early Hohokam canal system, but growth sputtered because of recurrent flood/drought cycles.

By controlling the vagaries of the area’s 13,000-sq-mile mountain watershed, the Theodore Roosevelt Dam generated today’s desert lifestyle, exemplified by Phoenix.

“The dam transformed a volatile water supply to a steady one,” says James LaBar, a principal historical analyst for Tempe-based Salt River Project, the largest provider of power and water to the greater Phoenix metropolitan area and manager of the Roosevelt Dam as well as seven additional storage and diversion dams. “In doing that, the dam transformed Arizona and the Southwest.”

“Because of the foresight of early settlers and multiple engineers, and the work of land surveyors, contractors and laborers, the watershed was protected so that its abundant supplies would benefit everyone in the Valley,” says Shelly C. Dudley, SRP’s senior historical analyst.

Originally called the Tonto Basin Dam for its location at “The Crossing,” a narrow gorge just south of the confluence of the Tonto Creek and the Salt River, the cyclopean-masonry gravity-arch dam was, at its building, the highest of its kind in the world. The dam performs on the “keystone effect”: the fuller the reservoir, the stronger it is.

Begun in 1905 by the newly formed U.S. Reclamation Service, the approximately $3.8-million dam was 280 ft high at its 16-ft-wide, 723-ft-long crest — with a roadway configured to accommodate two Model-T Fords abreast. Anchored by a maximum 184-ft base width, the dam impounded a reservoir with a storage capacity of 1,336,734 acre feet intended for irrigation, flood control and power generation.

Left and right spillways could discharge 150,000 cubic ft of water per second in flood conditions and generate 36 MW of power. Its reservoir — at the time the largest man-made lake in the world — remains a recreational attraction in the Tonto National Forest.

Denver-based general contractor John M. O’Rourke Co.’s first hurdle was to simply get the manpower and materials to the remote site, Labar says. In order to build the 60-mile road through the mountains and desert from Mesa, the cities of Phoenix, Mesa, and Tempe bonded themselves for approximately $75,000 to aid in the construction of the Apache Trail, now S.R. 88.

Work continued through excavation, erecting the 1,200-ft-long cableways over the site and building the cofferdams and flume to keep river water out.

The dam was faced from boulders cut or blasted from the surrounding sandstone cliffs; these were bonded with mortar and concrete. The first stone, weighing six tons, was set Sept. 20, 1906 by stonemasons, many of whom were Italian immigrants from Pennsylvania. These boulders faced the downstream and the slightly bowed upstream sides.

Between these, laborers placed large stones weighing up to ten tons each, carried by the cableways, often at night to free the units for mortar hauling during the day. Each stone was lowered into waiting mortar and fitted into place. Workers filled gaps with spall, or smaller rocks, and vertical spaces with mortar.

Although construction hampered by floods through the building process, Roosevelt Dam was completed by February 1911. Four years later, the reservoir was full, and water was released over the left and right spillways April 14, 1915. Some of this was used to christen the U.S.S. Arizona, bombed at Pearl Harbor, launching the U.S. into World War II.

In 1963, the dam became a National Historic Landmark, and in 1970 the American Society of Civil Engineers named the dam a National Historic Civil Engineering Landmark.

In 1989, crews began to raise and fortify the dam, as mandated by the Reclamation Safety of Dams Act of 1976. Completed in 1996, the now 357-ft concrete-faced dam exceeds the original by 77 ft. Traffic was moved off the dam and onto the new 1,080-ft Roosevelt Lake Bridge.

The $434.4-million dam modification resulted from Dept. of Interior concerns that the aging dam might not safely handle a probable maximum flood or a maximum credible earthquake. As the only dam on the Salt and Verde rivers system with flood control capability, its stability is essential to the safety and vitality of the Phoenix metropolitan area.

The modification project added 557,000 acre ft of flood control, approximately 1.2 million acre ft of dam-safety space and 300,000 acre ft of water-storage space for consumption by Valley residents.

The J.A. Jones Construction Co. of Charlotte, N.C., completed the dam-raising, overlaying the original structure with 450,000 cubic yards of concrete placed in blocks varying from 10- to 50-ft thick.

Other work included modifications to the turbine and replacement of the generator to handle increased head pressures from the new capacity. A lake tap with steel intake structure that was added to improve low-level release capabilities was especially challenging due to the need to use divers for the underwater construction, says Tom Hepler, principal designer at the dam between 1990 and 1996.

On January 19, 1993, a 100-plus year flood caused reservoir waters to overtop the dam directly above the powerhouse. The flooding caused $1 million in damage and a six-month delay to construction.

After an extensive cleanup of the powerhouse, work continued on the turbine and the unit was completed in time for summer peak power demands in June 1995, says John D. Wilkie, resident engineer at the dam from 1987-1997.

Today, the dam continues to serve the Phoenix area, and water levels have increased to a healthy 93% of peak levels.

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