« PreviousContinue »
SALT RIVER PROJECT, ARIZONA
BY LEWIS J. WORKMAN, ASSOCIATE ENGINEER, BUREAU OF RECLAMATION
THE SALT RIVER PROJECT is located in the southcentral part of Arizona in the vicinity of Phoenix. It was one of the first irrigation projects authorized under the Reclamation Act of 1902, and comprises about 250,000 acres of irrigated lands on either side of Salt River. The first problem encountered was the provision of an adequate storage system with a controlled flow in Salt River, for which purpose Roosevelt Dam was constructed in 1906-11. The dam is located in a rugged, mountainous country, east and north of Phoenix, about 63 miles from Mesa and 35 miles from Globe. It is built in a narrow canyon of Salt River, a short distance below the junction with Tonto Creek.
The reservoir occupies the valleys of both streams for a distance of approximately 23 miles. As originally completed, it had a storage capacity of 1,284,000 acre-feet. The capacity was increased 83,000 acre-feet in 1913 by raising the crest of the spillway wier 5 feet. In 1923, piers and gates were installed in the spillway, further increasing the storage capacity by 270,000 acre-feet. In 1936 the spillway crest and gates were lowered about 6 feet to provide additional spillway capacity. After allowing for a reduction of 100,000 acre-feet by silting and the increased capacity provided by the spillway gates, the present storage capacity is 1,420,000 acre-feet, with a reservoir area of 17,500 acres.
The watershed, which covers about 5,760 square miles, varies from desert with a mean annual precipitation of about 8 inches to heavily timbered mountain regions with a precipitation of 35 inches. The flow of the river at the dam site has a wide fluctuation, varying from low flows of a few hundred second-feet to a maximum daily flow, estimated from records below the mouth of the Verde, of 150,000 second-feet, occurring in February 1891.
The contract for the construction of the dam was awarded to John M. O'Rourke & Co., of Galveston, Tex., in April 1905. Owing to the fact that the dam site was located in a mountain region, practically inaccessible for moving supplies, a large amount of preliminary work was necessary by Government forces before actual construction could be
started. The nearest railroad point, Globe, Ariz., was reached over a rough mountain road. This road was relocated in places and improved so that it served for the transportation of freight until 1905. Another road was built connecting Mesa, Ariz., with the dam site. Mesa had the advantage of being served by two competitive railroad lines, so that better freight rates could be obtained. The Mesa road was about 63 miles long, some 25 miles of it being over a flat desert and the remainder through a rough mountainous region which involved a great deal of difficult location and construction. A total of 112 miles of roads were built, a considerable portion of which became permanent highways. A part of the expense of the Mesa road was borne by the cities of Mesa and Phoenix. Apache Indian labor was used to a great extent on the road construction. All freighting to the dam site was done by horsedrawn equipment.
Due to the high cost, as well as the difficulty of freighting lumber from Globe, a portable sawmill was purchased and located in a heavily timbered region of the Sierra Ancha Mountains, about 30 miles from the dam. Practically all lumber used on the job was sawed by this mill at a substantial saving to the project.
Portland cement, if purchased on the open market and hauled to the job, virtually would have prohibited the construction of a masonry dam, due to excessive cost. An excellent supply of dolomitic limestone and clay near the damsite made logical the purchase of a cement mill and its erection at the job. Fuel for burning the clinker presented the greatest problem, but this was solved by using oil shipped from California. During its operation, the mill produced the cement used in the dam as well as in other structures of the project, the total output being about 338,000 barrels. A temporary steam plant of 150 horsepower capacity was installed on the job, to furnish electrical power until a power canal could be constructed and a temporary hydroelectric unit put in service.
Due to the scarcity of a good grade of sand near the dam it was decided to install a sand crushing plant. The dolomitic limestone produced too harsh a product, so sandstone was crushed with it, a mixture of half limestone and half sandstone giving the best results. About 87,000 cubic yards of sand were produced by the crushing plant in its 4 years of operation. Other preliminary construction included the camp buildings, refrigeration plant, telephone lines, and a water supply.
The dam is located in a narrow canyon, about 200 feet wide at the river level, with nearly vertical cliffs rising on either sides. The foundation was explored by drilling three lines of holes across the bottom. The rock encountered was a hard, tough, fine-grained sandstone with a few strata of quartzite. It dips upstream at an angle of about 29° from the horizontal, approximately at right angles to the dam. At the upstream face of the dam a minor fault was uncovered with a displacement of about 8 inches. The rock is of a good quality and required very little excavation for the foundation. A few seams were encountered in the foundation, most of which were filled with fine silt. Several warm springs found in the base were piped together and carried
to the powerhouse to furnish warm water. Seams carrying river water were grouted.
The river was diverted through a tunnel driven beneath the south abutment at river level. The tunnel was designed for use as an outlet after the dam was completed and was 12 feet wide, 10 feet high, and about 480 feet long. The intake is located 125 feet upstream from the dam and is covered with a reinforced concrete structure about 69 feet high, in which provision was made for installing trashracks. The diversion capacity was about 1,300 second-feet with water at the top of the cofferdams. To care for additional flow of the river, it was originally planned to build a sluiceway over the cofferdams. Owing to the unusual size of floods occurring at the beginning of construction, the sluiceway idea was abandoned and work on the lower part of the dam was carried on only at such times as the tunnel could handle the river diversion. A high flood with an estimated peak discharge of 130,000 second-feet in November 1905 completely destroyed all work completed in the canyon and delayed construction for several months.
The dam is of the arch-gravity type with a radius of 410 feet. It was designed as a gravity structure, the arch plan being added to give greater stability. The dimensions of the dam are: Length at the top, including spillways, 1,125 feet; length at the bottom, 235 feet; thickness at the top, 16 feet; thickness at the bottom, 184 feet; maximum height, 284 feet. It is constructed of cyclopean rubble masonry, the large stones being set in portland cement mortar, and the vertical joints being filled with concrete and spalls. The face stone was rough cut and laid in courses with mortar joints of about 2 inches. The masonry in the dam totals 343,000 cubic yards. The spillway excavation furnished practically all the stone required. Where the fault was encountered within masonry lines, it was cleaned out and a masonry cut-off built across the canyon. The curve of the arch misses the fault in the abutment areas.
Materials were transported from the top of the canyon to the dam by two cableways of about 1,200-foot span, and were placed in the dam by stiff-leg derricks. Pumping within the cofferdams was done by hydraulic ejectors operating under a head of about 220 feet from the power canal. The concrete mixing plant was located on the south side of the canyon. The faces of the dam were kept moist and were cooled in hot weather by spraying water from a line of pipes having holes drilled at intervals.
Six high-pressure, Stoney gates, arranged in three pairs, are located in the diversion tunnel at the upstream face of the dam. They are 4 feet 6 inches wide by 10 feet high and are operated by hydraulic cylinders located in a circular
well on the upstream face of the dam. Water can also be drawn from the reservoir through an outlet located on the north side of the dam. The inlet is 123 feet below the top of the dam and the outflow is controlled by three 58-inch balanced valves. Three 60-inch, cast-iron pipes led from the valves to a 9-foot diameter, concrete lined tunnel with the outlet end under the edge of the cliff in the north spillway.
There are two spillways, one on either end of the dam, with a total initial length of 402 feet and a total capacity of 150,000 second-feet. As first constructed, the spillways were of the plain weir type with uncontrolled crests 20 feet below the roadway surface. A highway, 16 feet wide, crosses the dam, with the approach across each spillway being over a three-span, reinforced concrete arch bridge.
The last of the masonry was placed in the main structure in February 1911, the dedication being held on March 18, 1911, at which the late ex-President Theodore Roosevelt was present, the dam having been named in his honor.
It was decided at the beginning of the work to utilize the fall of the river above the reservoir limits and to install a temporary hydroelectric unit until the permanent power plant could be placed in operation. A power canal 19i-. miles long, with a capacity of 225 second-feet, was built along the south side of the river. A concrete diversion dam 450 feet long and about 7 feet high, was built at the intake. Distributed along the length of the canal are 21 tunnels with a total length of about 2 miles. The lower end of the
canal was connected to a 1,200-horsepower hydroelectric unit, operating under a head of 220 feet, water being supplied through a 7-foot diameter penstock which passes under the left abutment of the dam. The unit was installed in a cave behind the permanent plant and was placed in operation in April 1906.
Provision was made in the main powerhouse for the ultimate installation of six units. The building, located just below the dam on the south side of the river, was constructed by Government forces. It is about 125 feet long by 36 feet wide, and has a total height of 33 feet from the floor to the top of the crane rail. It was constructed of concrete with stone facing. Two penstocks were originally provided, comprising the 7-foot diameter steel pipe connected to the power canal and a 10-foot diameter steel pipe passing through the dam. The intake for the 10-foot penstock is located about 165 feet below the top of the dam and is covered with a movable trashrack. The 10-foot diameter penstock has a drop of 50 feet between the intake and the powerhouse. A 10-foot diameter cylinder gate is installed at the powerhouse for emergency closure.
The first three power units were placed in operation in 1909. These units were 1,200-horsepower, 3-phase, 25cycle, 2,300-volt machines, operated by vertical type turbines under a head of 220 feet obtained from the power canal.
Two other units of the same type and output were installed and connected to the 10-foot penstock. The runners of these machines were designed for heads varying from 112 to 228 feet, to take care of changing elevation of the reservoir surface. The sixth unit is of the variable head type with a capacity of about 5,000 horsepower and operating in connection with the 10-foot penstock. It was not installed until 1915. Two reservoir outlets, controlled by two 43-inch balanced valves, were installed in the upstream end of the powerhouse and connected to the 10-foot diameter penstock. The transformer house was located farther downstream on the south side, below the spillway channel. It was built of concrete with stone facing. The voltage was stepped up from 2,300 to 45,000 volts. The power generated is largely used for drainage and irrigation pumping needs on the project.
The cost of the dam and reservoir up to 1913 totaled approximately $3,650,000. Lumber brought in from Globe would have cost S60 to $65 per thousand board feet. The portable sawmill produced 2,964,000 board feet at a cost of $44 per thousand delivered to the work. The cement mill produced 338,452 barrels of portland cement at a cost of $3.14 per barrel. Cement purchased on the market would have cost about $4.89 per barrel delivered at the dam. The unit cost of crushing 87,000 cubic yards of sand was $1.58 per cubic yard. Unit contract prices were as follows:
Per cubic yard
Earth excavation $1.75
Rock excavation (below low water) 5.00
Rock excavation (above low water) 1.50
Rubble masonry in dam 3.15
Rubble masonry in wing walls 4.75
Bridges (each) 7,500
Materials were furnished by the Government. The cost of diverting the river, but not including the diversion tunnel, and unwatering foundations was included in the prices bid for excavation and placing masonry.
The original power and outlet equipment at Roosevelt Dam was in a pioneer stage of development at the time of its installation. Since that time changes and refinements have been made in the various features. The project was turned over to the Salt River Valley Water Users' Association in 1917. All changes previous to that date were made by the Bureau of Reclamation. Since then the association has made most of the changes, subject to the approval of the Bureau.
The Stoney gates in the south tunnel did not operate satisfactorily under high heads. Two 58-inch-diameter bronze pipes were installed in a concrete plug downstream from the Stoney gates. Each pipe was equipped with a 30- by 38-inch bronze slide gate. Two 48-inch-diameter steel pipes were connected to the bronze pipes and extended to the outlet of the tunnel. The power canal was often washed out in places during heavy rains. To eliminate the interruptions from this source, two riser connections were made from the two 48-inch pipes to the 7-foot penstock. Two 38-inch needle valves were installed on the downstream end of the 48-inch pipes to permit operation of the three 1,200-horsepower machines from the reservoir when necessary. In 1923 the two 43-inch, balanced valves were removed from the powerhouse and a 10,000 horsepower unit installed in the space they had occupied. A 14-footdiameter tunnel was driven from the powerhouse to a chamber in the south tunnel. In this tunnel a 10-foot diameter penstock was installed to operate the new unit. Changes have been made in some of the units and in the
station power equipment, bringing the total installed capacity up to 24,000 horsepower. An additional story was erected on top of the powerhouse and new transformer equipment installed. The voltage is stepped up on the transmission lines to 110,000 volts.
The north outlet works have been altered by plugging the 9-foot tunnel and moving the outlet over to the left of the spillway. Three 54-inch diameter, steel liners were installed and three 54-inch needle valves placed on the outlet end. These valves were later removed and placed in service at the Mormon Flat and Stewart Mountain Dams. Two 54-inch butterfly valves are located on the outlet ends of the two outside pipes, the center pipe being close by a bulkhead. The three 58-inch balanced valves were removed from the inlets and trash bars installed.
The spillway crests were raised 5 feet, soon after the dam was completed, to provide additional storage. In 1923 the spillways were provided with radial gates and piers to further increase the reservoir storage. The crest was lowered 9 inches to compensate for the effect of the piers on discharge capacity. The radial gates are 15 feet 9 inches high by 20 feet long, 10 being installed on the south and 9 on the north spillway. The spillway was repaired and altered in 1936. The crest was then lowered 6 feet, to increase the discharge capacity, new motor operated hoists were installed and changes were made on the piers and gates. The power canal inlet was repaired and altered during the same year.
LATER POWER DEVELOPMENT
In 1923 the association, with the approval of the Bureau, undertook to develop the power resources of the river into one coordinated system. Horse Mesa, Mormon Flat, and Stewart Mountain Dams were built between Roosevelt Dam and Granite Reef Diversion Dam. These dams provide additional storage of irrigation water as well as creating an effective power system. Almost the entire fall of the river within these limits is now utilized for generation of power.
The Roosevelt Masonry Dam (and Specifications). Engineering News, Jan. 12, 1905.
Progress on Roosevelt Dam. Engineering News, Sept. 10, 1908.
Construction of Roosevelt Dam (Including Costs). Engineering Record Dec. 31, 1910.