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BIBLIOGRAPHY

Cableway Bucket Concretes Owyhee Dam at Rate of 1,000 cublic yards per shift. Constr. Methods 13: 34-8 March '31. illus.

Construction Progress on Dam for Owyhee Irrigation Project. Eng. N. 103: 248-9 Aug. 15, '29. illus.

Design of the Owyhee Dam, Owyhee Project, OregonIdaho. J. L. Savage. New Reclamation Era. 19: 82-5 June '28. illus.

Design of the Owyhee Irrigation Dam. J. L. Savage. Eng. N. 100: 663-7 Apr. 26, "28. illus.; Discussion 100: 648 Apr. 26, '28; Same. West. Constr. N. 3: 284-91 May 10, '28. illus.; Same. Hydraulic Eng. 4: 548-9, 574, 588-9 September "28. illus.

Electric Control for 1,300-foot Cableway at Owyhee Dam. R. F. Emerson. Constr. Methods 12: 44-5 November '30. illus.

Foundation Procedure at Owyhee Dam. Eng. N. 106: 178-82 Jan. 29, '31. illus.

Geological Suite From Eastern Oregon: pt. 2; The Owyhee project; abstract. W. D. Smith. Geol. Soc. of Am., Bul., 39: 169 '28.

Geology of Reservoir and Dam Sites With a Report on the Owyhee Irrigation Project, Oregon. K. Bryan. U.S.G.S Water Supply Paper No. 597: 1-72 Jan. 12, '29. illus.; Bibliography: p. 33-8.

Glory Hole Spillway: Owyhee River Dam. A. P. Connor. Power PI. Eng. 37: 492-3 November '33. illus.

Heavy-Load Cableway Installation for Owyhee Dam. Eng. N. 105: 62 July 10, '30. illus.

High Lights of Owyhee Dam Construction. C. A. Betts, Reclamation Era 25: 81-3 April '35. illus.

Outstanding Features in the Design of the Owyhee Dam, Owyhee project, Oregon-Idaho. J. L. Savage. Hydraulic Eng. 4: 548-9. 574,588-9 September'28. illus.

Owyhee Dam. Eng. & Contr. 67: 311-12 June '28; 67: 379-80 July '28. illus.

Owyhee Dam. J. L. Savage. West. Constr. N. 3: 284-91 May 10, '28. illus.

Owyhee Dam. W. A. Scott. Eng. W. 32: 277-8 June '28. illus.

Owhyee Dam. West. Constr. N. 4: 287 June 10, '29. illus.

Owyhee Dam Dedication Address. F. A. Banks. Reclamation Era 23: 153-5 September '32. illus.

Owyhee Dam in Oregon to be the Highest in World. Hydraulic Eng. 4: 533 August '28.

Owyhee Irrigation Project in Oregon and Idaho. New Reclamation Era 17: 154-7 September '26.

Owyhee Irrigation Project Notes. West. Constr. N. 6: 625 Nov. 25, '31. illus.

Owyhee Irrigation Project, Oregon-Idaho. P. Schuyler. West Constr. N. 6: 381-5 July 25,'31. illus.

Owyhee—Vale Project is Big Boost for Eastern Oregon and Southwestern Idaho. H. M. Sims. Modern Irrigation 3: 18-19, 41 April '27. illus.

Placing Concrete in Owyhee Dam at Rate of 50.000 Cubic Yards per Month. C. A. Betts. Eng. & Contr. 70: 305 November '31. illus.: Same. New Reclamation Era 22:191-2 September'31. illus.

President Coolidgc Approves Owyhee Project Construction. New Reclamation Era. 17: 186-7 November'26.

Pumps Hung From Cables Dewater Damsitc. Eng. & Contr. 69: 185 April '30.

Suspended Pumps Dewater Dam. Constructor 12: 39 September '30. illus.

Wider Horizon for New Equipment Found in Owyhee Project. J. L. Savage. Hydraulic Eng. 5: 32-4, 41 May '29. illus.

World's Highest Dam for Irrigation; Owyhee Reclamation Project. Sci. Am. 141: 39 July'29. illus.

AMERICAN FALLS DAM

MINIDOKA PROJECT, IDAHO

BY O. C. SMITH, ENGINEER, BUREAU OF RECLAMATION

THE AMERICAN FALLS DAM, located on the Snake River at American Falls, Idaho, was built to create a reservoir for storing surplus winter and flood run-off from 16,000 square miles of drainage area ranging in altitude from 4,300 to 10,400 feet. Water so conserved is used to supplement the irrigation supply for about 600,000 acres of developed lands within the Snake River Valley, located both above and below the reservoir: to furnish water for the irrigation of 85,000 acres within the recently constructed Gooding division near Shoshone; and to permit the future development of a large body of irrigable lands in the Minidoka north side pumping extension near Rupert, Idaho. Storage capacity reserved for future irrigation development is now being used on an annual rental basis by developed areas within the Snake River Valley.

RESERVOIR

The reservoir created by the construction of the dam is 25 miles long and has a maximum width of 12 miles. It covers an area of 56,200 acres and has a capacity of 1,700,000 acre-fcet with the normal water surface elevation 4,354.5.

Construction of American Falls Dam and Reservoir involved a number of complicated right-of-way problems. It was necessary to move about three-fourths of the city of American Falls, including the business district; to relocate 2 miles of the main line of the Oregon Short Line Railroad, its depot, industrial tracks, and facilities; to relocate several miles of highway and construct new highway bridges; to acquire about 60,000 acres of rural lands, about one-half of which was in the Fort Hall Indian Reservation and occupied by Indians; and to purchase a large part of the American Falls property of the Idaho Power Co., including more than one hundred town lots, several thousand acres of farm land, two small power plants, and a large part of their power rights. The total cost of the right-ofway and improvements exceeded the cost of the dam by about 61 percent.

DAM SITE

The dam is located about 500 feet above the Idaho Power Co. dam which was built on the brink of the falls several years earlier. At this point massive columnar basalt

60 feet in thickness is exposed in the river bed, while a short distance upstream the basalt is covered by a thick mantle of ancient lake bed sediments. Beneath the basalt lies a layer of obsidian about 20 feet thick, followed by tuff of unknown depth. At the west abutment which rises as a steep bluff, the basalt is covered by more than 100 feet of stratified sand and clay with some sandstone and gravel. The east abutment rises gradually and for a distance of about 2,000 feet from the river the basalt is about 60 to 90 feet thick and is overlain by 5 to 15 feet of soil. Beyond this point there is no basalt and the obsidian, 10 to 50 feet thick, is covered by 30 to 50 feet of sand and clay. A fault forming the falls in the river passes through the west abutment, and a fault or fold crosses the dam site about 2,000 feet cast of the river.

DESIGN OF DAM

The dam is about 5,200 feet long and is divided into six sections. The type used in each section, except the embankment sections, was adopted after extensive cost studies of alternative types for each section and of the use of radial and drum gates in the spillway. Plans for an earth embankment originally considered for the left abutment section, although estimated to be $237,000 cheaper than a concrete gravity section, was discarded due to uncertainty regarding the available supply of suitable material for an earth-fill dam, the greater safety of the concrete design as regards wave action, and the lower maintenance cost. The earth embankment was considered best suited to the right abutment due to the fault crossing the site near the west bank of the river.

The spillway section, located across the river channel and 540 feet in length, is of concrete gravity design with a permanent concrete crest at elevation 4,343.2, a vertical upstream face, and a two-thirds to 1 downstream slope ending in a curved bucket of 35-foot radius. The base of the dam being at about elevation 4,282.0 makes this section about 60 feet high. Resting on the concrete crest are 15 radial gates, each 33 feet long and 11 feet 4 inches high, operated by means of cables running over sheaves in recesses in the piers and attached to hoists installed in a gallery. When the gates arc open the spillway will discharge about 75,000 second-fect under normal reservoir surface.

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Twenty outlet conduits, three through the spillway section and seventeen through the left abutment section, controlled by 5- by 5-foot hydraulically operated slide gates, when fully open under maximum reservoir head, will discharge approximately 22,000 second-feet.

The penstock sections, with a combined length of 180 feet, are of concrete gravity type with vertical upstream face and a two-thirds to 1 downstream slope. The top at elevation 4,359.5 provides 5 feet of freeboard and is 10.5 feet wide, of which 5 feet are cantilevered over the upstream face. Two 15-foot diameter penstocks were installed through the left section, and four through the right section, which were capped at the downstream ends for future power developments. These are provided with concrete trash-rack structures.

The left abutment section, 2,376 feet long, is a concrete gravity section. It has a top width of 8 feet, a vertical up

stream face above elevation 4,325.0, and a slope of 0.2 below that elevation. The downstream face has a slope of two-thirds to 1. The normal freeboard of 5 feet increases to match the top of the embankment at one end and the spillway bridge elevation at the other. It is further increased by a concrete parapet wall 3 feet 8 inches high.

A drainage gallery, 5 feet wide by 7 feet high, traverses the entire length of the concrete sections of the dam and provides access to machinery for operating the slide gates. A radial gate gallery at a higher elevation traverses the length of the spillway section and provides access to the radial gate operating machinery. Transverse galleries connect the longitudinal galleries with convenient adits at the downstream face and with steps leading up to the downstream face to the top of the penstock sections. A 12-inch cast-iron water main, to supply the city of American Falls, was carried across the river through the drainage gallery. A 36-inch steel pipe was installed through the dam, adjacent to the 5- by 5-foot outlets, for future irrigation of land lying between American Falls and Neeley on the south side of Snake River.

The top of the left abutment section is widened to 18 feet between curbs by concrete bents on 18-foot centers and steel I-beam stringers carrying a 7-inch concrete floor and a 2.^-inch asphalt wearing surface. Over the penstock and spillway sections the entire bridge of similar construction is carried on concrete piers, 21 feet wide and 3 feet thick, spaced at 36-foot centers. The roadway elevation over this portion of the dam is 4,366.5.

A concrete cut-off was provided under the upstream face of the concrete sections and grout holes were drilled along the bottom of the cut-off, at 5-foot centers, to depths of approximately 17 feet. These holes were grouted under pressures of 90 to 100 pounds per square inch. Drain holes approximately 20 feet deep at 5-foot centers were located downstream from the grout holes and under the upstream edge of the drainage gallery to which they were connected by 3-inch wrought-iron pipe risers. A vertical well and a 15-inch cross drain in the spillway section conducts the drainage to the downstream edge of the spillway.

Concrete sections of the dam were designed for assumed uplift pressures varying from full reservoir intensity at the upstream side to tail water pressures at the downstream side, acting over one-third the area of the base; for an assumed reservoir water surface 5 feet higher than the normal water level; and for a maximum sliding factor of 0.65.

Vertical expansion joints were provided in the concrete sections at intervals averaging 36 feet, the concrete being poured in alternate panels and intermediate panels filled later. Each joint is provided with a 20-gage copper seal placed near the upstream face and extending from the base to the top of the dam, and with vertical keyways 3 feet wide by 9 inches deep, spaced 3 feet apart.

The embankment sections have 3 to 1 upstream and 2 to 1 downstream slopes with a 20-foot top width at elevation 4,366.5, widened to 25 feet for a roadway by means of the parapet wall. This free board of 12 feet was further increased by the 4-foot concrete parapet wall. The roadway is surfaced with 24 inches of gravel. The upstream face is protected by a 3-foot thickness of hand-placed paving resting on a 12-inch gravel cushion. The downstream face is provided with a dumped rock section on a 1 % to 1 back slope below elevation 4,354.5. The entire face is covered by a 24-inch hand-placed paving on the right embankment and by an 18-inch paving on the left embankment, The embankment sections, except a portion of the low left embankment, are provided with a reinforced concrete cut-off wall resting on rock or trenched one-third the height into impervious material, and extending 4 feet

1 inch above the top of the embankment to form the parapet wall. The right abutment was grouted under this wall in a manner similar to the concrete sections. At the junction of the embankments with the concrete sections they are supported by reinforced concrete, counter-forted retaining walls, the right embankment wall having a maximum height of 82 feet and a total length of nearly 400 feet.

CONSTRUCTION

The dam was built by the Utah Construction Co. of Ogden, Utah, under a contract awarded January 23, 1925. The bridge was built under a separate contract awarded July 31, 1926, to the Lynch-Cannon Engineering Co. of Salt Lake City, Utah. The work was completed in September 1927, and storage of water was begun in May 1926, the reservoir being filled for the first time in June 1927.

Construction of the dam was started by building a timber crib cofferdam enclosing the area to be occupied by the left abutment and left penstock sections which carry all the outlets and two 15-foot penstocks. Concreting was started in July 1925, and as soon as this part of the dam was carried up to elevation 4,300, the river was turned through the gate openings and the two penstocks, thus permitting the work to be carried on in the remaining section of the river.

A timber railroad trestle was built across the river just below the dam and the track was carried to the top of the right embankment section by means of suitable switchbacks on the west side. Most of the concrete, steel, rock riprap, and other materials were handled from this trestle.

The screening and mixing plant were located on the east side of the river below the dam. Endless belt conveyors carried the aggregate from the unloading pit to the revolving screens, where it was separated into sand, gravel, and cobbles; from the screens to convenient stock piles; and from the stock piles to suitable bins at the top of the mixing tower from which it could be chuted to the two 2-yard concrete mixers as desired. The mixers discharged into bottom dump skips, loaded on flat cars, which were hauled to the dam by dinkey engines, picked up by cranes, and dumped. Two independent mixing plants, equipped with two %-yard mixers, were used in constructing the west retaining wall and the right embankment core wall, material being supplied by trucks. Aggregate was obtained from the Michaud pit, located on the Oregon Short Line railroad about 15 miles east of American Falls, some sand from the Mary Franklin pit near American Falls being added as needed to replace that lost in washing at the pit.

A battery of two horizontal boilers heated the mixing water during the colder weather, and whenever necessary the fresh concrete was covered with tarpaulins and live steam from the dinkey engines applied until the concrete was well set.

Most of the material for the right embankment section

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