Site of Owyhee Dam.

the gates to vent outlets at the upstream face of the dam, above normal high-water elevation.

A semicylindrical trashrack structure, 36 feet in diameter and 24 feet high, bracketed off the upstream face of the dam, protects the sluice gate inlets. The trashrack bars, consisting of 6- by %-inch steel bars spaced on 6-inch centers, are designed to fail if plugged solid under a 40-foot head.

The irrigation outlet works, located 200 feet below the normal reservoir water surface, are for regulating the discharge of prior right water and controlling the reservoir storage. The outlet works consist of three semisteel, 48inch balanced, internal differential needle valves, split longbody type, located in a reinforced concrete valve house bracketed on the downstream face of the dam. Each needle valve is protected by a high pressure, hydraulically operated, 4- by 6-foot emergency slide gate, operated from a circumferential gallery in the dam. Three 57-inch diameter, cast iron, lined conduits connect the needle valves to the emergency gates through an 8-foot transition. Air vent pipes are provided to prevent vacuum below the emergency gates at partial gate openings. The irrigation outlet works are pro

tected by a semicylindrical trashrack structure, an exact duplication of the structure protecting the sluice gate inlet works.

The needle valve house is provided with two 8-inch galvanized pipes, extending through the roof to serve as stacks if oil heaters are used. A 5-ton hand power, single girder, traveling crane is installed in the valve house to serve the needle valves. The floor of the valve house has a 24-inch square drain sump located in the center line of valve no. 2. The sump is drained through a 12-inch, slip joint, pipe embedded in the mass concrete and discharging below low tail water level.

Two 72-inch diameter, power penstock outlets are located near the left abutment, 100 feet below normal reservoir water surface. The power outlets are controlled by 5- by 6-foot hydraulically operated emergency gates. The gates will be operated from a gallery in the dam. Air vent pipes and the usual by-pass valves are provided.

Penstock openings are protected by a semicylindrical trashrack structure, 23 feet in diameter and 35 feet high, bracketed off the upstream face of the dam. The rack bars are 6- by -inch steel bars, spaced 3 inches on centers, designed to fail before damaging the reinforced concrete.

The excavated sections of the power tunnel, extending downward and into the foundation rock, consist of 46 feet of 10- by 20-foot tunnel and 20 feet of transition. Only a small part of the topmost portion of the penstock tunnel has been constructed-merely enough to permit the installation of the power outlet works. The major portion of the penstock tunnel and power plant have not been constructed.

Sluice gate outlets have a total capacity of 4,200 secondfeet with reservoir water surface at elevation 2,530. The three 48-inch needle valves in the irrigation outlet work have a total discharge of 2,800 second-feet when the reservoir level is at the high water elevation of 2,670. The power outlet has a discharge capacity of 4,200 second-feet with the reservoir water surface at the normal high water elevation of 2,670.

Release of water from above elevation 2,590, for supplying the irrigation districts to be relieved from pumping operations and the additional lands to be irrigated, will not be accomplished by passing water through the dam. Such water will be diverted from the reservoir through tunnel no. 1 at the headworks of the main distribution system. This tunnel is located at elevation 2,585, in the right or northeast shore line of the reservoir, about one-half mile west of the dam.

PRELIMINARY CONSTRUCTION

Because the site was isolated, it was necessary to provide repairs and improvements on local roads, operating roads and trails, a construction railroad, a power transmission line, a telephone line, and a permanent camp at Owyhee Dam.

A railroad for transporting construction materials, particularly concrete aggregates, was constructed from the junction with the Homedale branch of the Oregon Short Line Railroad, near Dunaway Siding, Oreg., to the dam site, a distance of about 24 miles. The railroad was standard gage, with 70-pound rails, having a maximum grade of 0.5 percent toward the dam and 1 percent away from the dam. It was completed on December 7, 1928, at a total cost of $651,822.

A power transmission line, 19.4 miles long, was built from the Idaho Power Co.'s Ontario-Nyssa substation near the Government sand and gravel pits at Dunaway Siding, to the dam site. The line cost a total of $44,366, exclusive of the substation. The electric substation was built at a total cost of $20,925, and on November 1, 1928, electric power was available at the dam site at 2,300 volts.

A two-wire, single circuit, wood-pole telephone line, connecting with the Malheur Home Telephone Co.'s line at Adrian, Oreg., was built to the Government office at the dam, a distance of 14 miles. The telephone line was completed during October 1928, at a cost of $9,057.

A Government camp was built on a level tract of land, one-half mile below the dam site. It was provided with a sewer system and a deep well domestic water supply, with a 5,000-gallon capacity reservoir located on the hillside

above the camp.

A

The trail from the Nyssa-Adrian highway to the dam site was improved by a road crew during construction. The distance to Nyssa by road is 31 miles, 12 of this being on county roads between the Owyhee canal and town. road for operation and maintenance of the dam, spillway, and irrigation tunnel was constructed from the southwest corner of the Government camp to the gate shaft at the inlet of tunnel no. 1, using the roadway over the top of the dam.

The contractor built a road from the north end of the railroad bridge near the dam site to a point near the north end of the dam. A connection between this road and the road that crosses the top of the dam was made after the construction of the dam was completed.

CONSTRUCTION

Construction of the dam was commenced July 14, 1928, and completed in October 1932, about 41⁄2 months before the date specified in the contract.

The contractor's plant and equipment consisted of three standard gage trains and locomotives, three power shovels; a sand and gravel screening and washing plant, a central concrete mixing plant, and a remote control cableway. The head tower of the cableway was installed on a 500-foot trackage on the top of the right abutment, the tower of the anchorage being located on the left abutment. The contractor was also equipped with shops and various mechanical facilities; and with a well-built camp consisting of

Fault zone, Owyhee dam site.

bunk houses, mess hall, recreation hall, warehouses, office, store, field hospital, post office, and several cottages for employees.

Excavation of the open cut for the inlet portal of the tunnel was begun July 14. Simultaneously with this, the stripping of the canyon walls and erection of plant were started. Preparatory to sinking a 5- by 8-foot center heading for the spillway shaft, a head frame was built and a gasoline hoist installed. Broken rock, hoisted from the shaft, was loaded on home-made, horse-drawn cars and hauled upstream to a spoil bank. A 9- by 9-foot center heading was driven from both ends of the diversion and spillway tunnel, muck from the inlet end being hauled to a spoil bank on the north bank of the river about 500 feet upstream from the portal. The muck from the downstream center heading was hand-loaded on cars and transported by dinky across the river over a temporary timber pile trestle to a spoil bank on the south side of the river. When the upstream center heading reached a point about 50 feet beyond the intersection of the spillway shaft and tunnel a 5- by 8-foot rise was driven up through the bend of the shaft,

intersecting the down shaft at a point about 90 feet above the tunnel.

Preparatory to enlarging the tunnel, cofferdams of 3- by 12-inch sheet piling were built around the inlet and outlet portals and equipped with pumps. The spillway and diversion tunnel enlargement was started at the downstream portal on November 8, 1928, using the ring shooting method. Broken rock was loaded on 11⁄2-yard steel side dump cars by a %-yard air shovel and hauled by gasoline dinky across the temporary timber trestle and dumped along the left edge of the river to serve as a railroad grade. Rock to a depth of 3%1⁄2 feet was left in the invert for supporting the shovel and cars as the excavation progressed. The material encountered was hard, self-supporting rock, full of incipient cracks, with an occasional mud seam. The excavation overbreak was 5 percent of pay excavation, or 20 percent of the concrete yardage.

The spillway shaft enlargement was begun after the enlargement of the diversion and spillway tunnel was completed. The excavation was carried down from the top, trimmed to section, maintaining a slight conoid section which helped to guide the muck into the 5- by 8-foot shaft and to the tunnel below, where it was loaded on cars and hauled out of the inlet portal. The enlargement was timbered practically its entire depth, using laminated 2- by 12-inch circular segments, spaced on 51⁄2-foot centers. No timbering was required in the diversion tunnel. Tunnel invert and trimming muck was removed as the shovel backed out. The spillway shaft and tunnel excavation was completed in April 1929.

Before beginning the lining of the diversion and spillway tunnel an inner cofferdam of sheet piling was placed at each portal to hold out the river water that was leaking through the outer cofferdams.

The tunnel invert lining was begun April 26, 1929, at the inlet end of the tunnel and proceeded toward the outlet end. Immediately before placing concrete the rock surface was cleaned by air and water pressures applied through a common nozzle. Concrete was mixed by a 1-yard power mixer, located on a sand bar across the river from the outlet portal; then hauled across the river and into the tunnel in side dump cars. The invert arc was placed by hand and screeded to shape to a height of 2% feet above the finished invert of the tunnel. A temporary gutter was formed in the invert for carrying the narrow-gage track and for drainage. The concrete surfaces of the gutter were chipped, cleaned, and the gutter filled with concrete after the crown and side walls of the tunnel were completed. The crown and side walls of the tunnel were placed in 20-foot sections, using wooden forms built in place. A 1-yard concrete gun, mounted on a traveling carriage, shot the concrete through a 6-inch pipe and rubber hose with manganese steel bends into a V notch in the crown of the previous pour, from where it was carried along training

boards into place. The concrete was worked by hammering on the forms with air hammers and by men working behind the forms. When the tunnel lining reached the intersection of the spillway shaft and tunnel, the bend of the spillway shaft was concrete lined to the top of the elbow. Grout pipes were placed in crevices and holes drilled into the foundation rock at frequent intervals. A 5-sack per yard mix was used in the tunnel lining between the inlet and the spillway shaft bend, and a 6-sack per yard mix beyond to the outlet portal. The lining was completed in July, and on August 7, 1929, the river was diverted.

Placing of the spillway shaft lining was deferred until the cableway was put into operation on December 2, 1930. A bulkhead was placed at the top of the elbow and others were placed at approximately 70-foot intervals up the shaft as the concrete placing progressed, to catch falling rock and timbers. The bulkheads also prevented the circulation of air from drying out the concrete. The lining was placed in 10-foot lifts, using the same type of forms as in the diversion tunnel. Concrete, mixed at the central plant in 31⁄2yard batches, was delivered to the bottom dump cableway bucket at the landing near the downstream face of the dam; then carried by cableway to a radial gate controlled hopper near the shaft, where it was fed to the shaft bucket through a chute and lowered into the shaft by a stiff-leg derrick with a 90-foot boom. During the placing of the shaft and spillway structure practically all of the transition forms were left in place and used for supporting an 8- by 8-foot center tower against which the transition and crest structure forms were shored.

Grout pipe connections were set in the shaft lining, opposite all crevices, and in holes drilled into the foundation rock, spaced on about 10-foot centers along the circumferences and at 10-foot intervals up the shaft. A 6-sack per yard mix was used throughout the shaft lining with an average slump of 21⁄2 inches at the forms. After placing 50 feet of lining above the elbow, concrete operations were suspended until spring activities began on March 1, 1931; then continued with very little interruption until the shaft was completed to the base of the crest structure on May 27, 1931. A portable grout machine, mounted on a traveling platform and operated at an air pressure of 100 pounds per square inch, was used in grouting. The invert and side wall holes were grouted with a cement and water mix using a water-cement ratio of 1:0. A similar mix was forced into the roof holes, followed by a fine sand added in proportion of 1 cement and 1 sand, water-cement ratio 1:2. The tunnel grouting operations required 3,063 sacks of cement and 1,731 sacks of sand. The grouting of the contact between rock and spillway shaft lining was carried up after concreting. A total of 722.5 cubic feet of cement was used.

While the diversion tunnel was under construction, the downstream cofferdam was built. To facilitate the driving of steel sheet piling, a wood pile trestle, 30 feet wide, was

driven across the river. A stiff-leg derrick, equipped with a 90-foot boom and a steam-driven hammer, was erected on the trestle for driving the piling. A row of 50-foot steel sheet piling, held to alinement by a 12-inch slot formed by 8- by 8-inch timbers attached to the trestle, was driven to the limit of penetration. Concrete was placed around the contact between the diaphragm and the rock side walls. Two-inch pipes were driven into the alluvial material, 5 feet downstream from the piling, and grouted to solidify the adjacent material. River bed material from the foundation excavation was deposited on both sides of the sheet piling to elevation 2,365.0. The material on the downstream side was sluiced into place forming a watertight diaphragm. The elevation of the top of the sheet piling was 2,370.

A jetty was constructed for directing the river currents away from the lower cofferdam. It consisted of a row of steel sheet piling, driven from the south side of the tunnel portal 104 feet diagonally across the river; beyond was a rock fill to the railroad. The rock fill jetty and railroad fill were riprapped with large rocks. The cofferdam and jetty were completed in December 1929.

The upstream cofferdam, located 325 feet above the dam, consisted of an earth embankment 87 feet high, with face slopes of 2 to 1 and 11⁄2 to 1, upstream and downstream, respectively. The embankment contained a watertight diaphragm extending to bed rock. The temporary earth dam for diverting the river through the diversion tunnel remained fairly watertight during the excavation to bed rock of a trench for the diaphragm. The core wall consisted of a plank diaphragm with 3- by 12-inch sides and a 2- by 12inch center, embedded in concrete along the contact between the piling and bed rock. The cofferdam was constructed with alluvium excavated from the river channel in the base of the dam. Materials were loaded on 16-yard side dump cars by dragline and hauled to the cofferdam for distribution. The coarser materials were placed at the faces and the finer materials were puddled and sluiced toward the core wall. The cofferdam at elevation 2,433, and the core wall, at elevation 2,440, were completed on October 10, 1929. The upstream cofferdam was never put to use during the construction of the dam foundation, due to the extremely low precipitation on the water shed.

Two 10-inch, deepwell, sucker turbine pumps, suspended from cables, were used for keeping the foundation free from water, one pump being located at either end of the excavation. A maximum of 250 gallons per minute leakage through cofferdams and the fault zone was pumped from the sumps.

Canyon walls were stripped of loose rock, between the area excavated for the base of the dam and the upstream and downstream cofferdams, during the period between August and November 1928. Men lowered from the top of the canyon in boatswains' chairs removed all loose or weathered material.

Prior to diverting the river, the excavation of both abutment keyways, approximately 20 feet wide by 20 feet deep, was begun at the top and carried downward. From February to April 1929, most of the excavation was done on the northeast abutment. The material from the straightgravity section keyway was loaded on trucks and used to widen the contractor's construction road. The material from the cut-off trench was subsequently loaded by hand on cableway skips and deposited in the pool at the downstream toe of the dam.

On the left abutment a skidway and skip were constructed for handling drill steel and powder for the keyway, cut-off trench, and the power penstock inclined shaft excavations. A 2-yard dragline loaded the river bed material and broken rock from the abutments into 16-yard side dump cars running on a trestle up the river channel. The muck was transported by rail, to the fill along the left side of the river, over a standard gage pile trestle constructed from the railroad grade upstream through the center of the dam site.

Excavation of the cut-off trenches was carried down from the top. The foundation rock of both abutments was drilled with steel not more than 4 feet long and shot with delay fuses. The delayed explosion resulted in full effectiveness being secured from each prescribed charge of powder without injury to the foundation rock.

When the excavation of the left abutment had been completed to the level of the bottom of the power penstock shaft, a 7- by 7-foot drift was driven, on level grade, from a point beyond the downstream face of the dam to the bottom of the penstock shaft transition. The broken rock from the full size excavation of the inclined shaft was trapped on a small muck car and dumped from the adit on the foundation below, where it was subsequently loaded on cars by dragline. The excavation was started May 25 and completed October 4, 1929.

Excavation of the river bed material, between the trestle and the north abutment, was begun near the downstream cofferdam. After the foundation rock on the northeast side was uncovered, a 22-yard dragline removed the material between the trestle and the southwest abutment. All loose material was cleared from bed rock by sluicing. The foundation rock was drilled on 30-inch centers, shot in rounds to a depth of not over 18 inches and handled by dragline. Large boulders overlying the crushed felsite in the fault zone crevice and the material at the intersection of the fault zone and cut-off trench were loaded on cableway skips for disposal by train to the spoil banks down the river.

The main foundation grout system consisted of grout holes, not less than 1 inch in diameter, drilled in the bottom of the upstream cut-off trench. The holes, varying uniformly in depth from 14 feet near the top of the dam to 110 feet at the bottom, were drilled 5 feet apart, mostly using the successive method of drilling, grouting, and

redrilling in comparatively short intervals of depth. Grout holes, not drilled by the successive method, were fitted with 2-inch pipes which were carried up through the mass concrete; then grouted after a substantial depth of concrete had been placed in the dam.

Two portable grout mixers and placers, each with 14 cubic feet capacity, were used in the foundation grouting. One machine was operated by using 100 pounds per square inch live pressure. The other machine was mounted on a wooden frame, together with a 2- by 5-foot air receiver and a booster compressor. Grout was carried through a 2-inch hose built to withstand a working pressure of 200 pounds per square inch.

FAULT ZONE

Rock walls surrounding the intersection of the fault and the cut-off trench were scaled preparatory to sinking a 12by 30-foot shaft under the upstream toe of the dam in the fault zone. To facilitate the shaft excavation, six grout holes, surrounding the shaft, were grouted by the successive method. Most of the shattered fault zone material was solidified by the grouting and had to be drilled and shot. The loosened material was loaded by hand into a 1⁄2-yard bucket, hoisted from the shaft, and dumped on cableway skips for disposal.

The excavation of the shaft extended entirely through the felsite, the agglomerate, and about 10 feet into the underlying tuff, to elevation 2,145. Opposite faces of the shaft, adjacent to the fault zone, were protected from movement by timbering. One deepwell turbine pump, working part time, kept the shaft free from water.

As soon as the excavation was completed the shaft was concreted, to shut off some of the seepage water. Concrete was mixed at the central plant and transported by rail to the railroad trestle built along the south canyon wall, thence down the incline chutes to the top of the shaft, and down the shaft through several drops of 16-inch diameter "elephant trunks" with radial gate controlled hoppers attached for regulating the amount of concrete placed and preventing segregation.

The crushed felsite underlying the large boulders in the transverse fault near the center of the river channel was hand excavated by open cut methods to elevation 2,254, simultaneously with the shaft excavation at the upstream toe of the dam. The sinking of the shaft, however, was continued well in advance of the remainder of the fault zone excavation. To protect the vertical walls adjacent to the fault zone from movement during the remaining excavation, a bulkhead was constructed at the downstream end of the 12- by 30-foot shaft, and solid concrete placed in the fault zone extending from elevation 2,254 to 2,308 and to the downstream face of the dam, leaving five shafts 12 feet square through which the excavation could

be extended below. The bottoms of the concrete blocks between shafts were constructed on 1:1 slopes so that good contact could be made when the balance of the fault zone was poured. Grout pipes and connections were embedded in the blocks for grouting.

The remaining material in the fault zone beneath the concrete blocks consisted of hard boulders embedded in crushed felsite and infiltrated clay. It was excavated by pick and shovel to satisfactory rock within about 15 feet of the agglomerate. The material was loaded by hand on cableway skips and hoisted through the five shaft openings for disposal. The south wall consisted of hard self-supporting rock, while the north wall was badly broken and shattered. To insure against movement in the foundation adjacent to the fault, the crevice was timbered. Some shattered materials were left in place and held by the lagging, to support overhanging blocks of foundation rock on the north wall, until concreted.

The excavation was sloped for drainage toward the downstream end, where the accumulated water was pumped with one deep well turbine pump. The depth of the excavation below the level of the adjacent foundation of the dam varied from 128 feet at the 12- by 30-foot shaft to 158 feet at the pump sump. The width of the crevice varied from 8 feet minimum to 32 feet maximum.

The fault zone concrete was placed through the five shaft openings with the same equipment used in concreting the upstream shaft. The heights of the concrete pours were controlled by the amount of shattered materials removed in advance of each pour, but averaged about 6 feet. A horizontal run of 10-inch pipe with vertical risers near each shaft opening was embedded in the concrete for discharging seepage and cleanup waters into the pump sump. The sump was eventually filled with select materials and the system was subsequently filled with grout through connections made to each 10-inch riser.

Foundation rock adjacent to the fault zone and shaft was grouted through 2-inch risers, after a substantial block of concrete had been placed in the dam over the river section, grout connections having been placed in holes drilled on approximately 10-foot centers. Eleven carloads of cement were forced into the fault zone area, with a maximum of over 1,100 cubic feet in one grout riser.

CONCRETE

Aggregates for concrete were obtained from gravel pits at Dunaway. The contractor hauled 800,000 tons of aggregates at a cost of $0.0033 per ton mile or $0.16 per cubic yard. Loading materials with a 2-yard dragline added $0.08 per cubic yard to the cost. Sand was washed at the screening plant and coarse aggregates divided into the following sizes: 4 to 3⁄4 inch, 3⁄4 to 11⁄2 inches, 11⁄2 to 23⁄4 inches, 234 to 8 inches.