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McKAY DAM

UMATILLA PROJECT, OREGON

BY M. E. TRENAM, ASSISTANT ENGINEER, BUREAU OF RECLAMATION

McKAY DAM is located about 7 miles south of Pendleton, Oreg., on McKay Creek, approximately 5 miles above its confluence with Umatilla River. The reservoir created by the dam is about 4 miles long and 1 mile wide, with a storage capacity of 73,000 acre-feet at the maximum surface elevation, 1,322 feet above sea level. Stored water is used to supplement the natural flow of Umatilla River for irrigation of about 38,000 acres of developed lands in the vicinity of Echo, Stanfield, and Hermiston, Oreg. The principal features involved in the construction of the dam consisted of the gravel embankment, protected by a continuous, reinforced concrete slab on the upstream slope; a concrete-lined, outlet tunnel driven through the rock of the right abutment; and an open-cut, side-channel spillway located on the right abutment.

FOUNDATION

The foundation material consisted of exposed lava rock on the right abutment, lava rock overlain with soil and gravel to a depth of from 1 to 12 feet across the valley floor, and lava rock overlain with soil and cemented gravel on the left abutment. The depth of overburden on the left abutment varied from a few feet at the valley floor to an undetermined depth at the top of the dam.

All topsoil on the area occupied by the dam was stripped down to compact gravel, cemented gravel, or solid rock, and deposited above the upstream toe of the dam, where it was later spread to form an earth blanket over the upstream cut-off wall.

Foundation drainage was provided by constructing a rockfill embankment, to form the downstream toe of the dam, and by placing a loose-rock blanket, 12 inches thick, over the downstream third of the foundation wherever solid rock was exposed.

Trenches for the cut-off walls were excavated to solid rock or to impervious cemented gravel. Holes for pressure grouting were drilled in the botton of the trenches. The holes were spaced at from 2%- to 10-foot centers, spacings under 10 feet being determined by progressively grouting the holes as drilled. The holes varied uniformly in depth from 45 feet at the maximum section of the dam to a minimum of 20 feet at the abutments. Cement grout was

forced into each hole, until refusal, at a maximum pressure of 100 pounds per square inch.

THE DAM

The embankment has a crest length of 2,700 feet, a maximum height of 165 feet, and contains 2,287,000 cubic yards of material. The downstream slope is 2 to 1, and the upstream slope \% to 1. The unusual upstream slope was made possible by the stability of the available embankment material, which is composed of a well-graded gravel with the voids filled with earth, sand, and a small percentage of clay. All material was obtained from borrow pits on both sides of the creek channel, an average distance of 1 % miles upstream from the dam. The depth of cut in the borrow pits varied from 6 to 10 feet. Pumped water, applied by the irrigation method, ahead of the shovels, wetted the material before excavation. The quantity of water applied at the pit was controlled so that when the wetted material reached the dam, it had the proper consistency for maximum compaction. In general, this consistency was similar to a dry-mixed concrete.

The material was dumped on the embankment in longitudinal rows and spread in layers not exceeding 8 inches in depth. In placing material, each horizontal layer was extended at least 2 feet beyond the neat line of the upstream slope. Each layer of embankment material was then compacted by rolling with 11-ton traction engines, one rear wheel of the engine passing over each square foot of surface at least four times. For a width of 15 feet adjacent to the upstream slope, each layer received at least six passes of the roller. The placing of material beyond the upstream slope of the embankment and the additional compacting provided at this location was done to insure a uniformly firm and stable foundation for the concrete face slab. After each successive 20-foot lift of the embankment was in place, the excess material on the upstream slope was stripped by a dragline excavator and the material replaced in the body of the embankment.

All boulders over 8 inches in diameter which were dumped on the fill were either broken up before the layer was compacted, or removed and placed in the downstream toe drain. No material was placed in the embankment when either the material or the embankment was frozen. The maximum settlement of the embankment, seven months after completion, was less than one-half inch.

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The reinforced concrete face slab on the upstream slope has a minimum thickness of 8 inches at the top, the thickness increasing at the rate of 1 inch in every 70 feet down the slope. At the top of the slope the face slab is connected to a cantilever type-parapet wall, 6 feet 6 inches high, which extends 2 feet 6 inches above the crest of the dam. At the bottom of the slope the face slab is connected to the upstream cut-off wall by a waterproof joint. A series of five concrete steps was built as an integral part of the slab near the top of the slope, to dampen wave action. Steel reinforcement is continuous and consists of %-inch round bars, spaced at 18-inch centers both ways, placed approximately in the center of the slab.

SPILLWAY

The side-channel spillway is cut into solid lava rock on the right abutment and discharges into the creek channel about 300 feet downstream from the toe of the dam. The channel has a trapezoidal section with a bottom width of 16 feet and side slopes of % to 1, and is lined with reinforced concrete. A system of wooden V-drains back of the sidewall lining and sewer-pipe drains under the floor provide drainage for the foundation of the structure. Flow over the spillway is controlled by six radial gates, each 20 feet

long and 10 feet high. Each gate is individually operated by a motor and hoist, installed on an overhead reinforced concrete deck. Two of the gates are automatically controlled by float switches.

A two-barrel siphon spillway was constructed at the upstream end of the gate structure. Each siphon unit has a throat section, 8 feet 6 inches wide by 2 feet 6 inches high, with the crest at the same elevation as the top of the radial gates when closed. The spillway is designed to pass 10,000 second-feet through the radial gates with a 10-foot head on the gate sills, and the two siphon units will carry an additional 1,000 second-feet. The maximum recorded flood of McKay Creek at the dam site, since the beginning of records in 1918, was 3,700 second-feet.

OUTLET WORKS

Water for irrigation purposes is released from the reservoir through an outlet tunnel controlled by two 48-inch balanced needle valves. The tunnel has a total length of 705 feet and was driven through hard blue basalt and lava rock under the right abutment of the dam. The upstream portion of the tunnel between the inlet and the emergency gate chamber, a distance of about 550 feet, has a horseshoe section 10 feet in diameter. From the gate chamber downstream to the needle-valve house the tunnel is semicircular in section, 14 feet in diameter and 10 feet 9 inches high. The entire length of tunnel is lined with concrete having a specified average thickness of 12 inches. The rock surrounding the lining was thoroughly grouted after the lining was placed. The tunnel inlet is protected by a reinforced concrete trashrack structure. The portion of the tunnel upstream from the gate chamber is at all times under reservoir pressure.

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At the gate chamber the water flows through two 4- by 4-foot slide gates and enters two 54-inch diameter, riveted steel pipes which carry it through the downstream portion of the tunnel. Under normal operating conditions, flow through the tunnel is controlled by the two needle valves at the downstream end of the outlet pipes. The two 4by 4-foot, hydraulically operated slide gates, installed in the gate chamber at the upstream end of the outlet pipes, are for emergency use, to permit inspection of or repairs to the needle valves. The hydraulic-control mechanism for operating the slide gates is installed in the needle-valve house, which is a reinforced concrete structure, located at the outlet portal.

CONSTRUCTION

Construction work, performed entirely by Government forces, began in July 1923 and was completed in December 1926, except for the installation of emergency gates and balanced needle valves in the outlet tunnel, which were completely placed early in 1927. Excavation of the outlet tunnel was the first major item of work to be completed, as it was used to divert the flow of McKay Creek during construction of the embankment. The tunnel was driven from both portals and required about 3 months' time. About 4,000 cubic yards of rock, excavated from the tunnel, were placed in the downstream toe drain of the dam.

Excavation for the spillway was started in the fall of 1923 and was completed late in 1925. A total of 32,000 cubic yards of solid rock, excavated from the spillway channel, was placed in the downstream toe drain of the dam. Placing concrete in the spillway-gate structure and channel began in January 1926 and was completed in August of that year.

The gravel embankment was started in February 1924, and was completed in December 1925: continuous operation being maintained except for about 1 month during the winter of 1924-25. Embankment material was excavated at the borrow pits, using two electric-power shovels, loaded on 6-yard dump cars, and hauled an average distance of 1 % miles to the dam, using 18- and 20-ton, oil-burning, dinky locomotives. Two lines of track were carried across the embankment parallel to the axis. After the cars were dumped, the gravel was spread in layers not exceeding 8 inches in thickness, using horse-drawn grading machines, then compacted by rolling. The embankment was placed at an average rate of 110,000 cubic yards per month. The maximum daily run was 8,000 cubic yards in two 8-hour shifts, and the maximum volume placed in any one month was 165,000 cubic yards.

The concrete face slab was placed from the bottom of the slope upward in four main horizontal sections. Each section measured about 80 feet up the slope and extended the full length of the embankment. The foundation for the slab was first trimmed by hand to the proper slope, then the steel reinforcement was placed and supported at the proper distance above the slope by means of chairs bent from reinforcement bars. In each of the four horizontal sections, concrete was placed in alternate panels 12 feet wide, which were formed by fastening screed boards to the steel reinforcement at 12-foot centers.

The concrete mixing plant was set up on the right abutment and a level track built from the mixing plant along the face of the embankment just above the top of the section of face slab being placed. Concrete was mixed in a half-yard mixer, hauled in cars drawn by gasoline dinky engines, and dumped into metal-lined wooden chutes. After being screeded off to grade, the surface was finished by hand, using wooden trowels. Concrete with a maximum slump of 2 inches was required to properly stay in place without slumping on the \% to 1 slope. The parapet wall was placed in advance of the face slab in the top section, using a one-bag mixer and steel-lined wooden panel forms. The following tabulation gives the actual construction quantities, unit costs, and both the estimated and the actual total cost:

BIBLIOGRAPHY

McKay Dam Construction. Reclamation Era, September 1925.

McKay Dam Design, Construction and Cost. Reclamation Era. November 1927.

Building a Rolled-Fill Dam of Prewetted Earth. Engineering News-Record, Mar. 8, 1928.

Detail cost of McKay Dam

Item

Examinations and surveys

Clearing and care and diversion of river

Excavation:

Class I, darn. cubic yards..

Class I, stripping for embankment..do

Class I, dam do

Do .-- ..do

Class II, dam.. do

Class III, dam do

Class I, spillway do

Class II, spillway do

Class III, spillway do

Class III, spillway channel do

Class I, outlet —do

Class II do

Class III, open cut do

Class III do....

Class III, tunnel do

Embankment do

Structure drainage (dam)

Structure drainage (dam) cubic yards..

Structure drainage (dam) do

Structure drainage (spillway)

Grouting (outlet works)

Grouting (upstream cut-off in dam)

linear feet..

Concrete:

Dam, reinforced in cut-off trench

cubic yards. .

Dam, paving do

Dam, reinforced do

Do ..do

Spillway, reinforced do

Do do

Do do

Outlet:

Reinforced do

Tunnel lining do

Reinforced . do

Do do

Riprap do

Backfill .

Six 20- by 10-foot radial gates pounds..

Two 4- by 4-foot high-pressure emergency

gates pounds..

Two 48-inch balanced needle valves do

54-inch riveted steel outlet pipe

Gates, temporary control

Structural steel

Handrailing

Lighting system

Electric installation

Right-of-way and lands

Permanent improvements (gate tender's

cottage)

Credit freight add handling account..

Camp maintenance

Engineering and inspection

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Total estimated field cost.

Superintendence and accounts

General expense

Grand total actual cost. Estimated cost

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20, 787.78 256,735.04 15, 889. 79 10. 744.54 4,693. 89 31,301.07 14,154.62

2, 899.87 29,603. 75

1,181.75 10,439.88

2. 385.60

5, 324.49 17,526.99

13,810.49 11,380.80 10,860.66 730. 58 1, 377. 58 469.99 2,941.38 2,365.11 176, 133.25

3,097.19 38.976.95 34, 373.80 49,955.27

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TAYLOR PARK DAM

UNCOMPAHGRE PROJECT, COLORADO

BY L. R. DOUGLASS, ENGINEER, BUREAU OF RECLAMATION

TAYLOR PARK DAM is being constructed in a narrow steep-walled canyon through which the Taylor River finds outlet from a broad, even-floored glaciated basin known as Taylor Park. The area lies in a mountainous region. The basin floor has an average elevation of 9,250 feet, and surrounding peaks rise to heights of 13,000 feet above sea level. The dam site, located near the beginning of the canyon, is about 31 miles northeast of the town of Gunnison, Colo., and some 20 miles upstream from the confluence of the Taylor and East Rivers which form the Gunnison River.

When completed the dam will create a reservoir with a storage capacity of 106,200 acre-feet, and an area of 2,030 acres at the normal water-surface elevation of 9,330 feet. The reservoir will be supplied from the flows of the Taylor River, Texas Creek, and Willow Creek, which carry the run-off from a drainage area of approximately 230 square miles above the dam site. The average annual run-off at the dam site is about 130,000 acre-feet. The purpose of the Taylor Park reservoir is to conserve surplus winter and flood run-off, to supplement the water supply for the Uncompahgre irrigation project. The water drawn from storage will be conveyed down the Gunnison River and transferred to the Uncompahgre Valley through the 6-mile Gunnison Tunnel, which diverts from the river about 45 miles below the town of Gunnison.

Reconnaissance surveys were made as early as 1903. In 1912 and 1913 tentative foundation explorations by means of 9 diamond drill holes and 11 test pits or shafts, were made in the vicinity of the present dam site.

The work of extending and completing the foundation investigations begun in 1912 and 1913 was started early in the spring of 1934, as soon as weather conditions permitted. Five dam sites were examined; three for a concretearch dam and two for an earth and rock-fill dam. All were within a distance of 700 feet downstream from the upper site, which was located about 200 feet below the entrance of the river into the canyon. The 1934 investigations comprised some 730 linear feet of core drilling and wash boring, 11 test pits, 5 open trenches, and 8 tunnels, driven an aggregate distance of 450 linear feet into the talus slopes and morainal deposits on the abutments.

Designs and cost estimates were prepared for both a

concrete-arch and an earth and rock-fill dam. These design studies and estimates failed to indicate with certainty which of the two types would be the cheaper construction. Consequently alternate schedules were set up and both dams advertised for bids. The subsequent evaluation of bids received and materials required for each type of dam indicated a difference of $170,000 in favor of the earth and rock-fill structure. Accordingly, its construction was recommended and approved.

DAM SITE

The site selected was the lower one of the group investigated. At this location the right or north side of the canyon is characterized by massive and precipitous cliffs that rise in successive escarpments to heights of several hundred feet above the river bed. In strong contrast are the more gentle and even slopes that form the south or left canyon wall. The vegetation in the immediate vicinity is sparse; higher up on the slopes are thick patches of pines and spruce.

The geology of the dam site is interesting. The left abutment is composed of a dark-colored igneous rock, classed as a basic diorite because of its hornblende content. This rock extends across the stream bed below sedimentary strata which form the right abutment. The basal member of these sediments is a conglomerate quartzite about 30 feet thick. Resting on this layer is about 70 feet of thin bedded quartzite followed by a horizon, some 175 feet in thickness, that is composed of thin beds of ferruginous sandstone, becoming increasingly limy toward the top. This sequence of sediments belongs to the Sawatch formation of the Cambrian series. Continuing the geologic column, the next bed is a massive white quartzite, 75 feet thick, which changes abruptly into a unit made up of small layers of siliceous limestone with cherty nodules. These latter two horizons are identified with the Yule formation of the Silurian series.

The steepness of the canyon walls, together with the prevalence of a joint system facilitating weathering, has produced heavy accumulations of talus at points where the topography is favorable to the collection of debris. These talus cones are particularly extensive and thick on the right abutment. The bedrock overburden of alluvium or river

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