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CLE ELUM DAM
YAKIMA PROJECT, WASHINGTON
BY C. G. ANDERSON, ENGINEER, BUREAU OF RECLAMATION
CLE ELUM DAM, located on the Cle Elum River at the outlet of Lake Cle Elum, is situated 8 miles northwest of the town of Cle Elum. It is reached by 2% miles of gravel road from the end of the paved highway at Ronald, Wash.
The new dam replaces an old crib and rock-fill dam, completed in 1907, which held about 26,000 acre-feet of useful storage. The additional storage created, together with other storage developed within the Yakima watershed, will be used to supplement water supplies for 200,000 acres within constructed divisions of the Yakima project, 120,000 acres in the Wapato Indian Reservation, 72,000 acres of new lands now being developed by construction of the Roza Division, and about 50,000 acres of privately developed lands with Warren Act contracts.
Cle Elum Lake is approximately 7 miles from the junction of Cle Elum and Yakima Rivers, Cle Elum being the largest tributary of Yakima River. The drainage area of 202 square miles is on the eastern slope of the Cascade Mountains with an average annual run-off of 650,000 acre-feet The dam creates a storage reservoir in Lake Cle Elum, enlarging the natural lake to cover an area 8 miles long and about 1 mile wide. The capacity of the reservoir is 356,000 acre-feet to the spillway lip at elevation 2,223, but the installation of five 37- by 17-foot radial gates in 1936 increased the storage to 436,000 acre-feet.
Lake Cle Elum, originally a natural mountain lake of glacial origin, situated in an area of glacial physiography between more or less parallel exposed basaltic mountain ridges, normally included about 2,000 acres of lake surface. The outlet of the lake appears to be the thick upstream portion of an outwash apron, deposited by glacial streams which flowed over the glacier and which, after dumping a part of their contained debris against the front of the ice, strewed the remainder over the valleys below, making a broad fill, composed in part of very permeable material, extending down into the valley. The river from the lake later cut a gorge through this fill.
Numerous tests shafts and wash borings were made at the dam site and on adjoining ridges. It was found that no bedrock was available at reasonable depths in the dam site.
The surface and subsurface materials at the dam site were composed primarily of a form of glacial origin and of a certain type of glacial stream deposition, consisting of regular deposited layers of no particular persistency, variously composed of fine to coarser sands, silt, fine to coarser gravels and pebbles, and but few if any boulders. The surface condition of the lake shore showed that the lake had protected itself by depositing or laying down a blanket of impervious silt.
The main dam consists of a sprinkled and rolled-filled embankment, 750 feet long on the crest, with a maximum height of 135 feet above stream bed. The downstream slope of the main embankment was covered with a mixture of sand, gravel, and cobbles, placed in horizontal layers not more than 8 inches thick after rolling. This part of the embankment varies in thickness from 5 feet at the crest to a substantial gravel and cobble fill at the downstream toe. A gravel and cobble blanket of varying thickness was placed over the stream bed and a portion of the side slope of the canyon below the dam to a distance of about 900 feet below the axis of the dam. This material was not compacted or rolled, but dumped in order to obtain a free draining blanket.
The upstream slope of the dam is covered with a 12-inch layer of gravel or rock fragments and a 30-inch layer of dumped riprap. The stream bed and north abutment of the dam, to a distance of approximately 750 feet upstream from the axis, is protected by an earth blanket varying in thickness from 40 to 10 feet in the stream bed and having a minimum thickness of 10 feet on the north abutment slopes. The steeper portions of the earth blankets are covered with dumped riprap in a manner similar to the upstream slope of the dam.
A cut-off trench was excavated across the dam site, 25 feet deep in the bottom and tapering to 8 feet deep at the high-water line. The trench was refilled with selected material. Bond trenches, 2 or 3 feet deep, were excavated across the bottom and up the slopes at intervals of 50 feet upstream from the main cut-off trench.
The main dike, 850 feet in length with a maximum height of 40 feet, was constructed from the north abutment of the main dam parallel to a natural ridge extending in a northeasterly direction from the dam. The section of the main dike is 30 feet wide on top. It has a 3:1 upstream slope, covered by a 30-inch layer of dumped riprap on a 12-inch layer of gravel, and a 2:1 downstream slope, protected by a gravel and cobble blanket. Three smaller dikes of similar construction were built across low saddles of the ridge. The top elevation of the dikes was placed at the height of the concrete parapet on the main dam.
The dam is of the earth gravel type with conservative slopes, having tight blankets extending upstream and gravel blankets extending downstream, all on a foundation of river gravel, which in turn, at a depth about 70 feet below river bed, rests on sand. The bottom and sides of the old lake probably have become puddled in the course of ages, but river erosion exposed the gravel strata. This gravel permits rather free percolation of water and in the design and construction of the dam provisions were made
for restoring the puddled lake lining as far as possible. The percolation can only proceed toward the river valley and channel below the dam. The height of the percolation head is about 120 feet and a recommended percolation distance of 10 times the available head was chosen. In the design of the blankets this percolation distance was exceeded so far as travel directly under the dam is concerned.
The principal quantities involved in the construction of the embankment were as follows:
Earth embankment in dam and main dike 619, 700
Earth embankment in earth blankets 174,900
Earth embankment in saddle dikes 1,600
Gravel and cobble embankment in dam and dikes . . . 180, 300
Gravel and cobble embankment in blankets 311,000
Placing 12-inch gravel blanket under dumped riprap . . . 23,600 Dumped riprap on dam, dikes, and blankets 49,600
The total material excavated from the borrow pits was 735,700 cubic yards. The main borrow pit was located on the ridge at the south side of the dam, with an average haul of 2,000 feet. Other materials, such as excavation for the stilling basin and from the first 10 stations of the river channel enlargement, were used in the gravel and cobble fill. The excavation for the spillway inlet was suitable for use in the main embankment.
The general plan of the spillway is an open concrete chute over the right abutment, controlled by five 17-foot radial gates. It is 201 feet wide at the intake, with walls 27 feet high. The channel is 1,050 feet in length. The width between side walls is graduated from 201 feet at the intake to 100 feet in about 430 feet, and increases to 200 feet at the stilling basin. For the first 800 feet of the spillway the bottom grade has a slope of 0.07649. The water then drops down a 1 %: 1 slope into the stilling basin, which is 200 feet wide by 100 feet long on the bottom. The stilling basin is constructed with counterforted concrete side walls, 39 feet high, and with a concrete floor 4 feet thick. Rows of interlocking steel sheet-piling, 20 feet long, were driven under the walls and across the outlet end of the stilling basin.
The river channel for a mile below the dam has been improved by cleaning out the old river to a section 150 feet in width, with \ \ side slopes where possible. The floor and side walls of the channel are protected with riprap for a distance of 150 feet below the stilling basin. The spillway channel was designed for a discharge of 40,000 second-feet, with a water surface elevation of 2,240 feet.
Irrigation water is released by means of a 14-foot concretelined tunnel through the right abutment of the dam, controlled by cylinder gates. The tunnel was excavated at the beginning of the work and was used to divert water during the construction of the embankment. At the upper end of the tunnel is a concrete trashrack of low rectangular type, with eighteen 10- by 10-foot openings protected by %- by 6inch trashrack bars spaced at 6-inch centers. The tunnel connects at midlength to the vertical cylinder-gate structure by two 132-inch emergency butterfly gates.
The vertical shaft inside the outer lining is 26 feet in diameter, with an inner cylinder 2 feet thick and 14 feet in diameter. Water flows through the butterfly valves to the inner shell, then through sets of six openings in the vertical shaft, each protected by cylinder gates, at base elevations of 2,109.75 and 2,170. A gate-control chamber above the butterfly gates is reached by a 6-foot diameter stairwell from the cylinder gate operating house on the crest of the dam. The capacity of the outlet works is 5,000 second-feet at a lake elevation of 2,212.
The contract for construction of Cle Elum Dam was awarded to Winston Brothers Co. of Minneapolis, Minn., and work was started August 18, 1931. The railroad spur at Jonesville was used during construction. The contractor built 800 feet of track, a truck hopper to handle 10 cars of aggregate in an 8-hour shift, fuel tanks, and the necessary cranes to handle equipment. The plant on the west side of the river below the damsite consisted of a steel bending yard, carpenter shop, truck garage, machine shops, warehouse, tool shed, compressor house, and concreting plant.
Concrete was prepared in a central mixing plant located near the center of the construction activities. Aggregate was hauled by trucks and dumped from a trestle into storage piles, from where it was elevated to storage bins over the mixer. Pea gravel, then sand, and finally coarse gravel were fed to a 2-yard, nontilting mixer through weight batchers. Cement and admixture were added by hand. Concrete was hauled to the point of placement in bottomdump buckets. Aggregate for concrete was supplied by the Pioneer Sand & Gravel Co. of Seattle, Wash., and was hauled by railroad to the Jonesville siding where it was unloaded and trucked to the job.
After notice to proceed, the contractor started clearing and grubbing the dam and borrow pit sites. Work was concentrated on the diversion scheme which was to be completed by the following summer. The outlet tunnel was started at three places; the adit, which was 212 feet long; the lake portal; and the cylinder gate shaft. This work started October 1, 1931. The excavation of the adit was performed so the river could be bypassed without completing the stilling basin during the first season, thereby eliminating the necessity of stock piling the excavated material and rehandling in constructing the dam.
The outlet tunnel, which was 1,430 feet in length, was excavated to a 19-foot circular section. Considerable water and clay streaks in coarse and fine gravel were encountered during excavation and the material would not stand without lining. Both the outlet and inlet sections of the tunnel were driven by carrying a steel liner plate shell flush with the 19-foot diameter face and taking out the entire cross-section in one operation. Steel liner plates, 371 }i'6 inches long by % inch thick with 1%-inch flanges, were used. The tunnels were lined with concrete to a thickness of 30 inches and were heavily reinforced. The concrete was placed with a %-yard pneumatic gun, 20-foot sections being placed every 24 hours.
The gate control shaft presented the most difficult construction problem because of its depth of 140 feet, the gravel and fine sand formation through which it had to be sunk, a bell-flare at the bottom, and the transition inlet and gooseneck outlet. The gate shaft was almost entirely in original gravel material and was excavated 32 by 48 feet in plan, one end being a semicircle. Two derricks were used in the excavation of the shaft. A continuous course of 16-inch steel sheet-piling was driven around the entire periphery and the opening horizontally braced with 12by 12-inch cross timbers on 12-foot centers, both ways, spaced 6 to 8 feet vertically. The gate shaft excavation included a bell-bottom flare to spread the base load. This work was carried on in the fine sand at the bottom of the shaft with utmost caution. Holes were cut in the sheet piling and 6-inch channel lagging was driven. The lagging was braced against the floor with heavy H beams.
A transition section connects the inlet tunnel to the cylinder gate shaft. At the junction with the gate shaft, this opening is 34 feet wide by 25 feet high and is tapered in section to the main tunnel. The roof of the transition section, having nearly 100 feet of gravel cover, is supported by a metal lining, consisting of rolled H beams and roof carrier beams set on wooden posts. The introduction of the metal liner and reinforcement prior to concreting was an operation requiring careful work. The upper half of the work first was completed by running in wall plate drifts, and then a center heading to carry the large section beams. The ribs were then placed, and the roof lagged with 6-inch steel channels. The bottom half was excavated in four sections. The lining of the inlet tunnel was then completed and the placing of concrete was carried into the transition in sections, allowed to harden to carry the roof loads, and a succeeding section of floor was excavated.
The gooseneck outlet from the cylinder gate structure was completed in a novel manner. The top half of the section was excavated and the roof supported by rolled steel H beams, lagged with 6-inch channels. The section was then concreted. When the concrete had hardened sufficiently to take the roof loads, the bottom half was excavated in 12-foot sections, the concrete placed, and the next section opened. The gooseneck was heavily reinforced. The hoops of the upper section, or the first section placed, were bent at the spring line so that the steel protruded into the tunnel. This part of the reinforcement was covered with sand and the concrete placed in the upper half of the tunnel. The entire upper half of the gooseneck was concreted; then sections averaging 12 feet in length were excavated in the lower half, working from the cylinder gate shaft outward. The reinforcement steel in the hoops of the upper section was straightened for splicing to the lower hoops by heat applied with acetylene torches. The longitudinal steel in the lower half also had to be bent and later straightened to keep the excavation in the section at a minimum.
The concreting of the lower section of the cylinder gate shaft required careful planning, because of the necessity for removing lateral bracing. The concrete was placed in sections, dividing up the base until the structure was above the butterfly chamber. Concrete was lowered into place in
1-yard bottom dump buckets, using the same derricks as in the excavation. The main structure, including the outer shell, was concreted during the spring of 1932, so that diversion could be made. The inner shell was completed to about 10 feet above the upper gates during the fall of 1932. The structure was completed along with the control house and the installation of the cylinder gates the following summer.
Between the time of completion of the tunnel in April and the end of the spring flood in June 1932, the main dike was built with material from a borrow pit located on the top of a ridge at the east end of the dike.
After the diversion of the river, work was started on the main embankment, all the stripping operations having been completed. Gravel and cobbles were obtained from the excavation of the new river channel and the lower end of the spillway. A main borrow pit was opened on the ridge at the southwest end of the dam, to provide finer material for the impervious section. Although there was some variation in the material, this was easily cared for by the distribution of loads over the embankment area.
Embankment materials were loaded by four shovels and one dragline having capacities ranging from 1 % to 3% cubic yards. It was hauled to place in trucks which ranged from 4 to 8 cubic yards capacity. The average haul was around 2,000 feet. Material for the rolled embankment was distributed in windrows parallel to the axis of the dam. It was then spread and compacted by a caterpillar tractor pulling a hydraulic-operated scraper, followed by a water-ballasted sheepsfoot roller. Layers were specified not to exceed 8 inches in thickness after compacting and actually averaged a little more than 6 inches. The specifications required that the entire surface of each layer of the embankment should have the roller pass over it at least three times, but this was greatly exceeded. No sprinkling was needed until the middle of July. Thereafter an increasing quantity of water was applied with hose lines, sprinkling on the surface of the fill after rolling each layer.
Work was performed on a two-shift-per-day basis, with a maximum rate of 6,000 yards per 8-hour shift. Practically 1,000,000 cubic yards were placed in the 4 months between June 20 and October 20. The top of the dam was brought up to elevation 2,200 at the end of the first season. Placing of materials was resumed on April 17 and the embankment was completed to within 1 foot of the finished crest elevation in June. The three small saddle dikes were completed in July. The construction of the parapet wall on the main dam was deferred until 1936, to allow for settlement in the embankment.
A quarry site was opened less than a mile southwest of the dam and produced a very good quality of volcanic rock for riprap. The rock was dumped in place from trucks and spread to some extent by hand.
Excavation of the stilling basin was carried on during the summer and fall of 1932, in order that the spring floods of 1933 might be carried from the completed tunnel directly through the permanent outlet channel. This excavation was carried out in four 26-foot lifts, and the material was moved directly into the dumped gravel portion of the dam. A sump was constructed in the left downstream corner and a battery of pumps installed. About 6,000 gallons of water per minute were pumped when the excavation was completed to grade. This inflow remained practically constant while the surface elevations of the lake varied through a range of 55 feet.
Excavation was completed and concrete work begun in October. The concreting was finished by December. For most of the placing, a 120-foot mast carrying a 1-yard skip, counterbalanced chutes, and elephant trunks were used. Two moves of the mast were sufficient to reach the greater portion of the stilling basin. Concrete in the floor of the % : 1 slope was placed about 14 feet higher than the top of the outlet portal, to reach above spring floods.
Excavation was again resumed on the spillway chute in April 1933, and completed in May. Two shovels were employed on the excavation, one in the gravel at the lower end
and one in the clay at the gate structure. This part of the structure was concreted in June and July, using bottom dump buckets handled by a dragline.
The spillway gate structure was not included in the contract. The piers and bridge were constructed under an extra work order.
At the close of 1932 concreting in the gate shaft had been brought to ground level. Concrete work was continued during April and by the end of May the shaft and gate house foundations were extended to the top of the dam. The gate house and walls were finished early in July and the traveling crane erected preparatory to installing the cylinder gates. The Winston Brothers Company contract was completed on September 5, 1933.
Final cost reports on the dam and reservoir have not been completed, due to the fact that work is still in progress on the installation of gates and machinery for the spillway and outlet works. The total cost of the dam, exclusive of gates and machinery for the spillway and outlet works, amounted to $1,752,782.