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CONSTRUCTION

Funds for the construction of Kendrick project were allotted on August 1, 1933, and specifications for the diversion and outlet tunnels were prepared at once. A contract was awarded to Lawlor-Woodward & Co. of Seattle, Wash., on October 21, 1933. The tunnel excavation was sublet to Crook and Henno of Denver, Colo., and stripping and stock-piling of the sand and gravel for concrete aggregate to R. A. Schweiger of the Mountain States Co., Billings, Mont. Work was started on the tunnel excavation December 13, 1933, and was completed about June 3, 1934. The tunnel lining was started June 14, 1934, and completed in October 1934. The Lawlor-Woodward Co. completed all work under their contract on October 12, 1934.

On March 7, 1934, bids were opened for the construction of tunnel no. 1, which included the headworks for the canal system. The Utah Construction Co. of Ogden, Utah, was the low bidder. The contractor sublet the excavation for the outlet portal to J. A. Terteling & Sons of Boise, Idaho. The tunnel excavation was started July 6, 1934, and completed January 13, 1935. The tunnel lining was started March 9, 1935, and completed July 31, 1935. All work under the contract was completed September 5, 1935.

On July 15, 1935, bids were opened for the construction of Alcova Dam. The low bidders were W. E. Callahan Construction Co. of St. Louis, Mo., and Gunther & Shirley ot Dallas, Tex. The contract was not signed until October 12, but the contractors proceeded at their own risk on August 15, in order to take advantage of low water in the river and favorable weather conditions. On October 10, 1935, the river was diverted through the tunnel built under previous contract. Stripping of the foundation was started in September 1935 and completed in May 1936. The placing of the earth embankment was sublet to Geo. VV. Condon & Co. of Omaha, Nebr. The first earth was placed in the dam on May 25, 1936.

COST

The following tables give the quantities and costs pertaining to the construction of the outlet and diversion tunnel and canal headworks. The quantities for the dam are not complete and are not included.

Diversion and outlet tunnel for Alcova Dam

Item or class

9 10 12 14

15 16 17 18 19 20 21

22

202 209 224 212

Work or material

Diversion and care of river and unwatering excavations.

Excavation, all classes, stripping gravel deposits.

Excavation, solid rock, open cut, for tunnel inlet.

Excavation, common, open cut, for tunnel outlet.

Excavation, solid rock, open for tunnel outlet.

Excavation, solid rock, for outlet tower above elevation 5,506.

Excavation, all classes, for tunnel

Excavation, all classes, for outlet tower shaft. .

Concrete in tunnel lining

Concrete in portal headwalls, tunnel and outlet-tower transitions and foundation for trashrack.

Concrete in outlet-channel transition

Placing reinforcement bars

Placing 2-inch drain pipe for weep holes

Placing copper-grout stops

Placing grout pipe and connections

Drilling grout holes not more than 20 feet deep. Drilling holes for anchor bars and grouting bars in place.

Pressure grouting

Orders for changes

Extra work orders

Work by Government forces

Subtotal, all above....

Camp maintenance

Engineering and inspection . . . Superintendence and accounts. General expense

Total cost.

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LAGUNA DAM

YUMA PROJECT, ARIZONA-CALIFORNIA

BY A. A. LEWIS, ASSOCIATE ENGINEER, BUREAU OF RECLAMATION

FOLLOWING passage of the Reclamation Act in June 1902, surveys were begun on the lower 400 miles of the Colorado River in the United States. A feasible irrigation project was found in Arizona and California, near Yuma, Ariz. About 22 miles above Yuma was a site, the surface topography of which indicated possibility of a dam 70 feet high and 1,500 feet long; but subsurface exploration disclosed unsuitable foundation material for a structure of this height. This location was then abandoned in favor of another site about 12 miles above Yuma at Laguna, and a dam with overflow crest about 10 feet above river bed was selected.

The lower Colorado River offers engineering problems that are most difficult because of the wide variation in discharge and the poor foundation which its bed affords for control structures. In some late summer and winter months the flow drops as low as 1,200 second-feet. In the spring and early summer, when the snows melt in the high mountains in the upper part of the watershed, or in the late summer and winter months when cloudbursts occur in its lower drainage area, the river becomes a mammoth torrent with measured discharges that have exceeded 200,000 secondfeet at Yuma. For the lower 200 miles of its course the Colorado is a meandering stream, continually ox bowing, making cut-offs, eroding a bank here, building a bar there, confined only by mountainous canyon walls that are often miles apart. The normal gradient in these reaches is about 1.5 feet per mile when the river has its usual heavy burden of the fine silt and sand that constitute its banks and bed material.

The problem presented by the proposed Laguna Dam was to evolve a design for the structure that, although founded on extremely fine, bottomless sand, would pass the entire flow of the Colorado River; a structure that, even if the tail water should drop several feet, would not fail. There was the additional necessity of providing a structure that would remove as much of the silt burden as possible from the water passing through the headgates; so that the canals and laterals of the project would not become clogged.

The capacity of the Laguna Reservoir was so small as to offer not even temporary relief from the silt problem. The lake formed is about 10 miles long at low flow and is largely confined to the river channel.

THE DAM

A dam of the Indian weir or rock-fill type was finally adopted, contrary to the previous American practice of requiring a relatively inflexible structure. Selection of this type was based on its successful use by British engineers in Egypt and India.

The overflow dam is 4,844 feet long between rock abutments. The water surface rise and ordinary height of the dam is 10 feet, but a height of 40 feet was necessary in part of the river channel due to erosion during construction. The width, exclusive of talus, is 166 feet. At either end is a sluiceway channel, each serving its respective headworks and sluicing control structures.

The body of the weir consists of local rock dumped between concrete cut-off walls and paved with 18 inches of concrete, excepting a small area near the Arizona end which is paved with placed rock 2 to 3% feet thick. The concrete paving is drained by slots 7 and 10 feet long, 3 inches wide at the top, and arranged in checkerboard fashion. The surface of the paving is roughened by rocks projecting 6 inches. The surface of the dam has a 12:1 slope downstream from elevation 151 at the crest wall to elevation 138 at the toe wall. The crest, middle, and toe walls are, respectively, 57)4 and 93){ feet apart and each is 5 feet thick. The toe wall is 7 feet high, the middle wall 10 feet, and the crest wall from 10 to 19 feet high. Wooden sheet piling, from 12 to 32 feet long and 6 inches thick, was driven under the crest wall for its entire length, and shorter piling under the other two walls as required by poor foundation or excessive seepage. An apron of derrick stone, with a top width of 40 to 50 feet, was placed below the downstream wall to the level of the wall top. Upstream from the crest wall, quarry-run rock fill was placed to elevation 151, with a top width varying from 10 to 20 feet.

The original design of the dam provided for rough stone paving, 2 to 3 feet thick, over the entire surface between the core walls; but the rock available was of such poor quality that the 18-inch concrete paving was substituted. The rock fills above and below the body of the structure were also made wider than provided by the original design.

DESILTING WORKS, HEADWORKS,
AND SLUICEWAY

At the California end of Laguna Dam, where the Yuma main canal heads, there is a small bay in the reservoir a short distance above the dam. From this bay, a channel having abottom width of 116 feet and bottom elevation of 138 has been excavated around the end of the dam. The bay and sluiceway channel act as a settling basin. The channel is lined with 6- to 8-inch concrete paving on the bottom, and gravity-type concrete retaining walls on the sides. This lining extends upstream about 650 feet from the sluice gates and 60 feet downstream. The canal heading is a concrete structure, 296}, feet long, taking off from the right bank of the sluiceway channel. The sill of the regulator gate structure is a broad-crested concrete weir, 14 feet w'ide, with top at elevation 147. Supported on the sill are concrete piers, 12 inches thick, forming 35 gate bays. Atop the piers is a concrete bridge, 7 feet 6 inches wide, with deck at elevation 156. Diversion is controlled by stop logs which are handled through openings in the bridge and which ride in grooves in the piers. The piers are 7% feet apart.

Built across the sluiceway channel and downstream from the regulator gates is the sluiceway gate structure. The gate structure is 116 feet wide between end piers, and its flow line is at elevation 138, the bottom of the sluiceway channel. The four piers, 8 feet thick, support three structural steel Stoney gates. The clear opening of each of the gates is 18 by 33 feet 4 inches. The gates are controlled by electrically driven hoists on an operating bridge, topping the piers, with deck at elevation 178.75. The upstream ends of the piers are forked above elevation 156, forming an opening through which an auxiliary or emergency gate is moved from bay to bay by a traveling hoist bridge running on plate girders. At the downstream end of the piers is a spur track railroad bridge at elevation 158.

In ordinary operation the sluicing gates are closed and the canal inflow regulated by stop logs which act as a skimming weir. Approach velocities through the settling basin are as low as 1 foot per second, allowing coarser particles of silt to drop from suspension. When the settling basin has become filled with silt so that higher approach velocities decrease the desilting action, the sluice gates are opened and remain open until the collected silt has been flushed out. Velocities above 20 feet per second are attained in sluicing. There are two sluicing periods, of about 4 hours each, per week.

On the Arizona side there is a similar but smaller system, the sluiceway channel being 42 feet wide and controlled by one Stoney gate. This heading serves the North Gila Valley canal. The California heading permits a maximum diversion of about 1,700 second-feet and the one on the Arizona side 200 second-feet.

It was intended that the Yuma diversion should be made on the Arizona side, with the smaller diversion structure at the California end. After construction was started it was decided that floods from the Gila River would make maintenance costs for the Yuma Canal excessive; so the two headings were interchanged. Before excavation for the sluiceway channels was begun, it was thought that no concrete lining would be required and that the excavated material could be used for the body and paving of the dam. However, the rock was found to be so poor that concrete lining was necessary and other quarries had to be opened for the dam material.

The desilting works at Laguna Dam have been reasonably satisfactory, but have given far from perfect results. This is attested by the great expense which has been necessary for silt removal from canals and laterals. The cause of this inefficiency seems to be the relatively high velocity through the settling basin and the extreme fineness of the Colorado River silt.

CONSTRUCTION

The contract for the construction of Laguna Dam and sluiceways was awarded to J. G. White & Co. for a total sum, based on estimated quantities, of $797,650. Work was begun on July 20, 1905, with a contract time of 24 months. In August 1906 the contractors asked to be released and presented claims for extra compensation amounting to $397,000. They were met in conference by a board of engineers who would not grant their request. The board, however, recommended a supplemental contract that advanced the total bid price to $1,129,135 and the time to 36 months, which was approved. This relief was insufficient, and the contractors appealed to Washington for release. On January 23, 1907, the contract was annulled, with the job about 35 percent complete, and the Government took over the contractor's plant at an appraised value and finished the job by force account. The contract difficulties were caused by unforeseen changes and obstacles that arose after the work began, such as changes in design, inferior labor, floods, and transportation problems caused by poor roads and uncertain river conditions.

The contractor stopped work at midnight January 22, 1907, and the Government started the job by force account at 6 o'clock the next morning. Plants were established on both sides of the river, and the dam was built toward the center from each bank. Earth was excavated by suction dredges to an average depth of 12 feet. Close behind the excavation the wooden sheet piling was driven, followed immediately by the pouring of the concrete core walls. Material for the rock fill was quarried from the sluiceway excavations and hill quarries and transported by industrial railway to the dam, where it was either dumped in place or handled by derrick. The concrete for the core walls

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