and paving was also transported to the job over the industrial railway system, being either dumped directly from the cars or placed by traveling derricks. These railway tracks were moved, as required, on the rock fill or concrete pavement. The above procedure was continued until the two ends being built out from opposite banks left a gap of 625 feet in the river channel. Then the ends were cofferdammed and the work passed through the summer floods of 1908 without damage.

In the fall of 1908 railroad trestles were built across the river gap above and below the dam. From these, rock and spoil were dumped to form the closing cofferdams. In December, before the cofferdams were completed, a winter flood of 35,000 second-feet swept down the river. By working all available men and equipment night and day the upper cofferdam was built up to a point 10 inches above

the flood crest; so that damage was largely confined to the end and downstream cofferdams and railroad trackage. After the flood it was found that places through the gap has scoured to as much as 30 feet below the proposed base of the dam, necessitating 45,000 cubic yards additional rock fill. After the flood damage had been repaired two extra bridges were built across the gap and construction continued. The dam was completed on March 27, 1909.

Transportation was one of the major problems. The nearest railroad point was Yuma, some 14 miles away by poor roads. The contractor first shipped supplies from Yuma by steamboat, but after the river broke into Salton Sea in 1905, flow was too shallow for the boat. The Southern Pacific Railroad, aided by the Government, completed a rail line up the California side of the river in March 1908, which settled the transportation question.

An interesting feature of the job was the concrete proportions. In the core walls and paving on the dam the mix was 1:3:7. Throughout the sluiceways the mix was 1:22:5. The aggregate was produced on the job, using a rock crusher with sand rolls supplemented by river sand. Cement was furnished by the Government.

MAINTENANCE AND REPAIRS

The floods of the winter of 1908 wrecked the pavement downstream from the sluiceway gate structures. Apparently the pavement was blown up by uplift. After the floods receded, the wreckage was cleared away, and concrete varying in thickness from 2 to 9 feet was deposited. This new concrete paving had four weep holes and was fastened to the rock by anchor bolts. The new apron was reinforced with 40-pound rails laid in squares varying from 10 to 20 feet.

No further repairs were made to the dam until 1923. In 1920 the river made a cut-off between Laguna and Yuma that decreased its length by 6 miles and resulted in a grave lowering of the tail water. Repair of the damage due to the lowered water surface was begun in 1923 and completed in February 1924. The rock apron below the toe wall was repaired and its width increased to 95 feet for a length of 2,000 feet. Downstream from the toe wall a 6-inch concrete slab, 12 feet wide and 2,000 feet long, was placed. Below this slab the rock apron was built up to elevation 141. Concrete blocks, 2 cubic yards in volume, and large rocks were placed below the sluiceway aprons. Silt and debris had constricted the effective crest length to 1,500 feet and this was cleared off for a length of 500 feet. The total cost of this work was $94,237. Since 1923 minor repairs, largely on the downstream apron, have been made almost every year.

COSTS

According to the resident engineer's report the actual construction cost of Laguna Dam was $1,921,492, as compared to the contractor's original bid of $797,650. This great increase in cost was due to the previously mentioned difficulties of transportation, poor rock, inferior labor, and overrun of estimated quantities due to river scour, plus the tremendous expense incurred fighting floods. For about 4 months out of each year floods precluded construction and practically the entire force, as many as 700 men, had to be kept on the job protecting completed work, cofferdamming, and fighting bank cutting. The accompanying tables show detailed analyses of the quantities and costs.

$17,555.89 26,387.52

43,943.41

1,921,492.25

Upon the completion of the present construction program of the Bureau in the lower Colorado River country, Laguna Dam will have completed the job for which it was built. Imperial Dam, 5 miles above Laguna, will supply water to the All-American and Gila Canals; and these will furnish water to the Yuma project. Laguna Dam is to be maintained as a control for tail water at Imperial Dam, and the Laguna sluice gates are to be left open permanently to pass the silty discharge from Imperial Dam and desilting works.

BIBLIOGRAPHY

Electrically Operated Sluice Gates for Laguna Dam. Engineering News, Feb. 27, 1908.

Construction of Laguna Dam. Engineering News, Feb. 27, 1908.

Turning the Colorado River and Completing the Laguna Dam. Engineering News, June 10, 1909.

THE COLORADO RIVER DAM is the diverting structure for the Main canal of the Grand Valley project in western Colorado. The dam is situated about 8 miles northeast of Palisade, Colo. The diversion is on the right or west bank. For some distance above this point the river flows in a canyon; but at Palisade the canyon walls recede and the river enters Grand Valley where is presented the best opportunity for an extensive irrigation development.

PRELIMINARY INVESTIGATIONS

The first canal on the project was completed by private interests in 1884. High water in the year 1909 damaged the crib dams used by the irrigation districts, and in 1910 the districts contemplated building a new dam. Negotiations were already under way, however, between the Water Users Association and the Federal Government, and on August 19, 1913, the Secretary of the Interior gave authority to proceed with the constuction of the dam.

The drainage area above the dam site is 8,600 square miles. Records available since 1902 show a maximum annual run-off of 5,270,000 acre-feet in 1912, a minimum of 1,860,000 acre-feet in 1934, and an average of 3,900,000 acre-feet. The maximum recorded discharge at Palisade since 1902 was 52,400 second-feet which occurred on June 16, 1921. From gage heights on the Colorado River at Fruita, the flood of July 1884, is estimated to have been more than 50 percent greater than that of 1921. The minimum discharge of record at the dam site is 547 secondfeet, which occurred on December 30 and 31, 1932.

On account of the nearby railroad grade of the Denver and Rio Grande Railway, on the right bank of the river, it was necessary to pass flood waters at no greater elevation than was used for supplying the headgates during low discharge. In some seasons it was necessary to divert all the water possible. Consequently excessive leakage had to be avoided. The roller crest was favored over Taintor or Stoney gates on account of much wider waterways and simplicity of operation. At this time there were but two roller-crest dams in the United States. Investigations showed that there was little difference in cost for the various spans and heights proposed. Six spans of 70 feet, with a sluiceway of 60 feet, were adopted for the final plans.

In March and April 1913, the site for the dam was tenta

tively approved and topographic maps were made. Diamond drilling had been done on several sites as early as 1908 and 1909. Holes a short distance above and below the site indicated that rock would not be encountered at a depth of less than 30 feet; so the dam was figured as resting on a gravel base. The main foundation was on gravel; but some sand and cobblestones were encountered and some solid rock was encountered in the cut-off trench.

DESCRIPTION OF STRUCTURE

The dam consists of an ogee weir, normal to the river, with concrete aprons upstream and downstream from the weir, a cut-off wall under the weir, and curtain walls at the ends of the aprons. The weir is surmounted by six rollers to regulate the water height. At the right end is a sluiceway between the weir and the outlet gates to carry off silt.

The dam is 542.5 feet long between abutments. The width along the main weir is 85 feet. The cut-off wall under the weir extends to elevation 4,758, and the top of the weir is at elevation 4,782. The upstream apron extends 35 feet upstream from the weir, with the upstream end at elevation 4,772, and the surface at elevation 4,774, where it joins the weir. The upstream curtain wall extends to elevation 4,769. The upstream apron is a light concrete floor on which a puddle, 2 to 4 feet thick, was deposited. The downstream apron, 2 to 5 feet thick, extends downstream 50 feet from the upstream face of the weirs. The downstream curtain wall is 2 to 4 feet thick and extends to elevation 4,762. The surface of the downstream apron is at elevation 4,774 and a heavy riprap is provided below the apron. The river bed at the weir had an original elevation of about 4,774.

There are six roller gates, 70 feet long by 7 feet 1/4 inches in diameter, extending across the stream and provided with an extension arc which rests on the weir and which places the top of the roller 10 feet 3 inches above the weir when in the lowered position. Across the sluiceway at the right end is a roller gate, 60 feet long, provided with an extension arc which gives a height of 15 feet 4 inches above the weir. The sluiceway weir is 5 feet lower than the main weir.

Rollers extend about 21⁄2 feet into recesses in the piers and operate on smooth tracks embedded in the side of the recesses at an angle of 20° with the vertical. Around each

end of the roller is a toothed rim engaging a toothed rack fixed parallel with the track. The rollers are operated by means of a chain, one end of which is fastened to and partly encircles the roller, the other being wound around a drum in the hoist house on top of the pier. The ends of the rollers are sealed by means of oak strips attached to flexible diaphragms near the ends of the cylinders. A wooden strip, fastened to the extension arc, provides a bottom seal when the roller is down.

The roller is hoisted from one end, and each alternate pier is surmounted by a hoist house containing the hoists for two rollers. Hoists for the 70-foot rollers are driven by 10-horsepower motors and the hoist for the 60-foot roller is driven by a 20-horsepower motor. The motor, through a series of gears, rotates a 51⁄2-inch chain shaft, to which is forged an 8-tooth sprocket, winding up the chain which is attached to the rim at one end of the roller. Each 70-foot roller weighs about 40 tons and requires a maximum chain pull of 25 tons. The 60-foot roller weighs approximately 53 tons and requires a maximum chain pull of 45 tons. Chains are of special design and are made up of heavy pins and links of high-test steel, with an ultimate tensile strength of more than 80,000 pounds per square inch. The 70-foot rollers can be raised from the lowest to the highest position, a distance of 16 feet, in 15 minutes.

The sluiceway is 60 feet wide and is located at the west end, between the main weir and the headgates for the main canal. The sill of the sluiceway is at elevation 4,777, 5 feet below the main weir and 8 feet 4 inches below the sill of the headgates. It was assumed that a velocity of about 24 feet per second at the entrance to the sluiceway would be required to carry silt into the canal. The sluiceway will take a deposit of about 21⁄2 feet at its entrance before this velocity is reached. When the deposit of silt reaches this depth, the roller is raised and the channel cleared by flushing the mud down the river. In operation the rollers are raised about once a week.

The outlet structure at the west end of the dam contains nine gates, each 7 feet square. These gates are operated by a line shaft, installed on the head-wall platform, using a 3-horsepower motor. The gate sill is at elevation 4,785.25 and the normal highwater surface in the canal for 1,425 second-feet is 4,791.50. Eight of the gates can take the full discharge with a velocity of about 4 feet per second.

A power plant at the west end of the dam generates electric power for operating the rollers and headgates. The plant consists of a 4-cylinder, automobile-type gasoline engine, direct-connected to a 25-kilowatt, 250-volt generator. The generator charges a storage battery, which has a capacity of 108 ampere-hours, but can also be used to furnish power direct to the motors independent of the battery. The battery is capable of raising one roller and also furnishing lights for the dam.

With an assumed flood surface at elevation 4,792.5,

approximately the top of the 70-foot rollers when down, it was computed that a discharge of 50,000 second-feet could be taken by the six bays and the 60-foot sluiceway; and that, in addition, about 1,600 second-feet could be carried by the canal intake. A flood of approximately 50,000 second-feet occurred the summer following completion of the dam and was carried by the six bays, with the water at the elevation of the top of the sluiceway roller which was down at the time.

CONSTRUCTION OF DAM

The river was handled by completing the sluiceway and head wall at the west end, during low water, and excavating a channel above and below the sluiceway to facilitate the flow. Cofferdams were built above and below the dam, east of the sluiceway. Auxiliary dams were built parallel to the river flow, cutting off basins to reduce seepage, and different portions of the weir and aprons were completed. When the 70-foot rollers were in place and raised, the main cofferdams were demolished and a cofferdam built to enclose the sluiceway so that portion of the dam could be completed.

Foundation excavation was begun at the west end on August 27, 1913, using a small team outfit. By the middle of November wet excavation was started at the west end; and by the first of January the excavation necessary for the head wall and sluiceway was completed with the exception of about 1,800 cubic yards. By May 1914, this excavation was completed and the concrete poured; so that cofferdams could be completed and the rest of the excavation continued.

The Orchard Mesa Canal occupied the approximate site of the east abutment. This canal was diverted by a wooden flume. Excavation at the east end was started by a dragline with a 30-foot mast and a 60-foot boom; but after 3,000 cubic yards were taken out a flood occurred, October 3, 1914, which took out the east end of the upstream cofferdam and put the dragline out of commission. On the main weir, excavation was carried down to elevation 4,768 with teams. Below this elevation, which is the bottom of piers and main weir, the excavation of the cut-off trench was carried on by hand with the aid of skips handled by the cableway. Water was held to approximately elevation 4,768 by drainage to the main sump which was located below the first 70-foot roller east of the sluiceway. Auxiliary pumps were used to keep the water out of the core trench. Solid rock was encountered in the core trench at the east and west ends. Excavation for the upstream curtain wall was made without trouble; but the excavation for the downstream curtain wall was hampered by an excessive flow of water.

The first concrete was poured at the west end on January 9, 1914. The water was heated and during the coldest weather rough sheds were erected over the concrete and