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Page:Popular Science Monthly Volume 70.djvu/380

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376
THE POPULAR SCIENCE MONTHLY

estimate of stone masonry is fifty-three thousand cubic yards and of concrete one thousand cubic yards, together calling for forty thousand barrels of cement. The contract for the dam, exclusive of a cut-off and dike, was awarded September 1, 1905, for $482,000, the government to furnish the cement at the nearest railroad point. During the summer a tunnel was constructed through the canyon walls, the upper portal located above and the lower portal below the dam site, for the purpose of diverting the waters of the river during the construction of the dam and to be used later for the passage of stored water.

The annual run-off from the Pathfinder watershed is about 1,500,000 acre-feet, and the capacity of the proposed reservoir is 1,025,000 acre-feet, being sufficient to retain about two thirds of the entire discharge of the North Platte at this point for one year. A conservative estimate of the area it is possible to irrigate under favorable circumstances, with the amount of water to be stored in the Pathfinder Reservoir, lies between 300,000 and 400,000 acres. During the irrigating season it is proposed to allow the surplus water stored in the reservoir to escape into the river bed as needed, augmenting the normal flow, to be intercepted by diversion dams and turned into the headworks of the canals that are to conduct it to the lands it is intended to irrigate.

The irrigable lands lying below the reservoir have been surveyed, and wherever it seemed that any considerable area could be reclaimed for a reasonable expenditure, a preliminary location of canals and study of the necessary structures involved were made and the probable cost estimated. Some of the schemes were rejected because of excessive cost and others are in abeyance, but the Interstate Canal has been pronounced practicable by a consulting board of engineers and is now in process of construction. This canal heads at a point about eight miles above old Fort Laramie in Wyoming and follows the northerly side of the valley for one hundred and fifty miles to a point near Bridgeport, Nebraska. The land underlying this canal in the extreme eastern part of Wyoming and in Nebraska is of excellent quality, requiring but the application of sufficient water to yield bountiful returns. No alkali demands the construction of expensive underdrains on these lands, and, with the lands south of the river and those lying higher up the valley in Wyoming, there is an area sufficient to exhaust even the resources of the huge Pathfinder Reservoir. A conservative estimate of the probable area underlying the Interstate Canal, and to receive its service, is something more than 100,000 acres. The canal is designed to carry about 1,400 second-feet of water at the headworks. The first forty-five miles was divided into ten contracts, which were awarded during the months of June and July, 1905, and construction has been in progress throughout the summer, with the outlook bright for water in time for the irrigating season of 1906. In November the second fifty miles was awarded. There are no tunnels on the Interstate Canal and