Popular Science Monthly/Volume 70/April 1907/The Reclamation of the North Platte Valley
|THE RECLAMATION OF THE NORTH PLATTE VALLEY|
ASSISTANT ENGINEER, U. S. R. S.
THE North Platte River rises in the semi-arid region of the North Park Mountains in Colorado and flows into Wyoming, its course through the latter state describing a rough quadrant of about one hundred and fifty miles radius, having for its center the southeast corner of the state. Eighty miles from the state line it turns to the southeast and so continues to its junction with the South Platte in central Nebraska. The route through the last two states lies almost wholly
within the arid region and drains, in Wyoming, a mountainous country where the snow lingers long into the early summer. During the winter and spring the snowfall upon the peaks is considerable, and when the white mantle begins to dissolve under the increasing heat of the summer sun, the rivers are gorged with the flood waters. The North Platte, which trickles along the center of a broad gravel bed throughout the summer, a pigmy sporting the habiliments of a giant, assumes monstrous proportions at this season, swelling from a few hundred second-feet in August to as much as twenty thousand in May, and the uncouth pile bridges that, stretched meaninglessly for hundreds of feet over a stream confined within the limits of a single bent, find their shore abutments awash with the mighty swirl.
Were there no mountains to gather and release the frozen supply, the North Platte might always remain a comparatively small stream of equalized flow, as the precipitation is slight on these brown, arid plains, and the soil absorbs moisture with avidity. Because of this lack of moisture, the soil, though rich in plant constituents, is not susceptible to cultivation, excepting where its position relative to the river margin is such that irrigation may be practised. Many thousands of acres of land, favorably situated, lie along the banks of the North
Platte, especially in the extreme easterly part of Wyoming and in Nebraska, and the settlers have utilized the river waters individually and through cooperative associations for the past two decades.The strength of a heavy chain, when measured by the resistance of its weakest link, may be very small. The total annual flow of the North Platte is large, but the maximum discharge occurs in the spring and early summer at, or slightly before, the beginning of the irrigating season. Throughout the period of irrigation the flow diminishes until, in the sweltering days of August, the torrent of May is reduced to the dimensions of a respectable creek. The amount of land that may be successfully irrigated by waters diverted directly from the river must
be measured by this minimum flow during the irrigating season, and unless some method be found whereby the floods of spring may be utilized during the summer months, only a limited area of the fertile lands along the river can be reclaimed.
The solution of the problem obviously lies in the construction of a storage reservoir having a capacity sufficient to retain the flood waters of spring, releasing them during the summer months as needed. The construction of such a storage reservoir and dam, with the auxiliary diversion dams, headworks and canals, and the adjustment of rights of way, water rights and other perplexing legal matters, is a task requiring large sums of money and efficient organization—sums so vast and organization so perfect that no combination of settlers in a new, sparsely settled country could hope to achieve it. Private capital may be advanced by outside parties if a private monopoly of the water supply be granted, but in such a case the water users must be always resisting the encroachments that follow the private ownership of natural monopolies. The capital may be advanced by outside parties and the works constructed under their supervision, not for the purpose of obtaining a private monopoly, but to turn the whole over to an organization of the water users when they shall have refunded the cost of installation plus a reasonable return at current rates of interest. There is but one party powerful enough and philanthropic enough to do this, and, if the arid regions are to be equitably reclaimed without the creation of powerful private monopolies, it is to the national government that we must look for assistance. The disinterested position and financial sufficiency of the government and the power it possesses to coordinate those portions of projects lying in different states render it peculiarly competent to undertake this work.
As a result of thorough preliminary investigations, a reservoir site for the storage of the waters of the North Platte was located near the mouth of the Sweetwater River in central Wyoming. The site is a natural basin, the enclosure having but one outlet, through which the river escapes by a granite gorge extending for a quarter of a mile through the hills. This canyon is approximately two hundred feet deep and one hundred feet wide, and presents an ideal site for a dam by which to convert the basin above into an immense storage reservoir, while the surrounding hills of fine-grained granite contain the materials for construction. The one unfavorable feature is the location of the dam site with reference to the railroads, the nearest point being forty-five miles distant. The thousands of barrels of cement and the contractor's heavy plant must be transported over this long stretch of earth road, materially increasing the cost of construction. Yet the natural fitness of the site is such that the cost of the dam and appurtenances relative to the body of water impounded is but one dollar per acre-foot stored.
The dam to be constructed at this point will be of the arch type, ninety-four feet thick at the base, two hundred and ten feet high and about two hundred and thirty feet long at the crest. The preliminary
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 no expensive construction, the alignment following the outlying gravel knolls along the bluff that borders the valley, occasionally intercepting these or encountering short stretches of Brule clay. In the quality and extent of irrigable lands and their favorable juxtaposition to economical canal alignments, the North Platte project is favored in its distribution system as well as in storage facilities.
The average rainfall over the irrigated area will probably not exceed thirteen inches per annum. The mean temperature is 45°, the maximum 98°, and the minimum—20° Fahrenheit, and the length of the growing season is sufficient to mature most of the crops raised in this latitude, including corn. The principal crop at present grown is alfalfa, with some corn, oats, wheat, sugar beets and potatoes. The principal supply market is Omaha, but Denver, Kansas City and St. Joseph are contributory. The greater part of the produce will be marketed in the west, unless demand and supply shall be sufficiently disturbed to unsettle their present balance.
Taking eighty acres as a unit and assuming the total area to be irrigated under the North Platte project as 300,000 acres, there will be 3,750 farms. Assuming that the average family consists of five persons, we have 18,750 persons occupying these lands.
Adding to these the merchants, blacksmiths, carpenters, doctors, clergymen and others, with their families, for whom this population will provide patronage, the total becomes approximately thirty thousand persons, exclusive of a probable additional population employed in canning factories. This community will be based upon good homes on the land, free from tenantry and collectively participating in the natural opportunity upon which each irrigator depends. The population at present inhabiting these lands is small, numbering not more than a couple of thousand persons.
This work of the Reclamation Service with its promise of partial relief from the urban congestion that threatens the nation is carried forward by moneys received from the sale of public lands. These moneys are restored to the government by the water users and all possibility of initial tenantry is prevented by the stipulation that tracts exceeding a certain size, between 'forty and one hundred and sixty acres, must be subdivided and sold to persons who will use them to obtain a livelihood before water will be placed on the land.
It has been well said that the safeguard of a nation is a large population of working farmers, owning the land they use, and as a means for the partial accomplishment of this desirable condition, the work of the Reclamation Service deserves commendation.