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Page:Popular Science Monthly Volume 70.djvu/377

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373
THE NORTH PLATTE VALLEY

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

PSM V70 D377 Interior of pathfinder diversion tunnel.png

Interior of Pathfinder Diversion Tunnel.

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