Pathfinder Dam

Pathfinder Dam, located in central Wyoming, was the first large dam project undertaken by the United States Reclamation Service after it was established in 1902. When the cyclopean-masonry arch dam was completed seven years later, in 1909, it created the largest artificial impoundment of water in the United States (maximum storage of 1,012,000 acre-feet). Today, the North Platte Project, of which Pathfinder Dam is the keystone, irrigates 335,000 acres of farmland in eastern Wyoming and western Nebraska. When completed in 1909, Pathfinder Dam established the United States Reclamation Service (Bureau of Reclamation) as one of the premier dam design and construction organizations in the world.

The first American to describe the region around the confluence of the Sweetwater and North Platte Rivers was John C. Fremont in 1845 . Of the area, he wrote that “wildness and disorder were the character of the country.” Fremont’s reports were widely read by settlers travelling to Oregon and California in the following years—so much so that they called him the “Pathfinder  ” for showing them the way. Over the course of the next half-century, Wyoming promoters sought to construct a dam to store irrigation water at a Sweetwater River site but the Reclamation Service’s engineers selected a better dam site on the North Platte River instead   , which would intercept a greater flow.

For the dam’s design, the Reclamation Service turned to some of the most capable consulting engineers in the country. George Y. Wisner advocated for the development of an analytical procedure that would determine “the relation of the stresses in the horizontal arch of a dam to those in the vertical section under varying water pressure and temperature strains” so that “its safety will be beyond question.” Wisner worked with Edgar T. Wheeler, a civil engineer from of Los Angeles, to perform the analysis, which was completed on May 5, 1905. The Wisner-Wheeler analysis method became known as the “Arch and Crown-Cantilever Method”, which was used on several subsequent Reclamation Service arch dams. It formed the basis of the “Trial Load Method” of analysis, which is the basis of the “Arch Dam Stress Analysis System” (ADSAS), which is still used today.