Gigantic Fort Peck Dam near the Montana-North Dakota border, completed in 1940 , was the first step in realizing the long-held dream of chaining down the unruly and unpredictable Missouri River.
In 1944 Congress approved the plan, and military demobilization at the close of World War II provided the work force to put the concept into action. The objective was to build six main-stem dams and reservoirs on the Missouri River, which would hold back spring runoff to mitigate flooding downstream, and release water in the summertime to insure navigability of the lower Missouri and the Mississippi, as well as for irrigation and electrical power generation.
Tiber Dam was a spinoff from the dryland reclamation movement represented by the Pick-Sloan plan, and inthis case irrigation was the prime motivation. Preliminary plans developed by the Bureau of Reclamation around 1950 even included a proposal to import water into the Marias River Basin from the Waterton, Belly, and St. Mary Rivers, which are in the Hudson Bay drainage, but the International Joint Commission rejected that idea. Extensive supply canals and distribution systems were planned for the Lower Marias Unit, as well as two seasonal power generating plants.
Tiber Dam was completed in 1956, and since then has served chiefly as a means of flood control on the lower Marias; it bore the brunt of major floods in 1964 and 1975. Also, the reservoir regularly provides additional water to facilitate navigation on the lower Missouri. Some small individual irrigation diversions are functioning, but the original irrigation plan has not yet materialized, and the uplands are still drylands.