Gibson Dam

The dam is a high and long arch gravity structure, with a base thickness of tapering to at the crest. As a whole the dam contains about of concrete. When full, the reservoir covers , with a shoreline of roughly and a maximum depth of . Water releases are controlled by two sets of outlets: three release valves at the base of the dam have a combined capacity of , while a gated tunnel spillway, controlled by six radial gates, can pass a maximum of . ==History==

On September 26, 1906, the Department of the Interior authorized the USBR's Sun River Project, under pressure from local residents, namely those of Great Falls, who wanted the irrigation of lands east of the Rocky Mountains along the Sun and Teton Rivers. Early proposals included the diversion of streams from west of the Continental Divide to augment the arid region's water supply, but eventually the project was pared down to comprise two storage dams on the Sun River and a tributary, Willow Creek; two off-stream reservoirs and a diversion dam; and seven main canals. As early as 1889, the Gibson Dam site – located in a narrow mountain gap a few miles above the mouth of the Sun River canyon – had been identified by U.S. surveyor Herbert Wilson as an excellent location to develop water storage on the Sun River. More detailed studies in 1911 by the USBR (then the U.S. Reclamation Service) confirmed Wilson's idea, and the first plans for a dam were drafted around 1920. In the early phases of construction in 1926, a laborer, M. G. Miller, died from injuries sustained from a dynamite explosion. ==Flood control==

By halting the Sun River's spring freshet, Gibson Dam has prevented an estimated $3,044,000 in flooding damage between 1950 and 1999. when record snowpack followed by heavy early spring rains caused more than $438 million (2011 dollars) of damage in the Flathead and Missouri River basins. On June 8, after reports of at least three dam failures on tributaries of the Missouri sent local residents into a panic, there were rumors that the Gibson Dam had failed. A U.S. Forest Service pilot was sent to investigate and found that water was overtopping the dam by over . The USBR later estimated the peak flow over the dam at , of which at least half was over the crest. After this event the dam was retrofitted so that it could be safely overtopped by up to of water. ==Hydroelectric power proposal==

The Gibson Dam Hydroelectric Company "Gibson Hydro" is a two-member partnership proposing a renewable energy facility on the Gibson Dam. Tollhouse Energy of Bellingham, WA a small-business hydropower developer and Greenfields Irrigation District of Fairfield, MT a farmer-managed water utility, are proposing the addition of a 15 megawatt (MW) powerhouse at the base of the dam. The powerhouse would generate electricity from irrigation water releases with an estimated annual production of 42.9 million kilowatt hours. ==Climate==