Water Flow in the Bighorn River near Fort Smith, Montana

The Bighorn River below the Yellowtail Afterbay Dam near Fort Smith, MT.

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The U.S. Geological Survey operates two gaging stations on the Bighorn River; one station is located on the Bighorn River at Kane, WY (USGS 06279500), and the other is on the Bighorn River near Fort Smith, MT (USGS 06287800 Bighorn River near St. Xavier). The station near Fort Smith, MT, is operated in cooperation with the U.S. Bureau of Reclamation.

The Bighorn River near Fort Smith, MT, has a managed hydrograph due to operations of the Yellowtail Dam and Yellowtail Afterbay Dam. Construction of Yellowtail Dam was initiated in 1961 and completed in 1967. The unregulated, pre-dam hydrograph was characteristic of a snowmelt dominated system; the post-dam hydrograph shows a more regulated response to annual snowmelt runoff. Despite dam operations, the hydrograph for the Bighorn River near Fort Smith, MT, is generally highest in the spring with the months of April through June coinciding with the melt-off of snow at higher elevations within the watershed. Average annual peak flow between 1968 and 2019 was 7,872 cfs and on average occurred on June 9 (day 159 of the year). Minimum annual daily flows over this same period of record averaged 1,489 cfs. Peak flows in 2019 were considerably higher than the long-term average at this location.

Long-term summary of average daily discharge (in cfs) at the Bighorn River near Fort Smith, MT (USGS Gage 06287000). River flows are presented by day of year where day 1 is January 1st. The period of record summarized for this gage extends from 1934 to 2019. The gray, dashed lines are the 25th and 75th percentiles of daily flows on both graphs. The y-axes are held constant to help demonstrate the differences pre-dam and post-dam.

NPS

Long-term summary of average daily discharge (in cfs) at the Bighorn River near Fort Smith, MT (USGS Gage 06287000). River flows are presented by day of year where day 1 refers to January 1st. The period of record summarized for this gage extends from 1934 to 2019, however the period of record shown here includes records from after the Yellowtail Dam completion to the present. Mean daily discharge from 1969 to 2018, along with the 25th and 75th percentiles and a summary of 2019 are shown.

NPS