As a series of ice jams moving along the Bighorn River near Worland, Wyo., caused river stages to rise, the State of Wyoming requested technical assistance on March 7 from the Omaha District, U.S. Army Corps of Engineers.
The State cited concerns related to protecting critical infrastructure including a levee, tower and local bridge. With warmer temperatures and precipitation in the forecast, State officials were concerned about snow melt, the formation of additional ice jams and flooding that was occurring in Worland, Wyo.
Civil Engineer John Bartel from the Omaha District, deployed to the area to provide technical assistance in the towns of Worland, Manderson and Greybull. Because of the nature of ice jam flooding and the frequent bends in the Bighorn River between Worland and Greybull, Wyo., engineers Tom Johnson from the Wyoming Regulatory office in Cheyenne, Wyo., and Larry Bartel from the Fort Peck Project in Fort Peck, Mont., arrived in the area on March 9.
Additional personnel were sent to provide assistance to the Crow Nation in southern Montana and in Roundup, Mont., on the Musselshell River.
An ice jam that had earlier impacted the town of Worland with flooding in some neighborhoods and businesses dislodged and continued moving along the Bighorn River jamming and flooding at each bend in the river.
“With ice jams, it’s hard to look at a gage and predict river stages between locations,” said Chris Horihan, Natural Disaster Program Manager for the Omaha District Readiness Branch. “A jam can cause stages to drop in front of it and rise behind it and then even out as soon as it dislodges. It all depends on how much water is flowing beneath the jam.”
In the next town, Manderson, water began flowing along the railroad tracks, however, sandbagging crews were able to divert the flow into the town’s storm sewers.
By March 9, ice jams had raised river levels in Greybull to within 2 feet of the top of the 2.5-mile long federally-constructed, locally-sponsored levee. The levee is designed to accommodate typical high flows caused by ice jams and spring runoff but in some locations the freeboard, the distance between the water level and the top of the levee, began to drop to less than 2 feet.
Officials in Greybull cancelled classes at local schools for March 10 citing flooding concerns and wanted the buses to be available to evacuate people if necessary.
Sandbagging crews from the Wyoming Department of Transportation and the Wyoming National Guard began placing sandbags in low or threatened areas along the Greybull levee at the direction of John Bartel who was providing technical assistance. Additionally, the Omaha District deployed 2,000 feet of HESCO bastions to Greybull to further raise the height of the levee in the vicinity of the jam.
By the evening of March 9, the nearly 2-mile long ice jam broke apart allowing the Bighorn River to return to its channel. The morning of March 10, Larry Bartel and Johnson began a post-flood inspection of the Greybull levee and the city’s lagoon pond dikes.
Overall, the levee performed as designed enduring the ice jamming and experiencing no visible damage from the chunks and slabs of ice that had caused water levels to rise. Even where the river reached its closest point to the top of the levee, the jam itself prevented the slabs of ice, which had settled along the levee’s riverside bank, from moving and gouging into the levee embankment.
Under Public Law 84-99, the U.S. Army Corps of Engineers is authorized to provide temporary emergency assistance during flood events to meet the immediate threat and supplement State, Tribe and Local emergency response efforts.
Construction of the Greybull levee was authorized in 1950 by the Flood Control Act. Construction, contracted by the U.S. Army Corps of Engineers, began in Jun 1958 and was completed in July 1959. The town of Greybull fully assumed operations and maintenance responsibility for the levee in November 1959.
While snowmelt and ice jam flooding can occur at any time, they typically occur during early spring thaw. Any ice jam can cause flooding or rapid increases in water levels within a short time period. Residents living near these rivers are reminded to monitor reports closely for ice jam flooding and be prepared to relocate to higher ground if flooding occurs.