In February, ice jams made a natural dam in the Bighorn River, forcing water above the banks and causing more than 100 homes and businesses to be evacuated.
This winter, authorities are hoping that won’t be the case.
A contractor assisted city and county work crews as they dug out a sandbar in the river near Worland, a city of about 6,000 ravaged by the flooding.
That sandbar had been trapping ice blocks as heavy as 3,000 pounds, Washakie County Commissioner Terry Wolf said in a statement to a congressional committee led by Sen. John Barrasso in March.
The flooding is caused at least in part by ice melting near Thermopolis, where it breaks up into chunks, National Weather Service Meteorologist Chuck Baker said. When those ice chunks flow downstream into the sandbar, they jam up the river, backing up water and causing flooding along the river, he said.
“It has been a chronic problem,” Baker said.
Wolf estimated the cost of flood clean up at $150,000.
Wolf hypothesized that a fallen tree had come to rest at that point in the river years ago, trapping sediment which eventually led to the formation of the sandbar, capped by an island.
“Year after year, residents of Worland and Washakie County watched ice stack up on a sediment island that forced water from the Big Horn River into the community,” Wyoming County Commissioners Association Executive Director Pete Obermueller said in a news release. “It seemed like such an easy fix, just remove the island, but getting permission from the federal government to do such a simple task proved very difficult. So year after year, the sediment island continued to grow, exacerbating the problem.”
To remove the island, the Army Corps of Engineers drew on authority granted in a bill passed into law in December. That bill, called the Water Infrastructure Improvement Act for the Nation, authorized the corps to prevent and mitigate flood damages associated with ice jams.
After the corps inspected and approved the county’s sandbank removal plan, excavation began Sept. 20. The work was completed Oct. 4.
“This is Wyoming at its finest – the tireless work of local governments combined with strong partners in Congress to realize success,” Obermueller said.
Baker, the meteorologist, cautioned that the fix may not be permanent, citing the dynamic nature of rivers. As water flows into the river from the Boysen Reservoir, it pulls sediment with it. When the river slows by a bend or narrow section, some of the sediment is deposited, which can form sand bars.
“How long will it take for the sandbar to re-establish itself?” Baker said. “I don’t know.”
Wolf said he hopes the solution will be of the long-term variety, but said he will remain in contact with the corps of engineers, in case the problem recurs.
To supplement the improvement, Washakie County Emergency Manager Jeff Schweighart said he was working with the corps to install underwater jetties to keep the sandbar cleared out and a berm that would reduce the area’s floodplain. The federal government has accepted the projects, but work hasn’t started on them yet, he said.