Freezing Temperatures Bring Potential for Ice Jams and Related Flooding
February 2, 2022
HELENA, MT - Damaging floods caused by ice jams are a fact of life in winter along many Montana rivers and streams. The Montana Department of Natural Resources and Conservation (DNRC) reminds residents to be observant and prepared for flooding conditions as cold temperatures increase the threat of ice jam flooding.
Katherine Chase, Surface Water Specialist with the US Geological Survey, explained ice jams and subsequent flooding are common this time of year when temperatures fluctuate and drop below freezing. Ice jams occur when a river freezes, blocking the channel and causing flooding upstream.
"Waterways blocked by ice jams can cause rapid flooding, leaving home and landowners with little warning to evacuate," said Traci Sears, the Montana National Flood Insurance Program Coordinator with the DNRC. "Winter recreators should also be aware that fishing accesses, roads, and hiking trails can be closed or threatened by rising waters."
According to historical data collected by the US Corps of Engineers, nearly 80 percent of Montana ice jams take place between January and March with the highest number, more than 40 percent, occurring in March. The most ice jams ever recorded in Montana in a single season was 154 in 1996. The public can access the US Corps of Engineers' Ice Jam Database at https://icejam.sec.usace.army.mil.
While the surface may appear solid, it is never safe to walk on a frozen river or ice jam.
Thermal currents in rivers are unpredictable and ice can become unstable in an instant, leading to injury or drowning. It is also important to keep a vigilant eye on children and pets to ensure their safety.
Sears encourages residents living near a river or stream to have a flood evacuation plan and consider the following steps:
• Purchase flood insurance. In most cases flood insurance must be purchased 30 days before a flooding event.
• Keep extra drinking water on hand. Flooding can compromise local water systems.
• Shovel or plow snow away from homes and structures.
• Be ready to transport valuables or, where practical, elevate them.
Flooding risk also increases during breakup when the weather starts to warm and ice jams begin to melt and move, getting trapped at structures, bends, or narrower reaches of the river.
The sudden breakup of ice jams can cause flash floods as the released water and ice cascade downstream.
To learn more about floodplain management and the resources available to assist with floodplain management in Montana visit: http://dnrc.mt.gov/divisions/water/operations/floodplain-management
The Montana All-Hazards Weather Monitor web site offers up-to-date information on stream flows and potential flood conditions: http://www.wrh.noaa.gov/byz/state/current.php?wfo=tfx