Montana State University

Warm weather can bring sudden snowmelt floods

February 26, 2004 -- by Scott Freutel, MSU News Service


At the time this Montana home was built, the land it sits on wasn't considered to be at risk of flooding. Photo credit: NRCS   High-Res Available

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MSU News Service
Tel: (406) 994-4571
msunews@montana.edu
BOZEMAN - Most Montanans are enjoying the relatively warm weather the state has experienced lately. One of them is Montana State University Extension housing specialist Mike Vogel, who welcomes the break from the cold as much as anyone.

However, Vogel tempers his pleasure with a warning: Beware of flooding, which, in winter and early spring, can be highly unpredictable.

"Although much of the state is still in drought," Vogel said recently, "many parts of the state received heavy snowfalls this winter -- many mountains, the Hi-Line, the northeast quadrant."

According to numbers released by Natural Resources Conservation Service, mountain snowpack statewide was 100 percent of average and 136 percent of last year's. West of the Continental Divide, snowpack was 100 percent of average and 141 percent of last year. East of the Divide, snowpack was 94 percent of average and 128 percent of last year.

Under certain circumstances, Vogel pointed out, mild weather and frozen ground and lots of snow make the perfect combination for surface flooding. Even structures that aren't on flood plains can be affected by conditions in the neighborhood or on the lot.

"Late spring and summer snowmelts can be absorbed by the ground and routinely flow into creeks and rivers. But in the winter and early spring, because the ground is frozen and because of temporary ice dams, water flows are unpredictable, and areas that never experienced flooding before can flood."

"Remember that snow and ice can divert water flows as well as block them," Vogel said. "So when you're moving snow, place piles downhill from buildings and position them so that snowmelt will flow away from them. All through the winter, remove swales of snow that are against or close to the perimeter of the building. And make sure that your downspouts allow water to flow away from the foundation."

Vogel pointed out that areas that burned in wildfires, and lands below such areas, are particularly at risk. "Much of that ground is frozen too," he said, "and there's little vegetation left to help hold the moisture. So the runoff creates new flow patterns, new streams." Some of those new streams cause flooding. Where the soil is saturated, such streams can cause landslides as well, Vogel said.

What should people do to prepare for flooding?

"First, check a flood-plain map at the office of your county Flood Plain Administrator or your county Disaster and Emergency Services office or to see whether your home or business is at risk," said Vogel. "On flat ground, on alluvial plains, you can be miles away from a major river and still be prey to flooding.

"In winter, though, anticipate possible floods even if your area isn't typically prone to flooding. Even people who live well above a flood plain can be at risk of winter flooding

"If the weather is particularly warm, or if it's raining hard, tune in to a weather channel or check a Web site for forecasts," Vogel continued. A Web site sponsored by the National Oceanic and Atmospheric Administration (NOAA) -- http://iwin.nws.noaa.gov/iwin/mt/mt.html-- lets users click on the name of the closest Montana town to bring up detailed current local weather conditions.

"If you learn that your home or business is at risk, lay in a supply of dry sand, bags and shovels. If you can, provide pumps and a reliable source of electric power. Keep a portable radio, emergency cooking equipment and flashlights in working order.

"And lay in the same sort of supplies you'd need for any emergency, including bottled water and preserved foods.

"Finally, learn the safest route from your home or place of business to high, safe ground, in case you have to leave in a hurry," Vogel added.

MSU Extension hosts a Web site, Montana EDEN, linked to organizations to contact in the face of imminent or potential threats, including floods. Go to http://www.montanahelp.org/.

The National Disaster Education Coalition provides a comprehensive guide to floods -- preparing for and responding to and cleaning up after them. Go to http://www.disastereducation.org/guide.html and click on "Floods and Flash Floods."

For more information, telephone the MSU Extension housing office at (406) 994-3451.

Contact: Mike Vogel, MSU Extension, (406) 994-3451, mvogel@montana.edu