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NWS raises odds of flooding

Flood outlook shows 90 percent chance of moderate flooding

February 18, 2011
By Per Peterson

Although much of Minnesota has lost a substantial amount of snow cover this past week, the National Weather Service has increased the probability that some flooding will occur in the Marshall area and that the Redwood River will hit flood stage this spring.

The flood outlook, released Thursday, shows a 90 percent chance of moderate flooding in the region, up from 70 percent in last month's outlook.

The probability is measured by precipitation and moisture content in the soil, water in the snowpack and the expected spring thaw cycle. The forecast is scheduled to be updated again March 3.

"The good news is there's only a 30 percent chance that moderate flooding will occur," said Phillip Schumacher, meteorologist with the National Weather Service in Sioux Falls, S.D.

Moderate flood stage on the Redwood River in Marshall is 15 feet; flood stage is 14 feet. Last fall, the river crested at a record 17.09 feet, besting the level reached in 1993 of 17 feet. Major flood stage on the river is 16.5 feet. Historically, most major crests on the Redwood occur in the springtime. Four of the top five recorded crests have happened between March and May, with the exception of last September's crest, and 14 of the top 20 recorded crests have taken place in that period.

Schumacher said despite this week's warm weather, the moisture content in the remaining snow remains high.

"There's a lot of water in that snow that's sitting there right now," he said. "The best we can tell is while there will be some flooding, it's unlikely to be really widespread and not as bad as September of last year. That's not to say that you won't get that kind of flooding, but you won't see the widespread flooding unless there's a lot of heavy rain and snow and a rapid melt, and that's not considered a very likely scenario right now."

Marshall Public Works Director Glenn Olson said in a news release that surface drainage will likely continue to be the primary concern within the city.

While river levels in Lyon County weren't cause for immediate concern this week, Lyon County Emergency Management Director Tammy Van Overbeke said residents should be prepared for possible flooding. Communities like Minneota and Ghent, which experienced some flooding in the fall, could also fall victim again, Van Overbeke said.

And while the city of Marshall has made great strides in flood mitigation it's also hard to predict what city infrastructure will be able to handle now. Snow melt from this winter is one factor that could affect flooding and river levels this spring, said Van Overbeke and DNR hydrologist Lucas Youngsma.

In a report to the Lyon County Board this week, Youngsma said he had tested sites along the Redwood River near Ruthton and Russell, and found the equivalent of seven to nine inches of water in the snowpack. Youngsma said he will be testing other sites in the near future, to determine whether that reading was representative of the region.

The sudden drop in elevation from where the Redwood River enters Lyon County to Marshall can also affect potential flood damage, Van Overbeke said. When a flood comes, she said, "it comes at us fast."

Other factors include ice dams or debris buildup in rivers. Van Overbeke said there is still a lot of debris from last fall that hasn't yet been removed from area rivers.

The city of Marshall has sandbags available for 16 cents each. This is just for the bags and they must be paid for at the time of purchase. Property owners must make their own arrangements for sand.

Arrangements for purchase of the bags can be made at the office of Public Works on the second floor of city hall or by calling 537-6773.

Van Overbeke also received approval from Lyon County commissioners to order sandbags, which will be available for residents to purchase.

"It's very tough for residents to go out and find sandbags," she said.

The bags available through the county would also be sold at 16 cents each, Van Overbeke said, and she is also working with the Minnesota Pollution Control Agency to obtain "super sacks," which are giant sandbags that could be used for shoring up areas like the levee at Wayside Park in Marshall.

"We're also asking people to talk with their insurance agents about what coverage they have," Van Overbeke said.

Schumacher said area residents shouldn't get complacent in terms of the flood potential just because of the recent stretch of warm weather. He said this week's melt has helped matters but not enough to marketedly change the snowpack conditions.

"There's still a lot of water sitting in there and a lot of compacted snow,"?he said.

The long-term outlook calls for a good chance of below-normal temperatures and near-normal precipitation for March.

The 90-day outlook calls for slightly below-normal precipitation and near-normal temperatures.

Staff writer Deb Gau

contributed to this story.



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