An ideal gradual melting is reducing the chances that the St. Croix and Mississippi rivers in Washington County will flood this spring.
Despite the Twin Cities’ wettest April since 2006, potential flooding is not on federal or local officials’ radars, even though recent snowstorms have dumped more than 17 inches into Minnesota yards this month.
Factors like a dry fall season and an early snowpack melt help stifle concerns over what are normally unstable riverbanks in such communities as Stillwater, Bayport and Afton along the St. Croix and St. Paul Park and Cottage Grove along the Mississippi, National Weather Service hydrologist Diane Cooper said.
“Unlike rain, [snow] takes longer to melt,” Cooper said. “From what we can tell, it looks like water is actually being able to infiltrate the soil instead of going straight into the river system.”
City officials across the county have scrambled to rid streets of the late-season snow instead of their normal flood preparations this time of year.
An additional 4 inches of snow was dumped on the Twin Cities on Monday night, but the National Weather Service still predicts the St. Croix River at Stillwater to be 7 feet below flood stage on April 30.
As flooding downstream caused hundreds of school closures and evacuations across the central Midwest, Bayport public works director Mel Horak could see ice covering parts of the St. Croix from his office chair last week.
“That’s the wild card,” Horak said of the ice. “That’s the anomaly here.”
But Cooper said the eventual ice melt won’t overwhelm the St. Croix River.
The river at Stillwater has reached historically high levels each of the past three years, including April 12, 2011, when the river broke the flood plain for the first time since 2001.
“The river has been coming up maybe two feet this week,” Stillwater public works director Shawn Sanders said. “It would need to rise another six to seven before we take action with sandbagging.”
Cooper said that the flooding those three years was caused by an all-at-once snow melt or rainfall that hasn’t happened this year. Cooper said the late surge of frost, snow and ice happened at an opportune time, as most of this winter’s snow had already melted.
The U.S. Drought Monitor had one-third of Minnesota in a state of “extreme” drought on April 9. That was before more than 2 inches of rain poured down the second week of April.
Two weeks later, none of Minnesota was in the “extreme” zone due to 5 inches of rain this month, compared with a two-inch average.
In Afton, public works director Ken Johnson said the river has risen about a foot, but the timing of recent storms points to a low flood risk.
“We had an ideal melt,” Johnson said. “It looks controllable, but that said, it can change in a hurry. Flooding is always a concern.”
The Mississippi River is clear of ice for the most part, and Cottage Grove public works director Les Burshten said there’s little to no flood risk for the 14 homes in the city’s flood zone.
“But with this late freeze, we’re nearly out of salt to de-ice our roads,” Burshten said.
Andrew Krammer is a University of Minnesota journalism student on assignment for the Star Tribune.