High waters heading to St. Paul have roots in spring rainsby Dan Olson, Minnesota Public Radio
St. Paul, Minn. — Millions of gallons of water from last week's heavy rains in southern Minnesota have reached the Minnesota and Mississippi Rivers.
National Weather Service hydrologists say the Minnesota will go over flood stage this weekend in Savage, south of the Twin Cities. And in St. Paul, the Mississippi river fed by the Minnesota will exceed flood stage by Sunday.
Experts say the roots of the unusual fall flooding can be traced back to April.
At St. Paul's Holman Field, located on the Mississippi's flood plain, workers are fitting steel beams into place between a long row of columns.
The barrier will keep flood waters from reaching most of the airport's facilities.
Even so, airport officials say, Holman Field will be closed beginning Thursday afternoon as the Mississippi crests and likely reopen Monday.
In St. Paul and other communities with land in the flood plain, officials are closing low-lying roads.
National Weather Service hydrologist Diane Cooper, who is based in Chanhassen, said most of the flooding is water from the vast Minnesota River watershed.
"The Cobb river, the Blue Earth system and the Le Sueur system as well as some of those smaller creeks and streams that feed into the Minnesota," she said.
Cooper said last week's rain covered most of the southern third of Minnesota.
Many counties received 3 to 6 inches of rain.
And in some extreme cases, She says there were intense but very localized rainfall amounts exceeding 8 inches.
Minnesota Department of Natural Resources climatologist Pete Boulay said one reason for the major flooding is that starting this spring, rainfall in the south part of the state has been plentiful.
"The ground was already saturated and the rain that fell with the latest single, heavy rain event had nowhere to go," Boulay said. "So it rain right into the lakes and streams."
Another reason for the flooding is the drainage over the past 150 years of much of Minnesota's wetlands.
Hydrologist Diane Cooper says changes in landscape affect how fast rain water flows off fields and hillsides.
"We no longer have those pocket areas that help hold the waters," she said. "Now one benefit in Minnesota is we have a lot of lakes."
Those lakes, Cooper says, caught and held some of the water.
Cooper and climatologist Boulay said many factors -- the amount, the intensity, the duration of the rainfall, if it fell on more or less absorbent soils, the extent of ditches and other farm field drainage systems -- all affect flooding.
But Boulay does not connect last week's big rain with climate change.
His reaction to the observation that we seem to be having 100-year storms every five years is to look at the law of averages.
"In an area as big as Minnesota we're going to have more than one hundred-year storms somewhere in the state each year," he said. "Right over your point, your yard maybe you'll never see a hundred years, but then there might be some poor soul that will see three or four of them in their lifetime."
Boulay says last week's heavy rains traveled across a portion of Wisconsin all the way to Lake Michigan and caused local flooding there as well.
FLOOD PREPARATIONS UNDER WAY
In St. Paul, flood preparations include closing Shepard Road from Eagle Street to Highway 61.
A temporary levy is being set up on Shepard from Jackson to Sibley.
Water Street is also closed from Plato to Highway 13.
In addition, the Saint Paul Parks and Recreation Department have closed Hidden Falls, Crosby and Lilydale parks.
The Mississippi is expected to start receding in downtown St. Paul on Monday.
- Morning Edition, 09/30/2010, 7:25 a.m.