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Spring Flood Forecast SWMN

March 6, 2010

From the Worthington Daily Globe this morning:

Spring forecast: Chance of flooding

Outlook good now, but most of March remains
WORTHINGTON — While it’s exciting to finally see snow piles melting into puddles, the dream of green grass won’t come without the dreaded mud — along with the potential for localized spring floods.

The National Weather Service had placed much of southwest Minnesota in a high flood risk category this spring. New data was released, however, according to Tom Kresko, area hydrologist with the Department of Natural Resources office in Windom.

The latest information is that the area has a 90 percent chance of seeing minor flooding, a 50 percent chance of seeing moderate flooding and a 10 percent chance of major flooding.

“Of course, March weather will really affect how those numbers increase or decrease,” said Kresko. “Right now, we’re looking really good in terms of how things are melting.”

The cause for flooding concern this year is not simply in the amount of snow blanketing the region, but the amount of moisture in that snow.

Kresko recently sampled snow depths in the region and the moisture content in that snow. The depths measured from 19.5 to 21 inches, while the water equivalency ranged from 6 to 8 inches.

Typically, 10 inches of snow contains about one inch of moisture, but as those who live in southwest Minnesota know, there has been nothing typical about this winter.

With the weather outlook calling for chances of rain and freezing rain this weekend through the middle part of next week, those on flood watch are hoping for warming temperatures during the day and freezing temperatures at night.

Slow and steady will be the ideal melting condition to keep flooded streets and water-logged basements at bay.

Dwayne Haffield, Worthington’s city engineer, said the city’s primary concern is potential blockage on County Ditch 12. The ditch is used to drain a large portion of Worthington’s storm sewers.

“With the snow pack in there, water may not get out,” said Haffield. “Public works has contacted back-hoe workers to mobilize equipment to remove snow from the ditch. That’s the one manageable thing we can do.”

Ensuring that catch basins are open can also be done before the deluge of runoff flows into the ditch system and ultimately into Lake Okabena.

Just as Haffield keeps an eye on the water control structure on County Ditch 12, the Okabena-Ocheda Watershed District is monitoring all of its structures — from Herlein Slough in the northernmost area of the district, down to the Lake Bella dam near the Minnesota-Iowa line.

Dan Livdahl, OOWD Administrator, said the district’s main goal is to make sure the structures are working as they are designed this spring, and that they aren’t getting plugged up with things like ice chunks, reeds and cattails.

“There isn’t a whole lot we can do,” he said.

Despite the high flood risk placed on the area this spring, Livdahl said there is a bit of positive news. Because of the wet fall and the early snow pack, there is less frost in the ground, making it possible for more snow melt to soak into the ground.

That, coupled with evaporation, will help reduce the potential for flooding. The concern is just how much of the snow melt will turn into runoff and fill up the ditch systems, streams and lakes.

During the floods of 1993, Livdahl said there was a lot of water sitting in wetland basins and on low-lying agricultural land. The lakes were also rather high that year, which lead to some shoreline damage on lakes within the watershed.

“Our concern in the watershed district is that water will flow, create erosion and more pollution in the lakes and streams,” said Livdahl.

There is also concern for potential damage to township roads, he added.

Back in Worthington, Haffield said the city is in the process of evaluating County Ditch 12 for necessary improvements that will reduce future flooding concerns. The ditch system creates some of the most visible flooding problems in the community, such as 10th Street near the Atrium, and Eighth Street near the lake.

“That’s been looked at for a while, and it’s difficult to come up with some easy answers,” Haffield said. “We really want to make sure the outlet is appropriate.”

The city will be working on a master plan over the next several years to address flooding issues and, at the same time, seeking funding to help cover the costs of implementation.

Haffield said their best option is to update some of the city’s infrastructure during road construction projects.

“If roadways are going to be worked on, that may be the time to update culvert crossings,” he said.

Getting federal funds to help with flood control projects is considered rather unlikely, said Haffield. The focus and the funds these days are earmarked for reducing coastal flooding.

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From → Natural Hazards

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