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Prairie View spillway again damaged by flooding

WORTHINGTON -- For the second time in less than a year, the Flexamat material used in the construction of the water quality project at the former Prairie View Golf Links property has failed, leaving the Okabena-Ocheda Watershed District to consid...

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The Flexamat material over the spillway at Prairie View is shown after excessive flows from snow melt and rain undercut the soil below the mat last month. (Special to The Globe)

WORTHINGTON - For the second time in less than a year, the Flexamat material used in the construction of the water quality project at the former Prairie View Golf Links property has failed, leaving the Okabena-Ocheda Watershed District to consider its alternatives.

The Flexamat, which was anchored on a constructed spillway, was supposed to be filled in with plant life to filter water as it flows downstream. Flooding late last June and early July resulted in the first failure of the mat. The second came last month when a combination of snow melt and spring rains once again overpowered the system.

“It’s damaged about as bad as it was last year during the flooding,” Okabena-Ocheda Watershed District Administrator Dan Livdahl told board members Tuesday afternoon. “The Flexamat is in place, but the soil is gone underneath it. We don’t know what’s going on under there, but we need to fix it.”

Livdahl said walking across the mat is like walking on a trampoline - the soil base below has been washed out.

“I think we’ve lost our faith in the Flexamat and we need to do something else,” Livdahl said.

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After the failure of the mat last summer - in conjunction with the failure of the sand filter - Flexamat, the contractor and the watershed district each contributed to the repairs. Those were completed last fall. Livdahl said the contractor did everything it should have done and did it right last fall.

“That Flexamat material … should have held up to that sort of flow,” he added.

Livdahl said the next step will be to seek reimbursement from Flexamat and have the district’s engineering firm, Wenck Associates, design an alternative. Those alternatives could be installing rip-rap over the spillway or geotextile fabric.

On a positive note, Livdahl said the new sand filters installed last fall worked very well.

He was directed to submit information to Nobles County on the estimated cost of the damages at Prairie View, which will be included as the county seeks a disaster declaration related to damages from spring flooding.

In other business, the board:

  • Was notified that bid opening on the Lake Ocheda dam project is slated for April 17. Livdahl reported that Public Works Director Stephen Schnieder is interested in applying $250,000 it received for invasive species education and prevention toward the project, but it would need county board approval.

“It fits the Lake Ocheda project well,” Livdahl said.

  • Discussed the plans for radio-tagging and tracking of carp in Lake Okabena. Staff from Wenck anticipate capturing carp for tagging in May. Fishermen who catch a radio-tagged carp are asked to return the live carp to the water as soon as possible. If a carp is speared or will not survive, people are asked to report the radio-tagged carp to the Okabena-Ocheda Watershed District. The district would like the equipment returned so that it can be reused.
  • Authorized spending up to $2,000 on testing supplies to determine if the algae blooms on Lake Okabena are potentially toxic. Livdahl said he was contacted by Anne Wilkinson of Wenck Associates about testing when algae blooms are present in the Worthington lake.

The testing would look for the presence of microcystin in the lake water. The microcystin toxin can stay in the water for weeks or months after algae dies, Livdahl shared.
“We know (the lake has) cyanobacteria blooms. Is it toxic? That’s the question we’re addressing,” he said. “The question is whether it’s a harmful algae bloom or just an algae bloom.

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“Some algae blooms are toxic and some aren’t, and nobody knows why,” he added.

  • Received an update on the process to change the watershed district’s boundary, shifting about 6.4 square miles near Herlein-Boote Slough into the Kanaranzi-Little Rock (K-LR) Watershed District. The 30-day comment period is underway and will wrap up April 26. The petition will then go to the Minnesota Board of Water and Soil Resources for a decision, unless there’s been a request for a public hearing.
  • Discussed how to handle filter strip incentives that were offered to landowners living within the area that is now slated to be transferred to the K-LR. The incentives were paid to landowners for establishing filter strips along water courses, and were in combination with Conservation Reserve Program participation.

The K-LR isn’t willing to offer incentive payments to the landowners, and the OOWD can not pay incentives on land not within its watershed.
Board chairman Rolf Mahlberg and Livdahl will meet with the property owner involved and report back at the next board meeting.

  • Approved an erosion control permit to the city of Worthington during installation of a new water main on McMillan, between Oxford and Paulson streets, this summer.

040619.N.DG_.OOWD 2 web.jpg
The Flexamat material over the spillway at Prairie View is shown after excessive flows from snow melt and rain undercut the soil below the mat last month. (Special to The Globe)

Julie Buntjer became editor of The Globe in July 2021, after working as a beat reporter at the Worthington newspaper since December 2003. She has a bachelor's degree in agriculture journalism from South Dakota State University.
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