Stormwater runoff mitigation projects resume

Work began on a project to reduce the erosion caused by stormwater runoff near Crawford County Memorial Hospital this week. A terrace will slow and reduce the amount of water that enters a stream along Highway 59. Photo by Brad Bonner

Work on two stormwater mitigation projects that were approved a year ago are underway after being put on hold last year.

One project is near Crawford County Memorial Hospital (CCMH); the other will be at Denison Middle School (DMS).

“It was delayed because we did not receive any bids on the project the first time we went out for bids; that was the only reason,” said Rory Weis, Denison Municipal Utilities (DMU) General Manager.

Contact was made with local contractors to ask why they hadn’t submitted a bid, he said.

The contractors that might have been interested in the projects did not have time to get it in their schedule last year, he said.

“That’s why we decided to go back out and rebid it,” Weis said.

Bedrock Gravel and Concrete, of Schleswig, was the winning bidder this time.

Work on the first of the two projects started at the end of last week.

A terrace is being constructed near CCMH to alleviate problems caused by water runoff from the hill where the hospital sits.

Water from the area runs into the stream along Highway 59, causing erosion of the stream.

DMU has had other erosion issues near the intersection of Highway 59 and Arrowhead Road, including high voltage cables that were exposed when runoff washed away four feet of soil.

The terrace being added to the hill between CCMH and Highway 59 will capture and temporarily hold some of the runoff from the hospital area; the water will be slowly released into the stream, which will mitigate the erosion after a heavy rain.

Work near CCMH will take about four weeks, according to Derek Namanny, urban conservationist with the Iowa Department of Agriculture and Land Stewardship (IDALS).

Namanny is providing technical oversight of the projects.

After completion of the terrace near CCMH, attention will turn to the middle school project, which will utilize bioretention cells to deal with runoff from the building’s roof and the practice football field.

A large gully has formed south of the field due to concentrated stormwater runoff, Namanny said.

The bioretention cells will use several layers of rock, sand/soil and mulch as filtering material to slow the movement of water, according to Namanny.

Native prairie plants will be planted on the surface of the cells to absorb some of the nutrients in the water.

Over about 24 hours the water will pass through the filtering layers and will then be absorbed into the ground or go into a tile system below the cell.

Namanny said the current plan is to have students help with the planting, but that is subject to change due to COVID-19 concerns.

DMU is making the projects possible through a $4 million State Revolving Fund (SRF) loan for improvements to DMU’s wastewater treatment facilities.

Because the stormwater runoff projects are classified as “Water Resource Restoration Sponsored Projects” by the state, DMU will receive an overall interest rate reduction on the SRF loan that will offset the cost of the construction projects.

All the projects will be done for the same amount of money that would have paid for just the DMU project, Weis said.

Namanny said the DMS project should be complete by the beginning of the school year.

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