The Ottumwa Courier

July 25, 2013

Slowing erosion could improve water quality

Courier staff writer

---- — OTTUMWA — Improving watersheds on the north side of town will in turn improve the Des Moines River's water quality, which is why the city is hoping to snag a grant this fall.

If awarded the Clean Water State Revolving Fund (SRF) Water Resource Restoration Grant, the city will focus on Harrow's Branch and Memorial Park, a combined total of 1,721 acres that need extensive work.

This spring, city staff, Natural Resources Conservation Service (NRCS) district conservationist Lori Altheide and Wapello County Soil and Water Conservation District (SWCD) local coordinator Ryan Rasmussen walked the gullies in Harrow's Branch, looking for sources and severity of erosion and possible solutions.

"It's definitely concerning," Altheide said of Harrow's Branch. "Head cuts are advancing up the slope, which means they're not only eroding from the side banks but they're also cutting upstream and making the gullies bigger and longer."

The force of the water cuts out soil, leaving an open ditch, or gully.

All of this contributes to poor water quality from sedimentation and soil nutrients polluting the water, a problem that's plagued Harrow's Branch for the last 20 years, said city Public Works Director Larry Seals.

"Funding hasn't been available to fix the problem," Altheide said. "We have never been able to secure the funding ... to do practices in that watershed. This is the first opportunity we've had to receive some help from SRF funds."

Currently, it's estimated that 3,487 tons of sediment are delivered into Harrow's Branch every year.

Recently, Ottumwa Water Works and Hydro asked customers to cut back on water usage due to high nitrate levels in the river.

"Part of that is because you have nutrients in your soil, and when you lose soil, you also lose those nutrients, which will contaminate the water," she said.

Though Harrow's Branch residents have voiced concerns that flooding has worsened since levees were installed, Seals said that's not what this project will address.

"Their complaint is flooding, but if you have a 7-inch rain event in ... an hour, you're going to have flooding no matter what we do," he said.

The solution, Altheide said, is to create smaller sediment control basins and erosion control structures. A sediment control basin is "an earthen structure with a tile outlet that temporarily holds water and releases it slower," she said.

The erosion control structure is similar, though it permanently holds water — "it looks like a pond to you and I." The structure catches sediment and slows gully erosion, which then improves water quality.

Memorial Park also contributes to poor water quality, though its watershed is much smaller than Harrow's Branch.

The pond in Memorial Park has silted in over the years, Seals said.

"We cleaned it once [in 2004] but it silted up again," he said. "It has a lot of bank sloughing and soils that are carried down into the pond."

But the silt continues to erode into the pond, estimated at 232 tons per year.

"What happens is it fills in with sedimentation, and when it does that you don't have the aquatic fish type habitat in there because it's so full of sediment," Altheide said.

That pond feeds into the Des Moines River, so protecting it will improve water quality.

But the park's soil health also needs to improve, which will help its ability to absorb water so there isn't as much run-off. To accomplish this they'll use "aerating practices on the park's lawn area," she said.

"If you go out and walk there, it's hard and doesn't have a lot of organic matter," she said. "It doesn't have the root growth going down into the lawn for a very long distance, so the water just isn't able to infiltrate as it would if it had better health."

If they're able to improve soil health there, it could act as a demonstration project for homeowners, she said.

"If this practice is adopted by landowners in Ottumwa, then you would see less run-off," she said. "A lot of times, [individual landowners] will fertilize their lawns to have a greener lawn, and those have high levels of nitrogen. So if you have a heavy rainfall event and you have run-off after applying that fertilizer, then those ... nutrients would go into the Des Moines River."

Not only would this project improve water equality and slow run-off, it would reduce future maintenance costs to the city.

"We've got our annual maintenance expense of not only basin and clean out, but between the levees and the bridge ... we have to clean out every few years from the sediment that's moved," Seals said.

The state passed legislation that "basically rebates part of the interest we pay over the [SRF] loan to do water quality projects," he said.

The entire project is estimated to cost more than $480,000.

"The state said if you do these kinds of projects, we'll give you back 1 percent of the interest, but it has to be this type of project," he said. "Now, if we didn't do this project, we would still pay the same amount of interest, so this is just something the state has done in order to fund water quality projects."

If the city is awarded the grant in October, contracting would be finalized by March and the project would be slated for completion by the end of June.

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