Lake of the Woods SWCD ditch fix targets sediment-filled Bostic Bay
By: Minnesota Board Of Water, Soil Resources
Tags: Environment, Conservation, Fishing, Water

The two-stage ditch will provide more spawning habitat for northern pike within the channel and within connected waters. Talmage said slowing the water and reducing in-channel erosion would allow fish to more easily reach spawning habitat.

“The other part of it is the sedimentation,” Talmage said. “When we get sedimentation, we also usually get a lot of deposition. And when that happens, we end up with quality habitat being buried.”

Previous Minnesota Pollution Control Agency monitoring, DNR surveys, and an NRCS watershed assessment allowed the SWCD to target its work. DNR river ecology, watershed, fisheries and wildlife staff lent their expertise to project development and design.

“We are directly targeting the area where the sediment is coming from. You can visibly see. You go upstream, and the water is clear. You go to a certain point in the middle of our project, and it’s mud,” Corryn Trask, Lake of the Woods SWCD resource conservationist, said during a tour of the Bostic Creek watershed.

Trask stood on the steep banks of Judicial Ditch 28 during a tour of the project site before work began. The newly constructed two-stage ditch is an extension of a 1-mile stretch that was installed in 2008. Photo Credit: Ann Wessel, BWSR

Judicial Ditch 28 drains about 41,125 acres — roughly 10,000 acres of it cultivated — and benefits about 830 landowners. More than 75% of the drainage area is privately owned.

“Everything that we do on the land, eventually that water gets to Lake of the Woods,” said Josh Stromlund, Lake of the Woods SWCD and Land & Water Planning department director.

“It’s such a huge body of water, and so much of it is out of our control locally, and there’s no one single solution that’s going to make a huge impact. It’s going to have to be many small fixes,” Trask said.

The work that finished this summer widened the channel to 8 feet and more gradually re-sloped the banks to create a half-mile-long, two-stage ditch. The newly constructed two-stage ditch is an extension of a 1-mile stretch that was installed in 2008 and has proven to be a successful innovation. This year’s work took a proactive approach to stabilizing the channel, which was showing evidence of down-cutting. This summer’s work also rebuilt three rock riffles, installed 10 more and constructed two side-water inlets.

Stromlund took in a pre-construction, downstream view of Judicial Ditch 28 encompassing the section where a two-stage ditch was built in summer 2020. Among the benefits of the two-stage ditch: It will provide more spawning habitat for northern pike. Photo Credit: Ann Wessel, BWSR

A two-stage ditch includes a flat “bench” within its banks that serves as a floodplain when water tops the main channel that carries low flows. Rock riffles are positioned to cut velocity and provide access to fish habitat. The riffles are situated to help prevent down-cutting. Side-inlet structures connect the ditch to the field through a culvert in order to prevent the formation of gullies when runoff flows over the bank into the ditch. Higher flows and larger, more intense rains had, over time, destabilized the ditch banks.

“Looking at the stability of that stretch and how it was degrading, I think that was where the decision was made to go a little bit above and beyond,” Trask said.

A more permanent fix lies in flow reduction — a potential solution that’s been debated for 35 years or more. The SWCD is using watershed-based implementation funding to identify flow-reduction options within the watershed.

Reducing the flow is complicated by the fact that the 100-year-old ditch runs through Graceton Bog. Because it doubles as a road ditch, abandoning Judicial Ditch 28 would eliminate a long stretch of County Road 4, one of the county’s main thoroughfares.

The SWCD and county saw the channel stabilization as a necessary first step. While flow reduction might not happen for 10 years or longer, the fixes made now will prevent costlier repairs later — and keep the ditch from falling into disrepair.

Pre-construction views of Judicial Ditch 28 in the Bostic Creek watershed illustrate the need for Lake of the Woods SWCD and County’s channel stabilization project.

Trask described pre-2008 conditions:

“The banks were just a vertical straight drop 20 feet to the bottom. There were big chunks of the ditch sitting in the middle, so the water would swirl around (them). … This section was just on the cusp of heading in that direction.”

Monitoring will show what effect the stabilization has on sediment reduction.

Evelyn Ashiamah, Detroit Lakes-based MPCA monitoring coordinator, has been involved with the Bostic Creek watershed since monitoring started in 2017. She’ll continue to work with the SWCD.

From two stations on Bostic Creek, Ashiamah collects flow and water-level data monthly during the open-water season, and during peak flows. Together with data from continuous stage monitoring equipment, the information helps to fine-tune channel modeling. It’s also used to calculate the concentration of total suspended solids and pollutants such as nitrogen and phosphorus.

“They’re going to use it to calculate loads,” Ashiamah said. “It gives an idea how much of the pollutants are passing through with that water.”