BSWR Project C11-129, 37
CD20 Channel Stabilization
The Thief River is the source of drinking water for the City of Thief river Falls. Other designated uses include recreation and aquatic life. Water quality monitoring conducted by local agencies discovered that the Thief River is not meeting state water quality standards for both turbidity (muddiness) and dissolved oxygen. Approximately 12,376 tons of sediment (about 1200 truck loads) is deposited each year into the Thief River Falls reservoir by the Thief River. This excess sediment increases the risk of harmful byproducts entering into the city's drinking water, it increases the cost of water treatment, and degrades the fish habitat.
Marshall County Ditch 20 (CD 20) is an artificial drainage channel that flows into the Thief River 7.5 miles northeast of Thief River Falls. It has been shown to be a major source of sediment in the Thief River. The Erosive cutting has deepened the CD 20 channel, exacerbating gully formation in the fields along its course. To address this problem, project partners will collaborate to implement grade stabilization and erosion control strategies along the lower 2.5 miles of CD 20. A series of rock riffle grade stabilization structures will be used to reduce the head cutting and sloughing along CD 20, and side water inlet structures will be used to halt the gully erosion on adjacent field ditches.
Rock riffle structure
This project will help bring the Thief River closer to meeting the turbidity standard by reducing the average sediment by more than 400 tons per year. Reducing sediment and nutrients will reduce the amount of water treatment needed for the City of Thief River Falls and will improve habitat for aquatic life in the river.