Like many Illinois River tributaries, Coffee Creek has suffered from severe streambank erosion. Although some erosion is a natural phenomenon, the rate at which it now occurs in the Illinois and many other watersheds is far higher than natural rates. This is due to several factors: the removal of debris blocks and beaver dams from presettlement drainage ways, the installation of drain tiles in agricultural fields, and the construction of hydraulically efficient outlet ditches. The eroded materials are washed downstream, filling in lakes and wetlands.

TWI has developed low cost cable dams—modeled after beaver dams—as an effective and viable solution for this and other watersheds where sedimentation is a concern. The dams catch deposits of organic debris and sediment in the stream flow. Wetlands form behind these dams, creating wildlife habitat and important microbial conditions for nutrient reduction in the creek or stream.

Coffee Creek is a particularly apt location for this installation because it is adjacent to the Hennepin & Hopper Lakes Restoration Project. In the 1920s, a levee was installed to divert Coffee Creek away from the corn and soybean fields in the newly-formed Hennepin Drainage and Levee District. As a result, today the creek flows unencumbered directly to the Illinois mainstem, carrying its load of sediment and nutrients. One of TWI’s goals for the Hennepin & Hopper Lakes restoration effort is to restore Coffee Creek to its original flow path. Prior to reconnecting the creek, however, its sediment load must be controlled.

A dam consists of a 3/8-inch cable stretched low across the streambed and anchored into the banks. The cable supports a 48-inch galvanized chain link fence fabric that catches debris traveling downstream. The trapped material creates a barrier to stream flow, causing water to back up until it overtops whatever has been trapped. As additional material is trapped in the dam face, sediment begins to deposit behind the dam due to reduced energy and increased residence time. As more fines are deposited, they assist in ‘sealing’ the dam. Eventually, the prism behind the dam will completely fill with sediment, serving to raise the stream bed, reverse channel incising, reduce stream velocity and energy, broaden the channel bed, and increase the fines content of the sediment.

The Coffee Creek Sediment Control Project has been funded by the Grand Victoria Foundation and the Brinson Foundation.