North Mill Creek Channel Restoration
Firm: V3 Companies & Inter-Fluve
Owner:Lake County Forest Preserve
Description:The V3 & Inter-Fluve Team was selected by the Lake County Forest Preserve District to complete the engineering design and permitting of the North Mill Creek Channel Restoration project located on within the Ethel’s Woods Forest Preserve. The project involved the full removal of the Rasmussen Lake Dam, an earthen structure approximately 20 feet high that was built in the 1950s as well as an upstream low head dam that was previously submerged by the Rasmussen Lake Dam impoundment. The Rasmussen Lake Dam had been dewatered by six feet in depth to reduce the impoundment area through a previous project, but the full dam removal permit was not obtained from the USACE and IEPA.
V3 modified the dam removal design to addressed challenges which had blocked the full removal implementation. Permits were approved and the dam removal and restoration accomplished 51 acres of wetland and riparian enhancements. The channel remeandering through the prior dam impoundment area created more than 7,700 linear feet of riffle/stream channel habitat. This project accomplished significant water quality improvements within the North Mill Creek Watershed and enhancements to the natural habitat within this unique preserve.
Previously proposed dredging activities in the normal pool behind the original Lake Rasmussen Dam caused Section 401 Water Quality permit challenges from Illinois Environmental Protection Agency. V3 provided a creative water management system alternative which avoided wet dredging and removed this permit challenge. The water management and earthwork approach allowed sediment management and channel construction to be completed in the dry.
The V3 & Inter-Fluve Team identified the historic channel bed through sediment probing and designed the new channel configuration to mimic historic conditions in both plan view and channel profile. The North Mill Creek channel floodplain was terraced to provide a natural flooded overbank and filtration through native vegetation buffers. The 51-acre restoration area includes aquatic/stream channel habitat, wetland and floodplain habitat within the historic dam impoundment area as well as native prairie habitat on the surrounding hills and slopes. Erosion control was accomplished with a series of in-stream and near-channel sediment traps and bypass locations.
Large wood material was primarily used in combination with limited rock to stabilize the toe of the reconstructed channel. Large wood was also used to develop floodplain terrace habitat and flow restriction. This large wood material was readily available and more closely matches the historic bed and bank conditions of North Mill Creek as a forested stream, rather than importing significant amounts of bank run cobble. Large boulders were incorporated in the channel and scour pools excavated on outside bends, to provide flow regime variation within the aquatic system.
Lake County Forest Preserve