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inter;f luve Applied River and Wetland Restoration MEMORANDUM Founded 1983 To: Rob Davis, WDNR From: Beth Wentzel and Marty Melchior, Inter-Fluve Date: 2/10/2016 Re: Harbison Creek Flood Impacts Inter-Fluve is working with John and Rose Mary Harbison to restore ecological function to a creek that flows through their property. The area within and adjacent to the stream was previously excavated to create a small pond, which reduced the quality of habitat for native stream fish. The goals of the project are to (1) provide additional cold water habitat for trout that are currently within the watershed, (2) convert manmade pond habitat to floodplain emergent wetland habitat, (3) improve aesthetics of the stream corridor, (4) improve accessibility to the stream and adjacent wetlands, and (5) improve aquatic habitat conditions. The proposed work consists of constructing a new, meandering channel to the east of the existing pond and filling the pond to create floodplain wetland habitat. The basis for the design is described in the Token Creek Basis of Design Report (Inter-Fluve, 2015). As part of the design process, Inter-Fluve developed existing condition and proposed condition HEC-RAS models for Harbison Creek and analyzed hydraulic conditions for several flow events, including the 100 year event. A comparison of the existing conditions and proposed conditions model results suggests that the project will not cause any increase in the 100 year flood elevation or floodway extents along Harbison Creek. Due to backwater conditions from Token Creek, the 100 yr flood elevation along the entire project reach is predicted to be 865.5, consistent with the flood elevation in Token Creek at the downstream end of Harbison Creek (see attached FEMA flood map). Wisconsin DNR staff asked whether the proposed project would have any impact on flood conditions in Token Creek. The existing pond is not designed as a flood storage feature, so the proposed project is not expected to change the flood flow rates delivered to Token Creek. Further, although grading is proposed in the Token Creek floodplain to construct the new stream channel and restore the existing pond to floodplain wetland, these changes are not expected to affect the flood elevation or the floodway extents of Token Creek. Because the proposed Harbison Creek will flow effectively perpendicular to Token Creek during flood events and will be filled with water, excavation of this channel will neither increase nor decrease the flood conveyance capacity of Token Creek. The existing pond also does not contribute to flood conveyance capacity of the creek for the same reasons, so filling the existing pond will not have any impacts on flooding conditions in Token Creek. The berm around the pond that will be lowered in conjunction with filling the existing pond is currently at an elevation of 865 at its highest point. Given that the flood elevation is 865.5, Token Creek floodwaters currently flow over the top of this berm during the 100 yr event and lowering it will not affect either the flood elevation or the floodway extents. Offices Nationwide 301 S.Livingston Street,Suite 200,Madison,WI 53703 608 441 0342 www.intertluve.com