WATERWAY AND LOCATION: The project would affect wetlands and waters of the United States associated with an unnamed tributary of the Iowa River . The project/review area is located on to the west of Avenue of the Saints (U.S. Highway 218) and the review area is approximately 80-acres. The project is located in Sections 18, 19 and 20, Township 79 North, Range 6 West; at Latitude 41.642041 and Longitude -91.580063; in Iowa City, Johnson County, Iowa.
EXISTING CONDITIONS: Currently the 80-acre parcel is used for agriculture and row crops. Multiple wooded fingers of the stream extend from a large flat valley to form a small stream network. The area is bordered by multiple farms on each side with the downstream limits of the parcel being US Highway 218. This project will provide stormwater management for 490 acres of land. Iowa City is growing to the west and this project is needed to provide stormwater control for multiple planned developments in the near future. The site has 0.87 acres of delineated wetlands and just over 2500 linear feet of relatively permanent waters.
PROJECT PURPOSE:
Basic: Stormwater management
Overall: The overall project purpose is to provide regional storm water management, within the Willow Creek Watershed.
PROPOSED WORK: The applicant requests authorization to construct a new 24-acre stormwater management pond. The proposed project will result in the construction of an earthen berm across the tributary with a new lake outlet structure. Approximately 6000 cubic yards of sediment will be excavated from the stream channel to create the pool area. The top of the dam will be approximately 70-feet wide, and the lake will have a maximum depth of 17-feet. The outlet for the dam will be a new 13’ x 13’ concrete box structure and will empty downstream from the embankment through a 7’ x 7’ Reinforced Concrete Pipe into the unnamed tributary. The project will result in the loss of 2355 linear feet of stream and 0.87 acres of emergent wetland.
Immediately upstream from the proposed pond, the applicant has proposed to reconstruct and re-meander the two stream channels that enter the proposed pond. This will result in the re-meandering of two channels totaling approximately 2530 linear feet. The applicant has proposed to lower the floodplain and re-meander these sections which will improve channel width, depth, slopes and the meander geometry. Within these two areas, approximately 4.7 acres of wetland will be enhanced and restored. These restoration activities may not be used to offset the required compensatory mitigation requirements.
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