WATERWAY AND LOCATION: The project would affect waters of the United States associated with Buckeye Creek. The project/review area is located on an approximately 20.51-acre parcel located southeast of the Highway 30 and Highway 21 intersection just south of 74th Street and west of 13th Avenue along Buckeye Creek in Section 4, Township 82 North, Range 12 West; Latitude 41.9470693 and Longitude - 92.2504513; in Benton County, Iowa.
EXISTING CONDITIONS: The site primarily consists of undeveloped land along Buckeye Creek, surrounded by row-crop agricultural land, a county roadway, and homesteads on neighboring property.
PROJECT PURPOSE/BANK OBJECTIVES: The fundamental objective of compensatory mitigation is to offset environmental losses resulting from unavoidable impacts to waters of the United States (WOTUS) authorized by Department of the Army Permits. Other objectives include: enhance and create additional wildlife habitat; restore native vegetation within the riparian buffer; remeander the channel and pull back streambank slopes to increase cross-sectional area and reduce velocities, provide stability, and increase sinuosity; construct floodplain benches and establish oxbows to provide 1.5-2 year floodplain connection during frequent flows and increase flood storage capacity; and sell stream mitigation credits for project impacts proposed by
other entities.
PROJECT DESCRIPTION/BANK ESTABLISHMENT:
a. The bank sponsor proposes to complete activities on approximately 20.51 acres in which Buckeye Creek flows through the property. This project would result in the generation of stream compensatory mitigation credits. The goal of this project is to restore 3,550 linear feet of stream with buffers to generate an initial estimate of 40,839.10 stream credits.
b. The proposed concept alignment would shape streambanks along 3,550 linear feet to increase the cross-sectional area of the stream, reduce shear stress, reduce velocities which will reduce erosional effects within the stream channel and adjacent floodplain. In addition, a floodplain bench about 10 feet in width is proposed at the concept stage to be added along the full 3,550 linear feet at a 10:1 slope. Floodplain benches are proposed to transition at a 4:1 slope to the existing floodplain. The remeandered channel will provide floodplain connectivity, particularly to the proposed 1.5-2-year low floodplain benches, increasing the frequency of flooding of the riparian fringe. The overbank floodplain inundation is controlled by downstream road crossings, culverts, and stream hydraulics for the larger and less frequent storms. These features serve as grade control locations which limit the amount of flow leaving the Bank during
periods of flooding.
c. Two rock riffles proposed for grade control purposes: one at the downstream terminus of the project and a second at approximately the midpoint of the project. The midpoint riffle may also serve as a stream crossing for conservation easement access to both sides of the channel. Each riffle will be comprised of rock revetment with sloping upstream and downstream faces that are shaped to natural flow. Riffles will stabilize the stream and are also an ecological benefit.
d. Oxbows or two areas with deep water habitat are proposed along the existing channel at two primary locations. The existing channel would be plugged at one end and reconnected to the new channel alignment offering a place for fish refugia, spawning, and additional habitat for other species. If deep water habitat, these areas would be plugged at both ends retaining surface water for birds and amphibians as well as provide temporarily increase flood storage capacity.
e. Other improvements include removing the riparian buffer from pasture and seeding the current pasture and row-crop field within the buffer with native mesic species. Vegetation within the riparian buffer will be managed with mowing, prescribed fire, herbicide, and native seed. The Bank would be seeded with appropriate native ecotype seed mixes.
SERVICE AREA: The proposed mitigation bank will be in the Iowa Service Area.
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