Rock Island District Public Notices

Rathbun Land & Water Alliance (CEMVR-RD-2022-1208)

Rock Island District
Published March 1, 2024
Expiration date: 4/3/2024

Project Location: Near the town of New York in Wayne County, Iowa. Section 14, Township 70 North, Range 21 West, UTM NAD-83, Zone 15, Latitude 40.8610, Longitude -93.2386.

Project Description:
A. Rathbun Lake is a primary drinking water source for the Rathbun Regional Water Association (RRWA), the largest rural water system in Iowa. Rathbun Lake and three of its arms are listed on the Iowa DNR's List of Impaired Waters because of high levels of non-algal turbidity. Sediment that enters the lake from the watershed is a major cause of this impairment. The Rathbun Land & Water Alliance works with landowners to implement conservation practices and reduce sediment within the watershed.

B. This project will construct an earthen dam across an intermittent stream to create a sediment basin in effort to improve water quality by reducing sediment loads from entering Rathbun Lake. The permanent pool is designed at an elevation to capture and store approximately 50 years of sediment.

Avoidance and Minimization: The unnamed intermittent stream where the proposed dam will be placed has a drainage area of approximately 845 acres with land uses including pasture, row
crops, and upland woods. The intermittent stream will maintain surface flow through an outlet structure. Surface flow from the intermittent stream will slow within the basin, allowing sediment to drop out of the water column and reducing sediment transport to Rathbun Lake. The dam embankment will consist of 3H:1V upstream and downstream slopes, a 16-foot-wide
top width, and an upstream and downstream berm. The dam includes a 30-inch diameter smooth steel principal spillway and riser and a 35-foot-wide auxiliary spillway.

Impacts and Mitigation: The permanent pool, approximately 15.8 acres in size, created by the dam will affect approximately 3,948 linear feet of unnamed intermittent stream requiring 8,290.80 stream mitigation credits. The applicant intends to complete permittee responsible mitigation by improving an eroded, tertiary intermittent stream and associated riparian buffer
directly to the east of the project area. The Corps will determine whether the permittee responsible mitigation is acceptable, or mitigation will be a combination of purchasing mitigation bank credits and permittee responsible mitigation if there aren’t enough credits available to cover the entire project.

Click the link below to view the full notice.