WATERWAY AND LOCATION: The project would affect waters of the United States associated with the Raccoon River. The project/review area is located at the southwest corner of the intersection of Fleur Drive and W. Martin Luther King Jr near downtown Des Moines in Section 8, Township 78 North, Range 24 West; at Latitude 41.5737 and Longitude -93.6375; in Des Moines, Polk County, Iowa.
EXISTING CONDITIONS: Downstream of the Des Moines Public Works water plant intake structure on the Raccoon River. There is an existing low head dam in the northern section of the project area, to the east is a forested wetland and a Corps Section 408 levee, and a pedestrian bridge near the southern section of the project area.
PROJECT PURPOSE:
- Basic: Recreation and Safety
- Overall: Enhance Raccoon River recreational opportunities in downtown Des Moines, connecting adjacent water trails upstream and downstream through mitigation for trail hazards/obstacles, while maintaining existing City of Des Moines municipal water intake structures located upstream of the existing Fleur Dam. Additionally, the south site will provide Americans with Disabilities Act access to outdoor recreational facilities and emergency water access to the Raccoon River.
PROPOSED WORK: The applicant requests authorization to construct access at two locations (north and south sites) along the Raccoon River, a new in-river structure, and a parking lot at and downstream of the Fleur Dam in downtown Des Moines, Iowa. At the north site, where the existing Fleur Dam is located, accessible egress, secondary egress, pedestrian sidewalk/mowed path, and accessible launch would be constructed above and below the existing dam for recreational boaters to have a portage site around the dam structure. The south site includes an access road from an unnamed planned roadway over an existing Corps 408 levee, and then connects to a river access located along the north shoreline of the Raccoon River. Within the south site there is a planned parking area for vehicle access (20 stalls parking), a vehicle turn-around area, a boat ramp with watercraft launch (with ingress and egress to the river), pedestrian trails, and associated walkways and access for pedestrians along the river shore, as well as a trail connection to the existing pedestrian trail to the east. The in-river structure would include a fish bypass and habitat riffle channel, a recreational boat passage channel, a stepped boulder cascade with pneumatic flashboard gates, a mid-channel island structure to separate the fish passage and the boat passage, and associated in-river boulders, grouting, and riprap.
This project will result in the modification of 4000 feet of perennial stream (RPW) and the loss of up to 5.02 acres of forested wetland and 0.04 acres of emergent wetland. To compensate for this loss the applicant has proposed to mitigate the wetland loss through the purchase of wetland credits from an approved wetland mitigation bank in the service area of the impacts.
Within the south site, clearing and fill of forested wetlands will be due to cut and fill for establishment for road access, parking facilities, and boat ramp with vehicle turnaround, in addition to the pedestrian access and trail areas. For the in-river structure, loose stone, sculpted concrete, riprap, compacted fill, and grouted boulders will be used to create partial impoundment of the river to increase surface elevation of the Raccoon River to back up the hydraulic connection to flood out the existing Fleur Dam infrastructure. Currently to maintain water levels for the City of Des Moines municipal water intake structures, flashboards are installed during low water events to maintain up-river municipal water intake supply lines. During low to typical conditions, there is a dangerous recirculation current that develops below the low head dam that could potentially trap or drown a boater or swimmer within the current. The in-stream work will mitigate this safety hazard.
Work within waters of the U.S. (WOTUS) consists of 5.02 acres of forested wetland, 0.04 acres of emergent wetland, and 1.4 acres of fill below the ordinary high-water mark of the Raccoon River. The applicant is currently reviewing the plans to determine if these impacts will be permanent, temporary, or a combination of both. Any temporary impacts to wetlands will require a monitoring plan to ensure restoration success. Temporary impacts will be monitored and will have performance standards that must be met.
There is a United States Environmental Protection Agency (USEPA) Superfund Site that consists of four operational units in over 200 acres north of the project area, and that the access road will cross over the 408 Corps levee. Primary contaminants of concern consist of volatile organic compounds (VOC), polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), organochlorine pesticides, and resource conservation and recovery act (RCRA) metals. Subsurface soil tests were collected from geotechnical/environmental borings installed onsite has not been impacted at levels exceeding the Iowa Administrative Code (IAC) Chapter 137 statewide standards (SWS) except for arsenic. However, the reported concentrations of arsenic are within what is generally considered to be naturally occurring background concentrations and below the SWS previously utilized by the Iowa Department of Natural Resources. The USEPA has recommended that the proposed project would not affect the current remedy of the Superfund Site. The Corps will ensure compliance with Code of Federal Regulations 40 Part 230 Section 404(b)(1) guidelines prior to final permit issuance.
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