SD46 Wetland Delineation

South Dakota Department of Transportation | Yankton County, SD

Benesch completed a wetland delineation of approximately 12 miles of SD-46 and nine borrow sites in Yankton County for a rehabilitation project, including grading and interim surfacing, structure replacement, and lighting. Also included was the preparation of wetland delineation reports, functional classification, cultural resources survey and Jurisdictional Determination requests.

Benesch biologists identified 27 acres of wetlands within 56 wetlands during the field investigation. These wetlands were observed in three common areas: along stream channels, swales, and within US-46 road ditches. These wetlands consisted of Palustrine Emergent Temporarily Flooded (PEMA), Palustrine Emergent Seasonally Flooded (PEMC), or Palustrine Forested Temporarily Flooded (PFOA).

Each wetland’s jurisdictional status was assigned and confirmed by submitting a Jurisdictional Determination request to the Corps of Engineers. Wetland functions of Prairie Pothole, riverine and slope wetlands were assessed using the HGM approach using established field protocols. These assessments required specialize field data collection as well as computer software, such as ArcView.

Utilizing the functional assessment work sheets a Functional Capacity Indices (FCI) was developed for each wetland. Next, Benesch calculated permanent and temporary impacts and determined a corresponding Functional Capacity Unit (FCU) for that wetland. Finally, a mitigation needs assessment memo was prepared to determine the quantity and availability of FCU’s to offset impacts from the project.