AMI worked with the City of Stillwater to perform site investigations and rehabilitation planning for approximately 3,700 linear feet of failed riverbank along the St. Croix River. During the 2018 investigation, serious decay and failures of the riverbank were found to be undermining the existing trail and guard rail. The decay and failures resulted in public safety risks, as well as reduced accessibility to the St. Croix’s trail system.

Once investigations and Alternative Analysis were completed, AMI initiated the design process for the shoreline stabilization of 3,700 linear feet of eroded riverbanks along the western shoreline of the Lower St. Croix River. Incorporated within the shoreline stabilization AMI designed three river overlooks, a new Riverwalk trail and improvements to existing infrastructure to improve public safety and accessibility to the St. Croix river trail system.

The Lower St. Croix National Riverway is a State-administered component of the National Wild and Scenic Rivers System under the authority of the U.S. Environmental Protection Agency. As such, the project was subject to a strict regulatory compliance review in compliance with the National Environmental Protection Act to ensure the protection and enhancement of the Riverway’s outstandingly remarkable values. AMI worked diligently with the jurisdictional authorities to complete a detailed environmental evaluation as part of the permit acquisition process.

Protecting Endangered Species

Mussel surveys and initial relocation efforts revealed a significant mussel population in the project area, with the Threeridge mussel being the dominant species, supporting at least 16 other species, including the federally endangered Spectaclecase mussel and the state-endangered Salamander mussel. Both of these endangered mussels were primarily found in unique habitats characterized by steep slopes and anthropogenic features like construction debris and riprap. Detecting these species paused initial relocation efforts, leading to consultations between the City of Stillwater, the U.S. Army Corps of Engineers, and the U.S. Fish and Wildlife Service under the Endangered Species Act.

As a result of the consultations, project changes were made to limit impacts to river habitats, allowing a relocation effort to proceed. Federally endangered species were not to be moved if found alive, and the U.S. Fish and Wildlife Service was to be promptly informed. The Minnesota Department of Natural Resources approved a plan to relocate all other native mussels, including state-listed species.