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Blue Earth County discusses dam removal options, bridge foundations and agency support for natural channel stabilization
Summary
Public works staff briefed the board on bridge prioritization and project closeouts and provided an extensive update on a dam-removal and river-stabilization project, reporting that state and federal agencies provided letters supporting a natural channel stabilization approach while engineering work continues.
Ryan Till, Blue Earth County's public works and engineering director, presented several action and information items on Sept. 9, including a prioritized list of bridges for replacement and final payments on multiple state-aid road projects. The board approved an updated bridge replacement resolution and final contract payments for several state-aid projects by voice vote.
Till provided a multi-agency update on a proposed dam removal and bridge replacement project, summarizing coordination with MnDOT state-aid bridge staff, Barr Engineering, TKDA, the Minnesota Pollution Control Agency (MPCA), the Minnesota Department of Natural Resources (DNR) and the U.S. Army Corps of Engineers. He said the county's priority "is to remove the dam and replace the bridge," and that engineering and permitting work has identified several alternatives to manage channel armoring and foundation design.
Till described six options considered during meetings and engineering review: (1) rock channel armoring as previously proposed; (2) deep bridge pier (drill shaft) foundations with minimal armoring; (3) remove the dam without a bridge; (4) remove the dam with minimal armoring and grading; (5) lower the dam crest and remove the powerhouse while retaining a low-head structure; and (6) alternative armoring methods (flexible metal grid with concrete blocks). He said Barr and TKDA are reviewing options and that MnDOT and other agencies have been asked for guidance to avoid wasted detailed design work.
Till reported the county has received letters from regulatory agencies (MPCA, DNR and the U.S. Army Corps) supporting a direction toward natural channel stabilization and indicating reluctance to permit rock armor in the river. He said MnDOT state-aid will refer the matter to its central bridge office and foundation units for peer review because foundation type (drill shafts vs. driven piles) materially affects cost and design.
Till also warned that alternative materials such as chromium-reinforced bars (noted in consultant discussions) could increase bridge cost by multiples compared with epoxy-coated alternatives. He said bridge beam fabrication could take up to a year and that additional peer review is pending. Barr Engineering's hazardous-materials assessment inside the dam and soil-boring analysis are underway.
The board did not take a final policy vote on design alternatives at the Sept. 9 meeting; staff said a work session would continue the discussion.
