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Updated Yellowstone channel-migration map shows erosion and avulsion risks, warns against riprap as default fix
Summary
Freshwater Partners presented a 2024 update to channel-migration mapping for the Upper Yellowstone River. The map highlights erosive reaches, avulsion pathways and a new geotechnical overlay and is intended as a nonregulatory tool for landowners and planners.
Jen Blank and Wendy Weaver of Montana Freshwater Partners presented an updated 2024 channel-migration map for the Upper Yellowstone River to the Park County Planning Board on Feb. 20, describing lateral migration hazards, avulsion pathways and a new geotechnical-hazard overlay.
Blank said the product replaces a 2009 map and covers the Yellowstone from Gardiner to Springdale; it was funded through a Department of Natural Resources and Conservation grant awarded to Park County in 2023. The mapping identifies where the river has occupied its floodplain historically, computes average annual lateral migration rates and produces an "erosion hazard" buffer (the presenters said the buffer is the average annual migration rate multiplied by 100 to provide a consistent planning margin).
Blank described three main…
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