SEDHYD-2023, Sedimentation and Hydrologic Modeling Conference

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Connecting Flood-Related Fluvial Erosion With Risks To Downstream Road Crossing

Fluvial erosion is increasingly causing extreme infrastructure and building damages across the U.S. as the intensity of extreme-rainfalls hit rural and urban rivers in a variety of climate settings. Northern Wisconsin is no exception, and an extreme flood in 2016 caused widespread culvert blockages and road failures, including extensive damage along steep tributaries and ravines in the Marengo River watershed. Along with the flooding, there were fluvial erosion hazards (FEH) associated with a large amount of erosion in headwater areas. Of special concern for a study conducted by the U.S. Geological Survey, Wisconsin Wetlands Association, Ashland County, and the Northwest WI Regional Planning Commission were FEHs associated with gullying and channel-side landslides in headwaters and loss of wetland storage . In 2020, a pilot study was begun to map and classify ephemeral and perennial streams and wetlands in terms of their susceptibility to fluvial erosion hazards. This study combines field assessments of river corridor erosion and coupled sediment and debris delivery with stream network-wide connectivity tools in a Geographic Information System (GIS). The GIS approach uses nationally available 10-meter resolution topology to map hydrogeomorphic units based on stream order, channel slope, and the presence of steep near-channel side-slopes. Bankfull channel widths derived from regional hydraulic geometry curves combined with flood frequency equations were used to calculate a specific stream power metric. The results were overlain with soils and surficial geology to further locate valley sides as well as ravines that are most susceptible to erosion. The resulting susceptibility maps will include gullying and mass wasting in ravines as well as potential lateral migration and mass wasting for ephemeral and perennial streams. A GIS approach is under development that links large sources of potential sediment and debris to potential blocking of downstream culverts. Time-lapse camera technology has been utilized to help record flood flashiness, potential erosion, and debris movement. The FEH assessment results will ultimately be used by Ashland County and their collaborators to identify and prioritize natural flood management projects related to stream and wetland restoration.

Faith Fitzpatrick
U.S. Geological Survey
United States

Kyle Magyera
Wisconsin Wetlands Association
United States

Jason Laumann
Northwest Wisconsin Regional Planning Commission
United States

Clement Larson
Northwest Wisconsin Regional Planning Commission
United States

Julia Prokopec
U.S. Geological Survey
United States

Eric Dantoin
U.S. Geological Survey
United States

Tom Hollenhorst
U.S. Environmental Protection Agency
United States

Brandon Krumwiede
National Oceanic and Atmospheric Administration
United States

 



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