Marengo River watershed: Design for reducing coastal impacts of flooding

In July 2016, extreme rainfall of 8 to 10 inches within an 8-hour period caused severe flooding on the Bad River in Ashland County, Wisconsin on Lake Superior. Extensive flood damages impacted the Bad River community and beyond, washing out culverts and shutting down U.S. Highway 2, a major transportation route along the south shore of Lake Superior. Beyond infrastructure, brook trout and wild rice habitat were at risk as the Bad River Watershed provides some of the highest sediment and nutrient loading to Lake Superior. Climate change impacts in the Great Lakes are expected to produce more intense precipitation events, similar to events already occurring in northern Wisconsin in June 2012, July 2016 and again in June 2018 for this same Lake Superior region.

These events are causing flooding that result in both erosion and increased sedimentation on habitats in the uplands and coastal floodplains as well as damaging existing infrastructure such as culverts and roads, which ultimately impacts the local economy. Preserving and restoring the natural and beneficial functions of wetlands and floodplains is a cost effective means to preserve the health of a watershed and prevent future flood damages. Wetlands and floodplains are a critical part of the coastal and uplands watershed ecosystem, serving to filter and clean water that moves through watersheds and reducing flooding scenarios by retaining and detaining flood water during heavy precipitation events.

The Wisconsin Wetland Association (WWA) focused their research on the impaired Marengo River Watershed and smaller catchments in Ashland County that experienced significant rainfall and flooding in July 2016. This project proposes doing a comparative study between the Marengo and another unimpaired watershed in the region to be used as a baseline to reflect historic, functioning conditions to be used as indicators. Potential baseline watersheds include, but are not limited to the White River, Potato River, Cranberry River or Bark River in Bayfield County (was on the short list for NERR status).

This project has three facets: 1) improved hydrologic and hydraulic (H&H) modeling including a functional assessment of the river channel and riparian corridor; 2) impact assessments related to habitat, land use and infrastructure, ecosystem service valuation and benefit-cost analysis; and 3) stakeholder engagement.

FY2021: $575,000