State DNRC presents early floodplain study for Livingston; maps hinge on levee certification and federal funding

Nadine Wadsworth, outreach specialist with the Montana Department of Natural Resources and Conservation, told the Livingston City Commission on July 15 that the agency has finished lidar, hydrology and field survey work for the Park County and Livingston flood study and provided an early look at hydraulic results and risk scenarios.

The update matters because new maps could change which properties are shown inside the 100‑year (1% annual chance) floodplain and whether parts of downtown would be considered protected by an approved levee — a determination that would remove areas from the Yellowstone River inundation zone if the levee is certified.

Wadsworth said the project so far has produced: high‑resolution lidar topography (publicly available via the state library), hydrology completed in partnership with the U.S. Geological Survey, and in‑stream and structure surveys gathered by the contractor. She described four technical steps in the study: survey, hydrology (how much water), hydraulics (engineered flow models) and map delineation. Wadsworth also explained that the levee certification decision — which is the responsibility of the levee owner, in this case the city — has a large influence on mapped outcomes. “Anywhere you see that blue ... is considered the hundred‑year, that 1% annual chance,” Wadsworth said, noting that mortgage, permitting and building rules follow the mapped zones.

Why it matters: properties inside the federal floodplain typically must carry flood insurance under federally…