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 backed loans; property owners inside mapped zones also face additional permitting and building requirements. Wadsworth told commissioners that the draft hydraulics she showed were an early step and that the contractor’s mitigation technical assistance is examining ways to reduce mapped risk in sensitive areas such as the hospital corridor and Fleishman (also spoken of as "Flushman" in the meeting) Creek neighborhoods.

Key technical points and next steps

- Completed work: lidar topography, hydrology (USGS data), and in‑stream engineering survey. DNRC provided a flood history report and hard copies of datasets to city staff. - Levee influence: the project shows a “worst‑case” map if a city levee is not certifiable and an alternate map that would result if the city certifies the levee. Wadsworth stressed that levee certification is the owner’s responsibility and that a certified levee can exclude certain areas from the Yellowstone River inundation mapping. - Levee shadow: DNRC updated a national levee database footprint (“levee shadow”) to show the area below a levee’s top elevation and how backwater can affect adjacent neighborhoods. - Separate tributary flooding: the contractor restudied Fleishman Creek (presented as a separate source of inundation). Wadsworth noted the hydraulic interaction: a levee that blocks river inflow can leave neighborhoods vulnerable to rising tributary flows unless interior drainage is addressed. - Mitigation technical assistance: DNRC commissioned a 30,000‑foot mitigation analysis (Michael Baker as contractor) that will provide options — a menu of measures the city can consider and, if chosen, use to support grant applications. DNRC cited the town of Three Forks as a prior success story where mitigation technical work helped secure grants. - Funding and schedule: DNRC has funding to finish hydraulics but lacks confirmed FEMA grant awards needed to complete full floodplain mapping. Wadsworth said if federal grants come through the agency anticipates draft map data roughly within about a year (early 2026) and that FEMA’s full process to make maps effective could take up to three years after draft data is submitted. If FEMA funding is not awarded, the new data may never enter the formal FEMA mapping process even though DNRC will hold and may share the improved hydraulics information with the city.

Questions from commissioners and public

Commissioners and residents asked how maps affect mortgages, local permitting and city insurance. Wadsworth said lenders typically require flood insurance for properties inside the mapped 1% zone, and the city would issue floodplain permits and apply building standards where shown on the maps. She also confirmed that community buildings in mapped areas would likely need flood insurance if the city wants recovery after an event.

City staff asked whether DNRC would retain outreach support if federal mapping grants lapse. Wadsworth said outreach staffing depends on federal grant funding and urged the commission to contact congressional delegates if the city wants to prioritize the FEMA grant streams that fund mapping and mitigation support.

Public input and local partners

Jeanette Blank (online) asked whether contractors’ mitigation concepts would be preserved if DNRC’s grant funding ends; Wadsworth said the hydraulics work and work completed to date would remain accessible and that she would try to ensure the mitigation contractor’s interim products are available to the city. Kristen Smith, who identified herself as lead for Headwaters Economics’ Floodwise community assistance program, spoke to the commission to offer that organization’s support for grant applications and technical follow‑through.

What the city can do now

Commissioners and DNRC staff agreed on several near‑term actions: DNRC will post links and datasets on the agency project page and provide the city the hydraulics data that is finished; the city will consider levee analysis and certification steps (interior drainage and outlet connections are required components of a certification); and city staff said they would explore meeting with federal representatives to advocate for the grant funding that completes the mapping and outreach work.

Ending note

Wadsworth cautioned the commission that the draft hydraulic work is early and subject to change as mapping continues and FEMA’s review process proceeds. She said DNRC will return with draft maps and outreach plans if funding is available and invited the city to use the interim data to inform planning and emergency‑management decisions.