Water Resources of the United States

PROJECT ALERT NOTICE (MT WY) Flooding in Montana and Wyoming

Date: Wed, 20 Jun 2018 09:37:25 EDT

Summary: Minor to major flooding continues in western and central Montana and west-central Wyoming

Minor to major flooding from previous rainfall continues in western tributaries to the Missouri River along the Rocky Mountain Front and in central Montana. Minor flooding also continues in the Wind River basin in west-central Wyoming.

Annual exceedance probabilities (AEP) for flood crests at USGS streamgages on the Dearborn, Sun, and Teton Rivers along the Rocky Mountain Front in Montana ranged from 0.04 ("25-year recurrence interval") to 0.01 ("100-year RI"). Peaks were the second or third largest (28 to 49 years), exceeded only by the exteme flood event of June 1964. Flows in Elk Creek (ungaged) through Augusta, Montana, resulted in closure of highways and flooding of businesses and residences.

One streamgage on the Sun River is not functioning. Crews cannot reach the site as only road in has washed out.

Four crews of 2 or more are completing discharge measurements. At the request of State of Montana officials, USGS completed direct measurements of flood flows and flagged high-water marks on Elk Creek through Augusta for use in flood-inundation mapping.

USGS continues to inform NWS, USBR, and other stakeholders of our activities via email and NWSChat. Social media is being used as well (Twitter and Instagram @USGS_MT @USGS_WY).

USGS streamgaging sites, Sun River, Montana

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