PROJECT ALERT NOTICE (ID WY) Potential flooding on the Grey's River

Date: Thu, 08 Mar 2018 15:20:03 EST

Summary: Potential flooding of Alpine, WY from a debris dam breach on the Grey's River.

A landslide is occurring 17 miles S. of Alpine, WY on the Grey's River. The landslide is moving approximately 10-20 ft/day toward the river channel which is currently being constricted. Potential is high that the slide will reach and block flow in the river (currently flowing at approximately 300 cfs) this weekend through early next week. In the event that a dam is formed and then breached by flow, substantial flooding could be seen in Alpine, WY and dramatically increase flow into Palisade Reservoir below, which is currently at 93% capacity.

Bridger/Teton National Forest has requested 2 rapid deployment gages from the USGS to be deployed upstream and downstream of the landslide. The gages will be tied to NAVD88 using GPS survey to monitor relative water surface elevations.

One crew from Idaho Falls and one from Boise will be deployed 3/9/18 through the weekend to install and survey the RDG gages. Existing gaging stations downstream will also be armored and moved to higher elevations if possible. The area will be reconned for potential indirect mmts in the event of a breach.

NWS has been notified, USBR has been notified.