PROJECT ALERT NOTICE (ID) Potential Dam Failure

Date: Fri, 02 Jun 2023 14:19:11 EDT

Summary: the spillway for Chesterfield Reservoir has experienced significant scour and head-cutting due to sustained high flows on the Portneuf River.

Location: Chesterfield Reservoir Spillway. Lat 42.878629 Lon -111.952162. Potential spillway failure which will potentially double to triple current flood levels for downstream communities.

Spillway failure would impact all areas in the Portneuf River basin down to American Falls Reservoir on the Snake River. Communities potential impacted if the spillway fails: Chesterfield, Pebble, Lava Hot Springs, McCammon, InKom, Blackrock, Portneuf, Pocatello, Chubbuck, and Fort Hall Indian Reservation in ID. I-15, State Hwy 30, and numerous county and local roads are also in danger should failure occur.

Streamgages potentially impacted: 3 gages on the Portneuf River system could be impacted.

An RDG equipped with a camera will be installed today (6/2/2023) on the reservoir measuring water surface elevation and publish an image every 15 minutes via USGS-HIVIS (https://apps.usgs.gov/hivis/). Another may be installed below the spillway yet to be determined by on-site emergency personnel. One crew from the IDWSC Idaho Falls Field Office is deploying for the RDG installation in cooperation with the USACE and Caribou County Emergency Coordinator.