Porcupine landslide continues to move

The Porcupine Landslide near the town of Alpine, Wyoming continues to move.

The Bridger-Teton National Forest officials say the slide has moved completely across the river channel, creating a new channel on the west bank.

The movement created a 10 foot vertical cut bank on the west and 20 to 30 foot vertical cut banks on the east. That erosion will limit the river’s ability to move material and maintain a channel.

The resulting dam is retaining 12 to 14 feet of water on the upstream side.

The forest is concerned about public safety, especially given additional movement that will likely happen due to above-average snowpack and spring run-off over the next few weeks.

Re-opening the Greys River road remains a high priority. Several initiatives to do that are underway.

Web cameras are being installed within the next two weeks to allow real-time monitoring of slide conditions.

Jorgensen-Associations engineering is providing supplementary risk analysis. The firm will model different dam height scenarios and inundation areas and determine how those would impact the road and people using the area. That modeling is expected to be completed in May.

The forest is also engaged in obtaining soil analysis of the slide area. That information will help the forest reconstruct the road.

Future actions will include removing material from the head of the slide, reducing the amount of pressure on the toe area at the bottom. “We have used the best science and information available to us in our decision making and risk assessment,” said Greys River District Ranger Justin Laycock.

A federal agency, Emergency Relief for Federally Owned Roads (ERFO), will administer a road construction project. That project is expected to cost around $3.2 million.