Florence Siuslaw River Slope Stabilization Project

The slippage along the Siuslaw River is located on the end of Coast Guard Rd. It affects the Coast Guard Station, a City Stormwater easement, and private homes. The plan is to put in a Secant Pile Wall to temporarily halt the slipping so that we can engineer a more long term solution. 

Project Description: Siuslaw River Slope Stabilization Project

Coast Guard Road, Florence, Oregon: Recent 2024 Ice Winter Storm and ongoing groundwater and river action causing a landslide along the Siuslaw River edge threatening homes and the Coast Guard Station in Florence, Oregon.

Short-term solution project name: Siuslaw River Slope Stabilization Project - Secant Pile Wall (for the Siuslaw River Coast Guard Road riverbank stabilization)

Long-term Project name: Siuslaw River Coast Guard Road River Slope Stabilization, Erosion Prevention, and Stormwater Project

The cost of the Short-term project is $1,075,000 and it would enable a project to stabilize the banks of the Siuslaw River that is threatening to significantly damage federal, City, and private property. Funding would enable a project to stabilize a landslide and save the Florence Coast Guard Road and two housing developments consisting of 36 homes. These homes serve as the on base housing for the Coast Guard and a subdivision on the banks of the Siuslaw River.

Coast Guard Road is the sole ingress and egress to a residential subdivision (Sea Watch Estates) and US Coast Guard Station Siuslaw River. After a period of heavy rain in January 2022, a steep section of the bank of the Siuslaw River adjacent to Coast Guard Road began to fail, resulting in cracking of the Coast Guard station parking lot, disconnection of a City stormwater main, and deformation of a wooden deck on private property. The landslide is progressing at a rate of several inches per month however, it could catastrophically fail at any time. Realizing the magnitude of potential damage, the City took the immediate action of repairing the disconnected storm sewer, then contracted with a team of engineers to develop a solution. The monitoring and engineering plan has continued from 2022 through current day (February 2024).

With recent storms and significant rain events from January 12, 2024 to present, the slippage has become more acute, slipping more than 25 inches in less than four weeks! From the City’s evaluation the slope movement resulted in the formation of a scarp (a long steep slope or cliff at the edge of a plateau or ridge that is formed by erosion.

The engineering team concluded that improvements to provide long-term stabilization of the riverbank would require work within the river, triggering permitting through NOAA Fisheries, US Army Corp of Engineers (Corps), US Coast Guard – Homeland Security, Oregon DEQ, and Oregon DSL. The slope is anticipated to fail and cause significant damage to federal, City and private property. The City is requesting assistance from Corps for increased armoring of the river bank to prevent continued erosion along the eastern bank of the Siuslaw River from the US Coast Guard Station Siuslaw River to a point where the existing substantial rock reinforcement (revetment) is already located. This is approximately 750 feet in length along the Siuslaw River.

Additionally, due to climate change, increasing sea levels and increasing storm intensity, a long-term study to regarding these effects to the river bank and slopes should be undertaken to help define what types of human-made structures could be best utilized to safe guard homes, Coast Guard station/property, and stabilize the river embankment.

Since the long-term solution is many years in the making, the City will need to go through the process to construct a secant pile wall retaining system to immediately stabilize the shallow slide area in the short term while a long-term solution is being developed. The secant pile wall project is estimated to cost approximately $1,000,000 which includes environmental permitting and additional engineering.