Repairs to the Union Slough Levee started in earnest yesterday as the U.S. Army Corps of Engineers officials commenced construction on a 100-foot-long damaged segment on the southwest corner of Smith Island, just south of Everett’s Water Pollution Control Facility.
Located on the Snohomish River’s right bank, the $86,000 project will address sloughing, slope scour, and the loss of embankment material caused during high river flows in November 2014.
Damages reduced the levee’s flood defense to a five-year level of protection, or a 20 percent chance of occurring in any given year.
Once repaired, the levee will be restored to a 20-year level of protection, or a five percent chance of occurrence. Under a cost-share agreement, the Corps pays for 80 percent of construction costs and Snohomish County Diking District #5 picks up the remaining 20 percent.
Repairs to the segment include rebuilding erosion protection along the 100-foot damaged section with an additional 25 feet on both sides for tie-in purposes, regrading the levee slope to make it more gradual on the riverward side, and adding a blanket of rock armor to protect against erosive river flows.
The construction plan calls for the reuse of existing spall rock and riprap for the repair, meaning a minimal need for new materials.
Construction is expected to be complete by the end of September, restoring the levee to its designed 20-year level of flood protection.