Status
Levee construction was completed fall 2018 with mitigation planting in spring 2019.
Project Benefits
- Reduce the frequency of flooding of Slater Road and the community of Marietta
- Increase floodplain roughness and riparian habitat in support of salmon recovery goals
- Reduce maintenance costs and frequency of repairs
Background
The Marine Drive Levee on the east bank of the Nooksack River upstream of the Marine Drive Bridge has suffered damage over the past few years. Large scour holes formed on the levee crest and backslope, and some of the scour holes have lowered the elevation of the levee crest allowing floodwaters to overtop the levee more frequently. When the levee overtops in these lowered areas, it concentrates fast moving water and causes further damage to the levee. The floodwaters that overtop the levee pond in the floodplain and back up causing frequent flooding of Slater Road and the community of Marietta. These areas will experience more frequent and deeper flooding if no repair is made.
Project Description
The project consists of repairing approximately 1,500 lineal feet of levee on the left (east) bank of the Nooksack River upstream of the Marine Drive Bridge. The levee repair will include removing trees along the levee backslope (landward side), filling the scour holes along the damaged levee sections, creating a gentle (low gradient) backslope, and installing erosion control on the levee crest and backslope. Irrigation of the levee crest and backslope will occur from late July into October for grass establishment. Trees on the riverward side of the levee will remain in place for shade, edge habitat, and bank protection. Tree removal along the levee backslope is required to maintain an even surface, which reduces the potential for erosion when the levee overtops during high flood events (see cross-section view of levee below). Trees and tree roots on the backslope can cause scour holes to develop and eventual lowering of the levee in these locations.
As part of the mitigation plan for the project, the removed trees will be placed on the floodplain landward of the levee to provide habitat and roughness. As many trees as possible will be removed with rootwads attached to further enhance floodplain habitat and roughness. The mitigation plan also includes planting 460 trees within 150 feet of the river. The planting will include a mix of hardwoods (black cottonwood) and conifers (Sitka spruce and western red cedar).
Engineering Design
Engineering design was complete by the Whatcom County Public Works River and Flood Division. The mitigation plan was prepared by the Whatcom Conservation District.
Construction Contract
- Contractor: Iverson Earth Works, LLC
- Contract Amount: $197,549
Funding
- Whatcom County Flood Control Zone District
- Washington Department of Fish and Wildlife
