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.
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 was complete by the Whatcom County Public Works River and Flood Division. The mitigation plan was prepared by the Whatcom Conservation District.
This graphic shows a cross-section of the proposed east bank levee repair. The cross-section view is oriented looking upstream. Trees will be removed on the levee backslope (landward side of the levee) and fill material will be imported to fill the damaged portions of the levee and establish a gentle backslope. The levee crest and backslope will be seeded and protected with geotextile erosion control fabric. Removed trees will be placed on the floodplain landward of the levee for floodplain habitat and roughness.