American River - Residential Bank Armoring

This was a residential project that involved two homeowners. The homes back up to the American River, outside of Sacramento, CA. The two properties sit atop the right bank of the American River, near USACE river mile 13.4. Gunite slope protection had been installed in the 1960s, but it had become severely undermined. Large cracks and voids had developed.

This project site is located within the American River Flood Control District, and a Section 408 Permission from the U.S. Army Corps of Engineers (USACE) was required. Additionally, the project was within the Central Valley Flood Protection Board's (CVFPB) jurisdiction, so a permit from the CVFPB was required with the USACE Permission. Hydraulic and geotechnical analyses are the key components of the application submittal package. These analyses must demonstrate that the proposed project will not be injurious to the federal flood control project. Therefore, an experienced engineering firm was selected by the homeowners to ensure this was a smooth process.

Other requirements needed to obtain the Section 408 Permission as set forth by the following:
- California Environmental Quality Act (CEQA)
- National Environmental Policy Act (NEPA)
- Endangered Species Act: Section 7 consultations
- National Historic Preservation Act: Section 106
- Clean Water Act - Section 401: State Certification of Water Quality
- California Department of Fish and Wildlife (CDFW) Lake and Streambed Alteration Program

Equipment access was limited. The only access point for equipment and material via a small boat launch that connected to one of the residential driveways.

In order to utilize small equipment that would not damage the driveway, small customed-sized Flexamat Plus rolls were ordered. The rolls varied in length, but each were 7.5' wide and included geogrid and underlayment extensions. The installation began at the downstream end of the properties, with the next subsequent mat being installed over the previous mats extensions, thus creating a continuous armor.

The slope had steep sections that varied up to .75:1. Percussion anchors were incorporated throughout the slope in a diamond patten. The percussion anchors were also installed at the mat seams, through the top Flexamat Plus layer and through the extension underneath.

This project had a site specific planting plan. Prior to the Flexamat Plus installation, the slope was seeded with a grass seed blend. After the installation of the Flexamat and anchors was complete, the contractor planted plugs, live cuttings, and container plans.

This residential slope is now fully protected. The performance life of the new Flexamat Plus system exceeds the lifespan of the gunite that had been installed in the 1960s. The new slope protection will perform better and is also much more aesthetic.