Salt River Ecosystem, Riverside Ranch Tidal Marsh Restoration
Humboldt County Resource Conservation District
Approx. Contract Value:
Prior to construction, Riverside Ranch was a 300 acre dairy pasture located adjacent to the Salt River in Humboldt County near Ferndale, California. Anderson Dragline, Inc. excavated approximately 370,000 cubic yards to widen 2.4 miles of the Salt River, removed existing levees, excavated 2.8 miles of internal channels, and constructed a setback levee 2.2 miles in length. This created approximately 200 acres of tidally inundated marshes while increasing river capacity and reducing flood risk to Ferndale and neighboring properties.
Saturated soils along 2.4 miles of the bank of the Salt River Channel were excavated to increase the channel width to between 40 and 75 feet. Construction required continuously bypassing the river flow around the work area. A cofferdam and pumps were installed in the river upstream of the work area, and 3,000 feet of pipe was installed to bypass the river flow during the three month duration of excavation. Saturated soils created soft ground conditions necessitating the use of low ground-pressure equipment. All excavations and embankments were constructed utilizing GPS grade controls on the equipment.
Large Wood Debris (LWD) structures were installed at various locations along the new internal channels. Logs with rootwads attached were partially buried in the channel banks and anchored in place with smaller logs driven in place. Surfaces of the setback berm and fill areas were hydroseeded with seed species harvested from local plants. A temporary irrigation system was installed to maintain the 83 acres of seeded area for three months after seed application.
The work required extensive daily coordination with avian and fisheries biologists. Concurrent with the installation of the temporary bypass system, fisheries biologists collected and relocated native fish from the unwatered river channel. Avian biologists surveyed and monitored active nest locations to establish buffers and permissible work areas.