Nearly the Whole Dam Area Needs Erosion Control
Folsom Dam, located about 25 miles northeast of Sacramento, CA, is undergoing renovation. The dam, which was completed in 1956, is gaining an auxiliary spillway. This Joint Federal Project, which includes the US Army Corp of Engineers, the Bureau of Reclamation, the Central Valley Flood Protection Board, and the Sacramento Area Flood Control Agency, will raise the level of flood protection for Sacramento and surrounding areas
The project’s current phase includes a $62-million dollar contract with Martin Brothers Construction and its subcontractors. The work to be done includes two million cubic yards of spillway excavation, construction of a 7,000-cubic-yard concrete coffer dam, relocation of a 42-inch water supply pipeline that serves the city of Folsom and the nearby prison, and 100,000 cubic yards of riprap placed along the lake shore to prevent erosion. The main spillway excavation drains directly toward the American River. The close proximity of the surrounding water bodies, and approximately 80 acres of exposed soil, makes this project very sensitive to the effects of soil erosion. To meet the construction schedule and work through the winter, many types of erosion and sediment control BMPs were used to meet National Pollutant Discharge Elimination System (NPDES) requirements.
“We’ve been working for Martin Brothers, doing all their BMPs, since 2009,” says Jay Selby, president of Selby’s Soil Erosion Control in Newcastle, CA. “Our subcontractor, Decker Landscaping, is installing blankets on the spillway’s hillsides.”
Excavated material is stockpiled on the project’s east side, which is stabilized with three-step erosion control, blankets, and straw wattles before every forecasted rain event.
“We use FMI’s Rainier Fiber as the BFM,” Selby explains. “It wasn’t the originally specified BMP for these spillways, but the Army Corps of Engineers and Bureau of Reclamation have been really pleased with the FMI product’s results; it stands up to more rain. We apply it with a hydrosprayer and include it in our three-step erosion control. The first step is a hydroseed mix of virgin wood fiber, mulch, seed, and fertilizer. Next, we apply straw at the ratio of two tons per acre, then top it off with a tackifier and FMI’s Rainier Fiber wood mulch. We seed with a native mix that the Army Corps designed.”
Selby thinks the “F” in BFM can make a difference. “Fiber can be recycled newspaper; wood fiber made from recycled wood, old lumber, and recycled furniture; or virgin wood. Virgin wood holds moisture a lot better than the other two substances, and Rainier Fiber is created from virgin wood.”
With the massive amounts of materials being moved, the project’s haul road also needs maintenance. “Big rock trucks travel this road; it’s like a mining site with all the traffic. As the haul road itself gets a lot of runoff, that’s pumped to an existing advanced treatment system that uses chitosan-enhanced sand filtration. The water is then returned to Folsom Lake and the American River.”
Decker Landscaping, Selby’s “go-to” subcontractor, is securing the steep hillsides. “Decker’s placed approximately 12 acres of permanent EC blankets on surfaces that range from 1:1 to 2:1 slopes. Thirty- to 50-foot walls of rock or vertical slopes were sprayed with gunite below their area of work. Due to the terrain’s severity, Decker’s crews require fall protection, which includes full body harnesses and a rope restraining and rappelling system. Martin Brothers provided a steel safety anchoring system along the top of each slope.
“Because of the difficult working angles and the rocky subsurface, securing blankets was a challenge.” Selby continues. “Blankets were fastened with 8-inch steel nails with half-inch washers placed at 3-foot on centers. The slopes’ limited access did not allow the use of much equipment; most of the project was done by hand.
“We started work here in fall 2009; there are more phases to come. We’ve been onsite every week for the rainy season, although we put down blankets year round. The project’s current phase, completed in winter 2011, and future phases are expected to continue through 2015.”