Lower American River Site 2-1 Levee Erosion Control

In the winter of 1986, a series of catastrophic Pacific storms wreaked havoc across California. The high-velocity water flows from these storms flooded various rivers, tore bridges from their foundations, and breached levees. These events damaged or destroyed tens of thousands of homes and businesses, leading to mass evacuations. Dams and levees in surrounding areas failed, with the total damage estimated at $500 million.

From February 11th to February 20th, three storms of increasing intensity overwhelmed flood control measures. The record-breaking rainfall filled or overflowed streams and creeks. Major rivers flowed rapidly, and Folsom Lake saw a significant spike in inflows after the second storm.

The third and final storm pushed the Feather River watershed, American River, Lake Oroville, Folsom Lake, Sacramento River, and Yolo Bypass beyond their limits. The Mokelumne River broke through a levee and flooded the towns of Thornton and Walnut Grove, leaving roads inundated and closed due to flooding and mudslides. This last storm caused the collapse of the incomplete Auburn Dam, which gave way to the sheer volume of water.

These storms claimed 13 lives, injured 96 people, and forced more than 50,000 to evacuate. Many fled their homes in fear. Even smaller waterways, like Arcade Creek, threatened residents. The flooding of Sacramento County forced hundreds to seek shelter at the Grant High School gymnasium.

The rapid rainfall and water flow eroded and weakened levees and riverbanks. These effects continue to exacerbate flood risks in Northern California decades after this historic disaster.

In response to the flood risks, the United States Army Corps of Engineers (USACE) contracted Forgen in 2023. They performed essential heavy civil construction, erosion control, and flood protection work on the Lower American River Site 2-1 Levee Erosion Control project. The project aimed to reduce flood risks for residents, structures, and properties in Northern California.

Forgen undertook heavy civil construction tasks to build 5,500 linear feet of bank protection along the Lower American River. This river had endured heavy inflows during the 1986 storms, which left it vulnerable to erosion. Although the American River levee held during the storms, saving thousands from potential flooding, it suffered significant erosion.

To address this, Forgen cleared and grubbed the site. They carried out demolition, mass grading, and excavation with earthmoving and slope stabilization. They also managed stormwater and upgraded the levee infrastructure as part of this heavy civil construction project.

Forgen exceeded 250,000 cubic yards of excavation and soil/rock placement. They placed over 200,000 total tons of rock throughout the project. During in-water excavation and rock placement, they installed sediment control measures to mitigate turbidity and impacts on the American River.

The bank protection work involved creating and installing a launchable rock bench and a soil-filled rock slope protection. This bench anchored trees to provide safe habitats for juvenile salmon and steelhead trout, thus protecting the river’s ecosystem.

The final slope cover included biotechnical bank protection. This involved large woody material installations, erosion control blankets, sandbags, wattles, and final seeding.

This project, one of eight erosion control contracts under the American Common Features program, successfully reduced the flood risk for 500,000 residents. It also protected 129,000 structures and $62 billion worth of property. The project safeguarded native vegetation and wildlife.

Throughout the project, Forgen provided lasting erosion control solutions for the Lower American River Levee. They assisted the USACE in its mission to safeguard Northern Californian communities from future natural disasters and potentially life-threatening flood events.

Forgen’s expertise in heavy civil construction, erosion control, and flood protection enabled them to effectively implement flood control and restoration initiatives. This ensured the protection of at-risk communities and preserved the environment for generations to come.