By Mr Hunter Merritt (USACE)July 26, 2011
SACRAMENTO, Calif. - Many of California’s popular historic landmarks, such as the Golden Gate Bridge or Yosemite National Park, are famous as unique icons. This year, the National Park Service is preparing to add another California gem to its national list of historic places, not for its uniqueness but rather for its classic features, which NPS architects call “a perfect example” of bridge-building in the 19th century: the Knights Ferry Covered Bridge.
One of only two covered bridges in the nation currently nominated for inclusion as historic landmarks in the Library of Congress, the Knights Ferry Covered Bridge is located on land managed by the U.S. Army Corps of Engineers Sacramento District’s Stanislaus River Parks near Oakdale.
Architects from the Historic American Engineering Record, a NPS program, surveyed the bridge in June, and applauded the Corps for its care of the bridge and the surrounding area, a key factor in its preservation.
The 330-foot bridge, recognized as the longest covered bridge west of the Mississippi River, was built in 1864 to replace a bridge washed away during a historic flood two years prior. The New Melones Dam, built by the Corps in 1979, now reduces flood risk to the bridge, as well as to Knights Ferry and other towns downstream.
“There are a lot of factors that contribute to preservation, but ultimately, the Corps has done a great job as stewards of this historic structure,” said Christopher Marston, lead architect on the project.
Marston was part of the survey group who visited in June, along with architect Jeremy Mauro and student architect Pavel Gorokhov, to document the interior and exterior of the bridge using a combination of images from a state-of-the-art high-definition laser scanner, 360-degree digital photographs and hand-drawn sketches.
The architects were intrigued with the bridge for its Howe truss design, calling it a perfect example of 1850s engineering and bridge-building technology. Marston said the design used in this bridge was very common in the 19th century, noting that the combination of wood beams and steel fasteners established a model for future designs using all-steel construction.
“American engineers brought truss bridge design to a new level,” said Marston, “and this bridge design paved the way for steel bridges of the future.
“Most wooden bridges of this era have been rebuilt or altered so much that they are not considered original,” said Marston, “and often architects will come in who are used to working with steel and concrete, but not wood, which acts differently. This bridge hasn’t been all mucked up.”
The bridge, which was closed to regular vehicle traffic in 1981 by the Corps, has survived the weather and wear of similar bridges in the northeastern U.S., making it a great specimen for inclusion as a historic landmark, according to Marston.
“It is in great shape, and it could certainly handle a heavy load, but it helps to preserve the bridge to keep traffic to a minimum,” said Marston.
The Knights Ferry Covered Bridge has been cataloged once before, in 1934, by the Historic American Buildings Survey. HABS, the federal government’s first preservation program and a New Deal-era effort to support unemployed photographers and architects, sent Roger Sturtevant to take photographs and record the bridge.
HABS is the only depression-era program still in operation today, and it has catalogued about 100 covered bridges for the Library of Congress. It is a companion program to the HAER program, administered by the Heritage Documentation Programs of the National Park Service. The collections from HABS and HAER are among the largest and most heavily used in the Prints and Photographs Division of the Library of Congress.
According to Marston, the data gathered from Knights Ferry Covered Bridge will be processed over the next few months and the designation in the Library of Congress’ historic registry is expected in November.