Removal of dam supported because of safety concern
Park service, coastal panel act due to high risk of failure
The National Park Service is advancing its plan to remove a Tennessee Valley dam that has been classified as having a high risk of failure and threatens public safety at a nearby beach.
The California Coastal Commission voted unanimously Thursday to endorse the park service's proposed project, which also includes restoring acres of wetland habitat that has been effected by the dam over the decades.
“We have the removal of a dam for public safety but also to restore some of this natural process in the Tennessee Valley,” Kate Huckelbridge, the commission's executive director, said before the vote.
Built in the early 1960s by the former landowner to attract waterfowl for hunting, the earthen dam was one of the many artificial structures inherited by the National Park Service after the Golden Gate National Recreation Area was founded in 1972. The dam and its holding pond are accessible on the Tennessee Valley Trail and are about 900 feet from Tennessee Beach.
In 2017, the U.S. Bureau of Reclamation classified the dam as having a high risk of failure because of erosion, lack of compliance with seismic engineering standards and poor overall condition. The park service closes the Tennessee Valley trail during storms as a public safety measure.
Carolyn Shoulders, a project manager with the park service, said the agency has envisioned removing the dam since 2014 as part of work to restore habitat in the Tennessee Valley.
“I think that this is one more project where the Golden Gate
National Recreation Area is transitioning a lot of the inherited landscapes to a natural landscape with native vegetation,” Shoulders said. “The recreation area inherited a lot of agricultural lands and we've been transitioning a lot of it to more natural habitat. This is one more example of that.”
By removing the dams, the
agency will work to restore the area to natural wetland habitats and prevent erosion issues caused by the dam.
The estimated $10 million project would drain the pond and remove the dam. In addition to the new wetlands that would be created, three new ponds fed by groundwater and springs will
be built to make up for the lost habitat for endangered red-legged frogs living in the pond. Shoulders said the existing pond has been reduced to about half of its original size due to sedimentation.
Several hundred feet of trail damaged by erosion from storms will also be repaired.
Shoulders said the project is likely to take several years before it is completed. The estimated 18-month construction window would also prompt trail closures and block access to Tennessee Beach.
Marin Conservation League member Terri Thomas, a former employee for the park service and Golden Gate National Recreation Area, performed previous restoration work in the Tennessee Valley. She said the new ponds
will provide improved habitat for red-legged frogs and will be spaced out to allow for potential colonization to other areas, which occurred with similar restoration work near Muir Beach.
“Red-legged frogs generally like freshwater coming in or a little bit of movement in the water,” she said. “The new ponds will be groundwater-fed so it keeps the water fresh and springs nearby keep some water moving.”
Some attendees at the coastal commission hearing
on Thursday raised concerns about the project, including potential effects on red-legged frogs during construction and from the use of herbicides to remove invasive plants.
“We don't know about the long-term cumulative impacts,” Watershed Alliance of Marin chair Laura Chariton told the commission.
More information about the project can be found at parkplanning.nps.gov/GOGATVDamRemoval.