On February 20, 2020, FERC staff issued a letter to the licensee for the FERC-licensed Anderson Dam Project (“Project”), directing the licensee to immediately initiate a full drawdown of the Project’s reservoir by October 1, 2020. The Project is located south of San Francisco and serves as an important water supply resource, but has long been identified as vulnerable to flooding and seismic events that could result in the catastrophic spilling of floodwaters into Silicon Valley. As such, the licensee has been operating the Project at a restricted reservoir level (as low as 58% of capacity in 2020) to mitigate flooding and seismic risks.
In 2012, the licensee initiated a seismic retrofit project to permanently address safety and reliability concerns, which is scheduled to break ground in 2022; however, a November 2019 study by the licensee revealed that the Project is more vulnerable to earthquakes than previously understood. As a result of that study, the licensee recommended to FERC that it should continue to operate the Project at the restricted elevation level to preserve emergency water supply, avoid landslide risks, and prevent reservoir deformation. Further, the licensee proposed to construct a tunnel as a mitigation measure to allow for rapid drawdown of the reservoir if needed after an earthquake or heavy precipitation event.
Despite the licensee’s proposed mitigation measures, FERC staff concluded that there is presently no “safe” elevation level for Project operations and rejected the licensee’s plan to continue operating the Project at its current restricted elevation level. Specifically, staff stated that “[i]t is unacceptable [for the Project] to maintain the reservoir at an elevation higher than necessary when it can be reduced, thereby decreasing the risk to public safety and the large population downstream of Anderson Dam.” As such, FERC staff directed that the reservoir be drawn down to its deadpool level by October 1, 2020 to prepare for the winter rainy season. Thereafter, the licensee is instructed to engage in “all appropriate measures to maintain and quickly lower the reservoir to deadpool in the event of significant inflow once the elevation is reached.” FERC staff did approve the construction of the interim tunnel measure and agreed that it would serve as an appropriate risk reduction measure when complete. Additionally, FERC staff confirmed that the permanent retrofit project should continue to proceed.
The FERC letter directing the licensee’s drawdown is available here.