Phoenix Lake is an 88-acre water storage reservoir owned and operated by the Tuolumne Utilities District (TUD). Water stored in the reservoir is the primary drinking water source for the communities of Sonora, Jamestown, Scenic View, and Mono Village. It also serves as a fill source for CAL FIRE helicopter operations, supports aquatic habitat, and is used for public recreation. Since the reservoir was constructed, the lake’s storage capacity has decreased substantially due to sedimentation. In 2010, TUD received a grant from the Sierra Nevada Conservancy to prepare the Phoenix Lake Preservation and Restoration Plan (PLPRP) to address lake capacity, watershed sedimentation, water quality, and wetland habitat conditions.

Horizon developed the PLPRP by conducting technical studies and evaluating lake stressors carefully. In the lake plan, Horizon identified key strategiesto restore and preserve the lake’s functions and values. The Horizon team used the data gathered during these investigations to determine the rate of lake sedimentation and to develop a plan to restore lake capacity, enhance wetland habitats, and improve water quality.

When TUD obtained a second grant to implement portions of the PLPRP, the Horizon team prepared documents and plans necessary to support removal of approximately 400,000 cubic yards of sediment and evaluate the suitability of materials for placement at various locations around the lake, reuse in the lake, and for commercial uses. Horizon and its subconsultants also conducted reconnaissance-level wildlife surveys in Phoenix Lake and adjacent areas focusing on potentially suitable habitat for special-status amphibians, and performed topographic and bathymetric surveys to support design and permitting of the project. Horizon prepared an IS/MND for the project, which was adopted in fall 2017. Horizon helped TUD successfully obtain regulatory permits for the project from the RWQCB and CDFW by early 2020.

Implementation of the PLPRP began in July 2020. Horizon provided biological monitoring and regulatory agency coordination during the construction process, working closely with TUD, construction manager Anchor QEA, and contractor Steve Manning Construction, Inc. Over 160,000 cubic yards were removed to restore lake capacity, improve water quality, and protect wetland resources. Sediment removal in the main body of the reservoir was completed in September 2020. Horizon continues to provide biological and regulatory compliance support services for the PLPRP.