Granite Construction has ramped up a project to replace an aging dam spillway in its own backyard.
The Watsonville, California-based infrastructure contractor won an approximately $50 million contract to replace the spillway at Pacific Gas and Electric’s Tiger Creek Regulator Dam in Amador County, California, according to a July 22 news release. The project site, near Pioneer, California, lies in the heart of the state’s Gold Country.
The structure, which is part of PG&E’s Mokelumne River Hydroelectric Project, is a slab and buttress dam originally constructed in 1931. The project’s goals include enhancing long-term dam safety, operational reliability and compliance with updated regulator and engineering standards.
Granite’s scope comprises building a new spillway crest structure and chute, installing a temporary cofferdam for work to be performed in dry conditions, excavation and rock anchoring, according to the announcement. The firm will also place mass and structure concrete, as well as decommission the existing spillway. A new permanent access road will support ongoing maintenance of the new spillway.
The job is a continuation of sorts, with Granite completing a $600,000 preconstruction contract for the facility in 2024 to support early planning and constructibility.
“We have a long history of building critical dam projects for many clients in Northern California including the Folsom Dam Auxiliary Spillway Control Structure, Mormon Island Auxiliary Dam, Lost Creek Dam, and Log Pond Dam,” said Bob Mihal, Granite area manager, in the release. “Our team brings deep technical expertise and a collaborative approach, and we look forward to serving PG&E and strengthening our partnership on critical infrastructure that supports the region’s communities.”
California’s Sierra Nevada foothills are dotted with dams that provide both electricity and water storage throughout the state, and maintenance of these structures has received scrutiny over the past decade.
In February of 2017, the main spillway of Oroville Dam — the nation’s tallest at 770 feet — developed a gaping hole and water nearly overtopped the structure’s emergency earthen spillway. Repair costs exceeded $1 billion.
Nationally, there are 88,616 deficient non-federal dams which would cost $158 billion to rehabilitate, according to a 2023 report from the Association of State Dam Safety Officials.
Granite’s work on the Tiger Creek Regulator Dam began in May, with completion slated for May 2028.
