Building a bridge atop a 130-year-old dam that withstood two major earthquakes and helps store drinking water for millions of Bay Area residents has been no easy feat.

Now stretching into year eight of the Lower Crystal Springs Reservoir Dam Bridge Project, San Mateo County officials announced they anticipate a scenic stretch of Skyline Boulevard will reopen around the end of 2018.

But while the bridge project has taken longer than initially expected, once complete, visitors will also be welcomed to a new mile-long extension of a trail snaking along the pristine watershed.

The Board of Supervisors Tuesday agreed to apply for a grant to help construct a segment of trail that will connect a contiguous route for pedestrians and bicyclists meandering along the reservoir north of State Route 92. 

“This is a great opportunity to give the public a mile of beautiful Crystal Springs trail, and allow people to go from almost San Bruno to [State Route] 92,” said county Parks Director Jonathan Gervais. “It’s going to be a really neat experience to cross the dam and have these great views.”

The new trail winds south from the dam and is a rare chance to open another portion of the protected watershed to visitors.

There have been several delays to when authorities will be able to welcome motorists and pedestrians back to the unique portion of road that hovers above the dam’s spillway. The reconstruction has led to a yearslong closure of this section of Highway 35, also known as Skyline Boulevard.

The project offers recreational as well as safety benefits, and has involved collaboration between the county, Pacific Gas and Electric and the San Francisco Public Utilities Commission.

The SFPUC owns and operates the dam as well as the watershed connected by miles of tunnels to the Hetch Hetchy Reservoir. The utility completed its work in 2012 to meet state and federal standards requiring it more than double the spillway’s capacity. PG&E’s work involves relocating a high-voltage transmission line that powers communities in San Mateo and San Francisco counties. Slated to begin construction Feb. 5, it will remove overhead lines and relocate it under the bridge by the end of June, according to PG&E.  

The county’s responsibility has been to reinstate the road atop the spillway, realign the approaches and create the new route about 7 feet higher than before. Once complete, the bridge will also include a new 15-foot-wide pedestrian trail safely protected from two lanes of vehicular traffic, said Gil Tourel, a county engineer overseeing the project.

The new 626-foot-long, 51.5-foot-wide bridge is where the reservoir meets the San Mateo Creek.  

“The public will be able to enjoy the view in a safer setting,” Tourel said.

But visitors could have to wait before taking a scenic stroll atop a 130-year-old dam.

Its opening has been stunted for a variety of reasons and just last year officials had anticipated reopening by the end of 2017. At one point, federal funding for such projects was frozen. Construction on the bridge was temporarily delayed while the SFPUC finished up work on a major transmission line nearby. Most recently, during the bridge’s construction contractors discovered the actual dam extended further under the road than was originally believed, prompting design changes, Tourel explained.

“It’s an extensive planning and coordinated effort between the county and the SFPUC and PG&E and the contractor. Each party has to work and coordinate with the others to ensure the project keeps moving forward,” Tourel said.

A PG&E spokesperson echoed the need for close collaboration and the utility’s commitment to working in tandem with the county. The SFPUC has also noted the importance of the project and meeting current dam safety regulations.

“Given the dam’s importance to our system and location, this was a top priority project for the water system improvement program,” Dan Wade, SFPUC director of water capital projects and programs, said in an email.

Upgrading history

Built in 1888, the concrete Crystal Springs Dam is marveled for its unique three-dimensional molded brick design and has needed few improvements in its history. In fact, located just 400 feet from the San Andreas Fault line, it’s withstood both the 1906 and 1989 earthquakes with no loss of structural integrity, according to the SFPUC.

But state and federal mandates prompted a project to increase capacity of the dam’s spillway. Now, it must be able to withstand a release of up to 25,000 cubic feet of water per second, instead of its prior approximate 10,000 cubic feet per second capacity. That resulted in the SFPUC investing $35 million to widen the spillway from 89 feet to 208 feet, according to the utility.

The structure’s unique brick design was replicated by the federal government for construction of the Hoover Dam and tests have shown the pioneering concrete mixture used at Crystal Springs is getting stronger, the SFPUC said previously.

The man-made structure is wedged into a canyon to enable the SFPUC to store rainfall and water from the pristine Hetch Hetchy. Years ago the SFPUC was required to reduce the water level due to the updated capacity requirements, and has kept Crystal Springs lower due to a unique plant sprouting up along the rim of the reservoir. The SFPUC is now in the process of replanting the endangered fountain thistle plant before slowly raising the reservoir over the next decade.

The dam’s storied history and age may also be a factor in the public’s ability to enjoy a scenic view after the project’s completion. It’s not common to have a road atop a spillway, but officials have long planned to reopen it to motorists and pedestrians.

Construction of the new bridge, not including design costs, has a more than $13 million price tag and even the new pedestrian trail doesn’t come cheap. The county is applying for a $750,000 grant that will cover about of half the cost for its Close the Gap Trail Project — an 800-foot path connecting the bridge to the new South of Dam Trail section.

Gervais, the parks director overseeing the trail project, said he hopes the opening of the new trail will align with visitors being welcomed back along the bridge. The new mile-long stretch of paved trail will enable visitors to get a bit closer to the SFPUC’s protected reservoir, although people will still be kept behind a fence. While most of the expansive watershed is off limits to the public, the new segment of trail and reopening of the bridge will be a recreational asset, Gervais said.

“It’s going to increase use and enjoyment of this already popular facility,” he said. 

(650) 344-5200 ext. 106

Twitter: @samantha_weigel

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(2) comments


i've been riding my bike over the bridge since january when this was written and there's no reason to stop others from doing so (instead of forcing them on a long hour long detour). this is outrageous after all these years


it contains a man made reservoir with a massive concrete dam. so it may be scenic, but it's certainly not a "pristine watershed" by any stretch of the imagination.

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