Before breaching the last levee preventing sea water from rushing into Pacheco Marsh for the first time in generations, workers scrambled this week to make sure water wouldn't flow the wrong way.
Last weekend's record-setting storms brought more than 7 inches of rain to the marsh southeast of the Benicia-Martinez Bridge, forcing workers to pump out more than a million gallons of rainwater this week to get the desired effect at Friday's ceremonial flooding.
"The storm we had Sunday was off the charts," said Paul Detjens, the project manager and senior civil engineer from the Contra Costa County Flood Control District. "Locally, it created some problems for us out here. A week ago, this channel was bone dry. And now it's filled with rainwater, and in an hour, it's going to be full of tidal water.
"Bring it on. We're ready," he said.
An hour later, as earth movers dug out the last dirt barrier, to scattered applause among guests, event emcee and television personality Doug McConnell announced "Water's in. And it's coming home."
Friday culminated nearly 20 years of work restoring 200 of the project's 300 acres to its natural habitat, before 19th-century industry changed its landscape.
Contra Costa County spent $11 million on the Lower Walnut Creek Restoration Project, the largest public works project in county history. The site is just over the hill from the Al McNabney Marsh, across Interstate Highway 680 from the Martinez Refining Co.
Once the county Board of Supervisors approved the $11.285 million contract with Four M Contracting Inc. in March, shovels were in the dirt just weeks later. Now that tidal water is surging back into the marsh, the John Muir Land Trust can finish transforming the area into a birdwatcher's paradise and recreation destination.
"From here, the foundation of the public access has been set," said Linus Eukel, executive director of John Muir Land Trust. "We're basically icing that with public access. Our hope is we'll have that accomplished by 2023."
The earthmoving isn't done. Three elevated vistas more than 20 feet high will be created, surrounded by new hiking trails, boardwalks, interpretative displays, and bridges over the marsh's northern reach. A massive haul of native plants will be re-introduced, rich habitat for the marsh's endangered salt marsh harvest mouse.
The Mt. Diablo Audobon Society has already recorded more than 80 species of birds at Pacheco Marsh, species like the short-eared owl, white-tailed kite, American kestrel, northern harrier, and the loggerhead shrike.
"This habitat will just be flooded with new bird life, and we expect it's going to be an international destination, but also an important local destination for kids and families to learn about it as well," Eukel said, adding the group has raised $3.5 million of its $5 million goal. "We're in really good shape," he said.
The Walnut Creek watershed is Contra Costa's largest, draining more than 150 square miles from eight cities into a marsh that, over the past century, became a dumping ground for dredging and an industrial buffer to the Bay.
Engineers want to enhance the area's flood-carrying capacity, while naturalists want conditions closer to those existing before humans channelized the marsh and brought industry.
The marsh and Walnut Creek were home to grizzly bears, elk, salmon, and steelhead until the mid-1800s (opinions vary as to whether the restoration bring back the spawning fish).
Then humans arrived, filling in wetlands and building dikes. Merchant ships sailed up Walnut Creek, and other creeks feeding into Walnut Creek were diverted for humans developing Contra Costa. Refineries were built and the area was used as a dumping ground for dredging projects all over the Bay Area.
The county bought 122 acres of the marsh in 2003 from a towing company that once planned a junkyard there. Nearby Marathon Oil refinery bought another 18 adjacent acres formerly used for sand mining, and donated it to the land trust in 2020.
Planners envision the Iron Horse Regional Trail, which now ends near state Highway 4, to extend another 3 miles along Walnut Creek into Waterbird Regional Preserve near Martinez. There will be another 2.4 miles of trails into the marsh, with a staging area, parking lot, bird-watching blinds and interpretive panels in the elevated areas.
The project will not only alleviate stress on neighboring shores as the seas rise in coming years, it was also designed with sea rise in mind. As the marsh transforms, rising water will blend with more sediment, acting as a carbon filter helping to restrain greenhouse gases.
Workers will add 31,000 new native plants to the area. There's also talk of other amenities, like a kayak launch, which is still up in the air. Though the entire project is called Lower Walnut Creek Restoration, the northern reach -- the section north of Waterfront Road -- will be managed by the land trust and called Pacheco Marsh. The southern reach will include levee improvements.
Detjens called Friday "a real high point of my career."
"I've been with it from the beginning," Detjens said. "I'm really happy to see the turnout. Typically, a levee breach like this, maybe 20 people show up, some people in orange vests and some people who gave some money. But we have like 250 people. I'm blown over by it.
"Whether you call it lower Walnut Creek or Pacheco Marsh -- they're really the same thing -- and it's a really a cool place."