Bolinas Lagoon plan tackles flooding and sea-level rise
Wetlands project will involve redirecting creek, road work
Marin County plans to reroute a Bolinas Lagoon creek as part of an effort to prevent flooding along Highway 1, prepare for sealevel rise and restore habitat for threatened species.
The county’s Bolinas Lagoon Wye Wetlands Project aims to redirect Lewis Gulch Creek closer to its historic route and raise a nearby road to allow the creek more room to wind and flow during winter storms. The project would also restore floodplains at the northern end of the 1,100-acre Bolinas Lagoon that were lost over more than a century as wetlands made way for roads and pastures.
County planners say the expansion of wetlands will be needed as sea-level rise this century is projected to inundate coastal areas and threatens to cut off Bolinas residents from the rest of the coast and supplies.
“Now that we are experiencing climate change we have higher intensity storms that are shorter duration,” said Veronica Pearson, a county hydroecologist and restoration planner. “So that means we have a lot of water coming through that channel in a short period of time and that exacerbates the flooding because that channel can’t handle it.”
The California Ocean Protection Council recently allocated nearly $340,000 in Proposition 68 grants to Marin to complete the design of the project. As part
of rerouting the creek, the county plans to relocate and raise a section of Olema-Bolinas Road near where it intersects with Highway 1. A 200-yard crossover road connecting Highway 1 and Olema-Bolinas Road is also slated for removal to make way for the creek.
Development and ditching along Lewis Gulch Creek since the 19th century has diverted the stream from
its route that once ran from Wilkins Ranch to the north and flowed into the lagoon’s northern tip. As the land was developed for pastures and the construction of Highway 1, the creek was diverted to the western side of Olema-Bolinas Road. As a result, the creek regularly floods during storms.
“One of the reasons why is because it goes on to a
ditch along Olema-Bolinas Road and through a culvert,” Pearson said. “And that ditch and culvert system isn’t sized to be able to handle an annual event flow.”
The county plans to redirect the creek under OlemaBolinas Road and allow it to make its way through its historic floodplains before reaching the northern tip of the lagoon.
In its recommendation of the $339,000 grant, California Ocean Protection Council staff stated, “Restoration at this site is critical, as it is the only place in the lagoon that can accommodate wetland migration and where contiguous public lands will be protected in perpetuity.”
In addition to the state grant, the $1.3 million planning and design phase of the project will be covered by the county’s Measure A sales tax revenue, Proposition 1 state water bonds and a Golden Gate Parks Conservancy grant. Pearson said the county hopes to complete the design this year.
Construction is expected to cost $6 million, of which $815,000 has been secured so far from a federal grant. Once funded, the work is expected to begin by summer 2023, Pearson said.
A section of Olema-Bolinas Road will be raised and moved east through the construction of a 60foot span bridge. This extra space would allow for greater groundwater storage, reduce flooding in the winter and allow the creek to continue flowing during the drier summer months, Pearson said.
“It’s a positive feedback loop,” she said. “We have actually had steelhead recurring to the stream every year. One of the problems is they don’t have pools to hang out in. By putting the creek back into that section and adding complexity to the stream channel and connecting it to the groundwater, we’re hoping
that the channel will be able to create pools and habitat that is conducive to habitat.”
Restoration workers plan to install large wooden logs and structures along the creek both to stabilize banks as well as to create deep pools that threatened steelhead trout can use.
The West Marin Environmental
Action Coalition has been tracking the project and lauded the state’s funding support.
“It is critical that we work together to preserve and restore our coastal wetlands, as they are one of our best defenses against the climate crisis,” said Ashley Eagle-Gibbs, the coalition’s conservation director.