US-101, State Route 1 Sea-Level Rise Project

Project Overview

Flooding affects many residential, commercial, and industrial land, and Caltrans is looking for ways to mitigate the issue, especially with sea-level rise expected to affect the region in the next 100 years.

With the US-101, State Route 1 (SR-1) project, Caltrans proposes to enhance access and mobility by addressing recurring flooding and sea-level rise impacts that affect Marin City and the surrounding areas in the Richardson Bay area of Marin County.

Highway flooding occurs in this area due to winter storms as well as high-tide events. Sea-level rise is expected to increase in severity and frequency in future years and will impact the roads even more.

Photograph of flooding at the exit for Donahue Street on southbound US 101 near Marin City. Portions of the offramp are covered in water and a car stopped in the dirt separating the offramp from the highway.Photograph of flooding at the Manzanita/SR-1 intersection. There is a white car sitting in the water.

Project Location

The proposed project is located on US 101 adjacent to Richardson Bay and Marin City.  The project limits begin in Marin City near Donahue Street and extend to the southern end of the Richardson Bay Bridge.  Approximately a third of a mile of SR-1 will also be included.Map of area where the California Department of Transportation (Caltrans) proposes to enhance access and mobility by addressing recurring flooding and sea-level rise impacts that affect State Route 1 (SR-1), US-101 and the Manzanita Park and Ride lot in the Richardson Bay area. The proposed project area starts on US 101 to the south of the Donahue Street exit and continues northward to the Richardson Bay Bridge on US 101 and along State Route 1 before Coyote Creek.

Public Engagement

Caltrans representatives at the US-101, State Route 1 (SR-1) Sea-Level Rise project in Marin City on Thursday, Feb. 29. One representative is standing behind a table with an orange Caltrans tablecloth and talking to the audience about the presentation on-screen behind him. Two additional representatives sit behind another table with an orange Caltrans tablecloths.

Because this project is so important, Caltrans has held early public engagement sessions to get community feedback on the direction and development the project will take. 

In this early stage, Caltrans is defining the scope, cost and schedule while trying to find funds for the project.

The first public meeting was in Marin City on Thursday, Feb. 29. The meeting was well attended with 123 people online and 23 more at the Teen Center in Marin City on a rainy night in Northern California.  A second public meeting was held on Thursday, March 28 at the Tam Valley Community Center.

Community Input

The purpose of the meetings were primarily listening sessions for Caltrans as the project team fielded questions and comments. The project team also shared information about the PID stage.

Some of the goals in this stage are to learn from the community, share information and eventually receive funding, so the project can move on to the environmental stage. Public engagement will continue to be a priority throughout the project.

Project Development Process

What does it mean for a project to be in the initial planning phase?

Currently, this project is in the K Phase, where the project's scope, anticipated cost, and schedule are established.  Funding sources for the project are also sought out. 

Once funds are allocated, Caltrans will move on to the project approval and environmental document phase – the PAED phase.

In that phase, the public will help us determine which alternative they prefer, and environmental analysis will occur.

Caltrans is scheduled to circulate the Draft Environmental Document (DED) externally in the summer of 2027.

Once the project clears that phase, it will advance to the final design phase and eventually the construction phase.

Graphic laying out the Project Development Process. On the left side of the image is a downward-pointing arrow labeled "WE ARE HERE" that points down at a yellow, right-pointing arrow labeled Project Initiation Document (PID). Underneath the yellow arrow is a box that shows what that phase includes that reads "Define Scope, Cost, Schedule, and Find Funds". The PID arrow points at two additional arrows: a white, right-pointing arrow that's labeled "Public Engagement" and a green, right-pointing arrow labeled "Project Approval & Environmental Document (PAED). Beneath the Public Engagement and PAED arrows is a box that shows what this phase includes that reads "Prefer Alternative, Environmental Analysis". The Public Engagement arrow points at another white, right-pointing arrow that is labeled "Right of Way (ROW)". The PAED arrow points at a blue, right-pointing arrow labeled "Plans, Specifications & Estimates (PS&E)". Underneath the ROW and PS&E triangles is a box that shows what that phase includes that reads "Design Project". The PS&E arrow points at an orange arrow, which is also under the ROW arrow, that reads "Construction". Underneath the orange arrow is a box that shows what that phase includes that reads "Construction".

Project Alternatives

The project alternatives were developed based on the three adaptation strategies from the California Coastal Commission Sea Level Rise Policy Guidance, Final Adopted Science Update, November 7, 2018. 

Three adaptation strategies: Protect, Accommodate, and Retreat are proposed.

Graphic showing the Accommodate, Protect, and Retreat options. Graphic includes an icon of a bridge next to a shoreline. Underneath that graphic are arrows pointing to the three options. The leftmost arrow points to a version of the bridge icon in which the bridge now has taller legs. Beneath that graphic is the word

Protect

The protective alternative would elevate the Mill Valley-Sausalito path, part of the Bay Trail, using a levee and retaining wall system to safeguard the roadway. This raised pathway would commence at the Waldo UC/Donahue Interchange and conclude at Coyote Creek.

Graphic showing the Protect option in which Protect option which would elevate the Mill Valley-Sausalito path, part of the Bay Trail, using a levee and retaining wall system to safeguard the roadway.Concept graphic showing the Protect option which would elevate the Mill Valley-Sausalito path, part of the Bay Trail, using a levee and retaining wall system to safeguard the roadway. This raised pathway would commence at the Waldo UC/Donahue Interchange and conclude at Coyote Creek.
Please Click on the Image to View a Larger Version

Accommodate

SR-1, US 101, and the Manzanita Park and Ride lot would be elevated to the design sea-level rise (SLR) elevation. US 101 is proposed to be a causeway, allowing flood waters to pass under the structure. SR-1 and the park and ride are proposed on treated fill supported by retaining walls. 

Graphic showing the Accommodate option in which SR-1, US 101, and the Manzanita Park and Ride lot would be elevated to be a causeway, allowing flood waters to pass under the structure. The graphic includes a causeway with multiple lanes of traffic in each direction and a pedestrian/bicycle lane on the side closest to the water.Concept graphic showing the Accommodate option in which SR-1, US 101, and the Manzanita Park and Ride lot would be elevated to the design sea-level rise (SLR) elevation. US 101 is proposed to be a causeway, allowing flood waters to pass under the structure. SR-1 and the park and ride are proposed on treated fill supported by retaining walls.
Please Click on the Image to View a Larger Version

Retreat

The proposed NB 101 off/on ramps (flyover) would be realigned to the SB 101 off/on ramp location across from the Buckeye Roadhouse restaurant.  US 101 would remain at its current elevation while elevating the frequently inundated portion of SR-1, under US 101.  

Relocation of the Manzanita Park & Ride is also being studied as part of this alternative.

Graphic for the Retreat option in which the proposed NB 101 off/on ramps (flyover) would be realigned to the SB 101 off/on ramp location across from the Buckeye Roadhouse restaurant.  Image shows an elevated roadway with two-way traffic and a pedestrian/bicycle path on the side.Concept graphic for the Retreat option in which the proposed NB 101 off/on ramps (flyover) would be realigned to the SB 101 off/on ramp location across from the Buckeye Roadhouse restaurant.  US 101 would remain at its current elevation while elevating the frequently inundated portion of SR-1, under US 101.
Please Click on the Image to View a Larger Version

Next Steps

Caltrans representatives speaking with attendees at the US-101, State Route 1 (SR-1) Sea-Level Rise project in Marin City on Thursday, Feb. 29. Two representatives stand behind a table with an orange Caltrans tablecloth and talk with two attendees standing on the other side of the table about the proposed project.The PID stage will continue through the month of March. The next scheduled hybrid meeting is March 28 at the Tam Valley Community Center, 203 Marin Ave. in Mill Valley from 6 p.m. to 7:30 p.m.

You can log into the meeting at bit.ly/3wEy4e9. You can also email our project email at ManzanitaProject@dot.ca.gov