Highway 37 Corridor: Climate Adaptation

 

 

SB1 Adaptation Planning Grant: Initial Case Study

Challenge: Developing plans and strategies

 

Summary

Highway 37, an essential people- and goods-movement corridor in Marin County, is currently subjected to storm runoff and tidal flooding and will be further impacted by projected sea level rise. Building on recent Metropolitan Transportation Commission preliminary corridor analysis and other recent studies, this project will develop an action plan to address ongoing and projected flooding issues from increased storm flows and sea level rise in the east-west transportation corridor through the Novato Baylands, reducing the potential disruption to and/or closure of transportation facilities and mitigating impacts in the area from such flooding using (adaptation) best practices for stormwater and tidal flooding management. 

The study and its recommendations will be a collaborative effort, including the County, Transportation Authority of Marin (TAM), Caltrans, water and sanitary districts, regional and state agencies involved in flooding, sea level rise, and water quality issues, land management agencies, community organizations, and the public at large. The strategies developed through the study will also serve as a framework for policy language to incorporate into related planning and guidance documents, such as local General Plans, Community Plans, Specific Plans, and transportation planning documents overseen by Caltrans, MTC, TAM, and other relevant agencies.  Overall, the study aims to provide a specific group of vetted and prioritized projects that are ready to seek funding for design and construction.

The proposed study aligns with several stated goals and State policies by looking at the transportation and flooding concerns in the Highway 37 corridor comprehensively, and seeking to develop solutions that address the impacts of storm-related and tidal flooding which are realistic, cost-effective, environmentally sound, and durable.  Additionally, Caltrans’ Highway 37 Transportation Concept Report and the state’s Regional Transportation Plan both call out the need to address the transportation and flooding issues in this corridor.

Lead Agency and Partnerships

Marin County Department of Public Works, which also includes Flood Control District staff, is the lead agency, in partnership with TAM that will collectively be responsible for completion of the grant. Additional partners in executing the work include affected agencies such as Caltrans, the City of Novato, and Sonoma Marin Area Rail Transit.  Additional coordination will take place with other related groups and agencies, such as state and federal water and resource agencies, community groups, and other interested parties.

Drivers

There have been concerns for many years, especially after a month-long closure in winter 2017, about the viability of Highway 37, given its low elevation and high stormwater flows and increasing tidal levels. Recent studies of the entire highway, between Novato and Vallejo, by the Metropolitan Transportation Commission have identified the key areas of concern for the viability of the corridor and developed concept solutions that require further analysis. 

Engagement Process

Community engagement will build upon already-established efforts, such as through interagency and community interest groups that have been involved in recent study efforts related to sea level rise and stormwater flooding in the area. As the area surrounding the highway is uninhabited, outreach efforts will be more focused on roadway user groups and those regionally affected by the operation of the highway.

The project will conduct a multi-faceted community outreach approach throughout the process to inform and educate the community on issues in the corridor, solicit concerns and input on areas of interest, provide and discuss a range of alternative solutions seeking input on preferred approaches, preferred solutions, and strategies to move forward with the study’s adopted strategy. 

The highway is a primary route for workers commuting between their homes and places of employment, connecting Marin County with Vallejo and Solano Counties to the east, and Sonoma and Napa Counties to the north. The extremely high housing costs in the Bay Area force many workers to live far from their jobs, such as service and retail workers who commute into Marin, agricultural and tourism-support workers who commute northward, and other low-wage workers who work throughout the North Bay. Highway 37 is a lifeline to those workers who may reside in one of several disadvantaged communities around the North Bay region or beyond and face limited mobility opportunities. The closure of Highway 37 from flooding creates untenable circumstances in their ability to get to their place of employment.

Climate Impact Areas

Given its base elevation, projected sea level rise will further impact the roadway. Due to the lack of suitable alternative routes, closure of the roadway due to flooding diverts traffic to other routes not designed for current and projected volumes of traffic, particularly movement of freight between the North Bay and North Coast. In addition to a low base elevation, the corridor is affected by structures and bridges that impede water flow in the Novato Creek drainage out to San Pablo Bay, causing backups and pooling that floods the roadway. The increased intensity of storm flows down the constrained creek, combined with tidal action, sedimentation, and increasing sea levels are resulting in more frequent flooding situations that inundate the highway and render it impassible. Potential alternative treatments to raise the roadway or to improve upon the current system of levees, or a combination thereof, will be further analyzed.   

Funding Sources

The project is funded through SB1/Adaptation Planning grant funds ($130,170),Transportation Authority of Marin ($8,915), and Marin County Flood Control District #1 ($8,915).

Research and Data

The study will collect existing data and studies (additional information at www.marinwatersheds.org) relevant to the corridor and identify information gaps needing additional analysis and identify and analyze vulnerabilities in the corridor and what the implications are for various approaches and also if no additional actions are taken. The plan will incorporate both previous studies and ongoing flooding and sea level rise efforts in the Novato Creek watershed with targeted analysis and modeling of the Highway 37 transportation corridor to develop preferred, deliverable solutions, with priorities established and a viable funding strategy. 

Challenges

Budget constraints will limit the degree to which modeling can be done, but using other studies and data collected to date will provide baseline information from which more focused modeling efforts can be made.

Outcomes

The County of Marin and Transportation Authority of Marin (TAM) will provide an implementable action plan for improvements to the Highway 37 corridor in Marin County (Highway 101 to the Petaluma River) to address both ongoing and projected flooding and sea level rise which affect the transportation facilities in the corridor and surrounding lands. Desired outcomes and objectives include:

  • Modeling of both current and projected traffic diversion impacts that have resulted and could result from closure of the transportation facilities from storm-related creek flows and tidal surges, and projected sea level rise.

  • Hydraulic and hydrologic modeling of the effects of various proposed solutions on seasonal and tidal flooding and sea level rise.

  • Development and analysis of potential engineering solutions to the transportation corridor and related flood/baylands management facilities, their projected impacts, and estimated costs.

  • Develop viable conceptual designs that address identified concerns and vulnerabilities to the Highway 37 corridor and its essential role in the region’s transportation network through analysis and modeling of proposed approaches under various future scenarios.

  • Identify potential funding sources for preferred solutions in the corridor and develop a funding plan that enables projects to compete for available funding for design and construction.

Replicability

Since the study will be looking at alternative approaches to either raising the roadway or armoring it through levee improvements in an undeveloped, agricultural setting, similar approaches to analysis could be undertaken in comparable locations in which the base elevation of the roadway is subject to tidal or storm-surge flooding where temporary storage or diversion of floodwaters is not readily achievable due to the surrounding topography.

Additional Resources

Please see marinwatersheds.org

Further Information:

Dan Dawson, Marin County Department of Public Works 415-473-6287 / ddawson@marincounty.org 

Laurie Williams, Marin County Department of Public Works 415-473-4301 / lwilliams@marincounty.org