Creeks & Watersheds
Sea Level Rise
Richardson Bay

Marin Sea Level Rise

Preparing for change along our shores

Rising sea levels and more severe storm flooding as a result of climate disruption are impacting us here in Marin County now. Even when the sun shines, Marin County already experiences more frequent flooding, both on the Pacific coast in west Marin and along our bay shorelines, impacting roadways, drainage and utilities, and disrupting people’s lives. These impacts are expected to increase in frequency and severity as sea level rise accelerates. 

Marin County is facing the challenge by planning for climate change in collaboration with Marin’s cities and towns. By assessing what is vulnerable to rising tides, by creating opportunities for the community to learn with us, and by involving everyone in planning for these changes, we will be better prepared to meet these challenges as a community. While we know these changes are happening, we do not know how soon we will see more dramatic impacts. By beginning to prepare now, we can find ways to live with water, as well as create suitable defenses.

There are two main sea level rise assessment projects that are underway in the County – one along the coast (C-SMART) and one along the bayside (BayWAVE). But there are other community engagement and educational outreach programs that you can learn about here.  You can join the effort by subscribing here, staying informed, and contributing your ideas and thoughts. 

What can we do about sea level rise in Southern Marin?

A 36-inch increase in sea levels will greatly impact people’s lives throughout Southern Marin. Daily high tides will inundate major thoroughfares, schools, retirement communities, private homes, shopping areas, bike paths, and stormwater detention ponds. Valuable marsh and mudflat habitat will be permanently flooded. Infrastructure will need to be armored, abandoned, or relocated. Shorelines will be eroded by increased wave erosion, threatening even more infrastructure.

Adaptations to sea level rise are still in the early phases of evaluation. The Richardson Bay Shoreline Study: Evaluation of Sea Level Rise Impacts and Adaptation Alternatives investigates strategies that may help address the many risks associated with sea level rise. The extent of the problem requires collective action at the local, state, and federal levels of government. 

Hard Engineering Adaptation Tools

Hard engineering alternatives refer to barriers that work to prevent high tides from flooding inland. These include: 

  • Floodwalls and levees 
  • Large tidal gates 
  • Rip-rap (to armor shorelines against increased wave erosion) 
  • Pump stations 

These alternatives can be effective against sea level rise; however, they are expensive, barriers must be continuous, and can have a negative impact on aesthetics and habitat.

Soft Engineering Adaptation Tools

Soft engineering tools attempt to work more with natural processes to achieve engineering goals while also providing other benefits such as habitat. Wetland enhancement involves placing fill in marshes to keep pace with sea level rise and attenuate wave erosion. Horizontal levees are broad levees with gradual slopes that allow for extensive habitat on either side. Beach construction restores coarse-grained beaches along the shoreline to inhibit wave erosion.

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These alternatives attempt to work with natural processes and use natural systems to achieve engineering goals while also providing other benefits such as habitat for species. Wetlands systems have been proven to provide important flood control benefits by serving as natural buffers that attenuate wave heights and energies. Wetlands serve as a prime example of natural capital that should be available for use in any planning study.

Examples of “soft” adaptation tools include:

  • Wetlands enhancement/conversion
  • Wetlands creation/enhancement
  • Levees with wetlands transition zones
  • Shoreline erosion protection

Infrastructure and Lifestyle Adaptation

These alternatives involve modifying existing and proposed infrastructure to adapt to a rising tide level. They are considered with the recognition that it may not be possible (or affordable) to stop the tides under all conditions. Therefore, one important range of adaptation tools includes modifying the infrastructure itself. 

Specific examples of infrastructure and lifestyle adaptation include:

  • Structures elevated above future tides
  • Ground elevations and associated infrastructure raised above sea level rise conditions
  • Floodable and floatable developments (floating house boats, Dutch “polders”)
  • Planned retreat (allowing lands to become fully or partially inundated)
  • Infrastructure removed, relocated, or rebuilt at a higher location
  • Local zoning and permitting changes

Many of these approaches are not mutually exclusive and can work together. Developing a plan will involve finding the best combination of tools and approaches that work together to meet objectives.