How we're adapting

---

Sea level rise challenges

Floodwaters do not stop at jurisdictional boundaries

Sea level rise is a shared issue. This means solutions require cooperation across cities, towns, and even counties. And of course, projects to address sea level rise require willing landowners, meaning both public and private properties often have to be on board to deliver holistic solutions.

Solutions in one place can have unintended impacts on other places

Understanding these interrelationships is complex; it requires close coordination, shared science, and lots of work to get at shared agreement on what actions to take, when to take them, and how to fund them.

We need to act now, but in ways that don't prevent effective future actions

We need to address near-term sea level rise impacts, and retain the flexibility to plan for and respond to longer term impacts.

Project permitting can be difficult and expensive

This can be true even for adaptation projects that achieve environmental and public safety benefits. While some regulatory approaches are evolving to recognize the unique context of sea level rise, they continue to slow projects and drive up project costs.

---

Adaptation Responses

Sea level rise impacts are location specific. No two shorelines experience the effects of sea level rise in exactly the same way.

Answers to “how do we adapt to sea level rise” are also location specific. They depend on:

• Physical characteristics of the location
• What sea level rise impacts are occurring at the location
• the impacted community’s vision and goals in addressing sea level rise
• Priority functions of the location, both now and in the future
• Unique opportunities of the location
• Relative cost, benefits, and available funding

Adaptation measures are the individual tools or actions that can be used in response to, or in anticipation of, sea level rise impacts. Many different adaptation measures have been developed that can respond to the different location factors identified above. Some sea level rise adaptation measures are already being used here in Marin.

Different adaptation measures can be used alone or in combination. Several measures working together to achieve an adaptation goal is called an “adaptation strategy”.

Adaptation measures can also be sequenced to happen over time, using an “adaptation pathway”. An adaptation pathway breaks down complex decision making into a sequence of manageable steps or decision-points over time. A sea level rise adaptation pathway can help you identify and implement near-term adaptation measures while planning and staying flexible to use other adaptation measures in the longer-term.

Below is an overview of different types of adaptation measures.

Hard Armoring Adaptation Measures

Technological and engineered features can be constructed to block high tides from flooding inland and/or reduce wave energy along shorelines. They’re largely made from hard materials such as concrete, steel, and rock, and often referred to as “grey adaptation”.

Examples of hard armoring measures include:

• Floodwalls
• Levees
• Seawalls
• Large tidal gates
• Pump stations

Hard armoring measures can protect against sea level rise up to designed limits, but they come with difficult tradeoffs. They can:

• harm habitats
• deflect sea level rise impacts onto nearby shorelines
• block views
• be very expensive

Nature-based Adaptation Measures

Nature-based measures are either naturally occurring or can be engineered and constructed to mimic natural features. They work with natural processes, such as the flow of water and sediment, to reduce flood hazards while also providing other ecological benefits such as:

• native habitat
• carbon sequestration
• water quality improvement

They are often referred to as “green adaptation”, since they often include native plants. Many nature-based measures focus on wetlands and near shore systems such as eelgrass beds and oyster reefs, which can buffer against storm waves and hold tidal flood waters.

Examples of nature-based measures include:

• Wetland creation, enhancement, and restoration
• Coarse-grained beach construction (along bay shorelines) to reduce wave erosion
• Dune construction (along coastal shorelines) to reduce wave erosion and “feed” sediment to beaches
• Sediment augmentation to raise wetland elevations in pace with sea level rise
• Horizonal habitat levees, to provide habitat transition zones as sea levels rise

Nature based measures can protect a wide range of benefits, but their flood hazard reduction abilities are limited. They can:

• Be overwhelmed by sea level rise in the mid to longer term
• Be eroded or otherwise compromised during large flooding events and require major maintenance or rebuild events
• Require lots of physical space to implement effectively

Infrastructure Adaptation Measures

In situations when it may not be possible or affordable to prevent tidal flooding, existing and proposed infrastructure can be modified to accommodate rising tides.

Examples of infrastructure adaptation include:

• Elevating structures above current and future flooding risks
• Floodable and/or floatable structures
• Planned retreat to allow partial or full flooding of sites
• Removing, relocating, or rebuilding at a higher location