Question 1

Opportunities for Natural and Nature Based Features

Accepted Answer

The development of the Subregional Adaptation Plan presents an opportunity to plan for ecological and other community co-benefits as an integral part of our adaptation approach. The transition from historic to modern Baylands in Alameda and Oakland reflects a complex interplay between natural processes and human activities. As sea level rise accelerates, the future of these Baylands depends on effective management and restoration efforts that balance ecological needs with urban development. Protecting and restoring the Baylands will be crucial for mitigating the impacts of climate change on both natural ecosystems and human communities in the region.

Historic Baylands: Historically, the Baylands were vast expanses of tidal marshes, mudflats, and wetlands that stretched along the edges of the San Francisco Bay, including the area around Alameda and Oakland. These ecosystems were rich in biodiversity, supporting a wide array of plant and animal species. The Baylands acted as natural buffers, absorbing floodwaters and providing crucial habitat for wildlife, including migratory birds.

Tidal Marshes: These were dominant in the Baylands, characterized by their salt-tolerant vegetation and regular inundation by the tides. They played a crucial role in filtering water, trapping sediment, and stabilizing the shoreline.

Mudflats and Wetlands: Found in lower elevations, these areas were submerged during high tides and exposed during low tides. They supported various species of fish, invertebrates, and birds.

Modern Baylands: Over time, much of the historic Baylands around Alameda and Oakland have been altered or lost due to urban development, agriculture, and infrastructure projects. Large areas of tidal marshes were drained or filled in, particularly during the 19th and 20th centuries, to make way for cities, roads, and industrial facilities.

Urban Development: Cities like Alameda and Oakland expanded into former wetland areas, leading to a significant reduction in natural Bayland habitats. This development often led to the loss of the ecosystem services that these areas provided, such as flood control and water filtration.

Restoration Efforts: In recent decades, there has been a growing recognition of the importance of the Baylands. Restoration projects have aimed to re-establish tidal marshes and wetlands to help protect against sea level rise and restore ecological balance.

Question 2

Sea Level Rise and Future Impacts

Accepted Answer

Sea level rise, driven by climate change, presents a significant threat to the modern Baylands, particularly in low-lying areas around Alameda and Oakland. As sea levels continue to rise, these areas face increased risks of flooding, erosion, and habitat loss.

Increased Flooding: Rising sea levels lead to higher tides and storm surges, which can inundate low-lying areas, especially during extreme weather events. In Oakland, this threatens not only natural habitats but also urban infrastructure and communities.

Loss of Tidal Marshes: Many of the remaining tidal marshes in the Baylands are at risk of being submerged permanently as sea levels rise, unless they can migrate inland or be artificially raised.

Adaptation and Resilience: In response to these challenges, there are ongoing efforts to enhance the resilience of the Baylands through restoration and adaptation strategies. These include creating living shorelines, enhancing sediment deposition to raise marsh elevations, and planning for the migration of habitats inland.

Tidal Marsh Restoration
Description: Restoring and enhancing tidal marshes involves re-establishing native
vegetation and hydrology in degraded or former marsh areas. This can help to stabilize
the shoreline, reduce erosion, and provide a buffer against storm surges and high tides.
Benefits: Tidal marshes can absorb floodwaters, reduce wave energy, and trap sediments, which can help to elevate the marsh surface in response to rising sea levels. They also provide critical habitat for wildlife.

Living Shorelines

Description: Living shorelines use natural elements like plants, sand, and rock to stabilize the coastline. Techniques might include planting native vegetation, installing biodegradable materials, and creating oyster reefs or other structures that mimic natural features.
Benefits: Unlike traditional hard structures like seawalls, living shorelines can adapt over time to changing conditions. They help reduce erosion, improve water quality, and provide habitat for marine life.

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We will continue to:
Engage local experts within the OAAC, Scientific Partners, and consultant team
Use the green-to-gray spectrum, integrating nature-based features and hybrid solutions wherever feasible
Learn from existing pilot projects, and identify where new pilot projects may be needed in the Subregion

Question 3

Sea Level Rise Adaptation Targets

Accepted Answer

Adapting to sea level rise requires that we determine where our shoreline needs to be elevated, how much, and when that change needs to happen. In order to determine this new elevation for the near-term time horizon (2080), we start with the current high tide level. Some of the lowest areas of our shoreline already experience coastal flooding. Then we consider the current 100-year (1% annual chance) Bay water level, which is observed during severe coastal storms. Adding projected sea level rise and freeboard (a buffer that accounts for uncertainty in our sea level rise water level estimates) brings us to our target design elevation of 14.0’ NAVD88 (a standard reference datum for measuring elevation).

For the lowest points of our shoreline (those close to the high tide line), this means elevating the edge approximately 7.0 feet in the near term. Higher areas will require less elevation with the goal of achieving a consistent level of protection around the shoreline.

Question 4

Inland Flooding and Groundwater Rise

Accepted Answer

As our climate warms, the intensity of rainfall events is increasing and sea levels continue to rise. During rainfall events, precipitation infiltrates into the ground, reducing the capacity of the ground to absorb water from future storm events and temporarily raising the local groundwater table. As a result, localized flooding can occur, and it is more common with storms that happen back-to-back. Meanwhile, rising bay water gradually pushes the groundwater table closer to the surface. During a storm, this further limits the capacity of the ground to absorb rainwater. The groundwater table can also rise above the ground surface and create permanent ponding on the land in places that have historically remained dry, even long after storms have passed. Portions of this project area could experience this ponding (or “emergent groundwater”) with as little as 1 foot of sea level rise. Inland flooding is caused by rainfall and the rising groundwater table.

When we build adaptation measures along the shoreline to protect against coastal flooding, we also need to address the risks of inland flooding. This can be done by increasing stormwater pipe and pumping capacity while also building green infrastructure to detain rainfall and emergent groundwater. These detention and conveyance systems slow flooding, provide space for temporary
water storage, and remove pressure on drainage infrastructure until the storm has passed.

Alameda Northern Watershed and Storm Drain System
It is estimated that Alameda’s Northern Watershed requires an additional 37 acre-feet of
stormwater detention to mitigate the current 100-year, 24-hour storm event. The water
volume from this type of storm is estimated to increase by the following percentages in the
coming decades.

Proposed Detention Basins
In both the Alameda and Oakland project areas, space for new stormwater detention area
locations are being identified. Existing parks, such as Sweeney Park, could also be adapted
to detain stormwater and still maintain current uses for play when detention is not needed.
Green infrastructure basins provide additional benefits for habitat, parks, and streets when
there isn’t an active storm. Where space is limited, green infrastructure may be combined
with less visible gray systems.

Question 5

Conceptual adaptation strategies

Accepted Answer

OAKLAND SHORELINE CONCEPTUAL ADAPTATION STRATEGIES

Different adaptation measures — such as levees and seawalls — can be used in combination along the shoreline, based on the level of protection required, the amount of space available, adjacent land and water uses, and providing co-benefits of an improved public realm and/or shoreline and intertidal habitat.

These examples show two strategies that could be implemented along the shoreline from Harrison Street to the Lake Merritt Channel that take into account existing shoreline conditions and uses. These and other strategies will be refined with further study and developed into a preferred alternative.

Levee constructed to elevation 14.0 at current shoreline. Public realm elevated inland where wider setbacks allow. The Estuary Park design elevates the shoreline to 12.5 for near-term protection and adaptation to higher elevation in the longer term. Flood walls at rail bridge would provide shoreline protection while minimizing impacts to water quality and function of the current tidal channel. Flood walls would be engineered to a high elevation relative to adjacent grades, and may be difficult to implement within the limited footprint of the rail corridor and right-of-way constraints. Additional levees would be required along the channel to 7th Street to provide sufficient protection.

Levee constructed to elevation 14.0 landward. Shoreline sloped more gradually for rocky intertidal, marsh or gravel beach, and upland habitat. The Estuary Park design elevates the shoreline to 12.5 for near-term protection and adaptation to higher elevation in the longer term. A tide gate at the Embarcadero West Bridge would provide coastal flood protection for the rail bridge and the Channel outside of the limitations of the rail bridge footprint (closed only during very high tide events, increasing over time). The potential impacts of a tide gate at this location on water quality and habitat require further study. Additional levees north of the tide gate would not be required. The grade of the shoreline adjacent to the tide gate (for example at Estuary Park) would be raised to provide the same protection height as the tide gate.

ALAMEDA NORTHERN SHORELINE CONCEPTUAL ADAPTATION STRATEGIES

Different adaptation measures — such as levees and seawalls — can be used in combination along the shoreline, based on the level of protection required, the amount of space available, adjacent land and water uses, and providing co-benefits of an improved public realm and/or shoreline and intertidal habitat.

This is an example of a strategy that could be implemented along this stretch of Alameda’s northern shoreline that takes into account existing shoreline conditions and uses. This and other strategies will be refined and developed into a preferred alternative.

Oakland Alameda Adaptation Committee

Concepts and Glossary

Opportunities for Natural and Nature Based Features

Sea Level Rise and Future Impacts

Sea Level Rise Adaptation Targets

Inland Flooding and Groundwater Rise

Conceptual adaptation strategies

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