Tam Valley Sea Level Rise Task Force

Part of the Tam Valley NRG Network


Prioritized Guidelines for Addressing Sea Level Rise in Tamalpais Valley

Destructive tidal incursions into Tam Valley’s residential neighborhoods, the business district, and major access roads into and out of the valley are already increasing in frequency and magnitude.  The scientific consensus is that flooding will increase due to sea level rise, increasingly intense storms, and rising groundwater through the end of this century and beyond. The State of California is directing its agencies to plan for 3 ½ feet of sea level rise by 2050 and up to 10 feet by 2100.

Expand the PDF below to read the full document.

Comments by December 15

Please submit any comments/suggestions to TamValleyNRG@Gmail.com by December 15

To see the video of the November 17, 2022 forum, please navigate to: https://youtu.be/4-TJSwz9sW0 or the Tam Valley Sea Level Rise Task Force webpage:  https://nrgmillvalley.org/tam-valley-sea-level-rise/.


Rising Water – November 17, 2022 Meeting


Tam Valley Elevations and Flooding Risk Map

This map identifies elevations above “sea level” in the Tam Junction Business District, Birdland, and Kay Park neighborhoods ((note that elevations are based on detailed observations and not official data). Imagine a 7′ tide (there are several expected in December and January) combined with a storm surge of an additional foot or two.  The Coyote Creek levees could be breached.  And that is before sea levels really begin to rise.  Add a foot of sea level rise over the next 10-15 years and one can start to see the nature of our community’s challenge.

Map showing sea level and flooding risk in Tam Valley.
Tam Valley Elevations and Flooding Risk

Waters Rising – March 2022


Flooding in Birdland and Kay Park

You Talk, We Listen – This meeting took place on February 3, 2022

Watch the video of this meeting below:


February 3 Tam Valley SLR Listening Session Report to Community

To: The residents and businesses of Tam Valley

From: The Tam Valley Sea Level Rise Task Force

Re: Report on February 3, 2022 “Listening Session” – Flooding in Tam Junction, Birdland, and Kay Park

Date: February 18, 2022

Nearly 100 participants joined the meeting on Zoom.  We are thankful for our community’s engagement with the complex issues related to flooding and sea level rise.

The “Listeners” included:

  • Stephanie Moulton-Peters, Marin County Supervisor District 3
  • Dennis Rodoni, Marin County Supervisor District 4
  • Mike McGuire, State Senator, District 2
  • Steffen Bartschat, Member, TCSD Board of Directors
  • Chris Choo, Senior Planner, Marin County Department of Public Works
  • The Tam Valley Sea Level Rise Task Force – Doug Wallace, Alan Jones, Kim Rago, Chris Dorman, Ted Barone

The discussion was broad and varied.  In an effort to synthesize the comments, we have organized the community’s thinking into six categories – sea level rise projections; clogged drainage and maintenance issues; Tam Valley’s historic wetlands; subsidence at Manzanita and Birdland/Kay Park; adaptation strategies; and community organization.

Sea Level Rise Projections

The Manzanita interchange has flooded for decades but the frequency has been increasing.  Senator McGuire called it the “Canary in the Coal Mine” for sea level rise in the Bay Area.  The State of California is directing its agencies to plan for 3 ½ feet of sea level rise by 2050 and up to 10 feet of rise by 2100.  Most of the lower elevation areas of Tam Valley are under 10 feet in elevation.  The most recent king tides rose above 7 feet on a sunny day.  Imagine a storm surge of up to 3 feet plus just one foot of sea level rise.  Our levees would be easily breached.  A large majority of the affordable housing units that the County is proposing for Tam Valley as part of their SB9 obligations are located in low-elevation areas, at high risk for flooding from sea level rise.

Clogged drainage and maintenance issues

During the October, 2021 storms, culverts, storm drains, and garbage gates were clogged with debris from the hills.  Residents expressed concern about frequency of  maintenance both of the drainage resources and pump stations.  There was general agreement that clearing flood gates and drainage should be a priority.  Some suggested that neighbors could be trained to clear the drainage in anticipation of storm events but better coordination among agencies is needed. The Flood Control District 3 meetings are important places to lobby for greater focus on Tam Valley.

Tam Valley’s Historic Wetlands

Much of Birdland, Kay Park, and the Tam Junction business district are built on historic wetlands. Coyote and Nyhan Creeks, once the home of spawning salmon, were redirected into concrete channels or hemmed in by levees in response to flooding decades ago.  Sedimentation of the creeks exacerbates the problems associated with rising tides. Several residents expressed interest in the development of an “ecological health plan” to help guide our decision making.

Subsidence at Manzanita and Birdland/Kay Park

Increasing road closures, and sea water encroachment in Birdland and along Shoreline Highway are evidence not only of sea level rise but subsidence of roads and homes built on the historic wetlands.  Highway 1 under the freeway has subsided approximately 4 inches from its original height and creates problems not only for Tam Valley but all of West Marin.  The roadway on either side of the Flamingo Street bridge is dramatically lower than it was when first built in the 1950s.  How much have house elevations subsided?  Several participants advocated for raising the roadway elevation as a short term fix.  Others wondered whether raising the freeway itself was inevitable.  Similarly, is raising the elevation of houses, roads, and other infrastructure in the low elevation residential and business neighborhoods of Tam valley also inevitable?

Adaptation strategies

There is a spectrum of solutions from grey mitigation such as sea walls to green adaptation such as ecotone slopes.  Multiple strategies at various points along the spectrum are likely to be needed. There were several comments about learning from the Dutch who have had to deal with encroaching seas for centuries. One resident suggested that Tam Valley has a chance to become the “Netherlands of the Bay Area” as we figure out how to deal equitably and publicly with adaptations to sea level rise. A few questions arose, including what are limits on green solutions and where might be best utilized in our area?  And what are the costs and benefits of different strategies? A really good place to get an overview of different kinds of adaptation strategies that might be relevant to our situation is the Richardson Bay Resilience website in the section called “What’s Possible?”

Community Organization

            A cohesive Tam Valley voice will be needed to ensure that decisions made are appropriate for our desired future.  We need to be assertive in claiming our share of state, federal, and regional funding sources. The Tam Valley Neighborhood Response Group Network, which hosted the February 3 event, is a great way for residents to organize in small neighborhood clusters and build resiliency as we face disasters such as wildfire, earthquakes, and flooding.  The low elevation neighborhoods of Tam Valley are not currently well-represented so block captains are needed now.  For more information, email TamValleyNRG@gmail.com.

Next Steps

  1. The Tam Valley Sea Level Rise Task Force will conduct a series of community forums and surveys to help residents and business owners learn about different adaptation strategies and develop prioritized guiding principles. Please email TamValleyNRG@gmail.com if you would like to host a small neighborhood meeting.
  2. The Task Force will continue our collaboration with elected officials, agencies, and partner organizations to find resources and solutions to the problems we face.
  3. We will, by December 2022, produce prioritized guiding principles for Sea-Level-Rise adaptation in Tam Valley that are science-based, realistic, and reflects the will of residents and businesses.  These guidelines can then be used to guide decision-making at the local, state, and federal levels.

After the meeting, we sent a list of questions to Supervisor Moulton-Peters, Chris Choo from the Department of Public Works, and Senator McGuire’s office for answers.  Here are our questions and responses:

From Chris Choo, Department of Public Works

Questions that came up

  • What are the plans to upgrade the pump station that failed during the October storms?  What is the maintenance schedule for those pump stations?  What can neighbors do when they see a pump station isn’t working?
    • A meeting to review the work plan and baseline budget for Flood Zone 3 (which includes Tam Valley) is being scheduled for March.  The meeting packet will include a staff report with updates on pump station, levee, and channel maintenance including Coyote Creek.  (Note: We will post the meeting link on the Tam Valley NRG/Sea Level Rise website when it becomes available)
  • Given the subsidence of the roadway under the Manzanita interchange, can the roadway be raised by a couple of feet as a temporary fix?
    • Shoreline Highway is in Caltrans’ jurisdiction.  The Sea Level Rise Task Force will reach out to our contact there for their input.
  • Regarding $455 million in FEMA (HMGP) funding, are County officials requesting any of those funds?
  • When will the County or Army Corps of Engineers dredge Coyote Creek from Flamingo Road to Richardson Bay?  Is that in the plans?
    • The community has a resource in the Richardson Bay Resilience website. Reports on sea level rise and flooding improvements specific to the Tam Valley shoreline are available in the “What’s Been Studied” section of the site.

From Senator Mike McGuire (posed to Summer Cassel, his District representative):

  • Senator McGuire spoke about short term and long term fixes during his introductory comments.  Can we get some detail about what the short-term fixes would be and what he is thinking about for long-term fixes?
    • The short term fixes would be solutions similar to what Caltrans has implemented on Highway 37 to mitigate flooding as it happens. This could include added drainage, constructing a flood wall, and controlling flood water. The long term plan could consist of raising the road, which would require a full environmental review and planning process, which would take years. We are planning to discuss this with Caltrans District 4 Director Dina El-Tawansy during a tour (of Manzanita and Tam Valley) in April, to hear about the actual long term plan they have for the area. 

Resources

  • Evolving Shorelines has drafted a plan to move the multi-use path across Bothin Marsh to help restore some of the historic wetlands of Tam Valley
  • San Francisco Estuary Institute Adaptation Atlas which is a broadly used science-based framework for developing adaptation strategies in the Bay Area.

For more information, please email TamValleyNRG@gmail.com.

The Facts

1-foot sea level rise + storm surge

  • Realistic predictions for additional Sea-Level-Rise (SLR) range from 1 foot by 2035 and 2 feet by 2045 to 4 to 6.5 feet by 2100.    
  • The State of California’s Sea-Level Guidance calls for agencies to plan for a 3.5 foot rise by 2050 and 7.6 foot rise by 2100.
  • In Tam Valley, a one-foot rise combined with a storm surge (see image above) would breach levees and inundate almost all of Birdland and Kay Park. Access to Miller Avenue and Highway 101 would be blocked.
  • There is no simple answer! Solutions will be expensive, inconvenient, and take years to implement. 

We are not going to stop sea level rise. We have to adapt to it.

To learn more about our options, visit nrgmillvalley.org/tam-valley-sea-level-rise/ and click on the Richardson Bay Resilience link.

See you on February 3, 2022 at 7:00 p.m.


Manzanita Frequently Asked Questions (FAQ)

Published by the Tam Valley Sea Level Rise Task Force,

a project of the Tam Valley NRG Network

Dated: October 21, 2021

Why is there flooding in Manzanita and what can be done about it?

The Manzanita interchange is Tam Valley’s most obvious indicator of current and future sea level rise threats in our community. The Tam Valley Sea Level Rise Task Force has met with key County and State officials regarding the history of this flooding and plans to deal with it in the future. The answer is: it’s complicated, both technically and beaurocratically.

This FAQ was designed to provide quick answers (in italics) to key questions, background information to support those quick answers, and links to resources for those who wish to delve deeper into the topics. We hope you find it useful and will join us in the conversation.

  • Why does Highway 1 under the Richardson Bay Bridge flood so often?
    • The roadway and sidewalks under the bridge are subsiding, sea level is rising, and the culverts that enable outflow of tidal and rainwater are increasingly blocked with mud and debris.  The excess water flows into the roadway and parking lot.
    • History: The Richardson Bay Bridge was built in 1957 and seismic retrofits were completed in 1995, six years after the Loma Prieta earthquake.  The roadway under the bridge, which was built on marshland and bay mud, was not raised at that time.  Since then, there have been pavement overlays at the Park & Ride and improvements to curbs and sidewalks. 
    • Sources of flooding: One of the biggest sources is roadway subsidence.  The roadbed underneath the freeway has subsided 4 -12 inches since 1995 due to the weight of the road compressing the mud underneath. Fortunately, Caltrans reports that bridge inspections indicate the foundations of the bridge itself are not subsiding.  “The bridge foundation consists of spread footings sitting on competent soil/rock and piles embedded in bedrock.”  They note that the roadway and sidewalk subsidence “has no impact on the bridge’s structural integrity”.
  • If we do nothing about it, will flooding get worse?
    • Dangerous high tides are increasing in frequency and magnitude (NOAA).  Flooding will increase not just at the Highway 1 underpass but also in the Tam Junction business district and the Birdland and Kay Park neighborhoods.
    • Current Condition
      • It’s helpful to know what the land elevations in the vicinity of Manzanita are so we can predict the implications of sea level rise in the future.  Elevations (relative to 0’ NAVD-88) at the underpass range from under 6’ to 8‘. On the Bike/Multiuse path, elevations range from under 7’ to nearly 8’.  In the parking area around the Holiday Inn Express, the elevation ranges from 6’ to over 9’.  The entrance to the Park and Ride is under 6’.
      • The elevation of much of the Tam Junction business district is 7-8’; most of Birdland and Kay Park is under 10’ as is the Gateway Shopping Center in Marin City, the Tam High Athletic Fields, and the Redwoods Senior Citizen complex across from Tam.
      • In July, 2021, a 7.14’ high tide completely inundated and closed the underpass and the multi-use/bike path.  It was a “sunny day” tide, meaning there was no storm surge and no water flowing from the hills.  The maximum tide ever observed in San Francisco Bay was 8.72 in January of 1983.  There will be seven 7.0+ high tides in the next 12 months including five during December and January.
    • Predictions: Realistic predictions for additional Sea-Level-Rise (SLR) range from 1 foot by 2035 and 2 feet by 2045 to 4 to 6.5 feet by 2100.  Caltrans uses the State of California’s Sea-Level Guidance (2018 Update) which calls for agencies to plan for a 3.5 foot rise by 2050 and 7.6 foot rise by 2100. A predicted extended El Niño effect and accelerated melting of West Antarctic ice shelves would exacerbate the challenges. A five-year storm surge would increase tide levels by two feet. Add these numbers to the elevation figures above and you get a sense of what the future holds.
    • Marin County published Richardson Bay Resilience to describe visually what the County is doing to prepare for climate-induced SLR.  Check it out.  It is likely to be very bad. We also suggest you spend some time with the Bay Shoreline Flood Explorer and try different SLR and storm surge scenarios to better understand how Tam Valley will be impacted.
  • Who is responsible for fixing the problem? Is it a priority for Caltrans and other responsible agencies?
    • A complex network of federal, state, regional, and county agencies have jurisdiction over the Manzanita Interchange.
    • Relevant factors: There are many aspects to the present and future SLR-related flooding problem, not just the subsidence of the roadway. Tidal influence in creeks and culverts, lack of sediment flowing into Bothin Marsh, levees and sea walls diverting tidal flow – these are just a few relevant factors.  A good source for understanding the breadth of the problem is the Manzanita Flood Reduction Study Report  (2021). 
    • Responsible parties: Caltrans; the Transportation Authority of Marin (TAM); the Marin County Flood Control District; and the Board of Supervisors. Other agencies with some authority include Marin County Parks; Army Corps of Engineers; Environmental Protection Agency; San Francisco Regional Water Quality Control Board; California Department of Fish and Wildlife; Bay Conservation and Development Commission; and private property owners since solutions generally require addressing larger sections of the shoreline.
    • Priorities: Caltrans, to their credit, in their Adaptation Priorities Report (December 2020), listed the Richardson Bay Bridge and Hwy 1 underpass as one of 63 Priority 1 bridges to address in District 4 (which includes the entire SF Bay Area).  The Hwy 1 bridge over Coyote Creek is on the priority 1 list as is the Golden Gate Bridge.
      • Follow-up: Caltrans’ follow-up to the Adaptation Priorities Report is to undertake detailed adaptation assessments of each of the Priority 1 bridges, including a close look at the exposure to more localized climate projections and more detailed engineering analyses. Caltrans has initiated these assessments. If their findings warrant, they will develop adaptation options to ensure the bridge is able to withstand future climate changes.  They want multi-agency coordination and involvement of the private sector because the impacts of climate change cross jurisdictional and ownership boundaries.  They want to see communities engage in best practice land management in adjacent drainage areas to reduce stormwater and debris flows.
  • Is there a plan to improve the flooding situation? Does it take into account SLR?
    • Multiple agencies are currently in “study” phases, trying to figure out how to respond to current flooding.  Planning for sea level rise is inconsistent but there does appear to be an increasing focus on it, especially at the State level.
    • Flood gates and sandbags: Within the last few years, Caltrans replaced some of their flood gates and the Marin County Flood Control District (Zone 3) installed the sandbag wall that reduces the amount of water flooding into the intersection. These measures have helped the situation but obviously haven’t resolved the problem.
    • Caltrans’ Adaptation Priorities Report: Caltrans has initiated studies required in the Adaptation Priorities Report, as described previously.
    • Flood reduction study: Published in January, 2021, the Manzanita Area Flood Reduction Study (co-sponsored by the County of Marin and Caltrans) studied small-scale and generally lower cost solutions that can be implemented in the next five to 10 years to reduce impacts of flooding during King Tide events.  The recommendations did not account for longer-term sea level rise.  Caltrans engineers are concerned the estimated costs for the different fixes are insufficient given the scope of the work.
      • Recommendations from the study included continued coordination between Marin County and Caltrans; a more comprehensive evaluation of flooding to include not just tidal flooding but that which is caused by runoff from Coyote Creek and its tributaries during peak storm events in all phases of the tide; and a plan for implementation of short-term improvements called for in the study.
      • The short-term improvements include replacing tidal gates with Tideflex valves which block tidal water from flooding into culverts and drains but allow water to flow into the bay from the land. 
      • There is currently no funding for these projects. Some of the improvements called for in the Flood Reduction Study need to occur on private land.  The Marin County Flood District would be key to implementing the work.  Caltrans could partner with Marin County to fund portions of the project.  Community lobbying of elected officials, the Transportation Authority of Marin, and the Flood District is needed.
      • Caltrans has scheduled a pavement rehabilitation project for Hwy 1 in 2027.  They could probably add some of the recommended actions to that project.
    • Multiuse Path: The Evolving Shorelines project (sponsored by Marin County Parks, Golden Gate National Parks Conservancy, and OneTam) is developing a plan for moving the Multiuse/bike path westward to enhance ecological functions of Bothin Marsh and Coyote Creek and to remove that part of the trail from the tidal flood zone.  The changes being studied would likely reduce the impacts of increased tidal flows and improve ecosystem services. For an update of the status of the project, see the Adaptation Concepts report (August, 2021).
    • Clearance requirements: Clearance under the overpass has to be at least 15’ at the center of the roadway and 14.5’ over the shoulders.  Currently, the center clearance is 16’8”.  If the roadbed was raised to a height that solved the problem of current and future tidal flows, then the vertical clearance limitations would be exceeded. 
    • Raise the bridge: There is discussion within Caltrans to raise the freeway bridge. At this point, we have no more information than that.
  • Other information
    • On average, between November and March and Caltrans closes the intersection about 32x per year at an average cost of $138,000 per year.
    • That big bump in the intersection that was recently repaired was a culvert that crossed the highway.  The highway subsided adjacent to the culvert, but the culvert itself had not, resulting in the bump.  The culvert is still there but is sufficiently deeply embedded in the mud that Caltrans maintenance crews were able to flatten the roadway without moving it.
  • How can I help?
    • Understand that there is no simple answer! Solutions will be expensive, inconvenient, and take years to implement.  We are not going to stop sea level rise, we will have to adapt to it.
    • Start by learning more.  Click on some of the hyperlinks in this FAQ and explore.  Visit our website and read some of the research.  Then ask us questions and tell us what you think.  We will do our best to get answers.
    • At a minimum, get on our email list.  We are working hard and don’t send out much, but we want our neighbors to be informed. Shoot us an email to TamValleyNRG@gmail.com and we’ll put you on our list.
    • Get involved! Join one of the Tam Valley Sea Level Rise Task Force’s working groups in either Finance, Adaptation Science/Engineering, Jurisdictional Issues, or Public Relations/Education.  We need your help. Send us an email to learn more.
    • Our goal is by December 2022, to produce a prioritized framework for Sea-Level-Rise adaptation in Tam Valley that is science-based, realistic, and reflects the will of residents and businesses.  This framework can then be used to guide decision-making at the local, state, and federal levels.

Sea Level Rise Survey Results and Next Steps – April 2021

Thank you to the 163 members of the Tam Valley community who completed the recent survey on sea level rise.  Your voices have been heard and are having a strong influence on our planning.  Please read the survey summary below and find out what our next steps are.

Survey Results:

A large majority of the respondents are acutely aware of the challenges posed by sea level rise in Tam Valley, think we need to start working on solutions right away, and believe we have a collective responsibility to solve the problem.  Specifically:

  • 71% said that sea level rise needs to be addressed as soon as possible, and another 22% said within 5 years.
  • 62% believe that SLR will have either a moderate or high impact on their day to day life by 2035.
  • In order of ranking, flooded roads, infrastructure damage, and ecosystem harm were the highest concerns from SLR. Note that nearly a third of respondents stated they were most concerned about their homes being flooded.
  • 86% of respondents said that their mobility has been impeded  by flooding at least twice, and 38% said more than 10 times.
  • Nearly 71% believe that protecting private property is a shared responsibility of the government and the property owner.
  • In order of ranking, responsibility for funding infrastructure improvements to increase resilience was #1, state and federal government; #2, local government; and #3, the local community.
  • More than 74% said that Tam Valley residents living above the flood zone should contribute financially to resilience measures.

To see the complete data and graphs, click here to download a pdf of the survey results.

Next steps:

We are grateful that we live in a community with so many talented people.  Fifty residents so far have expressed an interest in serving in a working group to help figure out how we want to face the looming sea level rise challenge. We invite others to get involved.

Our goal is by December 2022, to produce a prioritized framework for sea level rise mitigation and adaption in Tam Valley that is science-based, realistic, and reflects the will of residents.  This framework can then be used to guide decision-making at the local, state, and federal levels.

Our process is collaborative and inclusive, science-based, flexible, responsive to community concerns, and realistic.

In the event of an emergency this site is not monitored. For current information go to:

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