October 20182019-01-09T20:53:33+00:00








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October 2018                                                                                             Issue 3

Eroding scarp at the edge of Tiscornia marsh in March 2018  The marsh elevation is approximately 5.5 feet above mean sea level and the adjacent mud salt is approximately 2 feet.

Tiscornia Marsh Restoration:
A First Step Toward Protection Against Bay Flooding

 
Most of east San Rafael and much of downtown San Rafael are below today’s high tide levels and would flood today were it not for three miles of levees along the bayfront and another seven miles along the Canal. Nearly 8 of these 10 miles of levee are below today’s “100-year flood” elevation and are very vulnerable to rising sea levels flooding over the top. Were flooding to happen, there could be as much as 2 to 3 feet of water today and deeper in the future with sea level rise.
 
And the future doesn’t look much drier: There is a clear progression of sea level rise that scientists predict will continue. Mean sea level at the Golden Gate have risen about 10 inches since 1850. The most recent sea level rise estimates by the California Ocean Protection Council project between six to twelve inch rise by 2030, 1.1 to 2.7 feet by 2050, and 3.4 to 10.2 feet by 2100.
 
The Tiscornia Marsh Restoration project is dedicated to using “nature-based” components to restore habitats and to improve flood protection from sea level rise. “Nature-based” means using natural environmental systems in place of or together with more traditional engineered structures to achieve bay shoreline protection from erosion and rising sea levels.
 
The project also aims to provide critical education to the Canal neighborhood about the potential impacts of sea level rise within the community and involve residents in adaptation planning and completion of solutions. 
 
The 20-acre Tiscornia Marsh property, located next to Pickleweed Park in the Canal neighborhood of East San Rafael, consists today of about 4 acres of tidal marsh, open bay, and adjacent levees. The property was donated by Mary Tiscornia in 2008 to the Marin Audubon Society. Since the late 1980s, tidal marshlands at Tiscornia have eroded as much as 200 feet, and a total of about 3 acres have been lost. Though comparatively small in acreage, the rarity of tidal marsh along the San Rafael shoreline gives this isolated small marsh outsized value as habitat for the endangered Ridgway’s rail and for migratory shorebirds.
 
Additionally, residents in the area have lost a significant buffer against rising sea levels that will eventually flood the Canal, Spinnaker and other inland neighborhoods without adaptation measures. If the marsh keeps eroding at its current rate, engineers estimate it will be entirely gone in 50 years.
 
The primary reason for marsh loss is wind-driven waves. Regional declines in sediment entering the bay and replenishing nearby mudflats may also contribute to marsh loss at Tiscornia. A small portion may be attributable to boat wake action.
 
Marin Audubon completed conceptual design alternatives in summer 2018 for a restoration project that will replenish the marshland with sediment, marsh plants, and a protective beach to hold back future erosion. The Marin Community Foundation funded this initial work. Marin Audubon is submitting a grant application in fall 2018 for Measure AA funds to move into the next project phase of engineering design, environmental analysis, and permitting.
 
Tiscornia restoration includes two separate elements. The first element is to raise the southern levee alongside Canal Boulevard by Schoen Park to strengthen this levee segment for sea level rise. Different alignments will be evaluated reflecting levee encroachment into the marsh and into the playground area.
 
The second element is to restore marsh that has eroded away and to bolster the marsh’s defenses against future erosion. A cobble and gravel beach would reform the 1980s marsh edge and include wood logs to help hold the beach in place. The north end would include some form of “jetty” to keep beach sediments from moving into the Canal itself. The area between the beach and the existing marsh would be filled with sediment dredged locally. The City-owned diked marsh north of the Pickleweed Park soccer fields would also be restored to the tides, which requires relocating the existing levee to the south to maintain and improve bay flood protection. The Bay Trail would be relocated atop the new and raised levees.
 
Funding for construction and marsh restoration will be secured following completion of environmental impact assessment and obtaining permits from several regulatory and resource agencies. Tiscornia Marsh is an important early test case for similar restoration projects around the bay.
 
Please visit http://www.tiscorniamarshp.org/ for more info.

Future San Rafael as imagined by Elevate San Rafael.

Letter from the Executive Director
 
Last month, I shared with you the inception details and our goals for the Resilient by Design Challenge. Today, I’ll follow up with additional thoughts about The Bionic Team’s (Bionic) design concepts, Elevate San Rafael, which were presented to the San Rafael City Council August on 20th.
 
Bionic identified three base assumptions before starting their work. These were:

  1. Existing housing in the Canal neighborhood and other at-risk areas is substandard and would likely be condemned after a flood.
  2. People living below sea level (and by extension this includes people living within a within the missing copy here? ) are at greater flood risk and future sea level rise.
  3. Any investments in infrastructure or new construction within areas subject to sea level rise are inadvisable, multiplying loss when the area is ultimately flooded by rising waters.

The team prepared a range of design concepts based on these assumptions. Their key expectation is the seas will rise and inundate much of the valley floor. The existing buildings and infrastructure will have to be rebuilt either in place and designed to accommodate higher waters, or people and businesses would move elsewhere.
 
Responses to Elevate San Rafael have been mixed. The task of rebuilding homes for a quarter of the city’s population and two-thirds of its business activity is daunting. Some see the outcome as displacement of the Canal emigrant community. Additionally, the design team was not responsible for identifying funding sources or redevelopment tools to rebuild a city.
 
However, some important information became clear. The community can determine if the team’s base assumptions and Elevate San Rafael design solutions are appropriate. Bionic conducted valuable research and prepared compelling exhibits.
 
A shore planning process will provide the opportunity to prepare additional design solutions. These can be based on different assumptions, including protecting existing communities in place. All design concepts can be vetted for their social, economic and environmental costs and benefits.
 
I am grateful for Bionic team’s work and confident we can benefit from it.  Next month we will discuss some specific Bionic design concepts and how we can move forward to protect and preserve the at-risk areas of our city.
 
Help us make our shore better and more resilient by making tax-deductible contributions to Resilient Shore through MarinLINK, our fiscal sponsor. Let’s make our shore world class. Together, we can do this!
 
Jeff Rhoads
Executive Director
Resilient Shore

SUPPORTER SPOTLIGHT

ENGEO is an employee-owned, award-winning firm of more than 300 geotechnical and civil engineers, geologists, hydrologists, environmental scientists, and construction quality assurance field representatives. Founded in 1971, the firm has offices throughout California, Nevada, New Zealand and Australia and is headquartered in the Bay Area. ENGEO serves projects in transportation; infrastructure; water storage, conveyance and treatment; industrial facilities; geologic hazard mitigation; flood control facilities; civic structures; healthcare; education; energy; manufacturing; ports, harbors and waterfront development; residential and mixed-use communities; and urban development.
 
ENGEO professionals share an absolute commitment to providing clients with practical, constructible solutions based on sound engineering and the firm’s long experience translating designs into successfully built projects. Specific to geologic hazards and flood control, ENGEO has a wealth of experience in complex levee, slope stability, shoreline and erosion projects with challenging seismic, regulatory, water quality and constructability considerations.

 
 
 

ABOUT RESILIENT SHORE

We’re a non-profit project dedicated to working with local people and businesses, listening to their concerns, and together creating the best-of-all-worlds flood mitigation plan that benefits everybody.

 
 
 

UPCOMING EVENTS

San Rafael City Council Meeting

Agendas are posted 72 hours in advance and you can watch the meeting live.

Copyright © 2018 Resilient Shore, All rights reserved.
Resilient Shore is a non-profit project of MarinLink

Our mailing address is:
828 Mission Avenue, San Rafael CA 94901

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