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6) Community Alternatives Appendix E). The level of potential community support for each strategy is expressed as A possible approach for adapting to near term percent of total respondents for that SLR and storm flooding in West Marin is to community’s section of the poll, expressed as protect existing homes and businesses with strong, moderate or little support. The poll elevation and retrofits, and protect assets in the results should be considered as one indicator of near‐ to‐medium term (with a preference for public support, but not as a definitive nature‐based protection strategies), while measurement. considering additional options over the long‐ term. dHybri approaches that include a mix of NOTE: The Community Alternatives section adaptation measures may be the most practical of this Adaptation Report provides an in many situations. Adaptive management over overview of possible measures to address time will allow for response to changing the impacts of sea level rise, with examples conditions (ESA 2015). Each community profile of potential locations for implementation. includes a No Action section which describes The strategies presented below do not general sea level rise impacts to various assets if necessarily reflect the position of Marin adaptation is not undertaken. Priority County, but are included for discussion adaptation actions for each West Marin purposes. Further feasibility analysis and community are based on the findings of the context‐sensitive design is a necessary next Vulnerability Assessment, input from step in developing any of the strategies. stakeholders and technical advisors and the guiding principles in this report.
Adaptation workshop in Stinson Beach, November 2015. Credit: Marin County CDA
A series of public meetings were held in West Marin during fall 2015 and spring 2016, and over 200 residents participated in the West Marin Sea Level Rise Adaptation Poll (See
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6.1) Community PATCHs (Plans for Adaptation To Coastal Hazards)
As next steps to move adaptation options outlined in this report forward, community‐scale plans could be undertaken for each of West Marin’s seven communities. Plans would focus on adapting infrastructure of community wide importance to coastal hazards. Plans would identify funding Fsgfsgfsgfsgfsgmechanism, and implementation opportunities. These Plans for Adaptation to Coastal Hazards s(PATCHs) would be for specified timeframes based on best available sea level rise/storm projections and trigger points at which flooding becomes nuisance. PATCHs would be conducted in conjunction with partners such as DPW or Caltrans. A proposed process to develop PATCHs is as follows:
1) Using the C ‐SMART Vulnerability Assessment, identify vulnerable infrastructure assets of
community wide importance. 2) With the use of CoSMOS, determine flooding frequency, intensity, and duration for the identified assets under different future scenarios. 3) Survey community members to determine ‘trigger points’ for vulnerable infrastructure. Trigger points would be the frequency/intensity/duration points at which flooding becomes nuisance, causing public inconveniences which may include frequent road closures, overwhelmed storm drains and compromised infrastructure.
4) Use the most recent adopted state policy to link the trigger points to specific timeframe s(e.g., 2030, 2050) 5) In conjunction with community members and asset managers initiate PATCHs around the identified timeframe (the planning horizon) with the objective of PATCH implementation prior to nuisance flooding occurring. 6) Develop adaptation alternatives for evaluation (e.g., elevation, relocation, alignment). Populate matrices with information including costs, impacts and benefits. The matrices would guide the
determination of a preferred alternative based on maximizing public benefits while minimizing costs and negative impacts. 7) Collaborate with partners such as DPW or Caltrans to implement the preferred alternative through a capital improvement program.
As the only road through Stinson Beach’s calles and patios and into Seadrift, Calle del Arroyo is of community‐wide importance for both daily use and emergency access. A PATCH could focus on adaptation alternatives for the roadway with a time horizon for preferred project implementation in advance of nuisance flooding. Stinson Beach residents would be consulted with through the planning process and asset managers would serve as project partners. Above – Stinson Beach’s calles and patios with Calle Del Arroyo at 3 feet SLR/no storms (CosMos)
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COMMUNITY ALTERNATIVES Muir Beach 6.2) Muir Beach PRIMARY VULNERABILITIES PRIORITY ACTIONS Flooding during extreme events already occurs Ensure safety of bluff top development
Long‐term impacts will compromise beach Improve bluff stability by following best access and tourism practices for drainage and vegetation
Those impacted include one business, property Continue outreach and education around SLR owners, Muir Beach Home Owners Association, and coastal hazards and Muir Beach Fire Department
Timeframe/Term: L=Low 0‐40% Strategy NT=Near M=Moderate 41‐70% MT=Medium S=Strong 71%+ LT=Long NA=Not available PROTECT Research dune maintenance NT M to S Research beach nourishment NT M to S Maintain existing armoring NT S
ACCOMMODATE Convene working group to explore solutions for Pacific Way NT S bridge vulnerability ID triggers for elevating Shoreline Highway and Pacific Way LT S Elevate buildings in flood plain MT M Monitor Redwood Creek restoration NT M Monitor water quality and require wastewater systems to NT S meet code Monitor water quality and move wells upland MT S
RELOCATE/MANAGED RETREAT Research managed retreat program including buy out option LT M Remove seawall to maintain sediment supply NT L Implement a rolling conservation easement program to LT L to M prevent new shoreline armoring
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COMMUNITY ALTERNATIVES Muir Beach
Map 7. Muir Beach Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES Muir Beach No Action Bluff top buildings could be impacted by erosion under all scenarios. Temporary flooding on Pacific Way may worsen with SLR, and the perimeter road around the edge of the restored wetland may flood in the long‐term. Habitats in Redwood Creek and Green Gulch Creek may shift landward with increased salinity downstream.
Map 8. Muir Beach Buildings Exposed to Erosion
Table 23. Muir Beach Blufftop Buildings Vulnerable to Accelerated Erosion*
Muir Beach during King Tide. Lighthawk Aerial, 2015 Buildings Scenarios 1&2 12 MUIR BEACH: LONG‐TERM SLR IMPACTS Scenario 3 17 Beach access compromised Property Scenario 4 49 Owners Scenario 5 53 Extreme event impacts MB HOA * This analysis does not include storms already occur MB Fire Source: Marin Map, CoSMoS 1 business Tourism Department
Source: Marin Map, OCOF, Asset Manager Interviews Ensure safety of blufftop development New development must be set back from the Priority Actions bluff edge a sufficient distance to ensure its In the near‐term, bluff top development should stability and structural integrity for a minimum comply with applicable setback standards in the of 100 years, and to eliminate the need for Local Coastal Program Environmental Hazards shoreline protective devices. Coastal hazards policies. Existing information about coastal analyses for individual sites must include a erosion potential can be found in the Marin slope stability analysis that considers historical Ocean Coast Vulnerability Assessment. In many bluff retreat data as well as accelerated erosion cases erosion rates are uncertain, and a site‐ specific analysis is necessary to determine the safety of a structure from cliff erosion.
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COMMUNITY ALTERNATIVES Muir Beach due to SLR.60 For informational purposes and to The community is well‐organized for emergency guide the identification of potential planning preparedness. The CSD Board is committed to triggers for removal of existing structures in furthering public engagement around the hazardous areas, ESA utilized past model input management of community assets such as data from the OPC study (PWA 2009)61 to model water, roads and recreation. Poll respondents and map coastal erosion amplified by the requested that the County notice the CSD of various SLR scenarios. For further discussion of any changes so they can bring it to the attention blufftop setbacks, see the “Bolinas” section of of residents most affected in a timely manner ‐ this report. This strategy received moderate to continue to work collaboratively with the support from poll respondents (58%). CSD and partner with both the CSD and Fire District on continued public outreach around Improve bluff stability by following best SLR and coastal hazard preparedness. practices for drainage and vegetation Homeowners can improve bluff stability by The following sections provide additional following best practices, which include: information about strategies considered during limiting surface and shallow subsurface the C‐SMART project. They are grouped drainage to the bluff edge that can cause according to general approach: protect, erosion and slides; limit disturbance caused accommodate, or relocate/ managed retreat. by vertical access, and identification of preferred vegetation for bluff stability, and Protect slope stabilization. These approaches are In Muir Beach, low dunes and surfgrass highlighted in “Green Strategy: Bluff immediately surrounding the beach play a Management in Muir Beach” in this section. significant role in helping reduce beach This strategy received strong support from exposure to erosion and inundation. Recently, poll respondents (92%). the NPS completed the Redwood Creek Continue public outreach and education Restoration at Muir Beach. The project around sea level rise and coastal hazards objectives were to create a natural creek Muir Beach residents, led by the CSD, expressed system, reconnect the floodplain, reduce interest in continuing to engage with flooding, improve access along Pacific Way, and government agencies to explore solutions to create habitat for Coho salmon, steelhead flooding and bluff erosion. For example, trout, and red‐legged frog. The beach and tidal residents would like more information about lagoon were allowed room to migrate landward the community’s ability to maintain long‐term with SLR and the parking lot was reconfigured safety, and the tradeoffs of maintaining vs. away from direct wave action to minimize 62 removing hard protective structures. storm surge impacts .
Research feasibility of dune maintenance Potential short‐ and medium‐term opportunities for habitat‐based protection 60 Marin County Community Development Agency. Draft Local Coastal Program, Environmental Hazards Chapter LUPA. April 2016 62 National Park Service. Redwood Creek Restoration and 61 PWA. CA Coastal Erosion Response to Sea Level Muir Beach. www.nps.gov/goga/learn/nature/muir‐ Rise – Analysis and Mapping. March 2009 beach.htm. Accessed January 2016. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 146
COMMUNITY ALTERNATIVES Muir Beach include dune maintenance, which would build Regular impacts to the perimeter road around upon the Redwood Creek restoration project, the edge of the restored wetland may not be and/or beach nourishment. felt until the long‐term, but storms may interrupt road access at any time, and residents Dune restoration may not be an effective should be prepared with emergency supplies. solution for protecting blufftop homes at Muir Beach, as the beach is already squeezed or Convene a working group of County and local absent in front of the bluff toe and sand placed stakeholders to brainstorm a resolution eto th for dune creation would likely not last. Pacific Way bridge vulnerability Additionally, nourishments would not affect the Earlier plans to widen and elevate the Pacific erosion processes at the bluff top. This strategy Way bridge were considered too large‐scale by received moderate support from poll the community. However, flooding exacerbated respondents (62%). by the current bridge continues to be a problem. Further collaborative work between Maintain existing seawalls and other existing government agencies and residents is needed hard protection to find an appropriate solution. One idea was Some armoring structures are already in place to have a separate pedestrian and bicycle at the bluff toe fronting homes at Muir Beach. bridge parallel to the main auto bridge, to This solution could be effective in limiting reduce the necessary width. The idea of erosion of the bluff face, but will result in less convening a working group around this issue sediment delivery, lead to local scour at the toe received strong support from poll respondents of structure and ultimately lead to rapid (85%). degradation and failure of the structure. Furthermore, a toe revetment may not prevent A related medium‐term strategy is to explore additional erosion of the upper bluff face. the feasibility of constructing a new Pacific Way Armoring requires maintenance and sea‐level bridge appropriate to the community character rise will result in increased loadings that will and to accommodate Redwood Creek likely require reconstruction. Therefore, floodplain. This idea received strong support armoring may not be a sustainable approach from the community (92%). (ESA, 2015). However, the ideas of maintaining Identify triggers for elevation of vulnerable existing hard protection received strong sections of Pacific Way and Shoreline Highway support from poll respondents (73%). Water levels for daily high tides or extreme high In addition to protection strategies that address tides could be identified to determine when erosion of the bluff toe, elements of drainage Pacific Way would need to be adapted to allow control, disturbance avoidance, vegetation for continued access to homes and the public management and slope stabilization could be beach. While the road sometimes floods during employed to limit (but not completely prevent) storms, it is not expected to be impacted by erosion of the bluff top and face. “permanent inundation” (daily during high tide) until later in the century. This strategy received Accommodate strong support from poll respondents (92%).
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COMMUNITY ALTERNATIVES Muir Beach Elevate buildings in the floodplain to meet received strong support from poll respondents FEMA safety requirements plus additional (85%). height for SLR Draft Local Coastal Program policies follow the Relocate/ Managed Retreat approach of requiring additional elevation for Any managed retreat strategy to remove or homes in the FEMA coastal flooding zones that prevent development in vulnerable areas would are also projected to be impacted by SLR. need to be carefully tailored and defined in Floodproofing is an alternative way to maintain consultation with the community. home safety from storm events. This strategy Research feasibility of a managed retreat received moderate support from poll program to provide property owners with respondents (62%). options for moving out of hazardous areas, Support efforts to monitor Redwood Creek especially after damaging storms restoration project as a nature‐based Marin County could research potential costs adaptation to SLR and community interest in a long‐term buyout Continued monitoring of the Redwood Creek or property acquisition strategy if rising sea project may provide evidence about the levels or erosion impacts become imminent resiliency and protective effects of restored threats to homeowners in Muir Beach. The natural habitats, building support for other County could also consider having a plan and restoration projects. This strategy received specific proposals in place in case of a major strong support from poll respondents (69%). storm/flood event that makes homeowners more likely to be interested in the buyout.63 Continue to monitor water quality and require This strategy received moderate support from onsite wastewater systems to meet code and poll respondents (62%). adapt to saltwater intrusion as needed As saltwater intrusion leads to degradation and Remove seawall to maintain sediment supply ultimately failure of septic systems, it will be The existing seawall may be effective in limiting important to monitor water quality and ensure erosion of the bluff face, but reduces sediment that septic systems continue to meet codes. delivery to the beach, which could eventually Over time, affected septic systems may need to disappear with SLR. Local scour at the toe of become above‐ground mound systems, have a the seawall could ultimately lead to degradation flip switch to prevent environmental and failure of the structure. The idea of contamination during flood events, or sealed removing the existing seawall received low tanks that are pumped out periodically. support from poll respondents (19%). Ultimately, affected homeowners might consider developing a community wastewater Implement a rolling conservation easement system on higher ground, similar to the system program to prevent new shoreline armoring developed in Marshall along Tomales Bay. This strategy received strong support from poll respondents (85%).
63 Center for Ocean Solutions, Natural Capital Project. A related strategy is to monitor water quality Coastal Adaptation Policy Assessment. 2016. and move wells upland if needed, which
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COMMUNITY ALTERNATIVES Muir Beach Because Muir Beach is bordered by land under state and federal protection and by lands protected by a conservation easement, over the long term there is a potential opportunity in the area zoned as “Residential Agriculture” for property acquisition/buyouts or purchasing conservation or rolling easements to allow for natural erosion. This strategy received moderate support from poll respondents (46%).
The following section highlights a few best management practices for bluff management.
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COMMUNITY ALTERNATIVES Muir Beach Green Strategy: Bluff to the beach, in turn increasing the buffer Management in Muir Beach the beach provides from wave action on the bluff toe. A planned retreat, realignment or landward redevelopment strategy may include one or more of the following:
Drainage control: Limited surface and shallow subsurface drainage to the bluff edge that can cause erosion and slides;
Disturbance avoidance: Limit access, especially uncontrolled vertical access;
Muir Beach from public parking lot. CDA, 2015 Vegetation management: Identify preferred vegetation for bluff stability; Muir Beach is characterized by low lying floodplain surrounding Redwood Creek Slope Stabilization: Surface and shallow flanked by steep eroding bluffs. Homes built stabilization techniques help slow the on the tops of bluffs will continue to be at risk pace and extent of bluff recession. as sea‐level rise accelerates erosion of bluffs. Interim approach before implementing a longer‐term retreat strategy; There are a few general best management practices that can be followed to reduce Structure Modification or Relocation: erosion of the blufftop and face. Finding Structures can be moved landward or appropriate solutions to these processes modified to allow for bluff recession. depends on local geology and existing Land use measures: Mechanisms like drainage patterns that must be gathered rolling easements and development through site‐specific analysis. Example regulations can facilitate fair and orderly solutions include drains to intercept and landward relocation. reroute groundwater from the bluff top. Eroding bluffs will continue to supply sand
Figure 8. Bluff erosion best management practices. (Source: ESA 2015)
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COMMUNITY ALTERNATIVES Muir Beach
Maps 9‐12 Muir Beach 1 Exposure Source: CoSMos
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COMMUNITY ALTERNATIVES Stinson Beach 5.3) Stinson Beach
PRIMARY VULNERABILITIES PRIORITY ACTIONS Storm and tidal flooding already occur Elevate homes subject to temporary flooding
Long‐term flooding will impact 773 homes (55 Elevate or reroute roads and utilities percent vacation rentals), 630 people, six businesses, and two principle access roads. Costs of long‐term flooding will reach nearly $200 Update onsite wastewater treatment million of assessed value and $1.5 billion in systems market value. Those impacted will include property owners, Elevate or relocate Water District Office Seadrift Association, Stinson Beach Fire Department, Stinson Beach Water District, Relocate Fire Station #2 County DPW, and residential tourism.
Timeframe/Term: Support: Strategy NT=Near L=Low 0‐40% MT=Medium M=Moderate 41‐70% LT=Long S=Strong 71%+ NA=Not available PROTECT Maintain existing Seadrift revetment and nourish beach NT NA Extend revetment along Stinson Beach MT NA Artificial reef funded by special assessment district MT L Enhance living shoreline in Bolinas Lagoon funded by special NT L assessment district Horizontal levee with impervious barrier NT‐MT L
ACCOMMODATE Elevate existing homes to comply with FEMA and Local Coastal NT‐MT NA Program Elevate Shoreline Hwy along Bolinas Lagoon NT S Realign Shoreline Hwy along Bolinas Lagoon NT L Elevate Calle del Arroyo MT S Elevate local roads in a coordinated neighborhood approach MT L Construct a flood bypass across Stinson Beach to convey storm NT NA runoff Boardwalk entire neighborhoods MT L Upgrade substandard septic systems NT L Convert septic tanks to holding vessels MT‐LT L Develop community wastewater system LT L
RELOCATE/MANAGED RETREAT Research long‐term buyout and rolling easement options NT NA Prevent total erosion of beach by removing all armoring and LT L homes in path of inland migration
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Map 13. Stinson Beach Exposure Map. Does not include geomorphic change.
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Map 14. Seadrift Exposure Map. Does not include geomorphic change.
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Map 15. Stinson Beach Adaptation Map
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COMMUNITY ALTERNATIVES Stinson Beach 6.3) Stinson Beach
No Action Homes, buildings, and facilities west of Shoreline Highway could be exposed to storm impacts, septic failure, water distribution pipe failure, and flooding. Calle del Arroyo, a principal access road to the Calles, Patios, and Seadrift neighborhoods, may face increased flooding in the near term, and eventually permanent inundation, severely limiting access to portions of the community. Flooding from Stinson Beach from above. Lighthawk Aerial, 2015. Bolinas Lagoon and Easkoot Creek already occur and will likely worsen with more extreme climate patterns and as they are combined with STINSON BEACH: LONG‐TERM SLR IMPACTS rising sea levels. Incremental beach loss due to 773 homes, 55 percent 630 people erosion is likely to occur by the end of the vacation rental century if development remains in its current Storm and tidal impacts location.64 6 businesses already occur The damage or destruction of Stinson Beach’s Property Nearly $200 buildings and natural resources would have Owners million of devastating impacts on the local economy, Seadrift assessed people’s lives, and sense of place. Excluding the Association value and Residential effects of storm waves, homes on the Easkoot SB Fire $1.5 billion Tourism Creek side of the Calles and Patios Department in market neighborhood may be vulnerable to permanent SB Water value SLR sooner than homes on the beach side. Due District exposed to topography, homes near Easkoot Creek sit County DPW approximately five to ten feet lower than those directly on the beach. Also, homes on the beach tend to be already elevated or otherwise Priority Actions fortified against storms. Accommodation of vulnerable structures, roads and utilities, primarily through elevation and retrofits, is a near‐ and medium‐term priority for Stinson Beach. Elevation of homes would protect them from temporary flooding and permanent SLR, though road access would continue to be an issue. Many poll respondents supported “reasonable policies that allow property owners to develop in ways that 64 Environmental Science Associates (ESA). Sea Level Rise protect against SLR.” However, permits for Adaptation Options for Marin County. 2015. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 156
COMMUNITY ALTERNATIVES Stinson Beach structures in vulnerable areas may be Maintenance of existing protective structures is conditioned to prove that the structure will be allowed by law under certain circumstances, safe from erosion over a set timeframe. but permitting the construction of new Calle del Arroyo is the County road of most shoreline armoring can be very difficult. In the immediate concern, as it frequently floods and long‐term, as accommodation and protection of provides the only access to Seadrift, the Patios, existing buildings becomes increasingly costly, and many of the Calles. nThe Stinso Beach exposure to coastal hazards grows, and Flood Study65 identified the potential negative impacts to coastal ecosystems mount, construction cost of elevating the entire length homeowners and government officials will need of Calle del Arroyo between State Highway 1 to identify alternatives. This could involve major and Seadrift Road as between $1‐$2 million, beach restoration and nourishment, along with several other flood control and prohibitions on rebuilding structures destroyed mitigation options. Private roads would also by storms, more restrictions on new need to be elevated, or at least sloped up to development allowed in hazard zones, buyout, meet Calle del Arroyo. Elevating Shoreline relocation and/or removal of structures. Highway along Bolinas Lagoon will become a priority toward the middle of the century, as The following sections provide additional access to the community becomes impaired information about strategies considered during with increasing frequency. the C‐SMART project. They are grouped according to general approach: protect, OWTS can be updated to meet code, which will accommodate, or retreat. Unless otherwise make them resilient to saltwater intrusion in indicated, cost estimates in this section are the near‐term. In the medium‐ to long‐term, from ESA, and more details can be found in code revisions allowing for mounded septic Appendix C. systems, or replacement of leachfields with holding tanks could be implemented. The It is beneficial to consider a range of adaptation Stinson Beach County Water District plans to measures to evaluate and select a preferred continue retrofitting water meter connections strategy, which may be a “hybrid” of hard or in the near‐term to withstand saltwater soft protection strategies. corrosion. Electric utilities located beneath buildings will also need to be elevated or retrofitted. The Water District office will likely need to be elevated or relocated in the near‐ term. Fire Station #2 is already elevated on a mound and the district has plans to relocate the facility before it is impacted by SLR in the medium‐term.
65 Marin County Department of Public Works. Stinson Figure 9. Example Solution Space of Adaptation Beach Watershed Program Flood Study and Alternatives Strategies Assessment. 2014. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 157
COMMUNITY ALTERNATIVES Stinson Beach roughly $6M while a 50‐ft wide beach Green Strategy: Beach and nourishment would cost roughly $11M each Dune Nourishment at time the beach is nourished. The dunes and beach would need nourishment after extreme Stinson Beach storms. A cobble berm would cost roughly $6M, and could be designed high enough to limit excess erosion if ethe entir dune is sacrificed during a large storm.
Due to uncertainties around the availability of local, clean sand, cost estimates are very approximate. This analysis assumes a cost of $61 per cubic yard to import sand from the central San Francisco bay, truck it to Stinson, and spread by bulldozer. Further Stinson Beach at King Tide. Lighthawk Aerial, 2015. analysis could estimate costs via a barge and slurry pipe. Benefits: Recreation, Tourism, Habitat Cost: $44M+ over long‐term Potential problems with beach nourishment include the near‐term construction impact Beach and dune nourishment provides to people and beach ecology, and long‐term protection against coastal storm erosion while changes to shore conditions. The success of maintaining natural habitat and geomorphic the nourishment depends on the volume of response mechanisms. Dune restoration would material, the grain size, and sand retention include placement of sand, graded and planted structures. As sea‐level rises, the frequency to form dunes. A variant of the beach and dune of required nourishment increases unless nourishment strategy includes placement of the beach is allowed to retreat landward. cobble (rounded rock), which can then be covered with sand. The cobble berm would be as far landward as possible. Details, including costs are from ESA, and more details can be found in Appendix C
Along Stinson Beach (3450 ft) a 13‐ft tall, 50‐
ft wide dune nourishment would cost
Figure 10. Example section profile of dunes and cobble berm. (Source: PWA, 2005)
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COMMUNITY ALTERNATIVES Stinson Beach Sand placement provides a temporary construction impact to people and benefit until the sand erodes and migrates. ecology, cost about $1‐$6M for 50‐ft Some of the sand potentially placed on wide dune nourishment along Stinson Stinson Beach could end up in Bolinas Beach depending on local free sand Lagoon, and some may migrate south availability ($6M cost assumes toward Muir Beach (PWA 2006). In general, dredged and imported sand). increased sand supply is considered beneficial to most beach areas, but can be Since the initial dune nourishment would problematic at harbors and drain outlets. occupy existing beach, the trigger distance Whether the sand could be dredged and is reached more quickly, requiring retrieved and recycled is not known, due to nourishment of the beach in 2040. the potential for impacts from dredging. Subsequent nourishments are applied on a With sea‐level rise, increased sediment 30‐year interval. Future nourishments will supply may be a net benefit to mitigate likely need to be more frequent. At any rapid changes. time a major storm erosion event may require beach nourishment. Beyond 2100, Monitoring will play an important role in the first seaward row of homes and utilities determining the timing of the first potential may be severely exposed. sand placement, and identifying the need for additional nourishments in the future. San Andreas Graben? Monitoring could focus on the annual minimum beach width and dune width. The While much more research is necessary storm erosion buffer for Stinson Beach for a to assess its feasibility, further 2‐ to 5‐year recurrence storm is 43‐52 ft.66 investigation could be done on the San Triggers and potential actions: Andreas Graben as a sediment source for nourishment of Stinson and other Maximum seasonal beach width (end of West Marin Beaches. The Graben lies summer) drops below 50 feet trigger: between two strands of the San o Beach nourishment of affected Andreas Fault, with 55‐60 m of reach. Implications: temporary sediment in 20 m of water (Sam construction impact to people and Johnson, USGS). C‐SMART staff are ecology, cost ($2‐$11M for 50‐ft wide currently discussing the Graben as a beach along Stinson Beach) sediment source through participation in the Sonoma/Marin County Sediment Dune width drops below 2‐year storm Management Working Group. buffer (50 ft) trigger distance: o Replenish and revegetate dune system. Implications: temporary
66 Environmental Science Associates (ESA). Marin County Coastal Hazards and SLR Adaptation Strategies. (2016) PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 159
COMMUNITY ALTERNATIVES Stinson Beach Table 24. Cost Estimate for Beach/ Dune restoration along the Stinson Beach coastline. Nourishment at Stinson Beach Coordination with NPS should be integrated Year Cost Estimate Note into strategy evaluation to understand potential Nourish 50 ft dune effects from strategies to NPS beach downdrift with cobble toe 2015 $ 12,000,000 of revetment. (takes up 50 feet of existing beach) Maintain Seadrift revetment Nourish 50 ft The existing bulkhead and seawall around beach when beach 2040 $ 11,000,000 drops below Seadrift is maintained by residents. Individual trigger homeowners in other areas of the community Nourish 50 ft also maintain protective structures, many of 2070 $ 11,000,000 beach after 30 which were constructed prior to the Coastal years Nourish 50 ft Act. The continued presence of seawalls and beach after 30 revetments could accelerate beach erosion, 2100 $ 40,000,000 years, raise homes which would need to be evaluated to better in FEMA V‐zone understand. Shoreline protective devices Total net contribute to erosion but SLR can drown beach present Assumes 1% $ 44,000,000 value discount rate altogether. This strategy would continue to be (2015) implemented by property owners or local Emergency 50 ft assessment districts, and received strong beach nourishment support from poll respondents (100%). if extreme storm *anytime $ 11,000,000 erosion occurs; dune nourishment not considered (add $6M) NOTE: The table above does not include the area fronting Seadrift, which is shown in Table .
Protect Stinson is a partially dune‐backed beach, with Seadrift rock revetment. Copyright (C) 2002‐2017 either homes or park facilities built behind. It is Kenneth & Gabrielle Adelman, California Coastal Records Project, www.Californiacoastline.org a major recreational attraction, and thus preserving the beach can be a priority when developing adaptation strategies.67 In Stinson Rebuild/upgrade of the Seadrift rock revetment Beach a potential short‐term option is to “hold would cost approximately $51M, every 30 the line” or protect existing green and gray years. Beach nourishment along the 7,500 foot infrastructure in place by using physical stretch would cost roughly $24M. The beach is barriers. These could include enhancement of projected to surpass the critical trigger width at shoreline vegetation along the Bolinas Lagoon 2050, requiring a 50‐ft beach nourishment. This side and beach nourishment and/or dune is repeated after 30 years in 2080.e Se Table The appropriate frequency of future 67 Environmental Science Associates (ESA). Sea Level Rise nourishments will likely be higher in reality. As Adaptation Alternatives for Marin County. 2015. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 160
COMMUNITY ALTERNATIVES Stinson Beach the required backshore modifications become Table 25. Cost Estimate for Revetment Maintenance at Seadrift Beach increasingly intensive, the homes will need to Year Cost Estimate Note be raised (assumed at 2100). At any time, a Assume revetment major erosion event may erode the beach to a 2015 ‐ was adequately dangerous condition requiring revetment maintained Rebuild/upgrade repairs and or beach nourishment. 2045 $ 51,000,000 revetment after 30‐ yr life Extend revetment along Stinson Beach Nourish 50 ft beach Some community members expressed interest 2050 $ 24,000,000 when beach drops in extending revetment from Seadrift southeast below trigger to Calle De Pinos to protect homes along Rebuild/upgrade 2075 $ 51,000,000 revetment after 30‐ Stinson Beach. Drawing on cost estimates yr life previously developed for Marin County (ESA Nourish 50 ft beach 2080 $ 24,000,000 2015), a revetment extension of 3,540 ft would after 30 years Raise homes in cost around $24 million. 2100 $ 81,000,000 FEMA V‐zone The revetment could be built along the Total net present Assumes 1% alignment of the existing dune face from Walla $ 130,000,000 value discount rate Vista to the residence at the end of Calle Del (2015) Embarcadero, and sand excavated for the Emergency 50‐ft revetment could be placed in front and on top beach nourishment if extreme storm of the revetment for aesthetic improvement, *anytime $24,000,000 erosion occurs; but additional sand may be required if complete revetment repair burial of the revetment is desired. not estimated Low‐profile wall and cobble berm For the remaining stretch of homes from Calle Del Embarcadero to Calle De Pinos, a new revetment would have to occupy existing beach area, and sand would need to be imported to cover the structure, increasing cost. This approach could limit erosion and wave run‐up on homes in the near term. However, without increased maintenance of the revetment and fronting beach, long term sea‐level rise will eventually overload the revetment as the fronting beach is eroded and waves damage and overtop the revetment. To remedy this, subsequent beach nourishments will be required to maintain the beach fronting the revetment. Narrow sections of beach in front of Seadrift serve as an example of possible future conditions in Stinson Beach without continued beach nourishment. See Table 26. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 161
COMMUNITY ALTERNATIVES Stinson Beach An alternative adaptation measure to a rock revetment, the low profile wall and cobble berm may be preferable owing to less wave reflection, flatter slopes, and easier walking under eroded conditions if the beach drops. This estimate was modified from the Ocean Beach Master Plan, and the cost equals $55M per mile. Considering construction of just the cobble berm that acts as a last defense behind a dune (no wall), the cost equals $8M per mile. Mouth of Bolinas Lagoon. Lighthawk Aerial, 2015.
Table 26. Cost Estimate for Revetment Strategy at Stinson Beach Offshore structures Year Cost Estimate Note 2015 $ 24,000,000 Construct revetment Offshore breakwaters and artificial reefs are along Stinson Beach large coastal engineering structures that are 2045 $ 24,000,000 Rebuild/upgrade often used in conjunction with large beach revetment after 30‐ nourishment to retain sand. Offshore yr life breakwaters are effective at preventing erosion 2060 $ 11,000,000 Nourish 50 ft beach when beach drops because wave sheltering and diffraction reduces below trigger sand transport directly. They consist of fill in the 2075 $ 24,000,000 Rebuild/upgrade surf zone, typically quarry stone arranged in a revetment after 30‐ mound that penetrates the water surface. yr life 2090 $ 11,000,000 Nourish 50 ft beach These solutions were found to net negative cost after 30 years benefit in Southern Monterey Bay primarily due 2100 $ 29,000,000 raise homes in FEMA to high construction cost of $44 million per V‐zone kilometer.68 Offshore structures are currently Total net $ 80,000,000 Assumes 1% discount present rate prohibited by GFNMS regulations. value (2015) Offshore artificial reefs consist of fill in the surf *anytime $ 11,000,000 Emergency 50 ft zone that reduces the wave power reaching beach nourishment if shore and changes the pattern of sand extreme storm transport, thereby conceptually reducing erosion occurs; revetment repair not transport of sand from the beach. Offshore considered reefs are considered less effective than offshore NOTE: The table above does not include the area breakwaters because the wave sheltering is fronting Seadrift. reduced by the low crest height which allows wave overtopping.
68 Environmental Science Associates (ESA). Ocean Beach Master Plan. 2012. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 162
COMMUNITY ALTERNATIVES Stinson Beach Artificial reefs installed to act as submerged structures must meet flood protection breakwaters have received increased attention standards, and in many cases there is a need to in recent years as a means of shore stabilization elevate existing structures. Instead of and erosion control, primarily due to their low constructing new revetment/dunes along the aesthetic impact and enhanced water exchange Calles, homes could be raised to limit wave run‐ relative to traditional emergent breakwaters up and erosion damages to homes as the dune and the potential to enhance local surfing is allowed to erode during coastal storms. conditions.69 If constructed offshore from Applying the cost estimate of $250 per square Stinson Beach, an artificial reef could reduce foot, to lift Stinson homes in the wave impacts, but would not provide protection effective/preliminary FEMA V‐Zone (89 from permanent SLR. This strategy received low individual structures), the total cost would support from poll respondents (13%). equal roughly $29M. It is important to remember, however, that actual project costs Enhance living shorelines will vary depending on building condition, site Enhancing the living shoreline of Bolinas Lagoon characteristics and more. could help with temporary flood protection. However, shoreline vegetation alone does not One advantage of raising homes over building a protect against permanent inundation that revetment is it allows limited migration and would become an issue in the medium and persistence of a fronting beach in the near long‐term. This measure would likely be funded term. If additional measures such as beach and by a government grant or local assessment dune nourishment are not taken in the future, district, and received moderate support from the shoreline may continue to migrate past poll respondents (28%). homes and potentially damage roads, infrastructure and even the homes if the pilings A horizontal levee, with an impervious barrier are undermined. Still, this option could have on the landward side of the wetland, would advantages over armoring in the sense that the require a large right of way. Further back beach is allowed to evolve naturally. As considerations for horizontal levees are the backshore migration approaches property discussed in the Bolinas section, since it may be lines, dunes could be replenished to improve an option for the Gospel Flats area. This the aesthetics and habitat function at the strategy could be implemented through a local backshore, as well as limit future damages in assessment district, and received moderate areas that are eroded during storm events. support from poll respondents (33%). A quantitative trigger for dune/ beach Accommodate replenishment could be tied to estimated storm Elevate homes erosion mentioned above: Most parcels in Stinson Beach are already Dune width fronting a home shrinks below the developed, and many structures are vulnerable threshold distance (50 feet) to flooding in their current condition. New Beach/dune replenishment needed.
o Implications: temporary construction 69 Environmental Science Associates (ESA). Sea Level impact to people and ecology, cost of Rise Adaptation Alternatives for Marin County. 2015. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 163
COMMUNITY ALTERNATIVES Stinson Beach about $12M for 50‐ft wide dune and and Inverness, respectively) property owners 50‐ft beach along Stinson Beach. may be eligible for the Marin County Structure Elevation program, a FEMA Hazard Mitigation Table 27 shows an approximate cost schedule Grant Program. Many Stinson Beach for structure elevation. Initially, homes in the homeowners would like to be able to elevate FEMA V‐Zone would be lifted. As the beach their homes to meet FEMA standards to be safe narrows with SLR, beach nourishments will be from storm flooding and SLR without facing needed to maintain a buffer to the back beach onerous permitting requirements. Some poll as well as for recreation and ecological function. respondents indicated that they would want to The first nourishment occurs at 2060 and again make significant improvements to their home at 2090. The appropriate frequency of future when they elevate it, especially for older homes nourishments will likely be higher in reality. At in poor condition. This would extend the life of any time a major storm erosion event may structures in known hazardous areas. Residents require beach/dune nourishment. Beyond 2100, felt that elevating structures would be the first seaward row of homes will likely need consistent with the existing eclectic. community relocation as they may be severely exposed. character.
Table 27. Cost Estimate for Home Elevation Many Stinson Beach homes are located within Strategy at Stinson Beach70 the FEMA special flood hazard area, or 100‐ Year Cost Note year floodplain – in which case elevating the raise homes in FEMA home results in a lower flood insurance rate for 2015 $ 29,000,000 V‐zone the homeowner. Homes are required to meet Nourish 50 ft beach at FEMA standards if a proposed remodel or 2060 $ 11,000,000 Stinson when beach drops below trigger building project exceeds 50% of the property’s Nourish 50 ft beach market value. 2090 $ 11,000,000 after 30 years Total net Development in flood hazard areas is regulated present $ 41,000,000 through the Local Coastal Program and Title 23 value of the Marin County Code, administered by the Emergency 50‐ft beach nourishment if Department of Public Works. FEMA FIRM maps extreme storm erosion in 2015 that identify BFEs for structures in *anytime $ 11,000,000 occurs, dune coastal areas, incorporating coastal wave nourishment not considered (add $6M) hazards.
The cost of elevating homes and associated LCP Program Policy C‐EH‐8 – Minimum Floor utilities would likely be borne by individual Elevations in Flood Hazard Areas, would apply homeowners though within West Marin’s Flood when a new or substantially improved building Control Districts (Zones 5 and 10, Stinson Beach requires a coastal permit, based on actual site conditions. This policy requires subject building elevations to accommodate three feet of SLR above and in addition to the FEMA Base Flood 70 Estimates from ESA (2016) and actual costs may vary depending on building condition, site Elevation requirements, as described below. characteristics and other factors. This would apply to properties within Special PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 164
COMMUNITY ALTERNATIVES Stinson Beach Flood Hazard Areas (Areas VE, AO or AE as required eBas Flood Elevation in Special Flood indicated on the Potential Sea Level Rise Maps). Hazard Areas (VE, AO or AE as indicated on the In areas outside FEMA Special Flood Hazard Potential Sea Level Rise Maps) and 3 feet above Areas that are nevertheless subject to SLR, the 3 existing underlying topography in areas foot building elevation would also be required projected to be affected by SLR located outside to accommodate for future SLR (Base SLR of Special Flood Hazard Areas (SLR Exposure Elevation). Zones as indicated on the Potential Sea Level Rise Maps). Three feet approximately equals The FEMA Base Flood Elevation is an existing 100 cm, which is a midpoint projection of SLR regulatory requirement for elevating and flood‐ for the year 2100 based upon the National proofing of structures located within Special Research Council’s Sea‐Level Rise for the Coasts Flood Hazard Areas based upon high‐intensity of California, Oregon, and Washington: Past, storm floodwater elevations that have a Present, and Future, which provides state level projected 1% chance to occur in any given year guidance for SLR adaptation. (commonly referred to as the “100‐year flood”). Special Flood Hazards Area include lands that FEMA’s Flood Insurance Rate Maps identify would be impacted by floodwaters, and for Base Flood Elevations used for National Flood West Marin consist of “VE Zones” (subject to Insurance Program regulatory purposes. Base wave velocity) and “AE”/”AO” Zones (subject to Flood Elevations used to inform the “Potential rising waters without waves) (see Appendix E Sea Level Rise” maps are from FEMA’s 2015 for West Marin maps with FEMA Flood Zones). Preliminary Flood Insurance Rate Maps for Special Flood Hazard Areas are delineated and Marin County. Base Flood Elevations are determined based upon historical flooding trends and do not The “Potential Sea Level Rise” (Appendix H) account for future SLR which is currently not maps illustrate Special Flood Hazard Areas, as reflected in FEMA’s Flood Insurance Rate Maps. well as areas exposed to 3 feet of SLR outside of Special Flood Hazard Areas (SLR Exposure The intent of the proposed County policy is to Zone). Numeric values in parenthesis represent fully prepare for future SLR conditions by Base Flood Elevations based on an official requiring buildings to elevate 3 feet above the vertical datum related to current sea level
Figure 9. Section Diagram of Potential Building Elevation for 3 feet of SLR
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COMMUNITY ALTERNATIVES Stinson Beach
(referred to as NAVD88) plus three additional California Coastal Analysis and Mapping Project feet to account for future SLR. Required (CCAMP) Open Pacific Coast Study building elevations would be determined by actual measurements on a case by case basis The Federal Emergency Management Agency (FEMA) completed detailed coastal engineering taking into account a building’s existing analysis and mapping of the Pacific coast of elevation above sea level (NAVD88). In “VE” California in 2015. The analysis and mapping are Zones, measurements are made from the sea used to update the flood and wave data for Flood level (NAVD88) toe th lowest horizontal Insurance Rate Map (FIRM) panels along the structural member (e.g., floor joists). In the “A” open coast. Public workshops were held in zones, the measurement is to the lowest Stinson Beach and Marshall in Spring 2016. finished floor. In Special Flood Hazard Areas, To learn more about Open Pacific Coast Study, the values in goldenrod represent the visit: www.r9map.org/Pages/CCamp‐Main.aspx/ approximate difference in elevation between the required BFE + 3 feet and the average For more information about flood protection and underlying topography shown on County base FEMA standards, visit: maps. Where the proposed County policy would www.floodsmart.gov/floodsmart/ apply to lots located outside of Special Flood Hazard Areas (i.e., no Base Flood Elevation Data are not comprehensive, and this analysis is requirement), those values represent the height only intended to give a general sense of how distances based on 3 feet of SLR alone. Most if many homes would potentially need to elevate not all existing buildings are already elevated in order to meet FEMA and County above the underlying grade, so the actual requirements for flood safety. A group of height to which existing buildings would have to homes Stinson Beach were selected for this be raised to meet the proposed policy is less visualization based on the availability of data on than the values shown in goldenrod (for Finished Floor Elevations (FFE) gathered during example, if a remodel project is subject to a a 2012 survey. required elevation of 9 NAVD88 pursuant to the proposed policy, and the existing home is Building improvements and designs should take currently at elevation 4 NAVD88, the remodeled a holistic approach which includes connection home would be elevated 5 feet to satisfy the to the existing infrastructure/utilities. The proposed policy). Finally, the white numbers current use of individual OWTS may not be a show the elevation of the white topographic viable long‐term solution for treatment and lines. dispersal of wastewater with a significant rise of sea level which causes homeowners to raise their homes. Before looking at building solutions, there should be a review of the existing infrastructure: gas, septic, water, electric utilities, and roadways. Homeowners seeking to make improvements to their homes are advised to consult with SBCWD staff before going to the County Community Development Agency, since building improvements are
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COMMUNITY ALTERNATIVES Stinson Beach limited by infrastructure (Stinson Beach County and site‐specific analysis could be elevated or Water District, 2015). otherwise protected. The concept of elevating Shoreline Highway along Bolinas Lagoon received strong support from poll respondents (81%). Realigning Shoreline Highway received much less support (22%).
Local roads do not qualify for Federal Transportation Bill funding with Congestion Mitigation and Air Quality (CMAQ) & Surface Transportation Program (STP) funds and are considered off system roads. Panoramic
Highway and Shoreline Highway do qualify for Stinson during King Tide. Light Hawk Aerial. 2015. CMAQ & STP federal funding; however, these roads have difficulty rising to the top when Elevate Shoreline Highway, Calle del Arroyo, competing with roads in the urban areas for and private roads limited funds. For emergency repairs, a local General approaches for adapting roads to SLR road would need to be covered under disaster include identifying water level triggers for assistance where FEMA could provide management actions, and coordinating with the funding. FEMA typically funds less than the DPW and Caltrans. They are further described in 88.53 percent that the Federal Highway the “Transportation” section of this report. Administration (FHWA) does for on system Even if homes are elevated, access will remain a roads. Also, adding improvements for SLR challenge during temporary flooding and a would be considered an enhancement and not severe problem with permanent inundation eligible with today’s FEMA rules. during daily high tides. Low‐lying sections of The Stinson Beach Watershed Program Flood Shoreline Highway along the Bolinas Lagoon Study and Alternatives Assessment (DPW 2014) could flood temporarily in the near‐term determined that a preliminary estimated cost to scenario, and progressively larger sections will elevate Calle del Arroyo and provide required flood and eventually become permanently drainage features is on the order of $1.0 inundated in the long‐term. million72. Local roads in the Calles and Patios Elevating the entire stretch of Shoreline would need to be elevated as well, or Highway that borders Bolinas Lagoon would engineered to slope up and meet Calle del cost approximately $50 million71. While critical Arroyo. This strategy would be most effective if for accessing coastal Marin communities, this all homeowners in the Calles, Patios and project must compete with many others Seadrift neighborhoods agree to pursue this statewide for limited Caltrans funding. strategy in a coordinated approach. However, Alternatively, low‐lying road segments identified through the Vulnerability Assessment 72 Marin County Department of Public Works. Stinson Beach Watershed Program Flood Study and 71 Caltrans, Personal communication. 2015. Alternatives Assessment. 2014. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 167
COMMUNITY ALTERNATIVES Stinson Beach the idea of elevating local roads received low Easkoot Creek flooding support from poll respondents (23%). Residents In addition to coastal hazards, Stinson Beach is in the Calles and Patios currently pool resources subject to fluvial flooding hazards from Easkoot to pay for maintenance of private roads, and Creek. Three of the ten strategies in the Flood could choose to elevate the road level by Study and Alternatives Assessment (DPW 2014) adding additional fill material. An extension of included a flood bypass across the beach that this idea would be for homeowners in the would convey enough flow during a storm affected areas to form a local self‐funded event to reduce flooding of the Calles and assessment district to finance the elevation of restore or enhance wetland habitat that once Calle del Arroyo. Elevating Calle del Arroyo existed in the NPS south parking lot. received strong support from poll respondents (94%). The preferred strategy identified in the DPW study is consistent with SLR adaptation planning. The restoration of a lagoon wetland feature and overflow to the Pacific across the beach is particularly attractive as it reduces the need for structural modification of homes while provides ecological benefits in a sustainable manner, and is consistent with restoration of historic conditions, and may have a broader potential for funding. Structural adaptation to use pile foundations and raise homes above flood levels is also potentially viable, and complementary to other strategies as well as responsive to coastal flooding.
Calle del Arroyo at King Tide, 2015. Credit: Loomans Boardwalk entire neighborhoods Construction of boardwalk access to elevated The Stinson Beach Watershed Program Flood Study and Alternatives Assessment homes would alter the community character, Marin County Department of Public Works, 2014 but reduce the need to place large amounts of This study describes the flood conditions fill on roads to maintain access under existing along Easkoot Creek in the Stinson permanent SLR inundation scenarios. Some Beach community, and develops a series of examples of boardwalk‐type communities exist possible alternatives for mitigating these on Marin’s bayside in Sausalito, Corte Madera conditions. Besides the alleviation of flood and Larkspur, with elevated homes built on conditions, one of the primary concerns of poles over tidal salt marshes. This strategy the study is the preservation of the creek as allows structures to be built upon an a habitat for spawning steelhead salmon. Ten alternatives are evaluated for encroaching shoreline or in a vulnerable area, effectiveness in achieving these goals, as with a low risk of flooding and may be a good well as for cost, possible permitting and tool for retrofitting certain low‐lying other issues. The full study is available at: infrastructure. Elevated development has the www.marinwatersheds.org/stinson_beach.html advantage of avoiding SLR threats for a longer PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 168
COMMUNITY ALTERNATIVES Stinson Beach time.73 Vehicular access could be restricted to Develop community wastewater system portions of the community. This strategy could The Marshall Community Wastewater System is be funded by a local assessment district, and an example of this strategy, with a centralized received low support (5%). treatment facility serving a neighborhood on Tomales Bay. Such a strategy could be pursued Elevate entire neighborhoods on fill in the long‐term by SBCWD and/or a local Elevating entire neighborhoods on fill would assessment district. The idea received low require a great deal of agreement and support from poll respondents. (9%) coordination among homeowners. “Super‐ levees” in Japan have removed existing Retrofit potable water pipes and connections development, added fill to create a large Beginning 2014, SBCWD began a program to elevated surface, and provided attractive replace all water pipelines in the Calles and financing options for displaced homeowners to Patios. SBCWD received a grant in 2015 to live in the new development. However, this continue retrofitting potable water meter approach would be extremely costly if applied connections to resist corrosion from saltwater. to protecting existing homes, or would require an intensification of development that is highly Allow small‐scale desalination plants unlikely to occur in Marin’s coastal zone. SLR can contaminate groundwater supplies with Elevation of entire neighborhoods on fill would saltwater due to landward and upward 74 also have negative environmental impacts. movement of sea water in coastal aquifers . Community members suggested that allowing Update substandard septic systems small‐scale desalination plants could improve Onsite wastewater treatment systems (OWTS) resilience without negatively impacting the west of Shoreline Highway are vulnerable to environment. Desalination could also reduce saltwater intrusion and failure, leading to the demand on wells facing increased salinity. potential contamination of surface water. The National Parks Service beach (SBCWD) recommends that homeowners The National Parks Service beach that extends continue upgrading substandard septic systems southeast of Calle Del Pinos is backed by to meet current codes. This strategy received nourished dunes and parking/ amenities. The moderate support from poll respondents (34%). low lying area was once a lagoon, and is subject An option for the medium and long‐term is to to flooding from Easkoot Creek. Landward of abandon leachfields and convert septic tanks to the Parks land are non‐NPS public or private holding vessels that would need to be pumped County assets that will become at risk if the out periodically or connected to a community natural shoreline defense is compromised. wastewater system. This strategy received low Adaptation alternative cost schedules were not support from poll respondents (15%), though developed for the National Parks Service beach. the SBCWD supports this option. Elevating However, National Parks is unlikely to armor to septic systems in earthen mounds would reduce protect the backshore, but would instead the impact of saltwater intrusion.
74 US Geological Survey (USGS). Coastal Groundwater 73 Sustainable Planning and Urban Research. 2009. Systems. Accessed August 2016. Strategies for Managing Sea Level Rise. http://wh.er.usgs.gov/slr/coastalgroundwater.html PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 169
COMMUNITY ALTERNATIVES Stinson Beach facilitate the natural development of future these habitats to shift in response to SLR, and habitat (Caffrey and Beavers 2013). support continued public access and Coordination will be required between federal recreational opportunities. Otherwise, without and local jurisdictions in the future to ensure beach nourishment, the beach is predicted to effective risk management of Stinson assets erode almost completely by 2100.77 However, that exist inland of NPS land. this strategy would endanger and ultimately eliminate, existing homes, and received low NPS will likely employ a retreat strategy that support (2%). may include maintaining the dunes/beach and reduce parking and amenities as the shore Potential locations for adaptation strategies are migrates inland with sea‐level rise. In 2015, NPS shown in Map 15. Stinson Beach Adaptation replaced the beach park’s four septic drain Map. These strategies respond to vulnerabilities fields with a centralized drain field located based on the C‐SMART scenarios using the inland where groundwater and anticipated SLR CoSMOS model. It is important to keep in mind are not an issue. Septic systems at each Park that additional geomorphological changes, such facility will provide primary treatment and as beach erosion, are not reflected in the settlement of raw sewage, then each facility’s CoSMOs models and therefore community lift station will pump effluent to a centralized vulnerabilities may be more extreme. Future drain field system for disposal.75 community scale analysis could combine all relevant models to date including coastal and Relocate/ Managed Retreat riverine sea level rise and storm surge, and coastal erosion. Marin County could research potential costs and community interest in a long‐term buyout or property acquisition strategy if rising sea levels or storm impacts become imminent threats to homeowners. The County could also consider having a plan and specific proposals in place in case of a major storm/flood event that makes homeowners more likely to be interested in the buyout.76 Rolling easements and other land use policies could be used to limit further construction and investment in the most hazardous areas.
Removing seawalls, bulkheads, homes and other development that would limit the inland migration of the beach and marsh would allow
75 Stinson Beach County Water District. Onsite Wastewater Management Program Report. 2015. 76 Sustainable Planning and Urban Research (SPUR). 77 Environmental Science Associates (ESA). Sea Level Strategies for Managing Sea Level Rise. 2009. Rise Adaptation Alternatives for Marin County. 2015. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 170
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Maps 16‐19 Stinson Beach 1 Exposure Source: CoSMos
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COMMUNITY ALTERNATIVES Stinson Beach
Maps 20‐23 Stinson Beach 2 Exposure Source: CoSMos
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COMMUNITY ALTERNATIVES Stinson Beach
Maps 24‐27 Seadrift Exposure Source: CoSMos
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COMMUNITY ALTERNATIVES Bolinas 6.4) Bolinas
BOLINAS
PRIMARY VULNERABILITIES PRIORITY ACTIONS Storm and tidal impacts already occur Protect sewage treatment facility
Long‐term flooding will impact 98 buildings and Continue restoring wetlands in Bolinas Lagoon 1,620 people
Costs of long‐term impacts to exposed assets Accommodate threatened structures through will be $18 million elevation and retrofitting
Those impacted will include the crabbing and Elevate or reroute threatened roads tourism industries, Bolinas Public Utilities Elevate or relocate grocery store, emergency shelter, and library
Timeframe/Term Support Strategy NT=Near L=Low 0‐40% MT=Medium M=Moderate 41‐70% LT=Long S=Strong 71%+ NA=Not available PROTECT Maintain existing shoreline armoring at risk of causing more NT NA bluff and beach erosion Install new armoring along cliffs NT L Beach nourishment, especially along Brighton Beach NT L
ACCOMMODATE Elevate development, particularly in downtown area MT L Elevate or realign Wharf Rd and Olema‐Bolinas Rd at the NT‐MT L bridge over Pine Gulch Creek
RELOCATE/MANAGED RETREAT Research costs and interest of long‐term buyout or LT NA acquisition strategy Remove armoring at Brighton Beach, relocate structures LT M inland, allow inland migration of beach Require bluff top setbacks based on 50‐year timeframe and NT NA analysis Establish a bluff top erosion trigger for removal of structures NT NA
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COMMUNITY ALTERNATIVES Bolinas
Map 28. Bolinas Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES Bolinas
Map 29. Bolinas Adaptation Map
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COMMUNITY ALTERNATIVES Bolinas to be planned for, incorporating future SLR and storm surge scenarios. No action In the near‐term, downtown buildings could be affected by temporary storm flooding. More intense storms and wave action may hasten bluff erosion, jeopardizing bluff‐top homes. Beaches trapped by armoring and development could disappear. SLR and erosion could significantly impact sewage collection and water distribution systems in downtown and on the Little Mesa. Inundation of the Olema‐Bolinas Road or its bridges for extended Bolinas at King Tide. Lighthawk Aerial, 2015 periods of time could have drastic impacts for both emergency access and regular usage by BOLINAS: LONG‐TERM SLR IMPACTS residents and visitors. 1,620 98 buildings people Priority Actions Storm and tidal impacts 12 Accommodation of threatened structures and already occur businesses utilities through elevation and retrofitting could be a priority action. Shoreline Highway Property 18 million Owners and Wharf Road are of primary concern in the Residential, worth of BPUD near‐term, while Olema‐Bolinas Road and the crabbing, assets County bridge at Pine Creek Gulch may need to be tourism elevated or rerouted in the medium term. Bluff exposed Public top homes may need to be removed once the Works bluff edge erodes to endanger the structure The following sections provide additional and those living in it. information about strategies considered during the C‐SMART project. They are grouped The Sewage Treatment Facility will need to be according to general approach: protect, protected, and other critical facilities and accommodate, or retreat. community resources like the grocery store, emergency shelter and library will need to be Protect elevated or relocated in the medium‐term. Maintain seawalls and revetments The Post Office and Bolinas‐Stinson School will Homes built at the top of steep eroding cliffs in need to be elevated or relocated in the long‐ Bolinas will become increasingly jeopardized. term. Existing hazards are apparent from the rock revetment and seawalls presently built in front Wetland protection and enhancement efforts of homes and along bluff toes in the area. In (currently underway as part of the Bolinas the near‐term, property owners could Lagoon Restoration Project) will also have maintain existing revetments, seawalls, and flood protection benefits and should continue levees. However, if shoreline protective PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 177
COMMUNITY ALTERNATIVES Bolinas devices remain along the cliffs in Bolinas, the assessment district, and received moderate beach can be expected to erode and be support from poll respondents (40%). inundated by SLR and eventually disappear, affecting recreational opportunities and Inside the lagoon mouth along Wharf Road, ecological function. If further armoring nature‐based strategies for managing SLR may measures are taken along the cliffs in Bolinas, be difficult to implement. This would require the supply of sediment from the cliffs to the an evaluation of how the lagoon mouth is beach will be further reduced, likely likely to evolve, how it interacts with the accelerating beach loss. Reduced beach widths lagoon and the cliffs and what opportunities or result in increased loadings and structural constraints this might create. The lagoon requirements on seawalls, and mouth configuration and slough channel along maintenance/improvement costs may Wharf Road are hurdles to implementing an outweigh the values of the properties.78 This adaptation measure such as a horizontal levee. strategy received moderate support from poll The slough channel would need to be respondents (40%). realigned, limiting boat access from Wharf Road homes. Place sand on beaches Beach nourishment could provide short‐term Support Bolinas Lagoon Restoration efforts benefits of maintaining a beach for ecology Many of the recommendations of the Bolinas and recreation services, while reducing wave Lagoon Ecosystem Restoration Project focus run‐up on seawalls and bluffs along the south‐ on removing impediments to the exchange of facing shores of Bolinas west of the Bolinas flow and sediment from the lagoon and its Lagoon mouth. For example, beach watershed and enhancing wetland habitats nourishment could be used to maintain using natural processes to allow the lagoon to Brighton Beach and the protection it provides move inland where possible, and to preserve to oceanfront homes. the adaptive capacity of the lagoon. Other key recommendations for restoration include: In the long term, beach nourishment will Remediate watershed disturbances; Restore become more expensive as sand sources are Kent Island as a dynamic flood shoal island; limited and the amount of sand required Restore eelgrass, if suitable habitat is available increases with sea‐level rise. The presence of in Bolinas Lagoon; Investigate managing tidal seawalls alongn the wester ‐facing stretch near exchange of Seadrift Lagoon to promote tidal the Brighton Avenue beach access has circulation; and actively plan and manage for contributed to accelerated erosion. As in SLR (see next page). The County and Caltrans Stinson Beach, this strategy would require could plan for roadway and culvert continued sand placement over time, and is improvements, including possible elevation of not a sustainable long‐term solution. Beach roadways to reduce impacts to the lagoon and nourishment could be financed through a local improve habitat connectivity. 79
78 Environmental Science Associates (ESA). Sea Level Rise Adaptation Alternatives for Marin 79 Gulf of the Farallones National Marine Sanctuary County. 2015. (GFNMS). Bolinas Lagoon Ecosystem Restoration PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 178
COMMUNITY ALTERNATIVES Bolinas The San Francisco Bay Joint Venture sponsored incorporated into the restoration a scientific panel of experts to evaluate the project. Bolinas Lagoon Restoration Project. Marin Armoring is a liability for lagoon County Parks hired one of the participants, Dr. resilience and adaptation to rising sea Peter Baye, to summarize the meeting. The level. following are the general recommendations which emerged from this group80: Finally, the DRG made the following project and area specific recommendations: The important new perspectives from the There was consensus that maintaining meeting are as follows: the channelization of Pine Gulch Creek Accelerated SLR replaces previous was detrimental to the long‐term concerns over the loss of tidal prism as evolution of the lagoon. the overriding impact to the lagoon’s The Pine Gulch Creek delta and its ecosystem structure and function. floodplain are essential for the future In the context of SLR, sediment can be rising lagoon edges and may provide an important asset to the lagoon. area for habitat to shift and evolve as Accommodation room for the lagoon sea levels rise. to migrate inland as sea level rises is There was no consensus about necessary for the long‐term health and whether the Pine Gulch Creek delta is stability of Bolinas Lagoon. a liability to the lagoon’s resilience to Bolinas Lagoon’s barrier spit and tidal SLR. inlet are essential components of its The Lewis and Wilkins Gulches (the evolution and response to SLR. area known as the “Y”) is another highly important zone for lagoon The DRG also made the following general accommodation space, tidal marsh and recommendations: floodplain migration, and sediment management opportunities in Revised conceptual models of Bolinas response to SLR. Lagoon should be developed to guide The drainages of the eastern shore of ecosystem planning, project Bolinas Lagoon are also important to prioritization, public education, and accommodate the lagoon’s inland project re‐evaluation. migration. Planning for various SLR and storm The DRG noted that Marin County and surge scenarios should be the GGNRA evaluated potential alternatives to address flooding along Easkoot Creek through a separate process. Project. Recommendations for Restoration and Management. August 2008. 80 Conclusions and Recommendations of the Bolinas Lagoon Restoration Project Design Review Group (DRG). March 2014
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COMMUNITY ALTERNATIVES Bolinas Accommodate need to be upgraded to convey higher peak Elevate homes flows. This requires either larger culverts or Many structures in Bolinas, particularly in the raising the roadway on piles to allow historic downtown area, are vulnerable to conveyance of storm runoff. In the context of flooding in their current condition. The typical sea‐level rise, a piled causeway design could cost of elevating a structure ranges from $140 provide further ecological benefit by allowing per square foot in the flood zone to $230 in the migration of habitat under the roadway and wave zone.81 The cost of elevating homes and upland. associated utilities would be borne by individual Relocate/ Managed Retreat homeowners. Buildings on Wharf Road could be further elevated on their existing pier Marin County could research potential costs foundations. By including proper stormwater and community interest in a long‐term buyout features such as flap gates, an elevated Wharf or property acquisition strategy if rising sea Road could also protect the low lying levels or storm impacts become imminent neighborhood behind it. See the Stinson Beach threats to homeowners. The County could also section for a discussion of FEMA requirements consider having a plan and specific proposals in and potential impacts of home elevation. This place in case of a major storm/flood event that strategy received moderate support from poll makes homeowners more likely to be 82 respondents (40%). interested in a buyout. Rolling easements and other land use policies could be used to limit Elevate roads further construction and investment in the General approaches for adapting roads to SLR most hazardous areas. include identifying water level triggers for To maintain Brighton Beach, existing armoring management actions, and coordinating with could be removed and development removed DPW and Caltrans. They are further described in or relocated. Services such as utilities and roads the “Transportation” section of this report. could be realigned in an orderly manner over Elevation (or realignment) could be considered time to limit costs and avoid catastrophic failure for County‐owned roads, including Wharf Road and hazardous conditions. The idea of removing and Olema‐Bolinas Road at the bridge over Pine shoreline protective devices that limit the Gulch Creek. However, these projects must inward migration of beaches received moderate compete with many others for limited funds. support from poll respondents (60%). This strategy received moderate support from Blufftop development setbacks poll respondents (40%). Under the County’s proposed LCP standards, Shoreline Hwy along Bolinas Lagoon will be new development must be set back from the impacted by SLR. If anticipated precipitation bluff edge a sufficient distance to ensure its patterns change with climate change to more stability and structural integrity for a minimum flashy storms, culverts on many streams will of 100
82 81 Environmental Science Associates (ESA). Sea Level Center for Ocean Solutions, Natural Capital Project. Rise Adaptation Alternatives for Marin County. 2015. Coastal Adaptation Policy Assessment Marin County. 2016. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 180
COMMUNITY ALTERNATIVES Bolinas years and to eliminate the need for shoreline affected by tolerance for risk such as loss of protective devices. Coastal hazards analyses for property or infrastructure. individual sites must include a slope stability analysis that considers historical bluff retreat Setbacks for development and planning in data as well as accelerated erosion due to SLR.83 Bolinas (and elsewhere) should use a minimum 100 year analysis timeframe and apply SLR‐ For informational purposes and to guide the accelerated erosion rates with a factor of safety identification of potential planning triggers for (1‐2 standard deviations of the erosion rate, removal of existing structures in hazardous with an additional landslide offset where areas, ESA produced bluff erosion hazard zones applicable). Site‐specific evaluation of erosion for both projected historic rates and amplified rates is required; the average values in Table rates from SLR. These rates and buffers are could be considered as a minimum. summarized and compared against other suggested values in Table below. Setbacks are New Construction: Setback that considers long specified for each planning timeframe; ESA term erosion plus accelerated erosion due to setbacks are referenced to 2010 conditions. sea‐level rise (sea‐level rise rate to be Corresponding erosion rates are reported for determined by County) plus factor of safety that historic and 2100 accelerated conditions from includes erosion variability and/or landslides or the 2009 Pacific Institute study84 that considers block failure widths where applicable. For the high SLR. example of a new structure with a structure life The ESA setbacks for each reach were of 50 years, this setback could be 225 feet (50 determined using the average erosion rate plus year offset from average erosion plus 2 StDev). one or two standard deviations within each Existing Structures (planning trigger): The reach. It is helpful to think about the average County could consider identifying a minimum and standard deviations of erosion rates as the distance between existing structures and bluff likelihood of exceedance; the average plus two edge, at which point planning for structure standard deviations describes a setback that is removal would be initiated. Local studies are not likely to be exceeded (around 2% of required to assess local geologic conditions and locations/ times), whereas adding one standard characteristic block failure (or landslide) widths. deviation indicates exceedance may occur Generally, a planning timeframe could be around 15% of the locations/ times, and use of established that determines a distance set by the average (no additional standard deviation) long term plus accelerated erosion and a factor indicates the distance could be exceeded at of safety. For example, assume it takes 5 years about 50% of the locations/ times. Thus, there for permitting/planning to remove or relocate a is uncertainty in all estimates of future erosion structure: using a near term retreat rate of 3.7 distances, and selection of the distances is feet per year (average plus 2 StDev) and a 45 foot block failure factor, the trigger distance (from structure to bluff edge) to start planning 83 Marin County Community Development Agency. would be 64 feet (3.7 ft/yr times 5 years = 18.5 Draft Local Coastal Program, Environmental Hazards Chapter LUPA. April 2016 feet, plus 45 feet). 84 Pacific Institute. The Impacts of Sea Level Rise on the California Coast. 2009. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 181
COMMUNITY ALTERNATIVES Bolinas
Table 28. Bolinas Open Coast Bluff Erosion Setbacks Considering Various Guidelines
Erosion Buffers and Rates 40 yrs 50 yrs 100 yrs 150 yrs Erosion FOS Equivalent (2050) (2060) (2110) (2160) Rate (R) (+X StDev) Rate (R+FOS) Coastal Commission Interpretive Guidelines for Marin County: Minimum setback for new (120 ft) 150 ft (300 ft) (450 ft) 3 ft/yr ‐ ‐ construction: Environmental Hazards Element of the Marin Countywide Plan: Little Mesa to Duxbury 80 ft (100 (200 ft) (300 ft) 2 ft/yr ‐ ‐ Reef ft) Duxbury Reef to Point 120 ft (150 (300 ft) (450 ft) 3 ft/yr ‐ ‐ Reyes ft) Bolinas Gridded Mesa Plan (1985): Overlook to Duxbury Point ‐ 145 ft 245 ft 345 ft 2 ft/yr ‐ ‐ (+45 ft) Duxbury Point to Poplar ‐ 170 ft 295 ft 415 ft 2.5 ft/yr ‐ ‐ Road (+45 ft) ESA ‐ considering only USGS historic (1929‐1998) erosion rates: Little Mesa to Duxbury 116 ft 145 ft 290 ft 435 ft 1.5 ft/yr 1.4 ft/yr 2.9 ft/yr Reef (+1 StDev) Duxbury Point to Poplar 80 ft 100 ft 200 ft 300 ft 1.3 ft/yr 0.7 ft/yr 2 ft/yr Road (+1 StDev) Little Mesa to Duxbury 172 ft 215 ft 430 ft 645 ft 1.5 ft/yr 2.8 ft/yr 4.3 ft/yr Reef (+2 StDev) Duxbury Point to Poplar 108 ft 135 ft 270 ft 405 ft 1.3 ft/yr 1.4 ft/yr 2.7 ft/yr Road (+2 StDev) ESA ‐ considering accelerated erosion rates due to SLR (PWA 2009): Little Mesa to Duxbury 212 ft 160 ft 475 ft* N/A 1.5‐4.3 1.1‐3.1 2.6‐7.3 ft/yr** Reef (+1 StDev) ft/yr** ft/yr** Duxbury Point to Poplar 82 ft 104 ft 228 ft* N/A 1.3‐1.5 0.7‐0.9 2.0‐2.6 ft/yr** Road (+1 StDev) ft/yr** ft/yr** Little Mesa to Duxbury 171 ft 225 ft 671 ft* N/A 1.5‐4.3 2.2‐6.2 3.7‐10.5 Reef (+2 StDev) ft/yr** ft/yr** ft/yr** Duxbury Point to Poplar 110 ft 140 ft 309 ft* N/A 1.3‐1.5 1.4‐1.8 2.7‐3.3 ft/yr** Road (+2 StDev) ft/yr** ft/yr** *Extrapolated to 2110 using 2100 rate **Range: historic to SLR‐amplified rate at 2100
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5) COMMUNITY ALTERNATIVES Bolinas
Maps 30‐33 Bolinas Exposure Source: Coastal Storm Modeling System (CoSMos) PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 183
COMMUNITY ALTERNATIVES Inverness Inverness
PRIMARY VULNERABILITIES PRIORITY ACTIONS Storm and tidal flooding already occur Accommodate existing development by elevating and retrofitting Long‐term flooding will impact 1,130 buildings, 10 businesses, and 1,304 people Protect assets with nature‐based strategies
Costs of long‐term impacts to exposed assets will be $11 million
Others impacted will include the residential tourism industry, DPW, Inverness PUD, NMWD, and property owners
Timeframe/Term L=Low 0‐40% Strategy NT=Near M=Moderate 41‐70% MT=Medium S=Strong 71%+ LT=Long NA=Not available PROTECT Restore/enhance wetlands along Tomales Bay shoreline NT‐MT S Create an oyster reef in Tomales Bay NT‐MT L Construct horizontal levees in Tomales Bay MT L
ACCOMMODATE Elevate buildings and utilities MT M Flood proof existing buildings NT M Elevate Sir Francis Drake Blvd on a levee to prevent flooding and MT M protect existing water pipeline under road Elevate Shoreline Hwy MT M Update old septic systems prior to saltwater intrusion NT S Develop a community wastewater system MT M Create offshore boat moorings as marinas become inundated NT M
RELOCATE/MANAGED RETREAT Relocate coastal access points MT M Remove shoreline protective devices that limit inland migration MT M of shoreline habitats Remove development that limits inland migration (phased MT‐LT M based on triggers) Realign Sir Francis Drake Blvd. MT M
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COMMUNITY ALTERNATIVES Inverness
Map 34. Inverness Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES Inverness
Map 35. Inverness Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES Inverness a
Map 36. Inverness Adaptation Map
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COMMUNITY ALTERNATIVES Inverness 6.5) Inverness Wetland restoration and oyster reefs in the No action near‐term and potentially horizontal levee in the medium‐term are potential nature‐based The main access road, Sir Francis Drake Blvd., solutions. could experience frequent flooding and erosion, impeding access for residents, tourists, and Protect emergency responders. Erosion of Sir Francis Drake Blvd. could lead to damage and Restore/enhance wetlands along Tomales Bay disruption to drinking water distribution Restoring and enhancing living shorelines along pipelines serving Inverness Park. Several Tomales Bay offers near‐ to medium‐term shoreline and pier developments are vulnerable protection against temporary flooding, storm to rising waters and storm impacts. surge, and wave impacts. Habitat restoration techniques can be used to manage the shoreline, reduce coastal erosion, and maintain INVERNESS: LONG‐TERM SLR IMPACTS coastal processes. Such techniques enhance 1,130 buildings 1,304 people habitat values and increase connectivity of wetlands and deeper intertidal and subtidal Storm and tidal impacts 10 businesses lands, while providing some amount of already occur shoreline protection. Wetland creation could be Marin DPW effective in limiting erosion of otherwise 11 million Inverness exposed road embankments (ESA 2015). worth of Residential PUD assets Tourism NMWD Wetland creation involves placing fill in a exposed Property manner that enhances wetlands but may result Owners in a conversion of wetlands type from subtidal to mudflats or mudflats to tidal marsh. This Priority Actions strategy may not be permitted by GFNMS at this time. Another approach to creating A possible adaptation approach is to wetlands, usually preferred by permitting accommodate development with elevation and agencies, is to excavate soils from existing retrofits, and protect assets with nature‐based vacant uplands down to the appropriate grades strategies in the near‐ to‐medium term, while to allow for tidal or seasonal wetlands to form planning for other adaptation measures in the (DPW 2015). Wetlands projects are complex to long‐term. Homes and other structures design and permit since they must currently over water could be raised higher, and accommodate habitat and flood protection portions of roadways like Sir Francis Drake and needs. This strategy may involve a moderate to Shoreline Highway that are critical roads for high cost, and will not prevent inundation of emergency access could also be raised to low‐lying areas unless it is backed by a flood maintain access at higher water levels. In protection levee (CDA, DPW 2015). The addition to protecting properties vulnerable in effectiveness of wetland solutions will diminish the near‐term, converting affected segments of with higher levels of SLR unless grades are Sir Francis Drake Boulevard into a levee could raised as the wave dampening ability of tidal protect water pipeline beneath the road. wetlands diminishes with increased water
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COMMUNITY ALTERNATIVES Inverness depth (DPW 2015). Wetland restoration could attenuation across a tidal marsh requires a be funded by a local assessment district or minimum width of several hundred feet. Costs government grant, and received strong support for importing and placing fill vary significantly from poll respondents (100%). depending on the location and quality of the borrow source of sediment. Generally, the Create oyster reef in Tomales Bay estimated cost is medium‐to‐high relative to Another component of living shorelines, oyster other strategies. reefs can mitigate erosion and flood hazards where waves are small and weak enough to be In the medium‐term, horizontal levees may dissipated by the limited reef structures. Oyster serve as protection against SLR where land use, reefs consist of a hard oyster settlement space and habitat allow. All the marshes in substrate placed onto a supporting structure, Inverness are vulnerable because they are such as wooden pallets or a PVC base, with confined by the roadway. As sea levels rise, eelgrass beds later planted between the oyster much of the low salt marsh will be converted to structures. Scientists and engineers are studying mud and sand flats. Because the Inverness pilot projects near San Rafael through the San shore is steep, marsh transition areas shrink Francisco Bay Living Shorelines project to with elevating sea levels. Areas near Martinelli monitor biological recruitment, as well as Park and Dana Marsh may be good candidates sedimentation rates behind the oyster reefs to for assessing the feasibility of a horizontal evaluate their erosion protection efficacy (ESA levee. 2015). An oyster reef could be funded by a local assessment district or government grant, and To the extent that other natural habitats in received moderate support from poll Tomales Bay can be protected, restored, or respondents (33%). enhanced, Marin County may bolster the benefits provided by a horizontal levee project Construct horizontal levee along Tomales Bay and mitigate some of the technical and financial “Horizontal levees” are earthen levees with risks associated with the project.85 The Bay itself flatter side slopes towards the water’s edge is zoned as Open Area, though more detailed that use the wave attenuation benefits of analysis would be required to understand if a expanded wetlands in front of the levee. horizontal levee would impose upon the Horizontal levee projects combine flood surrounding residentially‐zoned parcels. protection benefits with habitat benefits, and are frequently discussed by bay scientists and environmental engineers as a viable approach to multi‐objective flood protection. However, there are a number of challenges and uncertainties associated with horizontal levees. In addition to permitting challenges associated with any fill of Tomales Bay, there are also uncertainties associated with how much flood protection, water quality, and habitat benefits 85 Center for Ocean Solutions, Natural Capital Project. horizontal levees provide. Significant wave Coastal Adaptation Policy Assessment Marin County. 2016. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 189
COMMUNITY ALTERNATIVES Inverness Accommodate and costs vary significantly based on the type Elevate buildings and utilities and location of fill material. This measure could Cost estimates for structural elevation are be implemented by the County and/or local around $140/sf for structures in the flood zone, service providers, and received moderate and $230/sf for structures in the wave zone. support from poll respondents (67%). Continued livability within elevated structures Elevate Shoreline Highway would also require elevation of associated This strategy would be implemented by utilities and roads, which could increase the Caltrans, and received moderate support from overall cost significantly. This strategy would be poll respondents (67%). See the East Shore implemented by property owners, and received section of this report for further discussion of moderate support from poll respondents (67%). options for Shoreline Highway. One respondent commented that they only support this strategy if financial assistance is Update old septic systems provided to homeowners. Saltwater intrusion due to rising sea levels can lead to septic failure, especially for older Flood proof buildings systems. Updating old septic systems would be This strategy would be implemented by implemented by property owners, and received property owners, and received moderate strong support from poll respondents (83%). support from poll respondents (50%). Across Tomales Bay in East Shore, the Marshall Permit houseboats Community Wastewater system is a model for Houseboats are not recommended as an coordinated effort to protect water quality and adaptation strategy due to strong wind and share costs between government agencies and wave action during storms, and lack of property owners. houseboat marinas and services. This strategy Develop community wastewater system received no support from poll respondents. This strategy would be implemented by local Elevate Sir Francis Drake Boulevard service provider or a local assessment district, Like other SLR road adaptation efforts, and received moderate support from poll approaches include identifying water level respondents (50%). The recently installed triggers for management actions, and Marshall Community Wastewater System coordinating with DPW and Caltrans. They are relocated several independent leach fields to a further described in the “Transportation” shared leach field east of Shoreline Highway section of this report. due to water quality violations. However, individual septic tanks and the pipes connecting Sir Francis Drake Boulevard could be elevated these homes to the community system will still on an earthen levee to protect access to the be vulnerable to corrosion in the long‐term. communities, utilities under the roads, and assets on the landward side of the road. Conversion of affected segments of Sir Francis Drake Blvd. to levee would also protect the NMWD water pipeline in Inverness Park and downtown. Levees require a large right of way,
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COMMUNITY ALTERNATIVES Inverness Create boat moorings discussion above. Relocation of buildings could Once marinas become unusable due to be phased according to identified triggers, and inundation, the State, County or boat owners would be implemented by property owners, could create offshore moorings. This measure and received moderate support from poll received moderate support from poll respondents (50%). Realignment of affected respondents (50%). Currently the Marina at the segments of Sir Francis Drake Blvd. along Tomales Bay Resort is often silted in, so would Tomales Bay would be implemented by the potentially benefit from SLR. In 2014, GFNMS County in collaboration with affected and State Lands Commission commenced the landowners, and received moderate support Tomales Bay Mooring Program to permit and from poll respondents (50%). lease moorings in Tomales Bay. Due to the program’s costs and requirements, it is Marin County could research potential costs expected that a year from now there will be and community interest in a long‐term buyout even fewer moorings on the Bay. or property acquisition strategy if rising sea levels or storm impacts become imminent Ferry on Tomales Bay threats to homeowners. The County could also There is some interest among residents in consider having a plan and specific proposals in bringing back the ferry from Point Reyes Station place in case of a major storm/flood event that to Inverness. makes homeowners more likely to be interested in the buyout.86 Easements and other Relocate/ Managed Retreat land use policies could be used to limit further In the long‐term, realignment of development construction and investment in the most farther landward within a managed retreat hazardous areas. These easements would move context is an option that would maintain no net (or “roll”) with bluff and shore erosion. loss of ecological function of coastal assets, limit costs and increase resilience. For example, the cost associated with structural modification Potential locations of adaptation strategies are is reduced if the structure is moved inland, shown in Error! Reference source not found.. though moving costs would need to be considered to fully determine net savings/losses.
Relocation of coastal access points would be implemented by the County, and received moderate support from poll respondents (67%). Removing shoreline protective devices that limit inland migration of beaches and wetlands would be implemented by property owners, and received moderate support from poll respondents (67%). Removal of development that limits inland migration of beaches and marshes is noted in the horizontal levee 86 Natural Capital Project, Center for Ocean Solutions. Coastal Adaptation Policy Assessment. 2016.
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COMMUNITY ALTERNATIVES Inverness Green Strategy: Offshore projects, a wooden pallet has been used to support oyster shell or other substrates, Bio-beds in Tomales Bay while this project uses a PVC base structure. Oyster bag mounds were then placed on the base as an oyster recruitment structure (other small pilot cases use inexpensive modular cement structures).
Experimental treatment plots of 32 by 10 meters were constructed parallel to shore, SF Bay Living Shorelines project. Kiriakopolos, 2014. approximately 250 m from the shore, with eelgrass beds later planted between the Benefits: Public health, Recreation, Tourism, oyster structures using shoot transplants as Carbon sequestration, Water quality. well as buoy‐deployed seeding. In addition Costs: Unknown to biological recruitment monitoring by Living Shorelines projects use habitat others, ESA is actively monitoring the restoration techniques to manage the sedimentation behind these oyster reefs to shoreline, reduce coastal erosion, and evaluate the erosion protection efficacy maintain coastal processes while protecting, (ESA 2015). restoring, and creating natural habitat for Oyster reefs are considered potential aquatic flora and fauna. Such techniques erosion and flood hazard mitigation enhance habitat values and increase measures where waves are small and weak connectivity of wetlandsd an deeper intertidal enough to be dissipated by the limited reef and subtidal lands, while providing some structures. Hence, this measure is amount of shoreline protection. potentially viable only in estuarine areas ESA is currently monitoring the San Francisco such as Tomales Bay and Bolinas Lagoon Bay Living Shorelines project87. This pilot (ESA 2015). project is investigating the ideal configurations and size scales of oyster reefs and eelgrass beds for habitat enhancement. Oyster and eelgrass reefs were constructed at two sites in San Francisco Bay in 2012 (China Camp State Park in San Rafael, and near Eden Landing in Hayward).
Oyster elements all consist of a hard oyster settlement substrate of some type placed onto a supporting structure. In past Oyster Bag mounds. M. Latta, 2012.
87 San Francisco Bay Living Shorelines Project. http://www.sfbaylivingshorelines.org/sf_shorelines_about.html PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 192
COMMUNITY ALTERNATIVES Inverness
Map 37. Bathymetry of Tomales Bay Source: ESA (2015), DEM source: USGS (Foxgrover & Barnard 2012)
Oyster reefs may not be a viable solution to erosion and flooding hazards in deeper bay areas. However, relatively shallow areas may be suitable for oyster reefs as a nature‐ based erosion mitigation alternative to shoreline revetment. In the absence of detailed bathymetric data in Tomales Bay, the DEM utilized in e th OCOF hazard mapping study was used to identify potential areas where relatively shallow slopes exist near human development. These areas mostly occur along the Inverness shoreline and Millerton. A detailed feasibility analysis could be conducted to fully understand the possible Eelgrass in Tomales Bay. Kinyon 2009. opportunities and constrains to using oyster reefs in Tomales Bay.
Also studied in the San Francisco Bay Living Shorelines study, eelgrass beds are another possible means of wave energy attenuation. Various studies have examined wave attenuation from sea grasses in low‐energy environments (Bradley & Houser 2009; Fonseca & Calahan 1992; Wu & Cox 2015). Similar to oyster reefs, seagrass beds require shallow water among other factors to flourish, and are thus limited in applicability to wide shallow areas in Tomales Bay., including the Walker Creek Delta area.
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COMMUNITY ALTERNATIVES Inverness
Maps 38‐50 Inverness Exposure Source: Coastal Storm Modeling System (CoSMos)
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COMMUNITY ALTERNATIVES East Shore 6.6) East Shore East Shore
PRIMARY VULNERABILITIES PRIORITY ACTIONS Storm and tidal impacts already occur Elevate and retrofit existing development Long‐term flooding will impact 163 buildings and 10 businesses Protect assets with nature‐based strategies
The cost of impacts to exposed assets will be $14 million
Others impacted will be the residential tourism and aquaculture industries, Caltrans, and property owners
Timeframe/Term L=Low 0‐40% Strategy NT=Near M=Moderate 41‐70% MT=Medium S=Strong 71%+ LT=Long NA=Not available PROTECT Restore/enhance wetlands along Tomales Bay NT‐MT S Create an oyster reef in Tomales Bay NT‐MT M Construct horizontal levee in Tomales Bay MT L Armor segments of Shoreline Hwy NT S
ACCOMMODATE Redesign/relocate Walker Creek Coastal Access Point NT S Elevate Shoreline Hwy NT S Elevate existing buildings and utilities NT‐MT S Flood proof existing buildings NT M Create offshore boat moorings NT NA Develop a community wastewater system MT NA
RELOCATE/MANAGED RETREAT Research costs and interest of long‐term buyout or acquisition LT S strategy Relocate coastal access points NT M Realign Shoreline Hwy MT M
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COMMUNITY ALTERNATIVES East Shore
Map 51. East Shore Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES East Shore
Map 52. Inverness Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES East Shore
Map 53. East Shore Adaptation Map (South)
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COMMUNITY ALTERNATIVES East Shore No action Access to, from and along Shoreline Highway Marshall’s community wastewater system could be compromised by temporary flooding in Developed in 2014, the Marshall Community the near‐ to medium‐term and permanently in Wastewater System is an example of an the long‐term. The area near Walker Creek effective community‐level strategy to protect often floods during storms and high tides. water quality and adapt vulnerable individual Waterfront housing, which acts as a first line of onsite wastewater treatment systems. defense for Shoreline Highway, will face Community members in Marshall petitioned increasing challenges from rising waters. Homes Marin County to create an Onsite Wastewater on piers may see reduced ability to perform Treatment Zone, which was then approved maintenance or repair, as low tides also through a local election. Because Marshall is become higher and in some cases do not located near an impaired body of water, expose mudflats along the shore. Utilities such Tomales Bay, a Tier 3 system88 was developed as septic, water, and electrical systems may see and installed. The system serves over 90% of increasing damage from flooding and saltwater the properties in central Marshall (a 3+‐mile intrusion. Tidal marshes may convert to stretch) and over 50% of all the 90 homes and mudflats or open water, and beaches may businesses in Marshall. disappear where development or topography prevents inland migration. Marin County owns the septic system from the point of connection at each property up to and EAST SHORE: LONG‐TERM SLR IMPACTS including the treatment equipment and the 15‐ acre upland leach field which it purchased 163 buildings specifically for that purpose. Marin County 10 administers the program and outsources Storm and tidal impacts businesses operations and maintenance to a service already occur provider. Property owners pay the annual 14 million Residential Caltrans maintenance fee with their property taxes. worth of Tourism Property assets exposed Aquaculture Owners
88 Tier 3 refers to “Advanced Protection Management Programs for Impaired Areas”. State Water Resources Control Board. Onsite Wastewater Treatment Systems Policy. 2012. www.waterboards.ca.gov/water_issues/programs/o wts/docs/owts_policy.pdf. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 199
COMMUNITY ALTERNATIVES East Shore lands, while providing some amount of shoreline protection. While design and permitting could be complex, wetland creation could be effective in limiting erosion of otherwise exposed road embankments (ESA 2015).
This strategy may involve a moderate to high cost, and will not prevent inundation of low‐ lying areas unless it is backed by a flood protection levee (CDA, DPW 2015). The effectiveness of wetland solutions will diminish East Shore homes on pilings over Tomales Bay. Credit: Marin County CDA with higher levels of SLR unless grades are raised as the wave dampening ability of tidal wetlands diminishes with increased water
depth (DPW 2015). This measure could be funded by a local assessment district or Priority Actions government grant, and received strong support The recommended adaptation approach is to from poll respondents (100%). accommodate development with elevation and retrofits, and protect assets with nature‐based Create oyster reef in Tomales Bay strategies in the near‐ to‐medium term, while Oyster reefs may be feasible in limited areas of considering additional options in the long‐term. Tomales Bay, and are not likely to be effective Homes and other structures currently over at reducing wave impacts right off the town of water could be raised higher, and portions of Marshall since water is relatively deep just Shoreline Highway could also be raised to offshore. However, residents expressed support maintain access at higher water levels. Wetland for adaptation approaches that look holistically restoration and oyster reefs in the near‐term at all of Tomales Bay and the Marin coast. This and potentially horizontal levee in the medium‐ measure could be funded by a local assessment term are potential nature‐based solutions. district or government grant, and received moderate support from poll respondents (60%). Protect Restore/ enhance wetlands along Tomales Bay Construct horizontal levee along Tomales Bay Restoring and enhancing living shorelines along In the medium‐term, horizontal levees may Tomales Bay offers near‐ to medium‐term serve as protection against SLR where land use, protection against temporary flooding, storm space and habitat allow. To the extent that surge, and wave impacts. Habitat restoration other natural habitats in the bay can be techniques can be used to manage the protected, restored, or enhanced, Marin County shoreline, reduce coastal erosion, and maintain can bolster the benefits provided by a coastal processes. Such techniques enhance horizontal levee project and mitigate some of habitat values and increase connectivity of wetlands and deeper intertidal and subtidal
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COMMUNITY ALTERNATIVES East Shore the technical and financial risks associated with Improve coastal access facility or trail to the project.89 account for sea level rise The Walker Creek Access Point could be Fluvial inputs associated with two watersheds, relocated or redesigned to be resilient to SLR. Walker Creek and Lagunitas Creek, are large This strategy could be implemented by the enough to create local estuarine gradients County and State, and received strong support within the Bay. The largest tidal marshes are from poll respondents (100%). associated with the alluvial deltas of these creeks.90 These areas are also vulnerable to SLR Elevate Shoreline Highway and may be good candidate areas to investigate General approaches for adapting roads to SLR the feasibility of horizontal levees. As sea level include identifying water level triggers for rises the high marshes are able to transgress management actions, and coordinating with the inland along the valley profile. While these are DPW and Caltrans. They are further described in areas with gently sloping migrating transition the “Transportation” section of this report. zones, some realignment of infrastructure such as roads and culverts may have to occur if they The Walker Creek area in particular experiences are to be realized. temporary flooding which will only worsen with SLR. This strategy would be implemented by This strategy could be funded by a local Caltrans, and received strong support from poll assessment district or government grant, and respondents (100%). See “Transportation” in received moderate support from poll Governance section for discussion of road respondents (40%). A public meeting participant elevation considerations. suggested that Marconi State Park might be an appropriate location for a horizontal levee. Elevate buildings and utilities Structures fronting Tomales Bay may be Armor segments of Shoreline Highway impacted by rising waters to varying degrees Erosion and flooding currently threaten based on building construction and existing segments of Shoreline Highway, particularly elevation above the water. One solution is to where no structures are present. Armoring allow/encourage houses to be raised and exposed segments could be implemented by seawalls maintained to protect houses, septic the State and/or local service providers, and tanks and Shoreline Highway. Maintaining received strong support from poll respondents bulkheads under Marshall homes is a high (100%). For discussion of constraints to priority to protect the homes, as well as armoring segments of Shoreline Highway, see possibly protecting Shoreline Highway from “Transportation” in the Governance section. flooding.
Accommodate Although properties look the same on the map, the reality ond the groun varies significantly. and would require different adaptation
89 approaches. Homes are at varying elevations Natural Capital Project, Center for Ocean Solutions. Coastal Adaptation Policy Assessment. 2016. and construction methods have changed over 90 Environmental Science Associates (ESA). time. Around six houses are below high water. Geomorphic Response of Beaches and Marshes. Some places, for example the fisherman’s August 2015. PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 201
COMMUNITY ALTERNATIVES East Shore village on the peninsula, may need armoring, with government agencies, and received strong not elevation. support from poll respondents (80%).
Raising houses along the Marshall waterfront is Community members noted that policies very difficult and expensive, requiring creative requiring mitigation for loss of sand supply by solutions. As water levels rise, the area under preventing erosion and other matters could houses becomes less accessible for foundation make both coastal armoring and elevation of work. Home elevation is estimated to cost homes prohibitively expensive, even if approximately $100,000 per 1,000 square feet permitting requirements could be eased and in this area.91 streamlined.
There was a great deal of interest from Flood proof buildings residents in developing a community‐wide FEMA provides guidelines for wet and dry solution to raise all homes through a floodproofing. This strategy would be coordinated effort. This could help provide a implemented by property owners, and received better economy of scale for permitting, design moderate support from poll respondents (60%). work and construction. Such a pilot project could potentially acquire funding through a Boat moorings government grant and homeowners could pay Apart from Lawson’s Landing at Dillon Beach off their share over time through property (which provides seasonal moorings), there are taxes. The community set a precedent for no active marinas on the east shore of Tomales taking a collaborative approach through the Bay. There are pontoons in the Marshall Boat Marshall Community Wastewater System, Works that seasonally host a couple of where a State grant covered 50% of costs, and boats. The demand and number of moorings residents covered 50%. I‐Bank offered has dwindled over the years. In 2014, GFNMS reasonable loan rates, and everyone was and State Lands Commission commenced the assessed the same amount of $20,000 over 20 Tomales Bay Mooring Program to permit and years, despite differences in the scale of work lease moorings in Tomales Bay. Due to the that needed to be done on each system. program’s costs and requirements, it is expected that a year from now there will be Depending on community desires, the timing of even fewer moorings on the Bay. elevating structures could be determined by a Houseboats chosen acceptable level of protection against Houseboats are not recommended as an monthly high water (EMHW) or greater (1‐year adaptation strategy due to harsh wind and or 10‐year flood), as explained in the wave conditions, and the lack of houseboat “Governance: Triggers for Adaptive marinas and services. This strategy received low Management” section of this report. The support from poll respondents (20%). There are strategy of structural elevation would be no County, State or Federal laws that prevent implemented by property owners in partnership someone from living aboard a boat in Tomales Bay, except within a quarter mile of the Point Reyes National Seashore shore on the west side 91 Marshall homeowner. Personal communication. March 2016. of the Bay, north of Duck Cove. The NPS PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 202
COMMUNITY ALTERNATIVES East Shore formerly restricted overnighters through stakeholders, and received moderate support camping regulations, but they have since from poll respondents (60%). See changed their maps and enforcement activities “Transportation” in Governance section for to reflect revised jurisdictional boundaries92. discussion of considerations for road realignment. Relocate/ Managed Retreat Marin County could research potential costs Potential locations of adaptation strategies are and community interest in a long‐term buyout shown in Map 67. East Shore Adaptation Map or property acquisition strategy if rising sea (North) and Map 68. East Shore Adaptation levels or storm impacts become imminent Map (South). threats to homeowners. The County could also consider having a plan and specific proposals in place in case of a major storm/flood event that makes homeowners more likely to be interested in the buyout.93 Easements and other land use policies could be used to limit further construction and investment in the most hazardous areas.
Relocation of buildings could eventually be implemented by property owners, and received moderate support from poll respondents (40%). Relocation of any remaining shorefront septic leachfields to the east of Shoreline Highway could be implemented by a local assessment district and/or the County, and received strong support from poll respondents (100%).
Relocation of coastal access points at Walker Creek and Livermore Marsh Cypress Grove could be implemented by the County and State, and received moderate support from poll respondents (60%).
Realignment of affected segments of Shoreline Highway could be implemented by Caltrans in collaboration with affected landowners and
92 Clyde, George. West Marin Review. How Rep. Phillip Burton and a Magic Marker Hijacked Tomales Bay into the Golden Gate National Recreation Area. 2012. 93 ibid
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COMMUNITY ALTERNATIVES East Shore
Maps 54‐66 East Shore Exposure Source: Coastal Storm Modeling System (CoSMos)
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COMMUNITY ALTERNATIVES East Shore
PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 205 Map 67. East Shore Adaptation Map COMMUNITY ALTERNATIVES East Shore
PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 206 Map 68. East Shore Adaptation Map (South)
COMMUNITY ALTERNATIVES Point Reyes Station Point Reyes station
PRIMARY VULNERABILITIES PRIORITY ACTIONS Storm and tidal impacts already occur Accommodate existing development with elevation and retrofits Long‐term flooding will impact 36 buildings, 4 businesses, and 700 people Protect assets with nature‐based strategies
The cost of impacts to exposed assets will be $2 million
Others impacted will include the residential tourism industry, Caltrans, and NMWD
Timeframe/Term L=Low 0‐40% Strategy NT=Near M=Moderate 41‐70% MT=Medium S=Strong 71%+ LT=Long NA=Not available PROTECT Restore/enhance wetlands along Tomales Bay NT S Armor segments of Shoreline Hwy LT M Construct a horizontal levee along Tomales Bay MT L
ACCOMMODATE Elevate Green Bridge NT S Elevate Shoreline Hwy MT M Elevate Sir Francis Drake Blvd MT M Elevate existing buildings MT M Flood proof existing buildings NT‐MT L
RELOCATE/MANAGED RETREAT Research costs and interest of long‐term buyout or acquisition LT NA strategy Relocation of buildings LT L Relocation of Gallegher well upstream LT M Removal of development and shoreline protection that limit LT M inland migration of habitats
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COMMUNITY ALTERNATIVES Point Reyes Station
Map 69. Point Reyes Station Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES Point Reyes Station 6.7) Point Reyes Station This strategy would be implemented by No action Caltrans, and received moderate support from poll respondents (54%). See “Transportation” in Surrounding wetlands and marshes, including Governance section for discussion of Giacomini Wetlands and Olema Marsh could be considerations for armoring Shoreline Highway. degraded by flooding, erosion, and increased salinity. Water district pipes traversing under Horizontal levee along Tomales Bay the marsh and road could be damaged by This strategy would be implemented by a local higher groundwater. Flooding is probable on assessment district or government grant, and portions of Shoreline Highway in the long‐term received low support from poll respondents scenarios, however Green Bridge is vulnerable (15%). in the near‐term. For more information about horizontal levees, POINT REYES STATION: LONG‐TERM IMPACTS see section 2.7 of Appendix A. 36 buildings 700 people Accommodate Storm and tidal impacts 4 businesses Caltrans is planning improvements to Green already occur Bridge, and community members requested 2 million that the State and County plan for the same SLR worth of Residential Caltrans projections. Elevating the bridge received assets Tourism NMWD strong support from poll respondents (85%). exposed Improving coordination among government agencies is a key aspect of adaptation planning. Priority Actions Elevating affected segments of Shoreline Highway would also be implemented by The recommended adaptation approach is to Caltrans, and received moderate support from accommodate development with elevation and poll respondents (69%). Elevating Sir Francis retrofits, and protect assets with nature‐based Drake Boulevard received moderate support strategies in the near‐ to‐medium term, while from poll respondents (62%). considering additional options in the long‐term. Elevating buildings would be implemented by Protect property owners, and received moderate Restore/ enhance wetlands along Tomales Bay support from poll respondents (54%). This strategy could be funded by government Floodproofing buildings would be implemented grants, and received strong support from poll by property owners, and received low support respondents (100%). from poll respondents (15%).
Armor segments of Shoreline Highway Relocate/ Managed Retreat General approaches for adapting roads to SLR Marin County could research potential costs include identifying water level triggers for and community interest in a long‐term buyout management actions, and coordinating with the or property acquisition strategy if rising sea DPW and Caltrans. They are further described in levels or storm impacts become imminent the “Transportation” section of this report. threats to homeowners. The County could also
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COMMUNITY ALTERNATIVES Point Reyes Station consider having a plan and specific proposals in place in case of a major storm/flood event that makes homeowners more likely to be interested in the buyout.94 Easements and other land use policies could be used to limit further construction and investment in the most hazardous areas. These easements would move (or “roll”) with bluff and shore erosion.
Relocation of buildings would be implemented by property owners, and received low support from poll respondents (23%). Relocation of Gallagher well upstream would be implemented by North Marin Water District, and received moderate support from poll respondents (62%). Removal of development and/or shoreline protective devices that limit inland migration of beaches and marshes would be implemented by property owners, and received moderate support from poll respondents (62%).
Relocation of coastal access points would be implemented by the County and State, and received moderate support from poll respondents (46%).
Realignment of affected segments of Shoreline Highway would be implemented by Caltrans, and received moderate support from poll respondents (38%). See “Transportation” in Governance Section for discussion of considerations for realigning Shoreline Highway.
Potential locations of adaptation strategies are shown in Map 61.
94 ibid
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COMMUNITY ALTERNATIVES Point Reyes Station
Maps 70‐73 Point Reyes Station Exposure Source: Coastal Storm Modeling System (CoSMos) PUBLIC REVIEW DRAFT - Marin Coast Sea Level Rise Adaptation Report Page 211
COMMUNITY ALTERNATIVES Point Reyes Station
Map 74. Point Reyes Station Adaptation Map
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COMMUNITY ALTERNATIVES Dillon Beach 6.8) Dillon Beach PRIMARY VULNERABILITIES PRIORITY ACTIONS Storm and tidal impacts already occur Support dune restoration efforts as a protective measure
Long‐term SLR will impact two businesses, the Research alternatives for managing flooding on residential tourism and agriculture industries, as Bay Drive well as private tourism assets
Others impacted will include Ocean Marin HOA, Implement policies to ensure bluff top homes Lawson’s Landing, Dillon Beach Resort, and are safe from erosion property owners
Timeframe/Term L=Low 0‐40% Strategy NT=Near M=Moderate 41‐70% MT=Medium S=Strong 71%+ LT=Long NA=Not available PROTECT Dune restoration near Lawson’s Landing NT NA Support dune restoration pilot programs NT NA
ACCOMMODATE ID water level triggers for management actions NT NA Elevate and floodproof existing structures at Lawson’s Landing NT M
RELOCATE/MANAGED RETREAT Research costs and interest of long‐term buyout or acquisition LT NA strategy Relocate the well on Dillon Creek at Bay Drive NT M
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COMMUNITY ALTERNATIVES Dillon Beach
Map 75. Dillon Beach Exposure Map. Does not include geomorphic change.
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COMMUNITY ALTERNATIVES Dillon Beach No Action protecting Lawson’s Landing recreational Flooding could affect Bay Drive leading to facilities from wave run. up Lawson’s Landing. The centralized Oceana Marin Sewer System could be degraded by Protect erosion and waves. Bluff top homes could Dunes aid in protecting Bay Drive and the small experience heightened erosion risks as sea community at Lawson’s Landing while also levels rise. Camping capacity at Lawson’s providing key recreational beach going and Landing could be reduced due to inundation camping opportunities. The surfgrass along and erosion. North of Dillon Beach, agriculture Kailua Way leading north towards the could face vehicular access constraints and agricultural areas bordering Estero de San decreases in land area due to erosion and Antonio play a lower relative role in reducing 95 higher water levels. exposure to coastal impacts.
In the near‐term, managers of Lawson’s Landing DILLON BEACH: LONG‐TERM SLR IMPACTS may pursue a dune restoration project on the Storm and tidal impacts south end of the beach with experimental 2 businesses already occur design areas and monitoring to help test the Ocean Marin protective services dunes provide. Dune HOA restoration would help to protect exposed Private Lawson’s parcels zoned “Residential” (including Residential tourism Landing residential structures) as well eas th areas Tourism assets Dillon Beach zoned “Resort and Commercial Recreation” Agriculture exposed Resort including Bay Drive. Marin County could be at Property the forefront of helping to develop data to Owners determine dune restoration design metrics and elements of success as well as how hydrological and geomorphological conditions in different Priority Actions areas contribute to the success or failure of Support dune restoration efforts as a protective restored dunes as a natural infrastructure measure, research alternatives for managing alternative to armoring. This project would add flooding on Bay Drive, and implement policies to the body of evidence from similar to ensure that bluff top homes are safe from demonstration sites recently funded by the SCC erosion. Plans for dune restoration and in Humboldt and Monterey Counties. Coastal enhancement are being developed for Lawson’s dune restoration on the west coast of North Landing. Planting native vegetation to augment America was pioneered in the Lanphere Dunes existing beach grass may help encourage in Humboldt County in the 1980s and many natural augmentation of the dunes. This is case studies published from the dune considered a cost‐effective and environmental restoration projects can provide valuable approach, compared to importing sand. A monitoring plan will be developed to contribute to the body of research on the efficacy of this 95 Center for Ocean Solutions, Natural Capital Project. measure at reducing coastal erosion and Coastal Adaptation Policy Assessment. 2016.
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COMMUNITY ALTERNATIVES Dillon Beach support.96 Prioritizing dune habitat protection Marin County could research potential costs and restoration can ensure the protective and community interest in a long‐term buyout service for the community of Dillon Beach while or property acquisition strategy if bluff erosion also continuing to provide recreational become imminent threats to homeowners. opportunities so important to the region. Easements and other land use policies could be used to limit further construction and Due to relative exposure risks and relative investment in the most hazardous areas. These undeveloped nature of this area, this may be a easements would move (or “roll”) with bluff lower priority project for the County, especially and shore erosion. since such a monitoring and restoration project would require significant funding. However, SCC Relocating the well along Dillon Creek at Bay and other sources of funding are available for Drive inland would prevent saltwater intrusion these types of projects, and as mentioned that could occur in the near‐term. The above, would help reduce uncertainties community could also consider relocating associated with the extent of flood protection sewage pump (50%) and parking lot (100%) and habitat benefits dune restoration provides inland in the medium‐ to long‐term. Bay Drive, compared to traditional armoring. In addition, a which provides access to Lawson’s Landing, reduction in exposure to flooding for Bay Drive could be realigned inland. ultimately leads to a reduction in exposure for Lawson’s Landing as that is the main transportation corridor for the small community.
Accommodate General approaches for adapting roads to SLR include identifying water level triggers for management actions, and coordinating with the DPW and Caltrans. They are further described in the “Transportation” section of this report.
Continue to elevate and/or floodproof affected structures, primarily at Lawson’s Landing. The existing cottages are designed to be moveable. This strategy received moderate support from poll respondents (50%).
Relocate/ Managed Retreat
96 Pickart AJ. Dune Restoration Over Two Decades at the Lanphere and Ma‐le’l Dunes in Northern California. 2013.
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COMMUNITY ALTERNATIVES Dillon Beach Green Strategy: Lawsons coast, and Lawson’s Landing manages responsible recreation and conservation for Landing Dune Restoration the dunes, coastal meadows and wetlands that are home to Western Snowy Plover, seals and other species.e Th approximately 450 acres of wetland‐dune complex at Lawson’s Landing is under a permanent conservation easement with the Natural NRCS.
Lawson’s Landing is undergoing a major
Lawson’s Landing dunes. Flynn, 2014. redevelopment under a Coastal Development Permit, updating key Benefits: Habitat, Recreation, Tourism infrastructure, including a wastewater Cost estimate: $200,000/acre (ESA 2015) system, water lines, electrical services, communication lines, roads, and hazard Sand dunes act as a buffer to wave run‐up response center. As part of the erosion and minimize coastal flooding, while redevelopment, Lawson’s Landing is providing critical habitat to many species and transitioning from a facility that had many beautiful recreational areas. Lawson’s Landing permanent trailers to one that provides dune restoration project at Lawson’s Landing more temporary campsites and lodging for with experimental design areas and broader public access. monitoring would help test the protective services of dunes, and serve as a model to Given the environmental and public other coastal communities for a “green” SLR resource benefits resulting from the adaptation strategy. transition at Lawson’s Landing, it is prudent to seek protection eof thes resources in the Lawson’s Landing has been used for fishing, face of anticipated SLR. Low and high dunes boating and camping since 1957. The 960‐ at Lawson’s Landing currently protect built acre site is situated at the northern side assets. These natural systems show mouth of Tomales Bay, bordered by the potential to be improved upon to provide Pacific Ocean and Dillon Beach. Lawson’s additional adaptation and resilience to SLR. Landing has been formed by dune sand that is first deposited on the beach and then Potential dune improvements may include windblown southeastward into Tomales Bay. extending the existing foredunes toward Introduction of European beach grass by the the southeast to protect cottages and RV Soil Conservation Service in Northern campsites from storm surges, and in the California in the 1930’s has created elevated northeastern portion of the camping area. foredunes. Wind and waves occasionally blow These areas have a high habitat protection out the dunes, which re‐establish over time. value and good potential as pilot experimental design and monitoring areas. The Tomales Dunes are some of the last mobile dune systems on the California
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COMMUNITY ALTERNATIVES Dillon Beach Draft goals of the Lawson’s Landing pilot America was pioneered in the Lanphere project for natural adaptation strategies to Dunes in Humboldt County in the 1980s and address SLR: many case studies published from the dune restoration projects can provide valuable 97 1. Re‐establish certain native dune plant support. species while facilitating dune enhancement. 2. Protect environmental and recreational value using geomorphological processes to provide adaptation to SLR.
3. Assess effects of a biotechnical approach to SLR on nearby boathouse, pier, sea wall and other high value recreation assets. (i.e. how to best align with storm surges).
4. Determine appropriate interventions to improve resilience and adaptation. 5. Capture and stabilize sand moving through area rather than losing it.
6. Install interpretative signage to explain adaptation strategies and collaborative/ complementary efforts/ organizations. 7. Enhance public awareness of Lawson’s Landing efforts to mitigate and adapt to climate change and protect low‐cost coastal access. Accumulation of sand and dune plant colonization around high value recreation area at Lawson’s Landing provides a timely opportunity for natural adaptation strategies consistent with environmental and coastal access protection. Monitoring this project would add to the body of evidence from similar demonstration sites recently approved for funding by the SCC in Humboldt and Monterey.
This project would add to the body of evidence from similar demonstration sites recently funded by the SCC in Humboldt and Monterey. Counties Coastal dune 97 Pickart AJ. Dune Restoration Over Two Decades at the restoration on the west coast of North Lanphere and Ma‐le’l Dunes in Northern California. 2013.
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COMMUNITY ALTERNATIVES Dillon Beach
Figure 12. Lawson's Landing Proposed Resource Protection and Enhancement Area
Source: California Coastal Commission Staff Report Exhibit No. 3, 2011. documents.coastal.ca.gov/reports/2011/7/W10a‐7‐2011‐a1.pdf
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COMMUNITY ALTERNATIVES Dillon Beach
Maps 76‐79 Dillon Beach Exposure Source: Coastal Storm Modeling System (CoSMos)
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7) CONCLUSION on timing, area of impact, costs, equity, environment, economy or some combina 7.1) Next Steps tion of the above. If there is stakeholder interest and funding This report summarizes adaptation options that secured, in conjunction with community have arisen through the C‐SMART process to members and asset managers, initiate date. These options are not endorsed by the Community Plans for Adapting To County of Marin or project partners, are not all Coastal Hazards (Community PATCHs). necessarily feasible (economically, socially, Such efforts would build off C‐SMART’s environmentally, etc.), and in some cases may Vulnerability Assessment and conflict with one another. However, the options Adaptation Report. Vulnerabilities for presented in this report have been recognized assets of critical importance including as meriting further consideration. In flood timing, frequency and duration conjunction with willing partners, C‐SMART would be determined. Trigger points Staff can develop a work program to move would be identified in conjunction with strategy discussions forward. Option inclusion residents to understand the point at in this report does not imply financial which flooding creates recurring commitment by Marin County, and completion significant problems. Planning of certain tasks is dependent on acquiring timeframes would be developed around additional funding, which would require identified trigger points to plan for exploring various funding sources/types. Some continued use of assets critical to the potential next steps are listed below. community. (see Page 123 for a proposed process of PATCH development) Provide organizations recognized in the ‘Potential Partners’ column of the asset Develop an interagency SLR task force strategy options with a copy of this with representatives from various report for their consideration of agencies who oversee West Marin implementation. assets (transportation, utilities, public lands, natural resources, etc.). This task Develop a subcommittee with force will meet regularly to discuss representation from the Marin County options outlined in this report and Board of Supervisors, and prioritize recommendations. representatives of the communities and local agencies to prioritize work going o Among other topics, the task force forward. could discuss existing state law, building codes, and Coastal Develop a process with relevant Commission requirements that may stakeholders to identify subarea need to be modified to reduce and boundaries for prioritization. Utilize ease approval requirements, support from willing partners and including costs. Task force landowners and/or target areas based recommendations could facilitate
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CONCLUSION
the efforts of homeowners and o National Park Service local public agencies to protect (NPS)/Golden Gate National their properties in the face of sea Recreation Area (GGNRA)/CA level rise that actually threatens Department of Parks and structures and utilities. Recreation (CSP)/Marin County Parks to share science and Introduce Homeowners Guide to Sea integrate planning/ Level Rise to local property owners for management decisions for their consideration through public workshops, social media, etc. interlocking lands (e.g., Stinson Beach, Point Reyes National Consider options outlined in this Report Seashore). during the next update of the Marin o Marin County Office of Countywide Plan, as a basis for Emergency Services (OES) to developing Plan policies and programs formalize working relationship that address SLR resiliency countywide. with Local Hazard Mitigation Plan and SLR adaptation Utilizing ideas generated in the Resilient planning efforts. Stinson Design Charrette, develop o PG&E and local service performance design guidelines providers to discuss utility including alternatives to permanent adaptation. static elevation that reduce or eliminate
flood damage to structures which could Evaluate and accommodate for SLR in include wet/dry floodproofing, flood new capital improvement programs gates, drainage improvements, where cost effective, fully funded and amphibiation, etc. permitted. Formalize working relationships (e.g., Establish a citizens science monitoring Joint Powers Authority, MOUs, etc.) to program perhaps in coordination with oversee and carryout implementation GFNMS existing program. of highest priority options. Establish sub‐groups based on varying Continue to pursue funding and timeframes for different assets. Public partnerships to formalize a SLR public infrastructure may be considered on a education program longer timeframe than private homes. Specifically MOUs or other formalized Coordinate with other entities planning workshop agreements could be sought for SLR to share investigation and with: evaluation of specific adaptation o Caltrans, MTC and TAM for techniques. This can be done through Shoreline Highway planning existing networks such as the California support as part of the Regional Coastal Adaptation Network. Transportation Plan. Continue to work with GFNMS to support strategies recently approved by
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CONCLUSION
the GFNMS Advisory Council, and conduct sediment management planning.
Continue to work with the Sonoma/Marin County Sediment Management Working Group to assist with the development of a Regional Sediment Management Plan for Marin and Sonoma’s outer coastline. The Plan intends to develop consensus‐driven approaches to regional sediment management throughout the region; encourage beneficial reuse of available, non‐polluted sediment resources; restore and maintain coastal beaches and other critical areas with too much or too little sediment; reduce shoreline erosion and coastal storm damages; reduce the proliferation of protective shoreline structures; sustain recreation and tourism, and; enhance public safety and access to the coast. The plan is being developed by the Greater Farallones National Marine Sanctuary in partnership with the Greater Farallones Association and funded by the California Natural Resources Agency. A possible Working Group topic could be the feasibility of acquiring sand from the San Andreas Graben that could possibly support Marin County beach nourishment. If sand is available, initiate discussions with land managers and other willing partners to move renourishment efforts forward.
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CONCLUSION
7.2) Lessons learned SLR Adaptation plans and proposals tend to be Focus public outreach on existing relatively new endeavors with few existing groups. Due to ‘meeting fatigue’ and precedents to follow. Thus through this process buy schedules, it is often challenging for C‐SMART Staff have learned quite a bit of local residents to attend public valuable information that can be applied to meetings, especially for threats such as continued Marin County planning efforts and SLR which are perceived as distant and shared with other jurisdictions. Specific lessons far away. Thus to augment public learned include: processes, existing community groups should be identified and reached out to Adopt a process that is understandable. see if staff can participate in upcoming Public participation is critical to meetings. successful planning and implementation efforts. Processes should make sense to Collaborate early and often with other local residents to gain their support. agencies. As SLR sees no jurisdictional Avoid jargon and adopt consistent boundaries and can have widespread talking points for robust public impacts on a variety of asset types outreach. regular collaboration with entities carrying out similar work can Gain a full understanding of available strengthen processes and products. models. Several flooding/SLR models Formalized working relationships can are available for both the general public ensure regular communications and and professionals including FEMA, strengthen partnerships, setting the OCOF, and NOAA. As a professional it is stage for increased adaptation planning critical to understand the specifics of efforts as SLR intensifies. each model, and the rationale for applying the chosen model. Discussions of models will likely come up in public processes and having answers to FAQs can be critical for public outreach.
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BIBLIOGRAPHY
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Clyde, George. West Marin Review. How Rep. Phillip Burton and a Magic Marker Hijacked Tomales Bay into the Golden Gate National Recreation Area. 2012.
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