docSea Level Rise Impacts and Adaptation
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Sea Level Rise Impacts and Adaptation
Sea Level Rise Impacts and Adaptation Models, marshes, and moving forward in Marin February 8, 2014 Environmental Forum of Marin Miller Ave “King Tide 2012” Roger Leventhal, Marin County DPW Sarah Richmond, BCDC Aramburu Island Marin County and SLR • low elevation along eastern edge • Steep watersheds = flash flooding with downstream tidal boundary condition • Highest # roads at risk per capita Current Shoreline astronomical What forces influence bay tide levels? global Delta outflow local rising bay tide level regional ENSO forces (Pacific Ocean) Variations in monthly mean sea level, Fort Point Tide Gage, San Francisco, 1854 to 2013 ~ 8-9 inches in 100 years (2mm/yr) San Francisco Bay Sea Level Rise 1900 -2100 70 58 Sea Level Rise Relative to 2000, in 60 55 50 47 40 40 30 20 14 10 8 0 -10 -20 1890 1910 1930 1950 1970 1990 2010 Year 2030 2050 2070 2090 Extreme Water Levels 140 100 yr 50 yr 20 yr 10 yr 2 yr Sea Level Relative to MSL in 2000 ( Inches) 120 100 80 60 55 40 20 14 0 -20 1890 1910 1930 1950 1970 1990 2010 YEAR Source: ESA; Developed from Kriebel (2011) 2030 2050 2070 2090 2110 Extreme Water Levels 140 100 yr 50 yr 20 yr 10 yr 2 yr Sea Level Relative to MSL in 2000 ( Inches) 120 100 80 2000 2018 2033 2044 2060 60 55 40 20 14 0 -20 1890 1910 1930 1950 1970 1990 2010 YEAR Source: ESA; Developed from Kriebel (2011) 2030 2050 2070 2090 2110 Current Latest and Greatest – NRC 2012 from NRC 2012 for Northern California year Mean (in) Range low (in) Range high (in) 2030 5.7 1.7 11.7 2050 11.0 4.8 23.9 2100 36.1 16.7 65.5 http://www.nap.edu/catalog.php?record_id=13389 How to map direct bay flooding and SLR onto Marin County 1. Bathtub Models • NOAA SLR Viewer • USGS maps (previous BCDC maps) • PRBO viewer (impacts to marshes and species) 2. Wave Models • FEMA models (no SLR) • USGS Our Coast, Our Future (bay storms, SLR) NOAA Sea Level Rise Viewer (http://csc.noaa.gov/digitalcoast/tools/slrviewer) NOAA Sea Level Rise Viewer (http://csc.noaa.gov/digitalcoast/tools/slrviewer) Marin Map (http://www.marinmap.org/SilverlightViewer/Viewer.ht ml?Viewer=SeaLevelRise_Slvr) Bathtub SLR in Mill Valley (16 and 55 in) Bathtub SLR in Coyote Creek (16 and 55 in) Sea Level Rise Viewer – Impacts to Marshes PRBO (Pt Blue) Sea Level Rise Study www.prbo.org/sfbayslr Funded by the North Bay Watershed Association http://www.nbwatershed.org/ Wave Models – Our Coast Our Future (USGS/Pt Blue) Stinson Beach Pacific Ocean Golden Gate http://data.prbo.org/aps/ocof 16 Draft 2013 FEMA Maps (no SLR) FEMA Direct Coastal – Marin City FEMA Direct Coastal Flooding Combined Creek and Bay Flooding Coincident Frequency Analysis Major Adaptation Strategies Hard • • • • Soft • Wetlands creation/enhancement • Engineered beaches shoreline • T-zone creation Infrastructure/ Lifestyle • • • • • Flood/sea walls Levees/dikes High tide gates Rock Rip-rap Elevate structures Raise grades Lifestyle adaptation Zoning changes Planned retreat 21 BREAK… 22 Mudflats and marshes provide the first line of defense against coastal flooding Hayward Regional Shoreline (photograph courtesy of Matt Brennan) Corte Madera Baylands Sea Level Rise Adaptation Strategy © aerialarchives.com Acknowledgements Coastal & Marine Environments Corte Madera Baylands Tidal cycle at Corte Madera Baylands Low tides: Waves interact with mudflats Tidal cycle at Corte Madera Baylands Mid-high tides: Waves interact with mudflats and marsh scarp Photograph courtesy of John Callaway Tidal cycle at Corte Madera Baylands Extreme tides: Waves interact with marshes Shallow water reduces flood risk the most Wave height Largest waves offshore, decreasing towards marsh Low tide Mudflats reduced wave heights on average by 66% and in shallow water, up to 80% High tide Mudflat High tide Mudflat Deeper water requires a wider marsh 0.75 0.5 1-ft wave Wave height Increasing wave height reduction 1 0.25 1-foot water depth 3-feet water depth Marsh width (ft) North Muzzi Marsh ~1,000 feet wide; Muzzi and Heerdt Marsh ~2,000 feet wide. 4-feet water depth Vegetation reduces flood risk (theoretically, any species will do) Photographs courtesy of John Callaway Overall, a high, wide, vegetated marsh provides most flood risk reduction Corte Madera marshes projected to downshift (unless managed differently) Takekawa et al. 2012 2000 - 2100 Images courtesy of UC Berkeley Earth Sciences and Maps Library 1960 1853 Questions? Photograph courtesy of John Callaway Baylands have natural capacity to adapt Image courtesy of ESA PWA Conceptual model TIDAL Overbank deposition Channel levees HILLSLOPE Mass wasting TIDAL MARSH STREAMS Delta deposition W AV E Image courtesy of Peter Baye Wave deposition Barrier beach Hillslope Tides Stream Wave Image courtesy of Peter Baye Hillslope Tides Stream Wave Image courtesy of Peter Baye Harnessing variety of natural processes improves shoreline resilience Wave (clockwise) Hamilton, Aramburu Island, China Camp, Napa River Hillslope Stream 39 Suite of management measures 1. Reduce nearshore wave energy 2. Stabilize with coarse beach 3. Recharge mudflat and marsh 4. Improve sediment pathways 5. Enhance sediment trapping 6. Increase transition zone 7. Realign levees Photographs courtesy of California Coastal Conservancy Marsh edge erosion 1. Mudflat has generally been eroding 2. Marsh edge has retreated on average 485 feet (due to tidal/wave action, sediment supply, biological activity, etc.) James Zoulas (unpublished) Measure to decrease marsh edge erosion Coarse beaches buffer wave erosion and preserve wide marsh Photographs courtesy of Peter Baye Outer Bair Island Aramburu Island Vertical accretion 1. Marshes are accreting enough sediment to keep up with current sea level rise 2. Sedimentation on the marsh has been decreasing over time (opposite of most marshes) sedimentlimited system Photograph courtesy of John Callaway Measure to increase vertical accretion Mudflat and marsh recharge increase local sediment supply China Camp (photographs courtesy of Peter Baye) Measure to increase vertical accretion Increasing channel density also increases sedimentation Photographs courtesy of Peter Baye Two-phase sea level rise adaptation strategy Measure to allow upland transgression Create space to avoid coastal squeeze when sea level rise outpaces vertical accretion Revegetated older slurry deposit Illustration courtesy of Peter Baye Fresh hydraulic sediment slurry deposition Adaptive management: thresholds vs. timelines Sea level rise (feet) … tide gates, levee maintenance, regional sediment management? Collaborative planning at multiple scales Aramburu Island Engineered Beach Demonstration Project – Built 2011/2012 2007 Cosco Busan Oil Spill Aramburu Island, Richardson Bay 45+ yr shoreline retreat > 130 ft; boulder-cobble lag Graphic: Dan Gillenwater, WWR 0.5-1.0 m wave erosion scarp Central cell pre-construction profile: scarp above cobble-boulder lag Mill Valley Shoreline fringing high salt marsh wavedeposited tidal litter eucalypt us knoll scarped marsh shoreline slump block Seminary Drive boulder armored scarp steep scarp height approx. 6 ft drift-line and narrow gravel berm Seminary Drive, Tiburon approx 5 -6 feet Aramburu Site Wave Climate Wind-Wave Climate Fetch = 8 miles Significant wave height = 2-3 feet Wave period = 2-3 seconds Aramburu Island Demonstration Project • First constructed project in SF Bay designed to test natural shoreline approaches to windwave erosion and SLR – Gravel beach with sand foreshore (~$500k) for 1,300 linear feet • Constructed in 2011/2012 • Initial monitoring results from 2012/13 storms look great! Gravel/Cobble Berm Sandy Foreshore Dynamic beach v. static armor shorelines: Coarse sediment beach crest elevation responds to variable wave runup and water level given sufficient supply of suitable sediment size; rises with sea level Storm berm crest elevation ≈ 1 m > salt marsh plain Relict neap berms Freshly deposited swash bar (boat wakes) Bay Beach Reference Sites • • • • • Sanctuary Beach Radio Beach Pier 94 Brisbane Foster City Lowest wave energy Shoreline Design Oyster shell at north end Mixed gravels and oyster shell – central cell Highest wave energy Coarser sediments at south facing slopes Wood micro-groins and habitat “complexity” Initial coarse sand beach profile and initial placement of oyster shell hash Placing larger wood groins – eucalyptus logs Multiple large (back, upper beach profile) and small (lower beach profile) wood pieces combined for artificial driftwood groin Placement of oyster shell hash at N end, lowest wave energy gradient Initial Placement of Oyster Shell Hash, Prior to Wave-Reworking Initial Placement of Oyster Shell Hash, Prior to Wave-Reworking Sandy Foreshore Construction 2012 Monitoring Photos 2012-2013 Dec 5, 2012 post-construction Sept 2013 Feb 2,19, 2013 post significant storm Apr 16, 2013 post southern storms High-energy, waveexposed HEADLAND gravelcobble beach Stable beachface – cobble lag with interstitial fines Beach crest elevation: mobile coarse sediment accretion to EHW Beach Profile Changes Aramburu Island Birds 2013 Elegant terns Oyster catchers Our IWRMP Proposal • Design, permit and construct at 2-3 sites • Demonstrate engineered beaches as a viable approach to shoreline erosion • Determine limits of applicability 1 3 Mill Valley shoreline Outer Bothin Marsh scarp 2 Blackies Pasture? 4? N Seminary Drive 2000 ft Tour of Eastern Marin Shoreline Erosion Blackie’s Pasture Beach, Tiburon The shoreline future? rock and walls San Rafael shoreline walls and rock Engineered “Wall” Barriers New Jersey shoreline 2013 Aesthetics impacts? Muting the Tides - High Tide Flood Gates • Currently not easily permittable by agencies (if at all) • Would require mitigation for impact (i.e. ACMdP has steelhead) • Report could provide basis for permit requests in future Richardson Bay– SLR Laboratory • Currently floods on “King” tides • Flooding from both ends (river/tidal) • SLR Impacts to everything… – infrastructure flooding – residential/commercial – roads/utilities – wetlands – public access/users NW corner of Miller Ave and Locust 2005 Two major SLR adaptation projects nearby – Aramburu Beach and Corte Madera marsh study – use to obtain grants Mini-ART Richardson Bay • Supervisor Sears Citizen Task Force • Marin CDA • DPW Flood Control • BCDC 78 Major Adaptation Strategies Hard • • • • Soft • Wetlands creation/enhancement • Engineered beaches shoreline • T-zone creation Infrastructure/ Lifestyle • • • • • Flood/sea walls Levees/dikes High tide gates Rock Rip-rap Elevate structures Raise grades Lifestyle adaptation Zoning changes Planned retreat 79 Coyote Creek – Bothin Marsh alignment 2 Coyote Creek – Bothin Marsh alignment 1 Coyote Creek – Bothin Marsh Coastal Barriers Alignment Barrier Length, feet Year 2030 Barrier Height, feet Year 2050 Barrier Height, feet Year 2100 Barrier Height, feet # New Tide Gates Total Public Private Max Mean Max Mean Max Mean 1 12475 9816 2659 5.6 1.4 6.5 2.3 9.7 5.5 1 2 13143 10484 2659 5.6 2.0 6.5 2.9 9.7 6.1 2 (both minor) 3 3208 3208 0 5.5 1.7 6.4 2.6 9.6 5.8 2 (one major gate across CC) (1) Available and Required ROW depends on barrier type and height and how ROW is calculated (public/private/limits) SPUR 2013 Right of Way Width, Feet Lifestyle Adaptation…life in “Hydropolis” Adaptation Choice…Going Dutch Forget the Dutch, look to the Italians What? You want to build flood walls – No Way! Want to Stimulate Public Discourse What? You want to install a gate to hurt fish – No Way! What? You want to save birds and I still have to buy flood insurance – No Way! What? You want to protect the Mill Valley dog park– No Way! But Our Goal Remains… Marin resident already starting his adaptation training December 2012 “King tide” Conclusions 1. Know your site and work with it No one-size fits all for shoreline resilience. Management measures can support natural processes. 2. Triggers instead of timelines The Bay is a dynamic system – phased sea level rise adaptation plans and adaptive management are needed to achieve resilience goals. 3. Collaborative, comprehensive planning is our best bet Engage diverse stakeholders and work through tradeoffs. Vulnerabilities may overlap and adaptation strategies can have multiple benefits.
