Some Thoughts on the Role of Elevation

Transcription

1 Some Thoughts on the Role of Elevation Data in Sea-level Rise Impact Assessments Rob Thieler* U.S. Geological Survey Coastal and Marine Geology Program Woods Hole, MA *i l d t i l d f D C h D G h *includes material drawn from Don Cahoon, Dean Gesch, and John Masterson.

2 We need better science* to prepare our local responses to climate change, especially in our coastal areas. (David Carter, Delaware Coastal Management) *science = better understanding of processes + better situation awareness

3 Coastal Flooding in Charleston, SC (Built environment impacts) NOAA NWS Charleston issues shallow coastal flooding advisories for 7 ft tides 7 ft tides typically predicted to occur twice a year With 1.6 ft of relative sealevel rise, this advisory could be issued 355 times (NOAA CSC)

4 Sea-level rise rates since the Last Glacial Maximum mwp-ia mwp-ib Global delta initiation (Stanley and Warne, 1994) U.S. Atlantic, U.K. wetland initiation; barrier island stability (Shennan and Horton, 2002; Engelhart et al., in press) Rate of SLR (mm m/yr) Thousands of 14 C years before present (SLR rate based on Fairbanks, 1989)

5 Past and Projected Sea-level Rise There are now several projections that suggest ~ cm rise is possible over the next century IPCC AR4 A1B envelope (modified after Rahmstorf, 2007; AR4 data from Bindoff, 2007)

6 Issue: Potential future rates of SLR far exceed recent experience 20 th Century eustatic rate was 1.7 mm/yr IPCC (2007) rates for the decade A1FI : mm/yr A1B : mm/yr There are only a few places in the world currently experiencing >5 mm/yr Geologic past (Fairbanks, 1989; Horton et al. 2009) Projections (Rahmstorf, 2007) Instrumental record (Church and White, 2006) Rate of SLR (mm/yr) Years before present

7 Coastal Vulnerability to Sea-level Rise: A Preliminary National Assessment (Thieler and Hammar-Klose 1999, 2000a, 2000b) Vulnerability Ranking

8 Coastal Vulnerability Studies in the National Parks Study sites in the Contiguous U.S. Study sites in Hawaii, Alaska, and U.S. Territories Cape Cod NS Cumberland Island NS Golden Gate NRA Fire Island NS Assateague Island NS Point Reyes NS Gateway NRA Dry Tortugas NP Olympic NP Gulf Islands NS Padre Island NS Apostle Islands NL Cape Hatteras NS Channel Islands NP Indiana Dunes NL Sleeping Bear Dunes NL Kenai Fjord NP Glacier Bay NPP Kaloko-Honokohau NHP NP of American Samoa Virgin Islands NP War in the Pacific NHP

9 Cape Alava Assessments help managers plan for hazards Sand Point Norwegian Memorial

10 Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region U.S. Climate Change Science Program Synthesis and Assessment Product 4.1

11 Coastal Elevations Elevation is a critical factor in assessing potential impacts (specifically, inundation) Current elevation data do not provide the degree of confidence needed for quantitative assessments for local decision making Collection of high-quality elevation data (lidar) would be valuable (Gesch et al., 2009)

12 Eastern North Carolina Kilometers Elevation source: 30-m DEM Elevation source: 3-m lidar data Dark blue Land 1 meter elevation Light blue Area of uncertainty associated with 1 meter elevation High quality elevation data reduce uncertainty of potentially inundated areas (Gesch et al., 2009)

13 Geoid Tide Ellipsoid model model model USGS topography NOAA bathymetry Integrated topo/bathy elevation model

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15 Coastal Elevations - Key Findings Elevation is a critical factor in assessing potential socioeconomic and environmental impacts in areas that are vulnerable to inundation It is important to understand the accuracy of the elevation data used in sea-level el rise assessments and its effects on the uncertainty of any resulting vulnerability maps and statistics Most current elevation data do not provide the degree of confidence needed for quantitative assessments for local decision making Collection of high-quality elevation data (lidar) will narrow the range of elevation uncertainty and improve the ability to conduct detailed assessments SAP 4.1 Coastal Sensitivity to Sea-level Rise

16 CCSP SAP 4.1 Coastal Elevations Future SLR vulnerability assessments: Determine where inundation will be the primary response to sea-level rise Use lidar elevation data (or other high-resolution, high-accuracy elevation source) Test and report absolute vertical accuracy as a measure of elevation uncertainty Apply elevation uncertainty t information in development of vulnerability maps and area statistics Produce spatially explicit maps and detailed statistics that can be used in local decision making

17 Mid-Atlantic Assessment of Potential Dynamic Coastal Responses to Sea-level Rise Bluff erosion Overwash Island Breaching (Gutierrez et al., 2009) Threshold Crossing

18 Coastal Wetlands Respond Dynamically to Environmental Change R. Carlson Wetland Vertical Development Mineral sediment deposition Plant matter accumulation - soil (root production/decomposition) Compaction Shrink-Swell D. Cahoon (Cahoon et al., 2009) D. Cahoon

19 Mid-Atlantic Wetlands Assessment (Cahoon et al., 2009)

20 Assessing wetland vulnerability to sea-level rise: STEP #1: Determine the elevation of your marsh relative to local sea level. Is your marsh located high s you a s ocated g or low within its optimum growth range?

21 Elevation Capital McKee, K. L. & W. H. Patrick, Jr The relationship of smooth cordgrass (Spartina alterniflora) to tidal datums: a review. Estuaries 11:

22 Elevation Deficit Relative to Sea-Level Rise Marsh elevation gradually gets lower within the growth range, which leads to increased hydroperiod (frequency, depth and duration of flooding). When marsh elevation reaches the bottom of the growth range, the vegetation becomes stressed. Eventually marsh elevation falls below optimum growth range, the plants die, and marsh habitat converts to intertidal mudflat or subtidal open water.

23 For Spartina alterniflora salt marsh, plant production increases as depth of flooding increases. Big Egg Marsh, Jamaica Bay, New York City, Aug 2007

24 Jamaica Bay, New York City, April 2002 Remnant marsh peat Severely degraded marsh Black Wall Marsh, Jamaica Bay, NY

25 Assessing wetland vulnerability to sea-level rise: STEP #2: Determine the trend in elevation change of your marsh relative to local sea level. Is your marsh keeping pace with the local rate of sea-level rise or is it experiencing an elevation deficit?

26 Keeping Pace vs. Surviving Keeping Pace: no Surviving: no Keeping Pace: maybe? Surviving: yes, elevation capital Even though this marsh appears healthy, it could be experiencing an elevation deficit, and is surviving on its elevation capital

27 SET-MH Method The surface elevation table marker horizon method provides high resolution measures of vertical accretion, elevation change, and shallow subsidence such that the separate influence of surface and subsurface processes on elevation can be determined Surface Elevation Table (SET) Marker Horizon Cahoon et al. 1995

28 Assessing wetland vulnerability to sea-level rise: STEP #3: Determine the factors controlling elevation change (i.e., vertical development) in your marsh. Which environmental drivers and surface and subsurface processes most control elevation change in your marsh? Improve your ability to manage your marsh to Improve your ability to manage your marsh to survive future climate change!

29 Environmental Drivers Influencing Vertical and Horizontal Wetland Development Wetland Vertical Development Mineral sediment deposition Plant matter accumulation - soil (root production/decomposition) Compaction Shrink-Swell Cahoon et al CCSP SAP 4.1

30 Assessing wetland vulnerability to sea-level rise: STEP #4: Estimate the ability of your marsh to build vertically under future sea-level rise and global change scenarios using models developed d with the information acquired in Steps 1-3. Improve your ability to manage your marsh to survive future climate change!

31 SLR Effects on Groundwater Flow

32 Change in Water-Table Elevation Subsurface flooding: Subterranean structures Septic systems Beach erosion Increased Surface-Water Discharge: Increased streamflow Expansion of riparian wetland areas Changes in hydraulic gradients Changes in delivery mechanism by which nutrients discharge to coast

33 Freshwater Flow Lens: Cape Cod, MA Source: Masterson and Garabedian (2007)

34 Freshwater Flow Lens: Cape Cod, MA Modified from McCobb and Weiskel (2003)

35 Depth to Water: Shoreline Erosion Coastal Stabilization, Inc., 1989

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37 Tide Control Structure: CCNS Marsh restoration would improve: flushing rate, water quality, habitat diversity, and regain balance between local sea level and wetlands in upper Pamet basin Marsh restoration efforts hindered by local community concerns regarding water supply and flooding

38 South North N S

39 Summary There are good protocols for integrating survey and lidar data, and how to express bathtub-type inundation i model results Outstanding potential to address salt marsh and gp groundwater issues