Sea Level Rise and the Scarborough Marsh Scarborough Land Trust Annual Meeting April 24, 2018

Transcription

1 Sea Level Rise and the Scarborough Marsh Scarborough Land Trust Annual Meeting April 24, 2018 Peter A. Slovinsky, Marine Geologist Maine Geological Survey Funded by:

2 50% 40% Figure modified from Griggs, %

3 Global Sea Level Rise Driving Factors: Volumetric Increase (melting of land-based ice sheets and glaciers) Glaciers (m of water equivalent thickness) 30 well-studied glaciers have decreased in average thickness by 60 feet

4 Global Sea Level Rise Driving Factors: Thermal Expansion (expansion of the water column due heating) Ocean Heat (10 22 joules) compared with average Global sea level (mm) as difference from 1990 Global sea level rise average over the last century: 1.8 mm/year

5 Since 1993, global sea level has risen at 3.1 mm/yr

6 Locally, sea level is rising in the long term P.A. Slovinsky, Maine Geological Survey, February 2, 2018

7 is rising faster in the short term and can rise abruptly P.A. Slovinsky, Maine Geological Survey, February 2, 2018

8 Sea level can also change abruptly. Portland saw an average of approximately 5 higher than normal tides in the summer of 2009, and, especially in winter of This was the highest along the whole east coast.

9 Five of the highest monthly sea levels since 1912 occurred in winter We suspect similar conditions likely in winter Higgins Beach, Scarborough, April 7, 2010 P.A. Slovinsky

10 Global Mean Sea Level (m) Adapted from NOAA Technical Report NOS CO-OPS 083, January, 2017 and sea level is expected to continue to rise. Global Mean Sea Level Scenarios to ft Scenarios 6.6 ft 4.9 ft Satellite data 3.3 ft Tide gauge data 1.6 ft 1.0 ft

11 and in New England, may rise higher than global averages ft 8.7 ft 6.0 ft 3.8 ft 1.5 ft 1.0 ft

12 How do we simulate potential marsh migration in response to SLR?

13 LiDAR - Light Detection & Ranging Data 100,000 pulses of laser light per second are sent to the ground in sweeping lines Sensors measure how long it takes each pulse to reflect back to the unit and calculates an elevation Image from the Kelly Research and Outreach Lab, California Coastal LiDar Project Algorithms are used to remove buildings and vegetation types to create a bare earth digital elevation model (DEM)

14 LiDAR Digital Elevation Model (DEM) for Scarborough, ME

15 Coastal wetlands Coastal wetlands means all tidal and subtidal lands; all areas with vegetation present that is tolerant of salt water and occurs primarily in salt water or estuarine habitat; and any swamp, marsh, bog, beach, flat or other contiguous lowland that is subject to tidal action during the highest tide level for each year in which an activity is proposed as identified in tide tables published by the National Ocean Service. Coastal wetlands may include portions of coastal sand dunes. Required in Maine s Municipal Shoreland Zoning P.A. Slovinsky, MGS

16 Using Tidal Elevations as Proxies for the Marsh Highest Annual Tide (HAT) - spring tide, the highest predicted water level for any given year but is reached within several inches numerous tides a year Mean High Water (MHW) the averaged daily high water mark Mean Tide Level (MTL) = average height of the ocean s surface (between mean high and mean low tide). Marsh Side Ocean Side Coastal wetland Coastal Wetland - MTL to HAT Mean Tide Mean High Highest Scenario Level (MTL) Water (MHW) Annual Existing Beach Tidal elevations are determined from nearby applicable NOAA National Ocean Service/CO-OPs tidal prediction stations (Old Orchard Beach) P.A. Slovinsky, MGS

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19 Very accurate method of delineating coastal wetlands!

20 What about potential changes to coastal wetland areas and wetland types? Low Marsh (MTL-MHW) High Marsh (MHW-HAT)

21 First, some Assumptions Topography stays static we are using 2010 LiDAR data that represent a snapshot of topography that may have changed. Simulations use a bathtub approach that assumes that the topography stays the same, i.e., it doesn t account for erosion, accretion, or dynamic processes like waves. Using tidal elevations as proxies for wetlands can t account for changes in tides due to tidal restrictions such as roads, etc. Although our vertical accuracy is around 6, lines and boundaries drawn on the following maps should not be deemed as absolute ; instead, they should be used for general planning purposes only.

22 A detailed look: Scarborough Marsh

23 For general planning purposes only.

24 For general planning purposes only.

25 For general planning purposes only.

26 For general planning purposes only.

27 Conversion to open water For general planning purposes only.

28 For general planning purposes only.

29 State and Town-owned lands For general planning purposes only.

30 State and Town-owned lands For general planning purposes only.

31 State and Town-owned lands For general planning purposes only.

32 State and Town-owned lands For general planning purposes only.

33 For general planning purposes only. State and Town-owned lands Conversion to open water

34 Take home point: Wetlands may convert to a low-marsh dominated system (high marsh expansion limited by steep sloped or developed uplands) and Scarborough may lose marsh to open water under higher scenarios.

35 What kind of land cover types might be impacted? Maine Land Cover Dataset (MELCD) Multiple different land cover types grouped into 3 main categories by the Maine Natural Areas Program: Natural Developed Agricultural

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37 Existing Conditions

38 For general planning purposes only. HAT + 1 ft SLR

39 For general planning purposes only. HAT + 2 ft SLR

40 For general planning purposes only. HAT ft SLR

41 For general planning purposes only. HAT + 6 ft SLR

42 Summary Table Potential Impacts to Adjacent Land Cover Types Scenario Maine Land Cover Type (acres)* Natural Agricultural Developed Total Cum.Total 0.3 m (1 foot) SLR m (2 feet) SLR m (3.3 feet) SLR m (6.0 feet) SLR Totals * difference in acreage from overall wetland areas is due to some areas not actually being classified by MELCD Take home point: the vast majority of land cover type (80% or more in each scenario) that may be impacted is characterized as Natural or Agricultural ; developed impacts are generally limited to undeveloped portions of parcels and existing roads

43 Summary The existing Scarborough marsh is dominated by high marsh as opposed to low marsh (73% 27%) Based on simulations, this will likely change as high marsh is pinched out against steeper sloped uplands and migrating low marsh Simulations show that Scarborough marsh will likely lose overall marsh area when compared with existing conditions, especially under higher scenarios. High marsh will be lost and low marsh will likely be converted to open water

44 Summary (cont d) Simulations show that the marsh has the potential to expand into about 1,900 acres of adjacent uplands in a 6 foot SLR scenario Based on MELCD, much of the 1,900 acres (80% or more) are in natural or agricultural land use classes. Not covered here, but several roads with major emergency access importance (especially Route 1, Black Point Road, Pine Point Road) appear to be at risk starting at a 1 foot SLR, with impacts increasing significantly with higher scenarios.

45 Available Tools Statewide sea level rise scenarios can be viewed at the Maine Geological Survey s Coastal Hazards website:

46 Available Tools (cont d) Statewide marsh migration scenarios can be viewed at the Maine Natural Areas Program s website:

47 Available Tools (cont d) Statewide coastal resiliency/land management planning tools can be viewed at ME TNC Resiliency website:

48 Thank you! Peter A. Slovinsky, Marine Geologist Maine Geological Survey (207)