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Sea Level Rise: Natural Resource Impacts and Considera8ons for

Great Marsh Community Resilience

Julia Knisel, Coastal Shoreline and Floodplain Manager Kathryn Glenn, North Shore Regional Coordinator Massachuse8s Office of Coastal Zone Management

Coastal Inunda8on Mapping Elements •  Water Level:

–  Local @de ranges –  Sea level rise data & projec@ons –  Flood event data (surge & precipita@on)

•  High Resolu8on Eleva8on Data: –  Topographic & bathymetric LIDAR –  Digital eleva@on models referenced to

@dal datums

•  Natural & Human Responses: –  Current ecosystems (beaches &

wetlands) –  Landform changes (erosion & accre@on) –  Physical barriers to migra@on

(development, seawalls, culverts, etc.)

Cri8cal Parameters for Modeling Marsh Migra8on

•  If sediment accretes (traps on surface or accumulates) as fast as sea level rises, then marsh may avoid being converted or submerged

Marshes on the Move, 2011

Mean Higher High Water Tidal Datum

Sea Level Rise Scenarios

Historic Rate of Sea Level Rise (Boston Tide Gauge)

•  Mean range (MHW-‐MLW) = 9.5 feet •  Record = 1921-‐2012 (91+ years) •  Sea level rise = 0.9 feet/100 years

Historic Sea Level Trends from 1921 to 2006-‐2012 (Boston)

•  Linear mean sea level rates ( ) & 95% confidence intervals (mm/yr) calculated from 1921 to recent years (2006-‐2012) at the NOAA Boston @de gauge sta@on

•  Values are trend of en@re data period up to that year

•  Marshes accrete by trapping sediment & by organic ma8er accumula@on from roots & rhizomes

•  Maximum accre@on for Great Marsh currently recorded ~ 6 mm/yr

Great Marsh Sediment Accre8on

Courtesy of Anne Giblin, Marine Biological Lab

Wetland Types

Water Unconsolidated Shore*

Salt Marsh

Brackish/ Transi@onal

Freshwater Wetlands

Mean Low Water

Mean Tide Level

Mean High Water

Mean High Water Spring

66% wetland Majority

Dry Lands

Eleva@

on

*includes silt, sand, or gravel that is subject to inunda@on and redistribu@on due to the ac@on of water; substrates lack vegeta@on

Marsh Migra8on Limited by Development & Infrastructure (Newbury)

Current 75-‐Year Time Horizon (2080)

Net marsh impact = MHHW + 4.5 l sea level rise – 1 l accre@on

Marsh Migra8on Limited by Development & Infrastructure (Salisbury)



Marsh Conversion to Unconsolidated Shore (Gloucester)



Marsh Conversion to Unconsolidated Shore (Salisbury)



Marsh Migra8on Modeling Resource www.csc.noaa.gov/digitalcoast/publica@ons/marshesonthemove

Applying SLR Data/Mapping

•  Great Marsh communi@es are currently grappling with retrofinng areas that were developed before SLR and climate change issues were recognized

Applying SLR Data/Mapping

•  Past experience

•  What do we know now?

•  What can we do differently?

•  What have we learned?

Altera8ons that Limit Natural Resilience

•  Development in flood prone areas

•  Impervious floodplains •  Culverted streams and

rivers •  Tidal restric@ons •  Armored river and coastal

banks •  Hardened shorelines •  Barriers to marsh

migra@on

NOAA photo


•  Development in flood prone areas


•  Impervious floodplains


•  Confined stream and river beds


•  Tidal Restric@ons •  Causeways •  Low-‐lying roadways


•  Armored river and coastal banks


•  Hardened shorelines


•  Barriers to marsh migra@on

Photo: Maine Sea Grant


•  Dams •  Culverts

Sea Level Rising/Climate Changing: Key Resource Func8ons to Consider

•  A8enua@on of flood waters •  Ability of storm/flood waters to recede

•  Sediment availability and transport

•  Energy dissipa@on •  Natural resource adapta@on

•  Ecosystem con@nuity

AXenua8on of Flood Waters

•  Limit impervious areas •  Preserve open space in

developments •  Incorporate LID •  Avoid hardening

stream and riverbanks •  Rethink new

development in flood prone areas

Ability of Storm/Floodwaters to Recede

•  Limit new impervious/incorporate LID and

•  Address restric@ons and inappropriate culvert designs

•  Dam removal •  Preserve open space in

developments •  Where do floodwaters

go? •  Consider ousall

loca@ons

AP photo

Reuters photo

Sediment Availability and Transport

•  Unarmored banks •  Bioengineering alterna@ves

•  Re-‐nourishment •  Open pilings for development

•  Re-‐vegeta@on

Energy Dissipa8on

•  Protect dune stability •  Sediment supply •  Maintain floodplain func@on

•  Sol bank stabiliza@on techniques

Natural Resource Adapta8on

•  Marsh migra@on and accre@on

•  Barrier beach migra@on

Ques8ons?

Julia Knisel CZM Coastal Shoreline and Floodplain Manager 617-‐626-‐1191; [email protected] Kathryn Glenn CZM North Shore Regional Coordinator 978-‐281-‐3868; [email protected]

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