CT’s Coastal Marshes and Roads Response to Sea Level Rise (SLR)

Using Sea Level Affecting Marshes Model (SLAMM) to Identify Marsh Conservation & Management Priorities

David Kozak [email protected], CT DEEP-Coastal Mgt. Program East River Marsh & Preserve, Guilford, CT Manage Road  Manage Marsh

Lost Marsh Lost Lake

Great Harbor Marsh Marshes as Coastal Flooding Pathways

Road/Neighborhood Flooding

As the extent and frequency of coastal road flooding increases, will flood control structures in marshes such as tide gates be a less $ road flooding control alternative to road elevation? Objectives: How Will SLR . . .

1. Change the kind and extent of CT’s (largest) coastal marshes?

2. Change road flooding frequencies?

3. Affect marsh restoration/creation opportunities? CT’s Embayment Dominated Estuarine Shoreline

low-energy, sediment poor, bedrock-dominated Glacial Meltwater Deltas Fill Valleys at Ice Margins

sea level hundreds feet below Future tidal marsh area present shoreline, Lake CT drains, ocean water enters LIS basin Source: Lewis and Ouellette at: www.lisrc.uconn.edu/lisrc Marshes in Glacial Meltwater Valley S&G Deltas

Legend: Tidal Marsh/glacial S&G deltas ------Bedrock/till ridges SLR on Coastal Plain vs. CT’s Drowned Valley

CT Coastal Marsh Aerial Imagery

Coastal Plain Drowned Valley Coast

Imagery by Ocean/Estuary Basin SLAMM’s LIS Projected Sea Level Rise

(inches)

CT planning for 20”/50 cm by 2050s SLAMM: Marsh & Upland Response to SLR 2-dimensional model long term wetland change . . .

. . . as function of: • Sea-level rise changes wetland  dryland bdry. elevation • Marsh surface elevation change Shoreline Habitat Boundaries’ Response to SLR

Coastal Marsh Coastal Marsh

SLR

Wet to Dry Land Boundary-(WBE*) Mean High Water

Mean Tide Level Elevation Mean Low Water

Irregularly Regularly Open Water Tidal Flat & Rocky Flooded Transitional Undeveloped and Flooded (“Low”) (Subtidal) Intertidal (“High”) Marsh Developed Dry Land Marsh Marsh

Habitat * ~ 30-day tidal water inundation elevation SLAMM Progression of Saltmarsh Response to SLR Marsh Surface Change Parameters

• Existing marsh platform elevation • Vertical datum corrections • Tide range • Erosion • Wetland boundary elev. • Marsh accretion (SET / MEM derived) More on How SLAMM Works? See warrenpinnacle.com/prof/SLAMM/SLAMM_Presentation.pdf Even More on How SLAMM Works

http://warrenpinnacle.com/prof/SLAMM6/SLAMM_6.7_Technical_Documentation.pdf Coastal Marsh Response to SLR

Locations -  Viability - (sort of) Landowner response - ? Protected vs/ unprotected - ? MARSH LOSS

SLAMM doesn’t assume this SLAMM – One Model, Two Types of Results

• Deterministic –single SLR rates and marsh attribute values

• Probabilistic – multiple SLR rates and marsh attribute values East River Marsh Change – Deterministic (High SLR) 2010 2085 East River Marsh Change – Probabilistic Results (all SLRs) 2010 2085 Predicted Marsh Change by 2100 All CT Tidal Marshes- Alternative SLRs CT High Marsh Dominated Coastal Wetland

Dry Upland

LLow Marsh High Marsh

High Marsh

Transitional Marsh No. Shore L. I. Low Marsh Dominated Coastal Wetland

Low Marsh

High Marsh

Caumsett State Park, Kings Park, NY LIS’ Saltmarsh Future?

Colonel Green Marsh, Mark Stolt, URI Narrow River, Jim Turek, NOAA CT’s 21 Largest Tidal Marshes Large (> 10 acres) Higher Probability* New Marsh (2085) # new marsh Total Area Acres in Marsh areas (acres) # tax parcels % of Area POS POS** Hammonasset River 5 115 24 91% 104.62 Barn Island 3 124 80 50% 61.34 4 39 48 16% 6.45 East River 5 41 71 7% 2.87 Hammock River 3 14 47 1% 0.09 4 31 31 0% 0 Great Island 7 49 82 43% 21.36 Lord Cove 1 34 11 89% 30.06 Plum Bank Oyster River (PBOR) 2 20 88 10% 1.99 6 63 28 27% 17.1 Selden Creek 7 103 14 77% 79.57 Stratford Great Meadows 7 107 48 29% 31.46 * New marsh with majority of area with probability of new marsh > 33% ** Protected Open Space Coastal Marsh Resilience to SLR by 2100* 2010 High 2100 High Marsh (>33%) 2100 Total Marsh 2100 Marsh Ratio Resilience Ranking Marsh Marsh (acres) (acres) (acres) High : Total High Marsh / Total Marsh 2100 Stratford Great Meadows 383 128 777 0.164 1 Ferry Point 97 19 126 0.150 2 Nells Island 398 86 691 0.125 3 West River 333 50 525 0.095 4 Gulf Pond Indian River 150 26 292 0.091 5 Ragged Rock Creek 338 36 412 0.087 6 Pattagansett River 145 21 250 0.082 7 Plum Bank Oyster River 376 49 611 0.080 8 Barn Island 316 54 680 0.080 9 Hammonasset River 300 80 1086 0.074 10 Black Hall River 92 22 342 0.065 11 Selden Creek 2 24 426 0.056 12 Great Harbor 35 9 162 0.055 13 Menunketesuck River 182 16 301 0.055 14 Hammock River 300 26 481 0.054 15 Great Island 697 51 960 0.053 16 Hoadley Neck Stony Creek 118 9 198 0.047 17 Essex Great Meadows 164 10 209 0.046 18 Lord Cove 403 24 579 0.042 19 East River 778 50 1285 0.039 20 Quinnipiac River 530 45 1316 0.034 21 * Ranked according to % of total marsh forecasted to be high marsh (with >33% probability) by 2100 - considers ALL SLAMM SLR scenarios East River Large Higher Probability New Marsh Migration Area Scoring Protocol*

MARSH MIGRATION AREA CRITERIA Weighting

Probability 3x 67-100% (3 points) 34-66% (2 points) 1-33% (1 point)

# landowners within the parcel? 2x 1 to 5 land owners (3 points) 6 to 10 land owners (2 points) Greater than 10 land owners (1 point)

Ownership of the parcels 67-100% public or conservation ownership (3 points) 34-66% public or conservation ownership (2 points) 0 - 33% public or conservation ownership (1 point)

Size/Area 3x 101 - 216 acres (4 points) 51 - 100 acres (3 points) 26 - 50 acres (2 points) 10 - 25 acres (1 point)

Position of parcel within the larger "marshscape" 2x seaward of tidal restriction (1 point) inland of tidal restriction (0 points)

Soil suitability 1x High (2 points) Medium (1 point) Low. (0 point) * Additional criteria: marsh supporting nesting birds, conservation interest of landowner, erosion/ flood protection benefits etc. SLAMM Limitations

George P. Box (1919-2013) State Model Improvements  Marsh Change

• Flooding frequencies effects (storms?)

• Upland characteristics (woodland, shrubland, field . . )

• Soil type

• Effects of tidal restriction/muting Road Flooding Bluff Pt. State Park, Groton, CT 11/26/18 Extreme High Tide Event

2 feet of tidal water at Amtrak overpass from catch basin surcharge/Poquonnuck River flooding Ground-truthing SLAMM’s Existing Tidal Flooding Frequencies

SLAMM Predicted 2010 Road Flooding Conditions

30-60 day confirmed road flooding SLAMM Predicted Road Flooding Frequency Change

SLAMM Existing (2010) Road Flooding Conditions 2050’s Road Flooding Conditions ~18 inches SLR Statewide All Roads Flooding Frequencies (floods at least every ___ days) 300

250

Road Flooding 200 Recurrence Intervals (days)

90 150 60 miles 30

100

50

0 2010 2025 2040 2055 2085 2100

Year

20.00

15.00 100yr 10yr

miles 90 60 10.00 30

5.00

0.00 2010 2025 2040 2055 2085 2100 Mid-Century Road Flooding Near Coastal Marshes

What do these marshes have in common?

?

(Hint: ) Modify Hydraulic Connections at Road Crossings

Existing Marsh Future marsh migration area or or housing development?

Modified hydraulic connection? SLR Marsh Creation/Restoration Opportunities as Mitigation for TW Filling For Road Reconstruction in Tidal Wetlands

Tidally- unconnected inland wetland/dry upland below future WBE  TW by 2100 with 1 m SLR if non- connected tidal direction of following tidal image of culverts Invert elevation restricts tidal flow to north side of road?

tidal marsh

Future marsh?

Future road reconstruction requiring TW fill? Road Flooding Mgt. = Marsh Management

Road Flooding Management Marsh Migration Management

new marsh migration area

Hmm?

CT Coastal Marsh Aerial Imagery

http://wp.stockerphotography.com/slamm/ Road Flooding Mgt. Questions

 Allocating scarce road flood-proofing $: • Road elevation/reconstruction ‘factors to consider’ (e.g., road flooding frequency 30 days, 60 days, … ?) • Other factors? (e.g., traffic volumes, sole neighborhood access, emergency access)

 Tidal wetland fill (for road construction) mitigation priorities?  Flooded road discontinuance / abandonment* ‘tipping-point’?  Road flooding planning horizon (10,20, 30 . . . years)?  Who is/should decide which road(s) to elevate (town engineer)?

* See CT Adapt legal analysis handout Marsh Management Questions

 Marsh migration area conservation vs. marsh restor./creation?

 Marsh migration area regulation vs. acquisition?

 Marsh migration conservation area priorities?

 Greatest obstacles to successful marsh migration conservation?* * (other than $)