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 Coast
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 West River 4 39 48 16% 6.45 East River 5 41 71 7% 2.87 Hammock River 3 14 47 1% 0.09 Black Hall River 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 Quinnipiac River 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 $)