Exploring Future Conditions Modeling

and Mapping Through the FEMA Florida

Sea Level Rise Pilot Study

Brian K. Batten, Ph.D., CFM, Rebecca Starosta, PE, CFM

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Study Team

FEMA

• Mark Crowell – Technical Lead

• Mark Vieria – Region IV Project Monitor

RAMPP Team (FEMA Study Contractor)• Emily Dhingra, P.E., CFM – Task Order Manager

• Rebecca Starosta, P.E., CFM – Project Coordinator

• Brian Batten, Ph.D., CFM – Technical Lead

Technical Team:

• Betsy Hicks, Sarah Hamm, Heather Zhao, Joel Plummer,

Patrick Snyder, Alaurah Moss, Chris Reed, Jared Dorvinen,

Taylor Asher

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Agenda

Introduction of FEMA’s SLR Pilot Studies

Technical Scope

• Storm Surge Modeling

• Detailed Wave Hazard Analysis and Mapping

Erosion Projections

• Approximate Wave Hazard Analysis and Mapping

Key Findings

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FEMA’s SLR Pilot Studies

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Technical Mapping Advisory Council Federal Advisory Council

• Initiated by Congress

• Ensure that FEMA uses the best available climate science and methodology to

address the impacts of sea level rise and future development on flood risk

Key Recommendations for Future Conditions

• Conduct future conditions analysis and mapping for non-regulatory informational

purposes

• Address accuracy, precision, and uncertainty of data and analyses

• Provide non-regulatory SLR and long-term coastal erosion map products

• Provide non-regulatory future conditions riverine flood risk products—specifically

future land use and riverine erosion products

• Communicate the risk

• Conduct demonstration projects

• Ensure that methods used for future conditions analyses should be consistent with

methods used to determine current conditions analyses, where appropriate

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FEMA Studies Addressing SLR

FEMA National Studies/Non-pilot efforts:

• Projected Impact of SLR on NFIP (1991)

• The Impact of Climate Change and Population Growth on the

National Flood Insurance Program through 2100 (2013)

• North Carolina Sea Level Rise Impact Study (2009-2013)

• Sea Level Rise Tool for Sandy Recovery (2013)

• National Flood Insurance Program, Programmatic Environmental

Impact Statement, Climate Change elements (2015)

FEMA SLR Pilot Studies

• R2 - Puerto Rico (2010 – Proof of Concept)

• R9 - San Francisco, CA

• R4 - Hillsborough/Pinellas Counties, FL

• R3 - Anacostia River & Prince George’s Co, MD. (Riverine, 2016)

• R1 – Shoreline Change Pilot

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SLR Advisory Layer Concept

Advisory (non-regulatory)

Low incremental production cost

Develop as add-on to Risk MAP studies

Convey future changes to coastal flood hazard

Guide long-term planning & adaptation

Develop for pro-active states & communities

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Technical Scope

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Pilot Study Questions

Evaluate non-linear responses for storm surge for

future conditions

• How different is a future floodplain between “bathtub” approaches

and numerical modeling?

Develop Future Flood Hazard Maps

• What are the challenges creating a future FIRM?

• How sensitive is the map to long-term erosion?

• Can innovative methods provide equally usable products as

compared to the standard FIS approach?

• Is it a useful product to the community?

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Study Area

Where:

• Hillsborough and

Pinellas Counties, FL

What:

• Storm Surge:

Full extent of both

counties

• Wave Hazards and

Mapping

50-miles of coast

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Selection of SLR Scenarios 1. Mid-Century: 0.44 m (1.44 ft)

• Used for creation of the SLR Advisory Products

2. End-of-Century: 1.3 m (4.26 ft)

• Used to provide insights into nonlinearity across diverse coastal environments

Municipal

Planning

Critical Infrastructure Planning

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Storm Surge Modeling

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Extreme water levels & SLR

Existing Flood Hazard + SLR = Future Hazard

Bathtub: 1 + 1 = 2

If we consider dynamics:

• Does 1 + 1 <> 2?

vs

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Detailed Numerical Modeling (FIS Approach)

Mesh Adjustments

for future conditions

Optimize storm suite for study

area

Production runs

Return Period

Analysis (RPA)

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Future Conditions Mesh –Marsh changes

“Surge relevant” changes incorporated:

• Marsh Loss

Source:

Gulf Coast Prairie Landscape Conservation

Cooperative (GCPLCC)

Sea Lever Rise Affecting Marshes Model

Projections

Compatible scenario (1.2 m at 2100)

ID new open water

Proxy elevations

Adjust for RSLR

Update mesh

Update land cover

Update friction

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Future Conditions Mesh –Dune loss

“Surge relevant” changes:

• Stranded dune ridges

• Assumed “to disperse” if stranded

by future high tide levels

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Storm Selection

West Florida FIS

• 6 counties

• 5 frequencies (10-, 4-, 2-, 1-, 0.2-percent-

annual-chance)

• 664 JPM-OS storms

• 80 extra-tropical storms

SLR

• 2 counties

• 1 frequency (1-percent-annual-chance)

• Optimized storm suite

Dropped extra-tropical storms

Reduced JPM-OS storm population (664 121

storms)

0 100 200 300 400 500 600 7000

10

20

30

40

50

60

70

storms

freq

uen

cie

s

1% SWEL contributions for each storm

Exit

Offshore

HC_LF

Inland

TS_LF

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Non-linear Changes in Surge

Clearwater Bay

Gulf of Mexico

Boca Ciega Bay

Tampa/Hillsborough Bay

Sarasota Bay

Tampa/Hillsborough Bay

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Future Flood Hazard Modeling

and Mapping

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Calculation of Future BFEs

Standard FIS Approach

• Realization of a future “FIRM” – advisory layer

with Base Flood Elevations

Erosion Sensitivity

• How sensitive is the FIRM to erosion hazards?

Approximate Methods

• Can approximate methods make reasonably accurate

products?

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Calculation of Future BFEs:Standard FIS Method

Full FIS Process, leverage

investment in data, framework

“Low” scenario: 1.44 feet

Same DEM as FIS (2007 FDEM)

50 miles of coast

313 WHAFIS transects

726 miles of Mapping Linework

Linear increase in SWEL

WHAFIS

RUNUP

Manual interpretation and cartographic mapping

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Calculation of Future BFEs:Detailed FIS Method

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Changes in BFE – linear?

Difference

(feet)

Hillsborough Pinellas

Area (acres) % of TotalArea

(acres)% of Total

0 306 1% 23 0%

1 7,945 21% 4,844 18%

2 27,567 72% 20,461 78%

3 2,182 6% 979 4%

> 3 120 0% 23 0%

SLR scenario

1.4 ft

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Shoreline Change Projections

Linear increase in SWEL

Edit DEM for projected profile translation

WHAFIS

Comparison

Calculation of Future BFEsWith Shoreline Change

Historical Shoreline Change

Historical SLR

Separate SLR related recession

Future SLRShoreline Change

Projection

Bottom before

sea-level rise

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Resulting Shoreline Change:Sand Key

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Resulting Shoreline Change: Pass-A-Grille Beach

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Initial Considerations for a Decision Tree

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Uncertainty in Projections

Calculation Uncertainty

• 43 year future period

• Compounding error:

historical change rate, depth of closure, slope, projected future

SLR scenario, …

• Uncertainty = ~63 ft of change, or ~1.4 ft/yr

• Average change = 124 ft

• Potential Error ~50% of projection

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Comparison of With and Without Shoreline Change

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Comparison of With and Without Shoreline Change

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Calculation of Future BFEs:Approximate Method

Approach: “Tuned” depth-limited equation

Typical

• BFE = 1% annual chance stillwater (SWEL) + controlling wave height (Hc)

• WHAFIS NAS Methodology: Hc = 0.78 x stillwater depth (d)

0.78 = wave height breaking index (i)

Challenge –

• Spatially static application of i

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Calculation of Future BFEs:Approximate Method

“Tuned” depth-limited application

• Leverage FIS WHAFIS to create a spatially-variable i

Solve for iSWEL +

SLRInterpolate i, solve for H

BFE = H + SWEL

Automate Cartography

Post-processing

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Approximate WHAFIS/Mapping

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Approximate WHAFIS/Mapping

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Approximate WHAFIS/Mapping

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Approximate Method – Accuracy

Areal Difference Detailed Product:

Pinellas Hillsborough

Observations:

• FIS cartographic adjustments

• Post-processing

DIFFERENCE

(FEET)% SFHA

< -1 3%

-1 20%

0 61%

1 13%

> 1 1%

DIFFERENCE

(FEET)% SFHA

< -1 1%

-1 15%

0 66%

1 16%

> 1 2%

94% 97%

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Approximate Method –VE Zone Accuracy

Zone Approach

Total

Area,

acres

Difference

(Detailed -

Approximate),

acres

Hillsborough

Detailed

Mapping 1,308 -306

Approximate

Mapping 1,614

Pinellas

Detailed

Mapping 1,582 684

Approximate

Mapping 899

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Summary

Surge Non-linearity

• Change in flood pathways – barrier islands, elevated roads, etc.

Hazard Mapping - Standard FIS Approach

• Feasible through FIS process

• Intermediate level of effort, with caveats

Future Shoreline Change

• Challenges remain, methods improving, high uncertainty

• Impact on map will be site specific

Approximate SLR BFEs

• “Tuning” allows for much improved accuracy

• Very efficient - Production of days instead of weeks

• Error Acceptable?

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Questions?