Southwest Florida

Coastal Storm Surge Study

Storm Surge Analysis Update MeetingSarasota County, Florida

March 7, 2018

2

Agenda

Introductions

Goals for Today

SWFL Coastal Surge Study

• Study Overview & Schedule

• Storm Surge Methodology

• Stillwater Elevation Information

Risk MAP Overview & Products

Next Steps

Meet to Gather Input

Hickory Mound Unit Bokeelia Fishing Pier

Town of Fort Myers Beach

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Welcome

Risk MAP Project Team

• FEMA

• RAMPP (study contractor)

Project Stakeholders

• State partners and officials

• Officials from local communities

CEOs / Elected Officials

Floodplain Administrators

Engineers

Emergency Planners

• Universities

• Other Federal agency representatives

• Non-governmental organizations

Pine Island near Edison Preserve

City of Cape Coral

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Goals for Today

Promote engagement with the communities

Discuss the Southwest Florida Coastal Surge Study and the

status of the study

Discuss the study methodology and results

• Mesh Development

• Storm Climatology

• Validation Storms

• Stillwater Elevations

Gather technical input and feedback from you

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FEMA Region IV Coastal Studies

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Study Overview: Surge Study Area

Counties in the Study Area

• Sarasota

• DeSoto

• Charlotte

• Lee

• Hendry

• Collier

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Study Overview: Project Schedule

Completed

• Discovery Kickoff Meeting: February 2014

• Discovery Meeting: March 2014

• Mesh Review Meeting: September 2014

• Storm Surge Analysis Update Meeting: Today

Currently Ongoing

• Overland Wave Modeling (WHAFIS): Spring/Summer 2018

Upcoming

• Flood Risk Review Meeting: Summer 2018

• Preliminary Flood Insurance Rate Maps: 2019

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Reason for Surge Update

Flood risk changes over time

• Effective surge analysis is based on older hurricane modeling and

topographic data

Sarasota: 1978 (FEMA’s Standard Surge Model)

Charlotte: 1976 (US Dept. of Commerce’s SPLASH model)

Lee: 1984 (FEMA’s Standard Surge Model)

Collier: 2009 (FEMA’s Standard Surge Model)

Study area was selected due to risk and ongoing studies

• Significant flood risk from coastal storms (hurricanes, tropical storms)

• Increase in population and development since Effective coastal FIRMs

were published

• Ongoing riverine watershed flood studies

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Example of FEMA Standard Surge Model vs ADCIRC

FEMA Standard Surge Model

Cells are 1500 ft x 1500 ft

ADCIRC Mesh

Spacing 90 ft to 300 ft

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Reason for Surge Update

Different methods and goals from the 2010 FDEM Surge Study

2010 FDEM Evacuation Study FY ‘13 FEMA Surge Study

Inundation levels for evacuation planning Mapping 1% annual chance flood hazard

Included entire Florida coast Focus on Southwest Florida counties

Base data includes recent LiDAR data Base data includes recent LiDAR data

SLOSH model ADCIRC and SWAN models

Example Coastal SFHA WorkmapExample Evacuation Map

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Project Overview: IDS Deliverables

IDS1

• Field Reconnaissance

• Digital Elevation Model (DEM)

• Development of ADCIRC Mesh

• Storm Climatology

• Validation Storm Selection

IDS2

• Tide & Storm Validation

• Statistical Method Development

IDS3

• Production Runs

• Return Period Analysis

• Stillwater Elevations

• Starting Wave Conditions

IDS4 and IDS5

• Nearshore Hydraulics

• Draft Flood Hazard Mapping

Mesh Review Meeting (Sept 2014)

All Hands Meeting (Feb 2015)

Report Review (Feb/March 2015)

All Hands Meeting (Oct 2015)

Report Review (Feb – Nov 2017)

SSAU Meeting (Today)

Flood Risk Review Meeting

(Summer/Fall 2018)

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Storm Surge Approach (IDS1 – IDS3)

Return Period AnalysisJPM-OS 10%, 4%, 2%, 1%, & 0.2% annual chance

Tide Gage Analysis 50% & 20% annual chance

Still Water Elev.

High-Resolution

Bathy / Topo Mesh

Storm Surge Modeling

Winds

Waves Water Levels

Storm ForcingHurricane Tracks

JPM-OS = Joint Probability

Method- Optimum Sampling

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IDS1 Recap: Field Reconnaissance

72 locations in study area

Applied this data during mesh

development

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IDS1 Recap: Digital Elevation Model

Shoreline

Topographic Data

• LiDAR

• FWC Enhanced Elevation

• National Elevation Dataset

Bathymetric Data

• NOAA GEOphysical Data

Management System

• Electronic Navigational Charts

• USACE Hydro Survey

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IDS1 Recap: Development of ADCIRC Mesh

Finite element model

Unstructured,

triangulated mesh

Node spacing set to

accurately represent

underlying topo/bathy

Feature arcs created to

represent important

topographic features

ADCIRC = ADvanced CIRCulation model

ARCIRC Mesh

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IDS1 Recap: Development of ADCIRC Mesh

Sarasota and Roberts Bay

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IDS1 Recap: Development of ADCIRC Mesh

Sarasota and Roberts Bay

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IDS1 Recap: Development of ADCIRC Mesh

Venice

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IDS1 Recap: Development of ADCIRC Mesh

Venice

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IDS1 Recap: Development of ADCIRC Mesh

Myakka River

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IDS1 Recap: Development of ADCIRC Mesh

Myakka River

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IDS1 Recap:Storm Climatology

Reviewed historical

storms

Selected tropical storms to

validate the hurricane /

surge model

Generated hundreds of

synthetic storms

LandFall Storm Population and Tracks

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IDS1 Recap:Validation Storm Selection

Storms Selected:

• Hurricane Donna (1960)

• Tropical Storm Gabrielle (2001)

• Hurricane Charley (2004)

Selected based on peak surge

and available data

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IDS2 Recap:Tide & Storm Validation

Validation Data:

• Tide harmonic constituent data

• Surge descriptions and

measurements

• Water level gages

• High Water Marks

• Wave buoy data

Simulated and known

tides

Simulated and recorded

surge elevations and wave

characteristics for three

historical storms

-2

-1

0

1

2

3

4

9/10/2001 12:00 9/11/2001 12:00 9/12/2001 12:00 9/13/2001 12:00 9/14/2001 12:00 9/15/2001 12:00

elev

atio

n (

ft N

AV

D8

8)

measuredmodeledmodeled-measured

Surge Elevations at Fort Myers during Gabrielle

Comparison of

PWEs for all storms

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IDS2 Recap:Statistical Method Development

Developed probabilistic model for the occurrence and characteristics of

hurricanes that generate significant surge along SWFL coast

Generated the JPM-OS storm set of representative synthetic storms

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IDS3: Production Runs

Simulation of synthetic tropical

cyclones using ADCIRC+SWAN

• Total of 395 synthetic storms

(hurricanes and tropical storms)

• Time steps selected based on model

efficiency and stability

ADCIRC time step = 1 second

SWAN time step = 15 minutes

Simulations executed at random

start times to represent the effects

of astronomical tides

Steric effect determined using

NOAA’s seasonal trend data

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IDS3: Return Period Analysis

Processed results of the production runs to develop:

• Coastal Stillwater Elevations (SWELs) for the 50-, 20-, 10-, 4-, 2-, 1-, and

0.2-percent-annual-exceedance flood levels

• Wave heights and periods for the 1- and 0.2-percent-annual-exceedance

flood levels

Developed surge-frequency curves for tropical cyclones from

the production runs output

• For 10-, 4-, 2-, 1-, and 0.2-percent-annual-exceedance flood levels

Analyzed historical NOAA water level gages

• For 50- and 20-percent-annual-exceedance flood levels

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Basic Elements of a Coastal Study

Base Flood Elevation (BFE) on a FIRM includes 4 components:

• Storm surge stillwater elevation (SWEL)

• Wave setup

• Wave height above total stillwater elevation

• Wave runup above storm surge elevation (where present)

All applied to an eroded beach profile (when applicable)

The above components are computed through

• Terrain processing and profile erosion

• Storm surge study for SWELs determination

• Coastal Hazard Analysis

Determined from

storm surge model

Determined from overland

wave modeling

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IDS3: Return Period Analysis

At the WFL/SWFL boundary: blended flood levels to obtain a

smooth transition

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IDS3: Stillwater Elevations

Calculated 1-percent-annual-chance stillwater elevations

(SWELs)

• These are intended to give you an idea of the results we are seeing

Comparison to Effective SWELs

• Does not correlate directly to what the FIRM may show because the

published SWEL does not include wave heights

• Effective SWEL locations are approximate

• Results are variable throughout study area

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IDS3: Stillwater Elevations

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IDS3: Starting Wave Conditions

Determined starting wave conditions to be used in the

subsequent overland analysis

Starting Wave Heights for 1-percent SWEL Starting Wave Periods for 1-percent SWEL

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Upcoming Work

IDS4: Overland Wave Modeling

IDS5: Mapping

• Special Flood Hazard Areas

• Base Flood Elevations (BFEs)

• Limit of Moderate Wave Action

(LiMWA)

Develop draft work maps

Develop Risk MAP non-

regulatory products

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Basic Elements of a Coastal Study

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Limit of Moderate Wave Action (LiMWA)

FEMA Procedure Memorandum No. 50, 2008 &

Operating Guidance 13-13

At present not a regulatory requirement

No Federal Insurance requirements tied to LiMWA

CRS benefit for communities requiring VE Zone

construction standards in areas defined by LiMWA

or areas subject to waves greater than 1.5 feet

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“a continuous or nearly continuous mound or ridge of sand with relatively

steep seaward and landward slopes immediately landward and adjacent

to the beach and subject to erosion and overtopping from high tides and

waves during major coastal storms” –NFIP regulations

Primary Frontal Dune(PFD)

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Risk MAP Products

Traditional products are

regulatory and subject to statutory

due-process requirements

Risk MAP products are non-

regulatory and are not subject to

statutory due-process requirements

DFIRM Database

Regulatory Products Non-Regulatory Products

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Risk MAP Products: Flood Risk Map

Visually Promotes Risk

Awareness

• Contains results of Risk MAP

project non-regulatory datasets

• Promotes additional flood risk data

not shown but located within the

Flood Risk Database

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Risk MAP Products:Changes Since Last FIRM

Makes it easy for communities

and homeowners to identify

impacts of new FIRM

Assists in prioritizing mitigation

actions

Helps identify reasons for

changes

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Work Breakdown

Work to be done by RAMPP (PTS):

• Support Discovery and outreach

• Perform coastal storm surge and wave height

analyses

• Perform coastal floodplain delineation and develop

workmaps

• Develop coastal Risk MAP products

Work to be done by COMPASS (PTS):

• Perform the Preliminary map production

• Perform the Post-Preliminary map production

• CCO/Open House Meeting

CCO = Community Coordination and Outreach

PTS = Production and Technical Services

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Upcoming Outreach

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Next Steps

Questions & Answers

Pick up RIV Coastal Analysis handout

Based on today’s discussion, we will finalize and email to you:

• Meeting minutes

• Copy of this presentation

• IDS3 report

Please provide your feedback and comments within three weeks

of receiving that email

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Thank You

We look forward to continuing to work with you to help the

Southwest Florida coastal area become more resilient to flooding.

Sanibel Island

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Points of Contact

http://www.southeastcoastalmaps.com/

Mark VieiraFEMA

Mark.Vieira@fema.dhs.gov

(770) 220-5450

Kevin SloverRAMPP

KSlover@dewberry.com

(678) 537-8639

Emily DhingraRAMPP

Emily.Dhingra@aecom.com

(301) 820-3259