Storm Surge Analysis Update Meeting Charlotte and DeSoto Counties, Florida March 7, 2018

Transcription

1 Southwest Florida Coastal Storm Surge Study Storm Surge Analysis Update Meeting Charlotte and DeSoto Counties, 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 Town of Fort Myers Beach Hickory Mound Unit Bokeelia Fishing Pier 2

3 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 City of Cape Coral Pine Island near Edison Preserve 3

4 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 4

5 FEMA Region IV Coastal Studies 5

6 Study Overview: Surge Study Area Counties in the Study Area Sarasota DeSoto Charlotte Lee Hendry Collier 6

7 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:

8 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 8

9 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 9

10 Reason for Surge Update Your flood risk is better defined through: Updated topographic elevation data and aerial imagery New climatological data based on recent storms Updated coastal hazard methodologies/modeling Improvement in GIS technologies to improve coastal mapping accuracy To gain a complete and current picture of coastal flood risks. This helps the community: Plan for the risk Communicate the risk to your citizens Take action to reduce flood risk to lives and property build smarter and safer 10

11 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 Evacuation Map Example Coastal SFHA Workmap 11

12 Project Overview: IDS Submittals 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) 12

13 Storm Surge Approach (IDS1 IDS3) Storm Forcing - Hurricane Tracks Storm Surge Modeling Winds Waves Water Levels High-Resolution Bathy / Topo Mesh Return Period Analysis JPM-OS 10%, 4%, 2%, 1%, & 0.2% annual chance Tide Gage Analysis 50% & 20% annual chance Still Water Elev. JPM-OS = Joint Probability Method- Optimum Sampling 13

14 IDS1 Recap: Field Reconnaissance 72 locations in study area Applied this data during mesh development 14

15 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 15

16 IDS1 Recap: Development of ADCIRC Mesh ADCIRC = ADvanced CIRCulation model Finite element model Unstructured, triangulated mesh Node spacing set to accurately represent underlying topo/bathy Feature arcs created to represent important topographic features ARCIRC Mesh 16

17 IDS1 Recap: Development of ADCIRC Mesh Peace River 17

18 IDS1 Recap: Development of ADCIRC Mesh Peace River 18

19 IDS1 Recap: Development of ADCIRC Mesh Punta Gorda 19

20 IDS1 Recap: Development of ADCIRC Mesh Punta Gorda 20

21 IDS1 Recap: Development of ADCIRC Mesh Lemon Bay, Little Gasparilla Island 21

22 IDS1 Recap: Development of ADCIRC Mesh Lemon Bay, Little Gasparilla Island 22

23 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 23

24 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 24

25 IDS2 Recap: Tide & Storm Validation elevation (ft NAVD88) 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 measured modeled modeled-measured Comparison of PWEs for all storms Surge Elevations at Fort Myers during Gabrielle /10/ :00 9/11/ :00 9/12/ :00 9/13/ :00 9/14/ :00 9/15/ :00 25

26 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 26

27 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 27

28 Basic Elements of a Coastal Study Base Flood Elevation (BFE) on a FIRM includes 4 components: Storm surge stillwater elevation (SWEL) Wave setup Determined from storm surge model Wave height above total stillwater elevation Wave runup above storm surge elevation (where present) Determined from overland wave modeling 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 28

29 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 29

30 IDS3: Return Period Analysis At the WFL/SWFL boundary: blended flood levels to obtain a smooth transition 30

31 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 31

32 IDS3: Stillwater Elevations 32

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34 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 34

35 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 nonregulatory products 35

36 Basic Elements of a Coastal Study 36

37 Limit of Moderate Wave Action (LiMWA) FEMA Procedure Memorandum No. 50, 2008 & Operating Guidance 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 37

38 Primary Frontal Dune (PFD) 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 38

39 Risk MAP Program Overview FEMA works with communities to develop flood risk products and flood hazard maps that are: Based on the best available data from the community and latest technologies Conducted by watershed (Riverine) Conducted by affected communities and counties (Coastal) Strengthened by partnerships You can use Risk MAP tools and data to: Create or improve your Local Mitigation Strategies Make informed decisions about development, ordinances, and flood mitigation projects Communicate with citizens about flood risk 39

40 Risk MAP Products Regulatory Products Non-Regulatory Products DFIRM Database Traditional products are regulatory and subject to statutory due-process requirements Risk MAP products are nonregulatory and are not subject to statutory due-process requirements 40

41 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 41

42 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 42

43 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 43

44 Upcoming Outreach 44

45 Next Steps Questions & Answers Pick up RIV Coastal Analysis handout Based on today s discussion, we will finalize and to you: Meeting minutes Copy of this presentation IDS3 report Please provide your feedback and comments within three weeks of receiving that 45

46 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 46

47 Points of Contact Mark Vieira FEMA (770) Kevin Slover RAMPP (678) Emily Dhingra RAMPP (301)