Coastal Flood Risk Study Project for East Coast Central Florida Study Area

Transcription

1 Coastal Flood Risk Study Project for East Coast Central Florida Study Area St Lucie County, Florida Flood Risk Review Meeting March 28, 2017

2 Introductions Risk MAP Project Team FEMA Region IV BakerAECOM, FEMA Mapping Partner Project Stakeholders Community CEOs Community FPAs Political Representatives Other State and Federal Agencies Public 2

3 Why We Are Here Project Review and Update Data Collected Modeling Approaches Hurricane Surge Overland Wave Analysis Questions and Answers Open Discussion of Draft Work Maps Nassau County, FL 3

4 Project Area Brevard County Indian River County St. Lucie County Martin County 4

5 Why the Coastal Flood Risk Study Is Being Updated Flood risk changes over time Effective study based on outdated hurricane modeling and topographic data Ability to more accurately define risk and account for significant development in project area To gain a complete and current picture of coastal flood risks. This helps 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 5

6 Why the Coastal Flood Risk Study Is Being Updated (Cont d) Current surge analysis is 30+ years old: SURGE FEMA Coastal Flood Storm Surge Model, last updated in the 1980s Climate data from 1975, 1978, and 1979 NOAA reports Your risk is better defined through: Updated elevation data (topographic data and aerial imagery) New climatological data based on recent storms Computing resources a lot has changed in 30 years! Updated coastal hazard methodologies/modeling Improvement in Geographic Information System (GIS) technologies to improve coastal mapping accuracy 6

7 Outreach Meetings Discovery Meeting May 2012 Technical Update Meeting June 2013 Storm Surge Analysis Update Meeting November 2014 Flood Risk Review Meeting Today 7

8 Basic Elements of a Coastal Flood Risk Study Base Flood Elevation (BFE) on FIRM includes four components: 1. Storm surge stillwater elevation (SWEL) Determined from 2. Amount of wave setup storm surge model 3. Wave height above storm surge elevation 4. Wave runup above storm surge elevation (where present) 8

9 Gathered Field Data Coordinated with community officials and stakeholders regarding available data Conducted thorough data investigation Conducted field investigations for surge and overland wave modeling efforts 9

10 Topographic and Bathymetric Data 10

11 Topographic and Bathymetric Data 11

12 Hurricane Model Mesh Development 12

13 Seamless Digital Elevation Model Mesh Resolution 1,406,658 Nodes Complex Terrain / Developed Areas: m ( ft) Offshore: m ( ft) Western Boundary: 1 5 km (3,000 16,000 ft) 13

14 14 Seamless Digital Elevation Model

15 Hurricane Model Mesh St. Lucie County Fort Pierce Inlet, FL 15

16 Hurricane Model Mesh St. Lucie County (Cont d) Fort Pierce Inlet, FL ICWW A1A 16

17 Hurricane Model Mesh Development 17

18 Comparison of Old and New Mesh Node spacing ~3000 feet (0.5 nm) Node spacing feet 18

19 Hurricane Modeling Validate tidal elevation modeling Review historical storms Use historic storms to validate the hurricane/surge model Generate hundreds of hypothetical storms 19

20 Validation Storm Selection: Tidal Elevations Astronomical tides simulated based on 8 tidal constituents Modeled Tides compared to 10 NOAA Stations Agreement based on amplitude and phase 20

21 Storm Climatology: In Study Area Tropical Storms: Passing within 175 nm of Melbourne, FL Limited data before

22 Storm Climatology: In Study Area Significant Events Storm type Landfalling Bypassing Exiting 22

23 Validation Storm Selection: Significant Surge Events 23

24 Validation Storm Selection: Significant Surge Events (Cont d) 24

25 Validation Storm Selection: Significant Surge Events (Cont d) Five Validation Storms Selected 1. Hurricane Irene (1999) 2. Hurricane Frances (2004) 3. Hurricane Jeanne (2004) 4. Tropical Storm Tammy (2005) 5. Hurricane Wilma (2005) 25

26 Validation Storm Selection: Significant Surge Events (Cont d) 26

27 Validation: Summary Validation completed for tides and five historical storms Demonstrated model capability to reproduce water levels and waves in project area Comparisons to available data showed reasonable agreement for water levels and waves 27

28 Hypothetical Storms Developed Using Five Parameters 1. Central pressure 2. Radius to maximum winds 3. Forward speed 4. Storm heading 5. Holland s B (shape parameter) Simulated Whole Range of Possible Storms for FL (Based on Historic Data for Area) Run Storms on High-Speed Computer Performed Quality Control of Results 28

29 Surge Modeling Gives 1-Percent-Annual- Chance SWELs, St. Lucie County Set up mesh for hurricane/surge model Validated hurricane/surge model Ran hundreds of hypothetical storms Computed return periods for study area Result: storm surge stillwater elevations for 1-percentannual-chance event 29

30 Overland Wave Analysis 30

31 St. Lucie County Transects 31

32 WHAFIS and Mapping 32

33 WHAFIS Modeling and Mapping 33

34 Wave Runup Modeling and Mapping 34

35 Wave Runup Modeling 35

36 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 36

37 Limit of Moderate Wave Action (LiMWA) FEMA Procedure Memorandum No. 50, 2008 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 then 1.5 feet 37

38 Combined Probability Mapping Coastal Riverine 38

39 Combined Probability Mapping (Cont d) 39

40 Combined Probability Mapping (Cont d) 40

41 Work Maps Example 41

42 Work Maps Example (Cont d) 42

43 Changes Since Last FIRM - Example 43

44 Upcoming Schedule 44

45 Timeline for Implementation Flood Risk Review Meetings Held: Today Preliminary FIRMs and FIS Reports Delivered: May 2017 CCO Meetings and Flood Risk Open Houses Held: June Day Appeal Periods Started: September 2017 Letters of Final Determination Issued: March 2018 FIRMs and FIS Reports Distributed: May 2018 Resilience Meetings Held: May 2018 FIRMs and FIS Reports Effective: September

46 Study Updates on FEMA Web Portal 46

47 Coastal Flood Risk Study Contacts Mark Vieira, PE (770) Chris Mack, PE, PMP (843) Paul Carroll, PE

48 Open Discussion 48