Coastal Flood Risk Study Project for Georgia

Transcription

1 Coastal Flood Risk Study Project for Georgia Georgia Storm Surge Analysis Update (SSAU) Meeting May 8, 2014 Agenda Welcome and Introductions Update on Coastal Flood Risk Study Stillwater Elevation Information Risk MAP Products Overview Project Milestones Open Discussion of Flood Risk Study Nassau County, FL 2 1

2 Introductions Risk MAP Project Team FEMA Region IV BakerAECOM, FEMA Mapping Partner GA DNR Project Stakeholders Community CEOs & FPAs Political Representatives Other State and Federal Agencies Public 3 The Study Project Area Georgia Counties: Bryan Chatham Camden Charlton Effingham Glynn Liberty Long McIntosh 4 2

3 Why the Coastal Flood Risk Study Is Being Updated Flood risk changes over time Effective study based on outdated hurricane modeling and topographic data Ability to more accurately define risk and account for significant development in project area To gain a complete and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 Why the Coastal Flood Risk Study Is Being Updated (Cont d) Current surge analysis is 20 to 40+ years old Chatham County - Environmental Sciences Services Administration s JPM Method 1970 publication Climate data from 1965 to 1981 NOAA reports Glynn and Camden Counties updated surge in 1989 using SURGE model 6 3

4 Why the Coastal Flood Risk Study Is Being Updated (Cont d) 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 7 FEMA Coastal Flood Risk Study Is Not An Evacuation Study 8 4

5 Basic Elements of a Coastal Flood Risk Study Base Flood Elevation (BFE) on FIRM includes 4 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) 9 Coastal Flood Risk Study Completed Work Coordinated with community officials and stakeholders regarding available data Conducted thorough data investigation Conducted field investigations 10 5

6 Coastal Flood Risk Study Completed Work (Cont d) LIDAR systemgenerated data Gathered bathymetric data 11 Seamless Digital Elevation Model (DEM) for GA-NEFL 12 6

7 DEM Extents 13 DEM Data Sources 14 7

8 DEM Source Data Diversity 15 Complex Bathymetric Features 16 8

9 DEM Quality Control (QC) and Corrections 17 Hurricane Model Mesh Development Hurricane Model Uses unstructured, triangulated mesh Node spacing set to accurately represent topography/bathymetry Created feature arcs to represent elevated or depressed features (i.e. roads or channels) Why do you care? 18 9

10 Hurricane Model Mesh Development (Cont d) 19 Chatham County 20 10

11 Chatham County (Cont d) 21 Chatham County (Cont d) Tybee Island 22 11

12 Chatham County (Cont d) Tybee Island 23 Bryan County 24 12

13 Bryan County (Cont d) 25 Bryan County (Cont d) Savage Island 26 13

14 Bryan County (Cont d) Savage Island 27 Liberty County 28 14

15 Liberty County (Cont d) 29 Liberty County (Cont d) Riceboro, GA 30 15

16 Liberty County (Cont d) Riceboro, GA 31 McIntosh County 32 16

17 McIntosh County (Cont d) 33 McIntosh County (Cont d) Darien, GA 34 17

18 McIntosh County (Cont d) Darien, GA 35 Glynn County 36 18

19 Glynn County (Cont d) 37 Glynn County (Cont d) Brunswick, GA 38 19

20 Glynn County (Cont d) Brunswick, GA 39 Camden County 40 20

21 Camden County (Cont d) 41 Camden County (Cont d) Kingsland, GA 42 21

22 Camden County (Cont d) Kingsland, GA 43 Comparison of Old & New Mesh 44 22

23 Hurricane Model Mesh Development 45 Storm Climatology Review historical storms Pick 5 storms to validate the hurricane/surge model Generate hundreds of hypothetical storms 46 23

24 Storm Climatology: in Study Area Tropical Storms: Passing within 175 nm of Jacksonville Limited data before Storm Climatology: in Study Area Tropical Storms: Passing within 175 nm of Jacksonville Limited data before

25 Validation Storm Selection: Significant Surge Events NOAA stations with water level (WL) data 49 Validation Storm Selection: Significant Surge Events (Cont d) NOAA National Buoy Data Center (NDBC) stations with wave data 50 25

26 Validation Storm Selection: Significant Surge Events (Cont d) 1. Local Landfall Cleo Dora David Chris Edouard Tammy Fay Criteria Sorting of Storms 2. Significant WL Difference Dora (5.91 ft) David (5.55 ft) Jeanne (4.22 ft) Tammy (4.07 ft) Fay (3.99 ft) Frances (3.85 ft) Gabrielle (3.82 ft) Floyd (3.8 ft) Ophelia (3.04 ft) Abby (2.93 ft) Irene (2.92 ft) Bertha (2.62 ft) Bob (2.44 ft) Erin (2.43 ft) Cleo (2.35 ft) Dennis 99 (2.24 ft) 3. WL Data Availability (> 3 Stations) Frances (15) Charley (14) Jeanne (14) Ophelia (9) Tammy (9) Dennis 99 (8) Edouard (8) Floyd (7) Irene (7) Fay (6) David (5) 4. Wave Data Availability (2 or more stations) Frances (5) Ophelia (5) Tammy (5) Fay (5) Jeanne (4) Edouard (3) Charley (3) Chris (2) Dennis99 (2) Floyd (2) Irene (2) 51 Validation Storm Selection: Significant Surge Events (Cont d) 1. Local Landfall Cleo Dora David Chris Edouard Tammy Fay Criteria Sorting of Storms 2. Significant WL Difference Dora (5.91 ft) David (5.55 ft) Jeanne (4.22 ft) Tammy (4.07 ft) Fay (3.99 ft) Frances (3.85 ft) Gabrielle (3.82 ft) Floyd (3.8 ft) Ophelia (3.04 ft) Abby (2.93 ft) Irene (2.92 ft) Bertha (2.62 ft) Bob (2.44 ft) Erin (2.43 ft) Cleo (2.35 ft) Dennis 99 (2.24 ft) 3. WL Data Availability (> 3 Stations) Frances (15) Charley (14) Jeanne (14) Ophelia (9) Tammy (9) Dennis 99 (8) Edouard (8) Floyd (7) Irene (7) Fay (6) David (5) 4. Wave Data Availability (2 or more stations) Frances (5) Ophelia (5) Tammy (5) Fay (5) Jeanne (4) Edouard (3) Charley (3) Chris (2) Dennis99 (2) Floyd (2) Irene (2) 52 26

27 Validation Storm Selection: Significant Surge Events (Cont d) Five validation storms selected Hurricane Dora (1964) Hurricane David (1979) Hurricane Frances (2004) Tropical Storm Tammy (2005) Tropical Storm Fay (2008) 53 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 54 27

28 Hypothetical Storms Using 5 parameters Central pressure, Radius to maximum winds, Forward speed, Storm heading, Holland s B (shape parameter) Covers full range of possible storms for GA Based on historic data for the area Storms run on high-speed computer QC results 55 Completed Work Summary Set up mesh for hurricane/surge model Validated hurricane/surge model Ran hundreds of hypothetical storms Computed return periods for study area Computed storm surge stillwater elevations for 1-percent-annualchance event 56 28

29 Recently Completed and Future Work Focus of Today s Meeting Recently Completed Work Calculated 1-percent-annual-chance stillwater elevations Intended to give you an idea of the results we are seeing Does not correlate directly to what FIRM may show because does not include Part 2 Overland Wave Modeling 57 1-Percent-Annual-Chance Stillwater Elevations Already in Effective FIS 58 29

30 1-Percent-Annual-Chance Stillwater Elevations:Chatham Does not include wave height data Results are variable throughout study area 59 1-Percent-Annual-Chance Stillwater Elevations:Bryan Does not include wave height data Results are variable throughout study area 60 30

31 1-Percent-Annual-Chance Stillwater Elevations:Liberty Does not include wave height data Results are variable throughout study area 61 1-Percent-Annual-Chance Stillwater Elevations:McIntosh Does not include wave height data Results are variable throughout study area 62 31

32 1-Percent-Annual-Chance Stillwater Elevations:Glynn Does not include wave height data Results are variable throughout study area 63 1-Percent-Annual-Chance Stillwater Elevations:Camden Does not include wave height data Results are variable throughout study area 64 32

33 Next Steps: Part 2 Overland Waves Overland Wave Modeling Mapping of Special Flood Hazard Areas (VE and AE zones), Base Flood Elevations (BFEs), Limit of Moderate Wave Action (LiMWA) Develop draft work maps and present at Flood Risk Review Meeting Develop Risk MAP non-regulatory products and present at Resilience Meeting Deliver regulatory products and administer due process 65 Basic Elements of a Coastal Flood Risk Study Base Flood Elevation (BFE) on FIRM includes 4 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) 66 33

34 Basic Elements of a Coastal Flood Risk Study (Cont d) Normal water level Storm surge level Wave setup Wave action 67 Basic Elements of a Coastal Flood Risk Study (Cont d) Dune erosion (540 ft²) 68 34

35 Basic Elements of a Coastal Flood Risk Study (Cont d) Dune erosion (removal) 69 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 Just for open coast CRS benefit for communities requiring VE Zone construction standards in areas defined by LiMWA or areas subject to waves greater then 1.5 ft

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 71 Part 2 Overland Waves 72 36

37 Outreach Activities 73 Coastal Flood Risk Map Depth Grid Areas Affected by Increased Inundation Wave Height Grid Flood Risk Assessment Erosion Risk Shore Protection Structure 74 37

38 Coastal 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 75 Projected Milestones Flood Hazard Work Maps: Fall 2014 Produce FIRMs: Spring 2015 Hold PDCC/CCO Meetings/Open Houses: Summer 2015 Appeal and Adoption/Compliance Periods: Summer 2015 Summer

39 Open Discussion Technical questions? General questions about Risk MAP products? General questions about project schedule? General questions about meeting fact sheet? Other outreach resources? Other questions? 77 Coastal Flood Risk Study Contacts Mark Vieira, PE (770) Christina Lindemer (770) Lynne Keating (770) Michael DelCharco, PE (904) Michael Taylor, PE (404) Todd Harris, CFM (404) Tom Shillock, CFM (404)