COAB Deliverable 2 MemoMEMORANDUM
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
2201 N.W. 40th TERRACE
GAINESVILLE, FLORIDA 32605-3574
386.256.1477
To: Justin Gregory, PE, Jones Edmunds
From: Heath Hansell, PE and Marc Gold, EI
CC: Nico Pisarello
Date : April 19, 2019
Re : Final City of Atlantic Beach Coastal Flooding Assessment
This memo summarizes the methodology and technical analysis utilized to determine future 100-
year flood hazards due to anticipated sea level rise (SLR) for the years 2044, 2069, and 2119. The
purpose of this analysis is to estimate future coastal flood risks from increased storm surge
elevations and wave heights at Atlantic Beach due to rising seas.
ATM’s analysis of potential future coastal hazards was conducted using the effective 2018 FEMA
Flood Insurance Study (FIS) for Duval County, NOAA 2017 SLR projections, and site-specific modeling
using FEMA’s CHAMP (Coastal Hazard Analysis and Mapping Program) v.2.0 model suite, described
in the subsequent sections. The Atlantic Beach digital elevation model (DEM), provided by Jones
Edmunds, was derived from LiDAR data originally obtained by the Florida Division of Emergency
Management (FDEM) in 2007 and processed to a resolution of 5 feet horizontally and an elevation
accuracy of 0.6 foot at the 95% confidence level. This DEM served as the basis of topographic data
for this assessment. Please note that all elevations referred to in this document are in feet and
referenced to NAVD88.
The resulting products of this assessment are the attached four flood maps depicting flood hazard
areas of inundation with assigned base flood elevations (BFEs) for the current year and each SLR
time horizon: 2044, 2069, and 2119. The digital map data was provided to Jones Edmunds under
separate cover.
Methodology
FEMA Flood Mapping
In the United States, present-day flood hazards associated with extreme event coastal storm surge
and waves are typically based on FEMA’s FIS and Flood Insurance Rate Maps (FIRMs). These
documents analyze rain event flooding, storm surge and wave impacts to provide map exhibits
showing the geographical limits and severity of coastal risk. In general, the more severe the risk at
any given location, the higher FEMA’s recommended flood zone and BFE. In general, FEMA coastal
mapping includes two major parts: water level/surge modeling and wave transect modeling.
Memorandum to Justin Gregory, PE
April 19, 2019
Page 2 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Water Level/Surge Modeling
Water level/surge modeling results in extreme event stillwater flood elevations (SWELs) based on
what is commonly referred to as a “100-year” storm event. SWEL flood elevations can vary by
location and are comprised of:
• Existing mean sea level (MSL) at the time of the study
• Tidal fluctuations
• Extreme event storm surge (including local wave setup)
These SWEL flood elevations do not include storm waves. Storm waves travel on top of the SWEL
and will increase flood risks and elevations.
Wave Transect Modeling
Once the 100-year SWEL is determined, extreme event storm waves are analyzed at select locations
along the shorelines (coastal analysis transects). Coastal analysis transects are typically spaced
several hundred feet or farther apart and represent detailed cross-sections of the shoreline and
upland from the ocean or from inland estuarine areas (flooding source) to higher ground. Figure 1
illustrates a coastal wave transect. Wave transect modeling results in FEMA’s BFEs which include
SWEL flood elevations from surge modeling and the elevation of waves on top of the SWEL. The
wave transect modeling results (BFE and flood zone type) are interpolated between transects to
draw the FEMA flood zones and elevations that comprise FEMA maps.
Figure 1. Illustration of a coastal wave transect
Water Level/Surge
Modeling Results
Wave Transect
Modeling Results
Upland Limit of Stillwater
Flooding Inundation
Memorandum to Justin Gregory, PE
April 19, 2019
Page 3 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Accounting for Sea Level Rise
FEMA flood maps are updated on a regular basis (typically every 10 years). FEMA only considers the
existing mean sea level at the time of the update and does not account for future sea levels (i.e.,
SLR). For the current assessment, ATM conducted an analysis based on the FEMA flood mapping
protocol and evaluated coastal flooding and wave risks under a range of SLR scenarios (25, 50, and
100 years into the future). In essence, FEMA-type flood maps were created for future, higher sea
level scenarios. This process included:
• Using established SLR predictions from NOAA, U.S. Army Corps of Engineers, and others to
determine the predicted mean level at Atlantic Beach at 25, 50, and 100 years into the
future.
• Using existing FEMA SWEL results but increasing the elevations to account for SLR and
evaluate future sea level conditions. These elevations were used to create inundation maps
that show the limits of extreme event flooding under future sea level conditions.
• Updating wave transect modeling on top of the increased SWEL elevations to predict BFEs
under future higher sea levels.
o Wave modeling is very sensitive to water depth and increased future sea levels will
allow larger waves to travel further inland during storms because there is more area
inundated with higher SWEL.
o These evaluations were used to create FEMA-type flood maps for future higher sea
level scenarios.
The process is generally illustrated in Figure 2.
Figure 2. Illustration of modeling effects of SLR
The following sections provide detailed information on ATM’s technical analysis.
FEMA Flood Maps and Supporting Data (Existing 100-Year Flood Risks)
The effective Duval County 2018 FEMA FIRMs and supporting FEMA data served as the basis of the
existing/present-day 100-year flood risks for Atlantic Beach.
Memorandum to Justin Gregory, PE
April 19, 2019
Page 4 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
The 100-year SWEL raster included in the Technical Supporting Data Notebook (TSDN) for the Duval
County FIS was downloaded from FEMA’s Flood Risk Study Engineering Library (FRISEL) website
(https://hazards.fema.gov/wps/portal/frisel) and imported into ArcGIS, version 10.6. Figure 3
depicts the 100-year (or 1% annual chance) SWEL surface over Atlantic Beach. The SWEL shown in
Figure 3 is referred to throughout this memo as the “existing” 100-year SWEL, as these represent the
1% annual chance SWEL under present-day conditions (without any additions to the water level to
account for SLR).
Figure 3. FEMA 100-Year SWEL and FIS analysis transects for Atlantic Beach
Memorandum to Justin Gregory, PE
April 19, 2019
Page 5 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Based on the most recent FEMA FIS, SWEL (storm surge) values are largest along the open Atlantic
Coast. Larger SWEL values are also observed on the western estuarine shoreline due to elevated
water levels from the St. John’s River Inlet and the Atlantic Intracoastal Waterway (AIWW) under
extreme conditions. The SWEL is essentially the starting water level for coastal flood mapping
purposes but does not include wave effects other than wave set-up. The other wave components
that need to be considered are wave heights, wave run-up, and overtopping. For coastal
communities such as Atlantic Beach, these unaccounted for wave effects from the open coast as well
as from back bays and sheltered waterways are added to the SWEL to determine the total BFE
depicted on FEMA flood maps.
ATM utilized two existing FEMA wave analysis transects at Atlantic Beach to evaluate wave
conditions on top of the future higher sea level SWEL scenarios. Figure 4 presents the transects
overlaid on Atlantic Beach topography (ground elevation). For consistency, ATM used the same
transect numbering as the FIS. Transect 44 is representative of “sheltered water” and begins in the
waterways adjacent to the AIWW and runs east across the marsh and onto the upland of Atlantic
Beach. Transect 25 is representative of “open coast” and begins in the Atlantic Ocean and runs west
across beach and onto the upland of Atlantic Beach. Both transects are considered representative of
the variation of topographic conditions occurring throughout Atlantic Beach. Transect 25 was
conservatively selected as the open coast analysis transect due to the relatively lower dune
topography and larger SWEL inundation extent observed along the more vulnerable southern
shorelines of Atlantic Beach. FEMA wave analysis transects are modeled using inputs such as
topography, vegetation, structural/building inputs, SWEL flood elevations, and storm wave height
conditions. The updated CHAMP wave modeling for analysis Transects 25 and 44 under future SLR
conditions is detailed in subsequent sections.
Memorandum to Justin Gregory, PE
April 19, 2019
Page 6 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 4. Atlantic Beach topography and transects
Based on effective FEMA flood maps, the majority of land within the jurisdictional limits of the City
of Atlantic Beach is outside of the Special Flood Hazard Area (SFHA) (see Figure 1). Areas outside the
SFHA are not predicted to experience flooding or wave hazards during the 100-year storm condition.
Areas within the SFHA are assigned BFEs depending on flood study results.
Memorandum to Justin Gregory, PE
April 19, 2019
Page 7 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 5. BFE inundation map based on FEMA effective 2018 digital FIRM for Atlantic Beach
Future 100-Year Coastal Flood Hazards
With anticipated rising sea levels, coastal flood hazards will increase both in terms of higher flood
elevations as well as the inland extent to which inundation of extreme flood waters can reach. As
greater areas of upland are inundated, larger waves are then able to propagate farther inland,
further increasing the potential for storm damage. The following sections summarize the analyses
used to assess the future coastal flood hazards from extreme (100-year return period/1% annual
chance) surge and wave conditions for Atlantic Beach based on projected sea level increases.
SLR Projections
ATM’s coastal hazard analysis of future sea level conditions utilized the NOAA 2017 Intermediate
High Sea Level Rise projection curve for the NOAA tide gauge station at Mayport, FL (see Figure 6).
Memorandum to Justin Gregory, PE
April 19, 2019
Page 8 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 6. Mayport Gauge - USACE Sea-Level Change Curve Calculator
The NOAA 2017 SLR curves are based on a year 2000 start date. Upon discussion with Jones
Edmunds, it was determined that the SLR curve values should be adjusted for a baseline start date of
2013 since this was the date the effective FEMA FIS and mapping were completed for Duval County
and represented existing sea level conditions at that time.
As a result, the curve values were adjusted for the three time-horizon scenarios by subtracting the
projected SLR value of 0.39 foot for the year 2013 from the projected 2044, 2069, and 2119 values.
The final values used for ATM’s analysis are shown in bold in Table 1.
Table 1. SLR Values for Coastal Hazard Analysis
Year Projected SLR
(2000 Start Date)
Adjusted Projected SLR
(2013 Start Date)
2044 1.65 feet 1.26 feet
2069 3.24 feet 2.85 feet
2119 7.34 feet 6.95 feet
Future SWEL and Inundation
Future 100-year SWEL elevations were developed for each time-horizon scenario by adding the
values in Table 1 to the existing 100-year SWEL flood elevations from the effective FIS. Next, as a
baseline assessment of inundation, a direct comparison of these surfaces to the existing Atlantic
Beach topography was conducted.
Figures 7-9 present the resulting baseline data showing the areas of inundation/flooding in blue
(“Below SWEL”) under each SLR scenario. As would be expected, the extent of areas submerged
during the 100-year event increase with elevated sea levels further into the future. As Figure 9
shows, almost all of Atlantic Beach will potentially be inundated during an extreme 100-year storm
event in the year 2119.
Memorandum to Justin Gregory, PE
April 19, 2019
Page 9 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
These figures provide very useful information but are not truly representative of future coastal
hazards possible for Atlantic Beach since wave effects (increases in BFEs) and increased flood extents
in the areas of combined riverine and coastal flooding were not accounted for. Therefore, the
inundation figures were used as a starting point for generating future flood hazards at Atlantic
Beach. Based on the updated transect analysis modeling and FEMA flood mapping techniques and
guidelines described in the subsequent sections, the inundation maps were assigned BFEs to
represent future sea level scenario coastal risks.
Figure 7. Year 2044 SWEL inundation (topography below 2044 SWEL)
Memorandum to Justin Gregory, PE
April 19, 2019
Page 10 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 8. Year 2069 SWEL inundation (topography below 2069 SWEL)
Memorandum to Justin Gregory, PE
April 19, 2019
Page 11 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 9. Year 2119 SWEL inundation (topography below 2119 SWEL)
Sheltered Water (AIWW) Flood Hazards
Flood hazards along the estuarine shoreline due to waves incident from the AIWW were evaluated
for Atlantic Beach along Transect 44 using the FEMA WHAFIS (Wave Height Analysis for Flood
Insurance Studies) overland wave propagation model. For conservatism, the entire transect was
assumed as open space Inland Fetch (IF); no vegetation or obstruction cards were used. The future
100-year SWEL values were extracted along the transect for each scenario using the generated
rasters mentioned previously. An input starting significant wave height (Hs) of 2.9 feet and a peak
wave period (Tp) of 2.9 seconds was used based on the effective FEMA FIS. Results of the WHAFIS
wave analysis for each SLR scenario are graphically depicted in Figures 10 - 12.
Memorandum to Justin Gregory, PE
April 19, 2019
Page 12 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 10. Estuarine transect WHAFIS results for year 2044
Figure 11. Estuarine transect WHAFIS results for year 2069
Figure 12. Estuarine transect WHAFIS results for year 2119
-4
1
6
11
16
0 500 1000 1500 2000 2500 3000 3500 4000El
e
v
a
t
i
o
n
,
f
t
N
A
V
D
8
8
Station, ft
Transect 44: 2044 WHAFIS Outputs
Transect 44 Topo 2044 SWEL 2044 WHAFIS Results
AE ZonesVE Zones Localized X Zones
Marsh
AIWW Upland
-4
1
6
11
16
0 500 1000 1500 2000 2500 3000 3500 4000
El
e
v
a
t
i
o
n
,
f
t
N
A
V
D
8
8
Station, ft
Transect 44 -2069 WHAFIS Outputs
Transect 44 Topo 2069 SWEL 2069 WHAFIS ResultsAIWW Upland
Marsh
AE ZonesVE Zones
-4
0
4
8
12
16
20
0 1000 2000 3000 4000 5000 6000 7000
El
e
v
a
t
i
o
n
,
f
t
N
A
V
D
8
8
Station, ft
Transect 44 -2119 WHAFIS Outputs
Transect 44 Topo 2119 SWEL 2119 WHAFIS ResultsAIWW Upland
Marsh
AE ZonesVE Zones Localized X Zones
MEMORANDUM
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
As mentioned previously, larger waves are able to progress farther inland due to rising seas. As a
result, BFEs can increase substantially since now there is both elevated water levels and increased
wave heights creating a higher wave crest elevation used for determining the total BFE.
The output VE zones and AE zones (representative of a 3-foot wave height delineation in this area)
are shown based on the WHAFIS results; however, it is more important to focus on the extent and
elevation as waves less than 3 feet can cause substantial damage and should be considered for
resiliency planning purposes. Similarly, although locations above SWEL are output as X zones and not
considered within the floodplain extent, these areas can still be at risk and subject to wave ramping/
splash effects.
Open Coast (Atlantic Ocean) Flood Hazards
Flood hazards along the ocean shoreline of Atlantic Beach were assessed at the Transect 25 location.
The original and predicted storm-eroded profiles along the open coast are shown in Figures 13 and
14. FEMA flood mapping guidelines require that dunes be eroded under certain extreme event
conditions. Based on calculated sand reservoirs in the existing dunes at Transect 25 being less than
540 square feet, FEMA guidelines (FEMA, 2007) dictate the dune be removed (erosion) for analysis.
The eroded profile exhibits a 1 on 50 slope passing through the dune toe per FEMA protocol and the
configuration is consistent with the erosion methods used for Transect 25 in the effective FEMA FIS
(IDS 4 and 5).
Following FEMA guidelines, the eroded profile was implemented for all modeling/analysis and
resulting mapping, and the erosion configuration was kept consistent for each SLR scenario. No
shoreline recession was assumed to take place between the time-horizon projections since it is
expected that Atlantic Beach will continue its beach renourishment efforts in the future.
Wave propagation and wave runup were assessed at Transect 25 using the WHAFIS and Runup 2.0
modules in FEMA’s CHAMP model suite. The same input 100-year storm wave conditions (Hs = 18.7
feet, Tp = 12.8 sec) that FEMA predicted for the effective FIS (IDS 4 and 5 model files) were used in
the updated modeling.
Based on WHAFIS and Runup 2.0 runs at Transect 25, wave runup elevations were significantly
higher than wave crest elevations along the open coast under the 2044 and 2069 scenarios.
Therefore, along the open coastline, wave runup is the controlling hazard determining flood
elevations per FEMA protocol. The final BFE in these areas is the sum of the SWEL and the 2% runup
value output from Runup 2.0 to give a total water level that is conservatively rounded to a whole
foot BFE. The resulting future BFEs determined from Runup 2.0 and the wave runup extents under
the 2044 and 2069 scenarios are provided in Figures 13 and 14, respectively.
Under the 2119 scenario, the entire dune topography, as well as the majority of the transect
continuing inland, is below the SWEL. Wave runup is not applicable in this situation as waves are
able to propagate over the coastal topography in this more vulnerable reach of shoreline south of
Memorandum to Justin Gregory, PE
April 19, 2019
Page 14 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Atlantic Beach. Under the 2119 SLR projection, WHAFIS outputs are used in determining the coastal
flood hazards along Transect 25 (see Figure 15).
Figure 13. BFEs under the year 2044 scenario
Figure 14. BFEs under Year 2069 scenario
0
4
8
12
16
20
0 50 100 150 200 250 300 350 400 450 500
El
e
v
a
t
i
o
n
,
f
t
N
A
V
D
8
8
Station, ft
Transect 25 -Year 2044 Wave Runup
Transect 25 Non-Eroded Transect 25 Eroded Topo 2044 SWEL 2044 Runup Limit
Ocean Upland
VE (Elev.14) Zone X Zone
0
4
8
12
16
20
0 50 100 150 200 250 300 350 400 450 500
El
e
v
a
t
i
o
n
,
f
t
N
A
V
D
8
8
Station, ft
Transect 25 -Year 2069 Wave Runup
Transect 25 Non-Eroded Transect 25 Eroded Topo 2069 SWEL 2069 Runup Limit
Ocean Upland
VE (Elev.17) Zone X Zone
Memorandum to Justin Gregory, PE
April 19, 2019
Page 15 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
Figure 15. BFEs under the year 2119 scenario
Merging Results and Flood Map Production
As previously mentioned, future inundation conditions were used as the starting flood hazard areas
for updated BFE flood map production. The final flood maps for each future scenario are based on
model results as well as engineering judgment using topography and ATM’s knowledge of and
experience with CHAMP modeling and the FEMA mapping process.
Additionally, existing/effective FEMA special flood hazard area zone designations were used to aid in
determining future BFE flood elevations and extents/coverages. For example, areas that are
currently designated as “Combined Riverine and Coastal Mapping” (as specified in the attribute table
of FEMA’s digital FIRM) were mapped under the future scenario through a conservative comparison
of WHAFIS output BFEs and the value of the existing BFE for that particular location plus SLR. The
greater of the two values was then assigned to that flooding area, which was extended to meet the
contour matching that predicted future BFE.
Interpolation (based on topography and exposure) is used in transitioning to create relatively
smooth, continuous flood boundary lines. Conservative mapping techniques considering map scale
limitations (based on the existing FIRM scale of 1 inch =500 feet) were also implemented so that
higher BFEs are assigned when model output transitions would suggest lower elevations, but over a
very short distance. Areas where the interpolation of model outputs overlap (e.g., the 2119 scenario)
similarly used conservative engineering judgment and flood mapping experience in creating the final
flood map polygons.
The final Atlantic Beach flood maps representing future coastal flood risk estimated for the years
2044, 2069, and 2119 are attached as PDFs and have been provided digitally in ArcGIS format.
0
4
8
12
16
20
24
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
El
e
v
a
t
i
o
n
,
f
t
N
A
V
D
8
8
Station, ft
Transect 25 -2119 WHAFIS Outputs
Transect 25 Eroded Topo 2119 SWEL 2119 WHAFIS ResultsOcean AIWW
AE ZonesVE Zones
Localized X Zones
Memorandum to Justin Gregory, PE
April 19, 2019
Page 16 of 16
APPLIED TECHNOLOGY & MANAGEMENT, INC.
Coastal, Environmental, Marine & Water Resources Engineering
References
Federal Emergency Management Agency (FEMA), 2007. Atlantic Ocean and Gulf of Mexico
Coastal Guidelines Update Final Draft. U.S. Federal Emergency Management Agency
Region VI. Denton, TX. February 2007.
Federal Emergency Management Agency (FEMA), 2007. Coastal Hydraulic Analysis Package
(CHAMP), v. 2.0.
BakerAECOM, 2015. Coastal Hazard Analysis and Floodplain Mapping. Intermediate Data Submittals
4 & 5: Duval County, Florida. Task Order 75: Georgia-Northeast Florida Flood Insurance
Study. Version 2.1. October 2015.
BakerAECOM, 2016. Coastal Hazard Analysis and Mapping TSDN. Duval County, Florida. March 2016.
Federal Emergency Management Agency (FEMA), 2018. Flood Insurance Rate Map (FIRM)12031,
November, 2018.
Federal Emergency Management Agency (FEMA), 2018. Flood Insurance Study (FIS), Duval County,
Florida (All Jurisdictions). FEMA FIS # 12031CV001B. November 2018.
Jones Edmunds, 2019. Atlantic Beach Stormwater Master Plan Update. Sea Level Task Authorization
#09 — Resiliency Support — Task 1. Jones Edmunds Project No. 95239-057-19.
“AtlanticBeach_ResiliencyAnalysis_Task1_DRAFT_20190311.docx”. April 11, 2019.
National Oceanic and Atmospheric Administration (NOAA) Tides and Currents
http://tidesandcurrents.noaa.gov/, Station: 8720218 Mayport, FL
US Army Corps of Engineers (USACE). 2017. Sea-Level Change Curve Calculator, Version 2017.55.
Revised July 18, 2017. Available at: http://corpsmapu.usace.army.mil/rccinfo/
slc/slcc_calc.html.
Atlantic Beach City LimitsFEMA 2018 Base Flood Elevations ft NAVD88
5
6
7
8
9
11
12
13
±
0 0.5 10.25 Miles
Atlantic Beach City LimitsBase Flood Elevations with SLR 2044ft NAVD88
7
8
9
10
11
13
14
15
±
0 0.5 10.25 Miles
Atlantic Beach City LimitsBase Flood Elevations with SLR 2069ft NAVD88
8
9
10
11
12
13
15
16
17
19
±
0 0.5 10.25 Miles
Atlantic Beach City LimitsBase Flood Elevations with SLR 2119ft NAVD88
13
14
15
16
17
19
20
22
24
±
0 0.5 10.25 Miles