Coastal Base Flood Elevations in Mississippi: 
Before and After Katrina 

Introduction and Summary 

This memorandum is intended for homeowners and 
community officials in the coastal portions of 
Jackson, Harrison, and Hancock counties, 
Mississippi. The purpose of this memorandum is 
two-fold: (1) to provide a post-Hurricane Katrina 
comparison of the base flood elevations (BFEs) that 
were adopted by communities as flood damage 
prevention ordinances in the aftermath of Katrina 
(termed “Ordinance BFEs”) with the new 2007 
Preliminary BFEs; and (2) to provide a description of 
the differences among the three coastal studies 
undertaken by the Federal Emergency Management 
Agency (FEMA) over the past 25 years (refer also to 
text box at right). 

In the aftermath of Hurricane Katrina in August 2005, 
FEMA conducted studies to develop Advisory BFEs, 
which were recommended for adoption prior to 
completion of the detailed study resulting in the set 
of 2007 Preliminary BFEs. As presented in this 
memorandum (pages 2 & 3), Ordinance BFEs were 
adopted by communities to guide construction in the 
aftermath of Hurricane Katrina. Typically, 
communities adopted the Effective BFE plus 
freeboard or Advisory BFE where needed. The 
Ordinance BFEs are generally higher than 2007 
Preliminary BFEs in communities that adopted 
Advisory BFEs, and lower where Effective BFEs plus 
freeboard were adopted. For communities that 
adopted Advisory BFEs, the change to the 2007 
Preliminary BFEs will result in no change or slight 
increases to BFEs near the open Gulf Coast, but will 
result in significant BFE decreases farther inland of 
coastal bays and along river floodplains. 

The differences among the Effective, Advisory, and 
2007 Preliminary BFEs derived from the three 
coastal studies are attributable to the data and 
methods used in their calculation, as discussed in 
this memorandum. The differences among the three 

Coastal Base Flood Elevation and Base Flood (100-year 
event) 

The coastal BFE is the expected elevation of storm surge waters 
(stillwater elevation, or SWEL) and wave effects during the 100- 
year flood (also known as the “base flood”). The base flood is the 
flood having a 1-percent annual chance of being equaled or 
exceeded in any given year, which is shown as the Special Flood 
Hazard Area (SFHA) on Flood Insurance Rate Maps (FIRMs). 
The BFE was adopted by the National Flood Insurance Program 
(NFIP) as the basis for floodplain management and flood 
insurance regulations. BFEs are described in Flood Insurance 
Studies (FISs) and shown on FIRMs. 

This Memorandum describes: 

Effective BFEs: The Effective BFEs are shown on the FEMA 
FIS and Effective FIRM that were in effect and adopted for 
unincorporated and incorporated areas of Hancock, Harrison, 
and Jackson Counties prior to landfall of Katrina in 2005. These 
Effective BFEs were based on a FEMA coastal study completed 
between 1982 and 1985, adopted by local communities for 
floodplain management and enforcement, and published in the 
FISs and FIRMs dated between 1983 and 2002.
 
Freeboard: Freeboard, as applied for flood damage prevention 
ordinances, is a factor of safety usually expressed in feet above 
a flood level for purposes of floodplain management. Freeboard 
can be added to an established BFE to compensate for the many 
unknown factors that could contribute to flood heights greater 
than the height calculated. 

Advisory BFEs: Advisory BFEs were developed immediately 
after Hurricane Katrina to provide communities with 
recommended building elevations for use in the reconstruction 
process until more detailed data became available. Advisory 
BFEs are based on a new flood frequency analysis that takes 
into account Hurricane Katrina, as well as additional tide and 
storm data from other events that have occurred during the past 
25 years since the effective coastal study was completed, and 
Effective FISs and FIRMs were adopted. 

2007 Preliminary BFEs: The 2007 Preliminary BFEs are based 
on a new hurricane storm surge modeling effort to update the 1- 
percent annual chance SWEL and detailed hazard modeling 
assessments of wave effects. These BFEs are being 
incorporated into Preliminary FIRMs and subjected to the 
regulatory 90-day appeals process. 
Technical Memorandum - Revised December 2007 
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December 5, 2007 
2 
data sets are as expected and substantiate FEMA’s guidance and recommendation to use Advisory 
BFEs following Hurricane Katrina. FEMA developed the Advisory BFEs to provide more accurate 
guidelines for rebuilding in lieu of using inaccurate Effective BFEs. If building permits had been issued 
during rebuilding efforts using the Effective BFEs, structures would have been built at an elevation that 
put them at greater risk of future flood damages. The Advisory BFE elevations may have been high in 
some areas, but they promoted safe rebuilding immediately following the disaster. The results of the 
2007 Mississippi Coastal Study, shown on the preliminary FIS and FIRM, depict accurate and up-to-date 
BFEs for the Mississippi coast, and can be used for effective floodplain management following their 
adoption. 


Post-Katrina Flood Damage Prevention Ordinance 

Following the devastation caused by Hurricane Katrina, coastal Mississippi incorporated communities 
and unincorporated county areas needed flood recovery guidance. This was required during 
reconstruction and recovery following Hurricane Katrina based on FEMA’s assessment of the 
inadequacy of the effective FIRMs and FISs to reflect the coastal hazards and risk of future flooding in 
coastal areas. 

Since the Effective BFEs were inadequate, all incorporated and unincorporated portions of the counties 
recognized the need to adopt a post-Katrina Flood Damage Prevention Ordinance to replace the current 
floodplain management ordinances. Primarily, the affected communities either adopted the Advisory BFE 
or the Effective BFE plus freeboard. In several communities, an even higher standard was adopted using 
the Advisory BFE plus freeboard. Refer to the Effective FIS and FIRM Coastal Study and 2005 Post- 
Katrina Advisory BFEs Coastal Study portion of this memorandum for additional details about Effective 
and Advisory BFEs. 

Advisory BFE: As part of their immediate response to Hurricane Katrina, FEMA prepared Advisory 
BFEs based on simplified studies performed immediately after Katrina using generalized data. The 
Advisory BFE information and maps provided the best available information on future flooding potential 
and hazards in the coastal areas. 

Effective BFE Plus Freeboard: The other primary flood recovery guidance option provided by FEMA 
allowed the use of the Effective BFE plus added “freeboard.” This option allowed communities to adopt a 
modified flood damage prevention measure that added 1 to 4 feet of freeboard to the Effective BFEs. 
The freeboard was required as a safety factor to account for unknown variables, such as wave action, 
bridge openings, and the hydrological effect of urbanization of the watershed that could contribute to 
flood heights greater than the height calculated for the Effective BFE. The Effective BFE plus freeboard 
required that the elevation of new construction and foundation repairs to substantially damaged 
structures exceed the Effective BFE by the specified freeboard in all SFHAs shown on the Effective 
FIRM. 

ORDINANCE BFES 

Some communities adopted the Advisory BFEs for floodplain management and hazard mitigation during 
post-Hurricane Katrina recovery. However, many communities chose to adopt Effective BFEs with 
freeboard. In some communities, the adopted Flood Damage Prevention Ordinance included only the 
Advisory BFE information and mapping; in others it included a combination of Advisory BFEs and 
Effective BFEs plus freeboard. For this memorandum and comparison mapping, the BFEs adopted by 
the communities are referred to as Ordinance BFEs. Refer to the table on the next page for a list of 
Ordinance BFEs by community and a description of where the Ordinance BFEs apply. 

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December 5, 2007 
3 
ORDINANCE BFEs IN COASTAL COMMUNITIES OF MISSISSIPPI 
County Community Current Ordinance as of 9/8/07 
Gautier BFEs on Effective FIRM + 5 feet freeboard and Advisory BFEs outside SFHA 
Jackson County Advisory BFEs in their entirety and, in the SFHA where there are no Advisory BFEs, the BFEs on 
Effective FIRM (manufactured homes only + 1 foot freeboard) 
Moss Point Advisory BFEs in their entirety (with commercial exemptions) 
Ocean Springs Advisory BFEs in their entirety + 1 foot of freeboard and, in the SFHA where there are no Advisory 
BFEs, the requirement is the BFE on Effective FIRM + 1 foot freeboard 
Jackson 
Pascagoula Advisory BFEs in their entirety 
Biloxi BFEs on Effective FIRM + 4 feet freeboard 
D’Iberville Advisory BFEs north of Interstate 10, and BFEs on Effective FIRM + 4 feet freeboard (V zones only), 
and BFEs on Effective FIRM + 3 feet freeboard (A zones only). Also adopted +14 feet elevation in a 
designated Community Flood Hazard Area (south of Brodie Road and Lemoyne Road). 
Gulfport Advisory BFEs in their entirety + 0.5 foot freeboard and, in the SFHA where there are no Advisory 
BFEs, the requirement is the BFE on Effective FIRM + 1 foot freeboard 
Harrison County BFEs on Effective FIRM + 4 feet freeboard and Advisory BFEs outside SFHA 
Long Beach BFEs on Effective FIRM + 3 feet freeboard and Advisory BFEs outside SFHA 
Harrison 
Pass Christian BFEs on Effective FIRM + 4 feet freeboard in A zone only, (BFEs on Effective FIRM + 1 foot freeboard 
in V zone only [no change in V zone from pre-Katrina Ordinance]) 
Bay St. Louis BFEs on Effective FIRM + 4 feet freeboard 
Hancock County BFEs on Effective FIRM + 4 feet freeboard 
Hancock 
Waveland BFEs on Effective FIRM + 4 feet freeboard 



COMPARISON OF ORDINANCE BFE WITH 2007 PRELIMINARY BFE 

This section presents a comparison of the Ordinance BFEs with the new 2007 Preliminary BFEs based 
on the new detailed study, and mapping of hazard zones and BFEs (refer to the 2007 Preliminary 
Mississippi Coastal Analysis Project section of this memorandum for additional details). Maps showing 
the comparison of BFE differences at specific modeling data points are included at the end of this 
memorandum. Comparison maps are presented in countywide form and also with finer-scale focus for 
selected communities within each county. 

Jackson County: The Advisory BFEs were primarily adopted county-wide, with only a few areas using 
the Effective BFE plus freeboard. However, Gautier only adopted Effective BFEs plus freeboard (refer 
to table above) and still had only slight differences with the 2007 Preliminary BFEs. The general 
comparison patterns along the open coast and inland floodplains vary greatly (shown on Comparison 
Maps at the end of this memorandum). The areas where the 2007 Preliminary BFEs are higher than the 
Advisory BFEs—in Biloxi Bay and Point Aux Chenes—have a similar flood pattern of focused winddriven 
surge into the bay and low-lying floodplains. These areas are where strong winds tend to pile up 
the shallow bay waters and amplify water levels at or near the height of the hurricane. Other inland areas 
with significant decreases among the Ordinance BFE (based on Advisory BFE) and the 2007 Preliminary 
BFE indicate where Advisory BFE methods overestimated the flood hazard compared to new, detailed 
modeling results seen in the 2007 Preliminary BFEs. 

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December 5, 2007 
4 

Harrison County: Advisory BFEs were adopted community-wide in Gulfport and the inland floodplains 
west of Biloxi Bay along Bernard Bayou. The differences among the Advisory BFEs and the 2007 
Preliminary BFEs along the open coast of Gulfport are negligible (no change or decrease), while 
significant decreases are noted along inland floodplains west of Biloxi Bay along Bernard Bayou (refer to 
Comparison Maps at the end of this memorandum). Effective BFEs plus freeboard were adopted as the 
Ordinance BFE in the remaining open coast incorporated areas of the county. These areas have 
significant increases among the adopted Ordinance BFE and the 2007 Preliminary BFEs (refer to 
Comparison Maps at the end of this memorandum). There are large differences along north and western 
areas of St. Louis Bay. These differences are a result of storm surge pile-up against the coast that then 
gets funneled into bays in a way that amplifies the water levels. This funneling effect was modeled in the 
2007 Preliminary Mississippi Coastal Flood Analysis Project (described later in this memorandum) and 
explains the statistically higher level for the 2007 Preliminary BFEs as compared to the Effective and 
Advisory BFEs along the coast and in St. Louis Bay, and no change or slight increase in the western 
portion of Biloxi Bay and up into the Wolf River. 

Hancock County: The Effective BFEs plus freeboard were adopted as the Ordinance BFE throughout 
Hancock County. The 2007 Preliminary BFEs for most of the county are higher than the adopted 
Ordinance BFE and the 2007 Preliminary BFEs (refer to Comparison Maps at the end of this 
memorandum). The amount of increase varies from the open Gulf Coast into the inland bays and 
floodplains. Relatively large increases are noted along the coastal areas of Waveland and Bay St. Louis, 
and inland of St. Louis Bay where wind-driven surge drives water up into the Jourdan River and adjacent 
waterways. Only slight changes (or no changes) are noted along the Pearl River and up near 
Pearlington; these areas experienced the smallest changes in the county. The Pearl River floodplain is 
heavily overgrown and forested, which would tend to inhibit the capability of the wind to drive the 
floodwaters inland. This dampening effect is captured in the storm surge modeling performed for the 
2007 Preliminary Mississippi Coastal Flood Analysis Project, and would explain why the 2007 
Preliminary BFEs are close to the Effective BFEs plus freeboard in this area. 



Mississippi Coastal Flood Studies 

Flood levels significantly exceeded the Effective BFEs in most of coastal Mississippi during Hurricane 
Katrina. Although FEMA and the State of Mississippi had already initiated a new limited coastal study in 
the area before Katrina, they realized the need to expand the scope and detail of the study given the 
nature of the damage and the extensive rebuilding needed after Katrina. To avoid underestimating 
coastal flood risks during initial reconstruction of coastal areas after Katrina, FEMA developed Advisory 
BFEs (2005 Post-Katrina Advisory BFEs Coastal Study). At the same time, FEMA also initiated a new 
state-of-the-art project (Mississippi Coastal Study) to prepare an updated hurricane storm surge and 
wave model. The preliminary results of the study are now compiled (2007 Preliminary BFEs from the 
Mississippi Coastal Study).
 
The three coastal flood studies performed by FEMA since the 1980s for the coastal counties of Jackson, 
Harrison, and Hancock are described briefly below. In order to understand the studies, a brief 
introduction to coastal BFEs is provided. 

UNDERSTANDING COASTAL BFES 

Coastal BFEs are the 1-percent-annual-chance SWELs modified by local wave effects. 
Stillwater Elevations: SWELs are the height of the storm surge, which is the rise of the ocean surface 
that occurs in response to barometric pressure variations (the inverse barometer effect) and to the stress 
of the wind acting over the water surface (the wind setup component). As a standard methodology, 
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December 5, 2007 
5 
FEMA’s 1-percent-annual-chance determination is made on total SWELs (consideration of astronomical 
tide, wind setup for storm surge response, and wave setup). 

SWELs do not include local wave effects caused by overland wave height propagation and wave runup 
at the shoreline, but there is an additional increase in SWEL across the open coast due to wave setup. 
Wave setup is an increase in the total SWEL against a barrier caused by the attenuation of waves in 
shallow water. Wave setup can be a significant contributor to the total water level landward of the open 
Gulf Coast shoreline and is an important factor in the determination of coastal BFEs. The 1-percentannual-
chance SWELs are determined using a FEMA-approved coastal storm surge model and standard 
methodologies for wave setup. 

Local Wave Effects: Local wave effects 
above the SWEL, ground surface, and 
normal water level (refer to the figure to 
right) are determined landward of the 
shoreline for open coasts and inland bays 
using wave height modeling for overland 
areas and wave runup calculations for 
steep shorelines and coastal bluffs. The 
wave effects are determined using 
standard coastal models, such as FEMA’s 
Wave Height Analysis for Flood Insurance 
Studies (WHAFIS) and RUNUP (or similar 
runup models).

 
EFFECTIVE FIS AND FIRM COASTAL STUDY 

FEMA completed the initial coastal flood studies of the three Mississippi coastal counties between 1982 
and 1985. The diagram below shows the steps used in that coastal study process. The resulting Effective 
BFEs are reported in the FIS reports and shown on FIRMs dated between 1983 and 2002. These BFEs 
were used to guide floodplain management and new construction prior to Hurricane Katrina.
 
Stillwater Computation: For the effective coastal flood studies, data was collected on historical 
hurricanes to help derive the storm parameter values (central pressure, forward speed, radius to 
maximum winds, landfall location, and storm direction) needed to create a population of synthetic storms. 
FEMA’s two-dimensional (2-D) standard storm surge model, TT-SURGE (Tetra Tech, Inc., 1981) was 
then developed, calibrated, and subsequently used to model the synthetic storm population of simulated 
hurricanes to determine the flood levels in the Mississippi Sound and the Gulf of Mexico. This storm 
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December 5, 2007 
6 
Sample of Advisory BFE Map 
Flood Frequency Analysis versus 
Numerical Modeling 
Flood Frequency Analysis: Based on 
historical long-term tide records. Using data 
collected from site-specific tide gages, the 
resulting SWEL is extrapolated across wide 
regional geographic areas. 
Numerical Modeling: Models such as TTSURGE 
and ADCIRC are based on regional 
hypothetical (synthetic) storms that are 
designed based on historic events. 
Numerical modeling details open coast and 
inland flooding with the site-specific 
modeling and simulation of storm effects 
across wide geographic areas. 
surge modeling was then used with the Joint Probability Method (JPM) to determine the 1-percentannual-
chance SWEL. 

Modeled Local Wave Effects: After completing the stillwater computation, the WHAFIS wave model 
was applied to determine the wave effects to be added to the SWELs. The 1-dimensional (1-D) overland 
wave analysis methodology was performed for wave transects (profiles) extending from the shoreline 
inland to the end of the coastal SWEL, and were completed for wave profiles located throughout the 
coastal area of Mississippi.


 
2005 POST-KATRINA ADVISORY BFE COASTAL STUDY 

Advisory BFEs were based on simplified 
technical assessments of SWEL studies 
performed immediately after Katrina for the 
1-percent-annual-chance flood levels and 
associated wave effects. The Advisory BFE 
information and maps included all the open 
coasts and inland bay floodplains affected 
by flooding from Hurricane Katrina, in some 
areas extending inland of the Interstate 10 
(I-10) highway corridor. The studies were 
intended to help State and local officials, as 
well as homeowners, identify existing and 
increased flood hazards revealed by 
Hurricane Katrina and other storms that have struck the region in the last 25 years. This information was 
intended to be used during recovery and redevelopment to avoid future flood damage.

 
Stillwater Computation: The SWELs for the Advisory BFEs were quickly developed using a flood 
frequency analysis based on tide gage records. This frequency analysis used actual historical recorded 
peak surge data obtained from tide gages located throughout the area, supplemented with field 
observations made immediately after Katrina. The analysis 
included more than 20 storms that had affected the region 
since the Effective FIS and FIRM Coastal Study, including 
Hurricanes Elena (1985), Danny (1997), Georges (1998), 
and Katrina (2005).

 
The Advisory BFEs were based on just two SWELs for 
each county—an open coast value and a back bay value. 
The back bay SWEL was based on flood frequency 
analysis only. The open coast SWEL was based on the 
flood frequency analysis plus wave setup. A constant 
value of 2 feet applied along the entire open coast was 
used for wave setup, based on calculations using the U.S. 
Army Corps of Engineer’s (USACE) Shore Protection 
Manual. This simplification was needed to expedite 
derivation of the Advisory BFEs. The resulting pair of 
Advisory SWELs for each county, which FEMA published 
on October 6, 2005, is shown on the next page. 

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December 5, 2007 
7 
ADCIRC 
The Advanced Circulation (ADCIRC) 2-dimensional, 
depth-integrated (2DDI) surge model uses the finite 
element computational method to solve the shallow 
water equations. The finite element method permits 
the use of triangular grid elements, which offer more 
flexibility in designing grids that closely mimic 
complex shorelines. The completed ADCIRC grid of 
coastal Mississippi has over 900,000 nodes. The 
grid includes features such as islands, roads, 
bridges, open waters, bays, and rivers. 
Advisory SWELs published1 on October 6, 2005 
Jackson Harrison Hancock 
Open Coast (includes wave setup value) 14 feet 18 feet 20 feet 
Back Bay 12 feet 16 feet 18 feet

 
Estimated Local Wave Effects: Given the expedited schedule for FEMA’s development and mapping of 
the Advisory BFEs, a simplified method was used to estimate local wave effects. This method was based 
on a procedure within FEMA’s WHAFIS model: the depth-limited wave height calculation. This simplified 
method did not include wind-wave sheltering by above-surge land masses or wave height reductions 
caused by obstructions to overland wave propagation. 



2007 PRELIMINARY MISSISSIPPI COASTAL FLOOD ANALYSIS PROJECT 

A thorough study—the Mississippi Coastal Study—was initiated after Katrina. The Mississippi Coastal 
Study, which will be completed by the end of 2007, is the basis for the 2007 Preliminary BFEs. Once 
reviewed and officially adopted by communities, the 2007 Preliminary BFEs in the Preliminary FIS report 
and shown on the Preliminary FIRMs will become the Effective BFEs. 

Stillwater Computation: The coastal study process used to 
develop the 2007 Preliminary BFEs was similar to that used 
in the 1985 coastal study. However, the 2007 process 
included updated topographic information and additional 
historic storm data, and used models that were capable of 
more sophisticated and detailed analysis. The 2007 
Preliminary BFEs are based on a study that used the 
Advanced Circulation hydrodynamic model (ADCIRC). The 
ADCIRC model is capable of much greater resolution than 
the TT-SURGE model used in the 1980s effective coastal 
flood study (see text box). 

The wave setup values were determined using a 2-D wave model (SWAN) in conjunction with ADCIRC, 
and included during the final surge model runs. In more advanced wave models like SWAN, the wave 
setup component is combined with the storm-surge modeling, resulting in SWELs that include both storm 
surge and wave setup. Thus, the wave setup values are implicitly included in the SWEL values by way of 
storm-surge modeling, rather than added later as a separate calculation. The diagram on the next page 
highlights the steps that were performed for the 2007 Mississippi Coastal Study, which differed from the 
effective coastal flood study completed between 1982 and 1985. 

In addition to using a different surge and new wave models to determine peak total SWELs, the statistical 
analysis process (JPM) was substantially updated as part of the 2007 Mississippi Coastal Study in 
cooperation with USACE and included additional historic storms that have occurred since the Effective 
FIS and FIRM Coastal Study. This modification minimized the number of synthetic storms needed as 
input to the ADCIRC model. The number of synthetic storms was reduced from over a thousand to a few 
hundred. The modified approach, which optimizes the procedure on a minimum number of synthetic 
storms, is called JPM Optimum Sampling (JPM-OS). 

1 http://www.fema.gov/hazard/flood/recoverydata/katrina/katrina_ms_maps.shtm 
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December 5, 2007 
8 

Modeled Local Wave Effects: Wave height was calculated using the same WHAFIS 1-D modeling 
method as in the effective coastal flood study completed between 1982 and 1985. The primary difference 
in methodology from the effective coastal study was the inclusion of wave setup in the total SWEL used 
in WHAFIS.


 
COMPARISON OF COASTAL STUDIES ANALYSIS TECHNIQUES 

The table below briefly summarizes some of the differences in calculating the BFEs for the Effective FIS 
and FIRM Coastal Study, the 2005 Post-Katrina Advisory BFE Coastal Study, and the 2007 Preliminary 
BFEs from the Mississippi Coastal Study. 

Comparison of Information Used to Develop the Effective BFE, Advisory BFE, and 2007 Preliminary BFE 
Effective BFE 
(1980s–2002) 
Advisory BFE 
(2005) 
2007 Preliminary BFE 
(2007–pending) 
Base Topography Best Available in 1980s Current Current (< 5 years) 
Stillwater Model Type TT-SURGE 2-D model 
Finite-difference grid 
scheme (w/ rectangular 
grids) 
None ADCIRC-2DDI model 
Finite-element grid scheme 
(w/ triangular grids) 
Model Grid Resolution Resolution of 1 nautical 
mile (6,067 feet or 1,852 
meters) 
N/A Resolution up to 260 feet (80 
meters) 
Wave Setup None Standard Shore 
Protection Manual 
calculation uniformly 
added on open coast 
SWAN 2-D Wave Model 
Included implicitly in SWEL 
prior to wave analysis 
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December 5, 2007 
9 
Useful Link for More 
Information 
www.mscoastalmapping.com 
Comparison of Information Used to Develop the Effective BFE, Advisory BFE, and 2007 Preliminary BFE 
Effective BFE 
(1980s–2002) 
Advisory BFE 
(2005) 
2007 Preliminary BFE 
(2007–pending) 
Statistical Analysis JPM Flood Frequency 
Analysis – Log Pearson 
Type III 
JPM-OS 
Historic Storms Considered 1900 to 1980 Varied based on gage 
data 
1940 to 2007 
Accounted uniquely for different coastal areas: 
open coast, bay, and overland 
Yes, with low resolution No—used simplified, 
extrapolated coast 
values extrapolated 
inland 
Yes, with high resolution 
Accounted for cultural and natural effects (unique 
flooding effects such as bridges, open waters, 
bays, rivers, and vegetation type) 
Yes No Yes 
Local Wave Effects – Wave Height WHAFIS 1-D model Simplified Depth-Limited 
Analysis 
WHAFIS 1-D model 



SUMMARY OF DIFFERENCES IN COASTAL STUDIES IN MISSISSIPPI 

As described in previous sections of this memorandum, there are differences in the nature of the three 
coastal studies that led to either the Effective BFE, Advisory BFE, or 2007 Preliminary BFE results. 
There are general explanations for the differences among these results 
that apply across all of the Mississippi coastal area, as described below. 
There are also explanations specific to each county. Note that the 2007 
Preliminary BFE calculation is based on the coastal study only, and 
does not consider riverine flooding effects. 


Effective BFE Compared To Advisory BFE: In all cases, the Advisory BFE elevation is higher than the 
Effective BFE. The difference varies between approximately 2 and 19 feet. The biggest difference in 
elevations is in Hancock County near Pearl River and farther inland near the riverine floodplains. The 
differences among the Effective BFEs and the Advisory BFEs are primarily a result of an updated coastal 
flood frequency analysis and the simplified local wave height analysis. The Advisory BFEs included the 
influence of additional data from the past 25 years, which includes severe hurricanes that made landfall 
in or near Mississippi. In addition, the calculated local wave analysis did not consider if an area was 
sheltered from wind, waves, or obstructions to wave growth. 


Effective BFE Compared To 2007 Preliminary BFE: In all cases, the 2007 Preliminary BFE elevation 
is also higher than the Effective BFE. The difference varies between approximately 1 and 13 feet. The 
largest differences in elevations are around St. Louis Bay and along inland rivers. The differences among 
the Effective BFEs and the 2007 Preliminary BFEs are primarily a result of improved modeling resolution 
and up-to-date topographic and storm data used during the 2007 Mississippi Coastal Study. Although the 
coastal study processes (2-D storm surge modeling and JPM) used for these two coastal flood studies 
(effective and preliminary) were generally similar, differences included the number of synthetic storms 
that were modeled, the resolution of the numerical models used to provide the peak surge value, the 2-D 
wave modeling that accounts for an additional component to SWEL caused by wave setup, additional 
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December 5, 2007 
10 
hurricane storm parameter values for infilling and storm radius, and the way that wave effects were 
included in the final results (refer to the table on page 8). 


Advisory BFE Compared To 2007 Preliminary BFE: The Advisory BFE and 2007 Preliminary BFE 
varied throughout the coastal region, and showed decreases between 0 and 14 feet and increases 
between 0 and 7 feet. The agreement between the 2007 Preliminary BFEs and the Advisory BFEs is 
generally better along the open Gulf Coast and not as good in inland areas. The source of the data used 
to determine the Advisory BFEs was coastal tide gages, and therefore all of the inland information was 
derived through a simple extrapolation scheme assuming a constant maximum SWEL inland of the 
coast. This approximation does not account for the effects from the overland propagation of the surge 
and related surge level decay due to ground friction effects. Similarly, the Advisory BFEs do not account 
for the way in which forests and wetlands reduce the impact of wind, the complex relationship between 
wind- and gravity-driven inland flow, and surge flow paths, nor does it include barriers to wave 
propagation in the flooded areas (forests, buildings, and roadways). 

The most fundamental difference among the Advisory BFEs and the 2007 Preliminary BFEs is the 
complexity of the studies. Both studies used up-to-date topographic and storm data. However, the 
Advisory BFE coastal study used a flood analysis procedure (flood frequency analysis) that was intended 
to provide quick answers and therefore used simplified values and extrapolated them over broad 
geographic areas. In contrast, the 2007 Preliminary BFEs are based on a comprehensive storm surge 
modeling study intended to provide a solid technical basis for coastal flood levels because of their 
importance in the future development of the whole Mississippi coastal region. Refer to the table (on page 
8) comparing the information used to develop the BFEs for additional information on the differences 
between these two approaches. 



Comparison Maps for Ordinance vs. 2007 Preliminary BFEs 

Note that the maps do not provide flood boundary information; this information will be published on the 
2007 Preliminary FIRMs. 

Jackson County 
• Ordinance BFEs compared to 2007 Preliminary BFEs for unincorporated areas 
• Subset of community maps include: 
o Gautier and Pascagoula 
o St. Martin and Ocean Springs 


Harrison County 
• Ordinance BFE compared to 2007 Preliminary BFE for unincorporated areas 
• Subset of community maps include: 
o Biloxi and D’Iberville 
o Gulfport 
o Pass Christian and Long Beach 


Hancock County 
• Ordinance BFEs compared to 2007 Preliminary BFEs for unincorporated areas 
• Subset of community maps include: 
o Waveland and Bay St. Louis 
o Pearlington 




The rest of this is text from  10 different maps.


§¨¦10 
§¨¦110 
tu90 
M i s s i s s i p p i S o u n d 
B i l o x i 
B a y 
Jackson 
County 
Mobile 
County 
Harrison 
County 
MS A L 
Vancleave 
Latimer
St. Martin Gulf Hills 
D'Iberville 
Escatawpa 
Hickory Hills 
Helena 
Grand Bay 
Gulf Park Estates 
Wade 
Big Point 
Ocean Springs 
Gautier 
Pascagoula 
Moss Point 
Trent Loft 
Airport 
De Soto 
National Forest 
¹ 
0 2 4Miles 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
Jackson County: Comparison of Ordinance BFEs to 2007 Preliminary BFEs December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change)
Jackson 
County 
Hickory Hills 
Helena 
Gautier 
Pascagoula 
Moss Point 
Trent Loft 
Airport 
§¨¦10 
tu90 
UV63 
UV613 
UV611 
90 
Main 
Old Spanish 
Gautier Vancleave 
Ingalls 
Old Mobile 
Denny 
Industrial 
Graveline 
Saracennia 
Shortcut 
Chi cot 
Grierson 
2nd 
Market 
14th 
Dolphin 
Frederick 
Griffin 
River 
Pascagoula 
Louise 
Washington 
Ladnier 
Orchard 
Kreole 
Jefferson 
Earl 
Old Stage 
Dantzler 
Telephone 
Belair 
Presley 
Bayou Cumbest 
De La Pointe 
Magnolia 
90 
611 
¹ 
0 1 2Miles Note: Use of the Preliminary DFIRM 
is recommended to identify site-specific 
flood boundary limits and BFEs. 
Jackson County: Gautier / Pascagoula - Comparison of Ordinance BFEs to 2007 Preliminary BFEs December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change)
Jackson 
County 
Harrison 
County 
Latimer 
St. Martin Gulf Hills 
D'Iberville 
Gulf Park Estates 
Ocean Springs
§¨¦10 
§¨¦110 
tu90 
UV57 
UV15 
UV67 
UV609 
57 
Beach 
Bienville 
Old Spanish 
Tucker 
Government 
Lemoyne 
Division 
Daisy Vestry 
Main 
Beachvi ew 
Irish Hill 
Washington 
Oak 
Hal stead 
North 
Gorenflo 
Fountainbleau 
Howard 
Popps Ferry 
Gautier Vancleave 
Old Hwy 67 
Bayview 
Ploesti 
11th 
Belle Fontaine 
Auto Mall Forrest 
Hammill Farm 
Elm 
Shearwater 
Mermaid 
D Iberville Bri dge 
Magnolia 
Center 
Beach 
Beach 
Old Hwy 67 
KKeeeesslleerr AAiirr FFoorrccee BBaassee 
¹ 
0 1 2Miles 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
Jackson County: St. Martin / Ocean Springs - Comparison of Ordinance BFEs to 2007 Preliminary BFEs December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change)
§¨¦10 
§¨¦110 
tu49 
tu90 
tu90 
M i s s i s s i p p i S o u n d 
S t . L o u i s 
B a y 
B i l o x i 
B a y 
Harrison 
County 
Hancock 
County 
Jackson 
County MS 
Latimer 
Lyman 
Pass Christian 
D'Iberville 
Bay St. Louis 
St. Martin 
Waveland 
Saucier 
Biloxi 
Gulfport 
Long Beach 
Gulfport-Biloxi 
Airport 
De Soto 
National Forest 
0 2 4Miles 
¹ 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change) 
Harrison County: Comparison of Ordinance BFEs to 2007 Preliminary BFEs
Harrison 
County 
Jackson 
County 
Latimer 
D'Iberville 
Biloxi St. Martin 
Gulfport 
Biloxi 
§¨¦10 
§¨¦110 
tu90 
UV67 
UV15 UV67 
Beach 
Pass 
Tucker 
Popps Ferry Lorraine 
Irish Hill 
Lemoyne 
Division 
Daisy Vestry 
Cowan 
Main 
Old Hwy 67 
Oak 
Ploesti 
Gorenflo 
Cedar Lake 
Howard 
7th 
John Ross 
Dedeaux 
Bayview 
Woolmarket 
Lamey Bridge 
Porter 
Oneal 
Beauvoir 
Auto Mall 
Forrest 
Mcdonnell 
D Iberville Bridge 
Popps Ferry Bridge 
Bay Shore 
Old Hwy 67 
Popps Ferry 
Gorenflo 
Howard 
Lorraine 
Old Hwy 67 
KKeeeesslleerr AAiirr FFoorrccee BBaassee 
0 0.5 1Miles ¹ 
Harrison County: Biloxi - Comparison of Ordinance BFEs to 2007 Preliminary BFEs 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change)
Harrison 
County 
Gulfport 
Long Beach 
Biloxi 
Gulfport-Biloxi 
Airport
§¨¦10 
tu90 
tu49 
UV67 
Beach 
Pass 
28th 
Canal 
Landon 
25th 
Dedeaux 
33rd 
Lorraine 
Three Rivers 
Airport 
Klondyke 
Cowan 
19th 
Railroad 
Washington 
Colby 
17th 
He we s 
John Ross 
Broad 
Courthouse 
Popps Ferry 
Beauvoir 
Commission 
Engram 
20th 
Mason 
Railroad 
Lorraine 
Popps Ferry 
NNaavvaall CCoonnssttrruuccttiioonn CCttrr 
0 0.5 1Miles 
¹ 
Harrison County: Gulfport - Comparison of Ordinance BFEs to 2007 Preliminary BFEs 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change)
Harrison 
County 
Hancock 
County 
Pass Christian 
Bay St. Louis 
Long Beach 
§¨¦10 
tu90 Beach 
Menge 
North 
Kiln Delisle 
2nd 
Vidalia 
28th 
Beatline 
Wittman 
Red Creek 
Dunbar 
Henderson 
Washington 
Central 
Railroad 
County Farm 
Kapalama 
Old Spanish 
Cedar 
Cuevas Delisle 
Kiln Firetower 
Firetower 
Diamondhead 
Longfellow 
Beach 
0 0.5 1Miles 
¹ 
Harrison County: Pass Christian - Comparison of Ordinance BFEs to 2007 Preliminary BFEs 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change)
§¨¦10 
tu90 
tu190 
tu90 
S t . L o u i s 
B a y 
M i s sis s i p p i S o u n d 
Hancock 
County 
St. Tammany 
Parish 
Harrison 
County 
L A 
MS Kiln 
Diamondhead 
Pearlington 
Waveland 
Shoreline Park Bay St. Louis 
Pass Christian 
Pearl River 
Stennis 
Airport 
0 2 4Miles 
¹ 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change) 
Hancock County: Comparison of Ordinance BFEs to 2007 Preliminary BFEs
Hancock 
County 
Harrison 
County 
Diamondhead 
Waveland 
Shoreline Park 
Bay St. Louis 
Stennis 
Airport 
§¨¦10 
tu90 
UV43 
UV607 
UV603 
UV43 
B 
43 
Lower Bay 
Central 
Washington 
Old Spanish 
Dunbar 
Waveland 
Lake Shore 
Old Lower Bay 
Lakeshore 
Beach 
Gex 
Golf Club 
Nicholson 
Longfellow 
19th 
Kiln Delisle 
Clermont Ioor 
Analii 
Stennis Airport 
Old Gainesville 
Hancock 
2nd 
Beach 
Lower Bay 
Beach 
Hancock 
0 1 2Miles 
¹ 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change) 
Hancock County: Waveland / Bay St. Louis - Comparison of Ordinance BFEs to 2007 Preliminary BFEs
Hancock 
County 
St. Tammany 
Parish 
L A Pearlington 
§¨¦10 
tu90 
UV604 
UV607 
Lower Bay 
34th 
Ansley 
Lake Shore 
Old Lower Bay 
Lakeshore 
Hancock 
Heron Bay 
Park 
Lower Bay 
0 1 2 Miles 
¹ 
Note: Use of the Preliminary DFIRM is recommended to 
identify site-specific flood boundary limits and BFEs. 
December 2007 
Elevation Change (in Feet) 
BFE= Base Flood Elevation 
Mississippi Coastal 
Flood Study 
Decrease 
in BFE 
Increase 
in BFE 
6 to 7 
8 to 9 
2 to 3 
1
4 to 5 
-9 to -8 
-7 to -6 
-5 to -4 
-3 to -2 
-1 
0 (no change) 
Hancock County: Pearlington - Comparison of Ordinance BFEs to 2007 Preliminary BFEs