Figure 5-3
Number of Flash Floods in Harrison County, 1998-2016
7
6
5
4
3
2
1
0
As shown on Figure 5‐2, there are many locations on the installation that are
within the 500 and 100 Year Flood Zone as defined by the Federal
Emergency Management Agency (FEMA), which account for all types of
natural flooding. There are particular vulnerabilities on portions of the
installation that border the Back Bay of Biloxi. For example, the north end of
the runway is within the 100 Year Flood Zone. The 500 Year Flood Zone
encompasses the majority of the runway, facilities, and housing. Flooding at
any of these locations can result in damage to real property though
proactive installation planning and revised construction practices have
reduced the potential. There are no locations within the installation that are
at immediate risk to flooding due to wave action, which is associated with
storm surge.
Although Biloxi has a history of storms, this is not the only source of flooding
in the city. According to the Biloxi Hazard Mitigation Plan, flooding in Biloxi
may also occur with heavy rainfall, such as flash floods. This type of flood
results from heavy and localized rainfall over a short period of time.
Seasonal rainfall, that is not associated with a hurricane or tropical storm,
can create flooding events when storm drainage conveyances cannot
manage the quantity of runoff generated from impervious surfaces.
Figure 5‐3 shows the history of flash floods in Harrison County since 1998.
Since 1998, four flash floods were reported countywide, four additional flash
floods were reported in Biloxi, and two were reported on Keesler AFB.
In addition to storm surge, riverine flooding can also affect the installation
and the surrounding community. Riverine flooding occurs when there is an
excessive rainfall and water runoff volume within the watershed of a river or
stream. Keesler AFB and surrounding communities are located along the
Back Bay of Biloxi fed by the Tchoutacabouffa River, making the installation
susceptible to flooding generated by riverine flooding.
Localized Flooding
1998
Storm surge can also be affected when bodies of water have high flow days.
From 2000 to 2009, the average number of high flow days per year was
20 days. According to the Natural Resources Defense Council (NRDC), high
flow days are classified as the average number of days a year that are
greater than the 95 th percentile relative to a reference period from
1961‐1990. Days above the flood stage per year decreased in the 1‐10 day
range for this period. The flood stage is the level above a body of water’s
natural banks at which structures begin to be affected by flooding. These
effects on the community are further discussed in CC‐3.
Source: http://www.ncdc.noaa.gov/stormevents/
Flooding can prevent access to the installation and travel within the
installation, preventing military and civilian personnel from reaching their
destination on Keesler AFB and / or reaching safety. Flooding can also
create an overall delay in the ability to perform operations at the
installation, such as training and medical functions.
Page 5‐14
Background Report