Potomac Waterfront Flood Mitigation Study - City of Alexandria

3.1.3 Floodproofing
Overview of Flood Mitigation Measures
Floodproofing is the process of modifying a structure or its contents in such a way that the
damages from future flood losses will be reduced or eliminated. The two types of floodproofing
are wet floodproofing and dry floodproofing.
Wet floodproofing involves modifications to a structure so that the contents of the structure are
protected when floodwaters enter it. The primary modifications involve elevation or relocation of
appliances, electrical, and utility systems, as well as use of flood-resistant materials inside the
structure. This type of floodproofing is most appropriate for structures that have a basement or
crawl space and a First Floor Elevation (FFE) above the BFE. It is important to note that
flooding will still occur within the structure, so extensive clean up may still be necessary after
flooding events, especially if the floodwaters are contaminated. However, these modifications
can reduce the total damages to structures and their contents.
Dry floodproofing is the process of making the portion of a structure that is below a certain flood
elevation watertight. This prevents floodwater from entering the structure and causing damage.
This process involves applying a membrane or coating to the surface of the structure as well as
sealing any openings, such as doors and windows, with permanent or removable barriers such as
a floodgate (see Figure 3-1).
Figure 3-1: Floodgate
Some risks arise when dry floodproofing structures. One is that dry floodproofing is generally
not recommended for structures with basements. This is because these buildings are susceptible
to underseepage, which can create a strong buoyancy force that might damage the structure.
However, floodproofing structures with basements is considered to some extent for this project
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