During pre-event planning, GIS-based databases incorporating flood inundation maps, aerial
photographs, and field surveys are used to identify locations where existing properties are threatenedby various levels of flooding. Existing damageable structures should be categorized by type and
number for each flood event throughout the range of the flood-frequency relationship. Frequencydischarge–
elevation-damage relationships are presented in tabular form. The information is used to
help in the development of warning and evacuation plans, location of mass-care centers, management
of vital services, and to estimate the number of structures and people impacted by an event. It
is also required to define actions and facilities for implementation of temporary flood-loss-reduction
actions such as flood fighting, installation of temporary barriers, removal of or raising building
contents, and relocation of potential hazardous materials. The threatened-properties analysis helps
refine response measures that might be dictated due to the warning time available. The location of
structures in the floodplain can determine whether more or less warning time is available.