Current Floodplain Studies in Ventura County

The digital Flood Insurance Rate Maps (DFIRMs) are not static in nature. FEMA updates major river floodplain maps approximately every 10 to 15 years. DFIRMs can also be updated through approved Letters of Map Change Floodplain maps are generated using the latest engineering standards and technological advancements in hydrology and hydraulic modeling of storm water flows/ velocities, topographical surveying, and other accepted engineering practices. Over time, accepted practices give way to improved modeling methodologies, thereby further refining previous mapped flood zones, floodplain and regulatory floodway boundaries, and 1% annual chance (100-year flood) base flood elevations.

These technical engineering mapping updates are referred to by the Federal Emergency Management Agency (FEMA) as Flood Insurance Studies (FISs) and they assess the flood hazard within a community. The area of floodplain study they cover varies from a single watercourse to several watercourses within a watershed. It contains a narrative of the flood history of a community, cross sections of floodplains, ocean wave height analyses, and flood profiles for studied flooding sources within the community. This information is used for the following purposes:

  • To determine flood frequencies within the community (i.e., probability and recurrence of flooding);
  • To predict how high flood waters are likely to rise on properties during the 1% annual chance flood; these flood heights are called ‘base flood elevations’;
  • To identify the flood hazard areas in the community;
  • To determine the boundaries of the regulatory floodway and floodplains; and
  • To prepare the digital Flood Insurance Rate Maps (DFIRMs).

A FIS typically takes between two and three years to complete. A FIS is also known as a flood elevation study. Additional information on Flood Insurance Studies and how to use them can be obtained at: