Flood hazard areas identified on the Flood Insurance Rate Map are identified as a Special Flood Hazard Area (SFHA). SFHA are defined as the area that will be inundated by the flood event having a 1-percent chance of being equaled or exceeded in any given year. The 1-percent annual chance flood is also referred to as the base flood or 100-year flood. SFHAs are labeled as Zone A, Zone AO, Zone AH, Zones A1-A30, Zone AE, Zone A99, Zone AR, Zone AR/AE, Zone AR/AO, Zone AR/A1-A30, Zone AR/A, Zone V, Zone VE, and Zones V1-V30. Moderate flood hazard areas, labeled Zone B or Zone X (shaded) are also shown on the FIRM, and are the areas between the limits of the base flood and the 0.2-percent-annual-chance (or 500-year) flood. The areas of minimal flood hazard, which are the areas outside the SFHA and higher than the elevation of the 0.2-percent-annual-chance flood, are labeled Zone C or Zone X (unshaded). Flood zone determinations are typically done when a building permit application is received but can be done any time one is requested. For a flood zone determination, please see the Public Works Department.
Flood Insurance Studies (FIS) use detailed hydrologic and hydraulic analyses to model the one percent annual chance flood event, determine Base Flood Evaluations (BFEs), and designate floodways and risk zones. The flood hazard data is portrayed in tabular fashion in the FIS narrative and graphically as flood profiles that are attached to the narrative. When areas have been designated as special flood hazard areas on the community's Flood Insurance Rate Map (FIRM) and no Base Flood Elevation (BFE) or an identified floodway have been developed, communities are required to apply the provisions of 44 Code of Federal Regulations 60.3(b)(4). Subparagraph 60.3(b)(4) that requires communities to obtain, review, and reasonably utilize any base flood elevation and floodway data available from a Federal, State, or other planning source. A FIS was last conducted for Patterson in 2008: Flood Insurance Study (FIS) 2008 (PDF)