Flood Insurance Risk Maps or FIRMs for the City of Lancaster became effective January 6, 2012.  The Tarhe Run map is effective July 19, 2018.
 
Flood maps are essential tools for managing flood hazard areas throughout the state. Floodplains are dynamic systems, and many maps do not reflect new development and/or natural changes in the environment. Since local planning decisions are based on data shown on the flood maps, it is imperative that actual flood risk is accurately and  precisely shown. 

The new Flood Insurance Rate Maps (FIRMs) are in a digital format. “Digital” refers to new and improved methods of storing and transferring flood hazard information and mapping with Geographic Information Systems (GIS). Digital Flood Insurance Rate Maps (DFIRMs) are easier to update, distribute, and incorporate into local GIS applications.

The 1989 effective FIRMs use a street network base map. Aerial photographs are used as the base maps on the new DFIRMs. Using a photo background on the new maps makes it easer to see how a flood zone relates to specific structure and project sites.

 The DFIRMs are created using a common (or standard) vertical datum—the North American Vertical Datum of 1988. Old flood maps for two adjacent communities may use more than one datum, making it difficult to link base flood elevations between the two. Using a common datum helps to eliminate this confusion.

The new DFIRMs are in a countywide format, which minimizes mismatched flood hazard areas across community boundaries and presents the flood risk across the county in a broader sense.

The new flood maps show the most recent flood studies and flood data available for your community. This does not mean that every river, stream, and creek has been restudied. It does mean, however, that all new data meeting FEMA standards are depicted on these maps.