What is a floodplain?

A floodplain is the area that may become flooded during or after a large storm. When a stream or lake overflows, the surrounding area is a natural storage area for the excess water.

What is floodplain management?

Effective floodplain management aims to both reduce flood losses and protect the natural resources and functions of floodplains. Floodplain management is accomplished using various methods, including a rigorous planning process, zoning and subdivision regulations, and enforcement of local flood damage prevention ordinances. The city’s ordinance meets or exceeds state and federal standards for all proposed construction and other development

Between 1995 and 2000, seven federally declared flood disasters happened in the states of Arizona, California and Nevada. The region’s vulnerability to flooding makes it crucial that communities and property owners have accurate, up-to-date information about flood risk. Floodplain management uses maps that show Special Flood Hazard Areas (SFHAs) which indicate high areas of risk for flooding and represent the 1% annual chance floodplain. SFHAs determined through detailed methods also reference Base Flood Elevations (BFEs), the computed elevations to which flood water is anticipated to rise during the base (1% annual chance) flood.

Why map a floodplain?

Mapping floodplains is vital for implementing all floodplain management strategies. It provides the data necessary for hazard mitigation programs and rating flood insurance for new construction on an actuarial basis and supports the decision-making process with respect to the natural values of floodplains. FEMA depicts these flood areas on Flood Insurance Rate Maps (FIRMs), with flood hazard areas, floodways, base flood elevations or depths, physical features such as roads and streamlines, and other information. FIRMs are created using aerial images from U.S. Geological Survey (USGS) Digital Orthophoto Quadrangles (DOQs) supplemented with topography, flood data and other information, such as street names and river centerlines. Accompanying a FIRM is a Flood Insurance Study (FIS) Report, which is a comprehensive document describing a FIS and typically includes a description of the hydrologic and hydraulic analyses, profiles and tables.

Is my property located in a floodplain?

Floodplains are mapped with zones on the city’s current FIRM. You are welcome to contact the city’s Floodplain Administrator, your lender or your insurance agency. For additional assistance, you may contact the FEMA Map Assistance Center at (877) FEMA-MAP.

How do I find the Flood Insurance Rates for my property?

Once you have identified the floodplain zone in which your property is located, contact your insurance provider.

What is the reference datum?

Like Global Positioning Systems (GPS), reference datums provide location information. Floodplain management uses the vertical datum to denote elevations.

The major impact by the new August 2008 digital FIRMs (DFIRMs) will be the change in reference datum. The new maps will reference the current federal standard for vertical datum, the North American Vertical Datum of 1988 (NAVD88), while prior FIRMs referenced the National Geodetic Vertical Datum of 1929 (NGVD29).

More information regarding vertical datum conversions can be found online at the FEMA and National Geodetic Survey websites.