Flood Map Modernization: Understanding the Effects of Map Changes
NEW FLOOD MAPS: BUILDING TO A SAFER STANDARD
Flood hazard maps can be valuable tools in the effort to protect lives and properties. The County’s current flood maps are nearly thirty years out –of-date. The new flood maps provide a much more accurate picture of flood risks and flood elevations to guide in land development and building decisions.
Engineers/Developers/Builders can plan for safer construction
When preliminary flood maps are released, the building industry will need to know the differences between the preliminary maps and the current effective map. The data from the more conservative map is typically used by communities for design and permitting purposes. This will remain the case until the preliminary maps become effective. When the preliminary map shows less restrictive information, it usually cannot be used until that map becomes effective.
The vertical datum is changing
As new flood maps are issued, they will no longer be using the National Geodetic Vertical Datum of 1929 (NGVD29) as the vertical datum (see the Federal Emergency Management Agency’s Procedure Memorandum 41). Instead, they will use the North American Vertical Datum of 1988 (NAVD88). Floodplain managers, surveyors, engineers, builders, and other users of elevation data from multiple sources (e.g., a FIRM and elevation certificate) must take care that the elevation values they use are based on the same vertical datum. If they are not the same, the values need to be converted to the same datum. Failure to do so can result in improper design (e.g., building at the wrong elevation). Note that the property owners’ risk is not affected by a vertical datum change because all elevations in the local area are changed by the same amount.
Additional information can be found on the Resources Page.
Santa Cruz Flood Control District
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