Most permanent FIS elevation reference marks are referenced to which datum?

The National Geodetic Vertical Datum (NGVD), which provides a consistent elevation reference framework, is the benchmark for most permanent Flood Insurance Study (FIS) elevation reference marks. This datum is crucial because it ensures that elevations are reported consistently, allowing for effective floodplain management and accurate risk assessments in various regions.

Using the NGVD as a reference allows local authorities, engineers, and surveyors to accurately compare flood elevations across different geographic areas, essential for floodplain regulation, planning, and insurance purposes. As the standard for vertical measurements, it ties together a variety of elevation data into a singular, reliable reference, facilitating communication and decision-making processes related to flood risk management.

Other datums mentioned, such as NAD83, are primarily horizontal datums used for mapping land features and do not provide the consistent vertical elevation needed for floodplain management. Similarly, UTM is a coordinate-based system used for mapping, not tied to elevations. The Vertical Datum of 1929 (VD29) is largely outdated and has been replaced by the NGVD in most applications, reinforcing the latter's status as the primary elevation reference for FIS marks.