An Explanation of NAVD88 and Base Flood Elevation (BFE)

The following article makes it very easy to understand the concept of NAVD88 and base flood elevations.  As you may know, base flood elevations, and therefore elevation certificates, used to be based on NAVD29 (which was created in 1929), but are now typically based on NAVD88, which was established in 1988. Though we rarely see it spelled out, NAVD stands for National Geodetic Vertical Datum.

Current research shows that sea level rise is a real threat, and is one of the reasons that experts predict that severe storms such as Sandy could continue to cause extreme flooding.  As sea level rise continues, NAVD88 becomes less accurate, because it was based on conditions as they existed in 1988.  Sooner or later, the government will need to establish a new NAVD reference point.

Definitions:

“Tidal datums are determined by averaging the level of water at a tide gauge over time. Some simple examples of these are Mean Sea Level (MSL), Mean Low Water (MLW) and Mean Higher High Water (MHHW).

In the United States, Mean Sea Level (MSL) is a tidal datum which is computed by NOAA?s (National Oceanic and Atmospheric Administration) Center for Operational Oceanographic Products and Services (CO-OPS) as part of the National Tidal Datum Epoch (NTDE) based on data collected over a 19-year tide cycle. It pertains to Local Mean Sea Level (LMSL) at the tide station at which it was observed and should not be confused with any other vertical datum, including LMSL at other tide stations. The current NTDE for the United States is 1983-2001.” (Courtesy of NOAA)

North American Vertical Datum of 1988 (NAVD 88)

North American Vertical Datum of 1988 (NAVD 88) consists of a leveling network on the North American Continent, ranging from Alaska, through Canada, across the United States, affixed to a single origin point on the continent:

  • Tide Station & Location = Pointe-au-Pere,Rimouski, Quebec, Canada
  • PID = TY5255
  • GSD* Designation = 54L071
  • Bench Mark = 1250 G
  • Height above LMSL(meters) = 6.271

* Geodetic Survey of Canada = GSD (Courtesy of NOAA)

The full article can be found here.