Is NGVD29 the same as Mean Sea Level?
No, it is not. Once thought to be close to Mean Sea Level (MSL), it was within a couple of feet for most of the northern rim of the Gulf of Mexico. The original datum was called the Sea Level Datum of 1929 and it was the first vertical (elevation) datum for an entire continent in the history of the world. With observations that started in the 19th century, a series of 26 tide gauges were recorded for over 19 years to establish Local Mean Sea Level (LMSL) for all of the coasts of the United States. However, since LMSL varies from place to place because not only from astronomical phenomena but also due to local winds, river stages, storms, and local gravity… LMSL was not equal to “0.00 ft” everywhere. “Zero” needed to be somewhere, so Galveston, Texas was selected as the “Primary Benchmark of the United States”, and LMSL there was set equal to “0.00 ft.” That elevation of the mean sea in Galveston was within a couple of feet or so to what it was in Biloxi, Mississippi where the closest
