Regulatory floodplains are defined by the elevation of the base flood in relation to the elevation of the ground. Base flood elevations are used to determine the required elevation of new buildings in the floodplain. Floodplain management will not succeed without accurate measurements of flood elevations, ground elevations and building elevations. Needless to say, if flood elevations are based on one system and ground or building elevations are based an another, things won’t work. NGVD 29 stands for National Geodetic Vertical Datum of 1929. It is a system that has been used by surveyors and engineers for most of the 20th Century. It has been the basis for relating ground and flood elevations, but it has been replaced by the more accurate North American Vertical Datum of 1988 (NAVD 88). Because it has such an impact on floodplain management, it is important for local officials to understand what’s happening.