Effect of Modernizing the National Datums on Floodplain Mapping A Cooperative Pilot Project between the National Geodetic Survey, North Carolina Floodplain Mapping Program, North Carolina Geodetic Survey, and the Federal Emergency Management Agency.

摘要

This study was conducted to examine the effects on floodplain mapping of replacing the national datums of the United States. By approximately 2022, NOAAs National Geodetic Survey (NGS) will modernize (replace) the official datums, currently the North American Datum of 1983 (NAD 83) and the North American Vertical Datum of 1988 (NAVD 88). Based on new technologies and methods, NGS will define new geometric and geopotential datums that will replace NAD 83 and NAVD 88, respectively. Georeferencing spatial data to the correct datum is extremely important to many geospatial applications, including construction, agriculture, resource management, navigation, and emergency management. These updates will provide a critical improvement to orthometric heights, which are offset up to 2 meters (over 6 feet). In addition to the new datums, NGS is also considering promoting appropriate use of the passive control network by publishing estimated orthometric height accuracies for bench marks. In order to investigate the effects of this coming change, a pilot study was conducted in cooperation with the North Carolina Floodplain Mapping Program (NCFMP) and the North Carolina Geodetic Survey (NCGS). This report reflects the outcome of that pilot study. For this study one stream reach, Tranters Creek in Pitt County, North Carolina, was chosen for analysis. Tranters Creek is in the coastal plain of North Carolina and has a recently updated detailed flood study using Light Detection And Ranging (LiDAR) data in addition to an effective1 limited detailed study. The coastal plain was selected as a conservative estimate since small changes in water levels have a larger effect on the floodplain than in mountainous areas (National Research Council, 2009). To understand the effects of the datum modernization, the first step was to model the change for specific coordinates. For the study location all geospatial data were transformed from the existing reference frame to available proxy datums that most closely resemble the future datums. For the geometric (horizontal) datum NAD 83 (HARN2) was transformed to the International Terrestrial Reference Frame of 2005 (ITRF2005)/Geodetic Reference System of 1980 (GRS-80).