The National Oceanographic and Atmospheric Administration is beginning to change how NOAAs raster nautical chart products show minimum depths in Corps of Engineers maintained channels.
Up until now, raster printout paper charts and corresponding digital raster navigational charts (NOAA RNC) reported minimum depths – also called controlling depths – that were collected during the Corps’ periodic sonar surveys of channels.
Instead, those controlling depths will now be replaced on raster charts with the original channel design dredging depths – also called project depths – set by Corps designers.
NOAA will change channel depths on its raster charts from controlling depth (top) to project depth. NOAA image.
“Standardizing depth presentation on these products will improve data consistency and overall safety,” according to an announcement from NOAA’s Office of Coast Survey, which is beginning to implement the changes in early 2019.
NOAA’s electronic navigational charts (NOAA ENC) are not affected by the changes. The agency is encouraging mariners to use the ENC suite of charts for critical safety information, because they typically get updated as much as one month before the raster charts.
NOAA officials said they decided to make the change because while the Corps makes its recent survey depths publicly online, it takes time for the new depths to be incorporated into NOAA nautical charts and published. Updating the ENC suite takes priority over the raster charts, so “this often results in RNC products not accurately reflecting the most current controlling depth values” that are found on the ENC charts and Corps’ online data.
Showing only project depths on the raster charts will eliminate that inconsistency, according to NOAA officials. The first stage of the changeover is focusing on deep draft shipping channels where mariners primarily use the ENC charts for navigation.
As individual charts are updated, NOAA will add a notation directing users to the Corps of Engineers website and the NOAA ENC for the latest, updated controlling depths. The agency and the Coast Guard are also publishing a weekly reminder about the change in the Coast Guard’s Local Notice to Mariners.
