Minimum depths are collected during periodic USACE sonar surveys of channels. These depths were provided on raster charts, but controlling depths will now be replaced with the original channel design dredging depths used by the USACE. Improving depth presentation on these products will improve data consistency and overall safety. The implementation will begin early in 2019.
NOAA’s suite of electronic navigational charts will not be affected and mariners are encouraged to use NOAA ENCs for critical safety information as these products are typically updated up to one month ahead of raster products.
NOAA has as a priority to update ENC over RNC products. This often leads to RNC products not accurately reflecting the most current controlling depth values. To avoid inconsistencies among controlling depths, NOAA will only show project depths on raster chart products in the future. The Initial implementation of this change will focus on deep draft shipping channels where the main product used for navigation is the ENC.
As the changes are made on individual charts, NOAA will include a note on each chart directing mariners to review the USACE website and use NOAA ENC to access the latest controlling depths. Additionally, a statement drafted jointly by Coast Survey and the US Coast Guard is being published weekly in the Coast Guard’s Local Notice to Mariners:
NOAA recommends that mariners take advantage of the most recent chart updates by using the NOAA Electronic Navigational Chart (ENC) for navigation in U.S. waters. ENCs provide the most up to date information, whereas paper and raster nautical chart updates may be up to one month behind the corresponding ENC coverage. Over the next few years, mariners will see continued improvement in the extent and detail of ENC coverage, while there will be a reduction in RNC and paper chart coverage and service. ENCs will include routine changes between editions that are not published through notices to mariners. One significant change to the RNC and paper charts will be the removal of controlling (minimum) depth information from many maintained channels. Controlling channel depths will still be provided on ENCs.
In addition, channels are divided into a series of individually named sections called 'reaches.' There are two different depths related with each reach that are reported by the USACE, the project depth and the controlling depth. Project depths are the original design dredging depths of a channel reach constructed by the USACE. They may or may not be maintained by dredging after completion of the channel. Controlling depths, or minimum depths, are the least depths within the limits of a channel reach. These depths are updated with each new USACE survey. Minimum depths limit the safe use of a channel to ships with drafts less than the minimum.
Finally, the change from showing, often outdated, controlling depths, to showing channel project depths on raster nautical chart products, will provide more clarity and safety for mariners. The project depths shown on raster charts will give users an idea of the original channel design dimensions. The updated controlling depths provided on NOAA ENCs and on the USACE website will give users the latest information on the safe depth in which ships may sail through federally maintained channels.