Benefits of Ocean Observing Catalog (BOOC)

Article Title

National Water Level Observation Network (NWLON)


The Charleston, SC Branch Pilots Association (end user 1) make “go-no-go” decisions based on data from the National Water Level Observation Network (NWLON), Official NOAA Tide Predictions and Physical Oceanographic Real Time System (PORTS) sensors for tall, deep draft vessels transiting through Charleston Harbor and into the associated tributaries.

Specific datasets for this use case include:

Data can be accessed in a variety of ways: graphic, text, Data APIs.

The NWLON and PORTS are sponsored by CO-OPS which is the source for accurate, reliable, and timely tides, water levels, currents, and other oceanographic data. The vision of CO-OPS is to support the Nation's economy and safeguard coastal communities with oceanographic information accessible by anyone, at any time, from any place.

Transformation into an actionable information service

Below is the air draft table to clear the Don Holt Bridge at North Charleston, SC. This table was calculated to allow for two feet of clearance above the mast of any ship on maximum predicted tides for the year. At that time, the maximum predicted low tide was +1.2 ft. above MLLW, and the maximum predicted high tide was +7.2 ft. above MLLW. Clearance tables assumed every low tide was a +1.2’ and every high tide was a +7.2’, to make sure our clearance table worked every day, including on those particular days that those were the actual predicted tide levels.

With the rise in sea level, predicted and actual tides exceed those levels fairly often. Rather than rewrite the clearance table, dispatchers check the Charleston NWLON Tide Gauge daily to see if the most recent low tide exceeded +1.2' or the most recent high tide exceeded +7.2’. When either of those occurs, they “add a foot” to the reported air draft from the ship, and then apply the table to the corrected air draft.

Pilot dispatchers work with the individual pilots and shipping agents (end user 2) to communicate the information and make any necessary changes to ship transit times. Real time NOAA Air Gap data at the Ravenel and Don Holt Bridges are used to validate available clearances at fixed points on the bridge for vessels transiting underneath one or both bridges. The Don Holt Bridge at North Charleston has a smaller available clearance and is more often a cause for concern tied to available air draft.

The geographic extent of this use case is Charleston Harbor, South Carolina and the tributaries of the Cooper and Wando Rivers near Charleston, SC. Two bridges along common commercial ship transits in this area include the Arthur Ravenel Bridge near downtown Charleston and the Don Holt Bridge over the Cooper River just south of the North Charleston Container Terminal. The benefits tied to use and application of the data sets help to improve the safety of coastal activities and environmental protection in the waterways. Deep draft vessels with large air draft benefit from having data sets used for critical decision making and avoiding a bridge allision or collision leading to an oil spill or infrastructure damage.

End user 3, South Carolina Port Authority as terminal owners and local system sponsor for the air gap systems have a vested interest in ensuring timely, safe and efficient vessel calls.

End user 4, USCG has vested interest in protecting bridge infrastructure and preventing a marine incident and damage to vessels and other assets in the waterway