NOAA installing sensors on bridges to measure air gap

The National Oceanic & Atmospheric Administration has installed sensors to measure clearances under two bridges spanning the Chesapeake and Delaware Canal.

A ship passes under the bridge over the C&D Canal at Chesapeake City, Md.
   Image Credit: Courtesy National Oceanic & Atmospheric Administration

The two air-gap sensors were deployed March 1 on the Chesapeake City Bridge in Maryland and the Reedy Point Bridge in Delaware.

The C&D installations are a response to demand from waterway users for accurate, timely measurements of the air gap under heavily trafficked bridges. NOAA expects to add sensors to other bridges over important navigation routes across the country.

According to Richard Edwing, deputy director of NOAA’s National Ocean Service Center for Operational Oceanographic Products & Services, the Port of New York and New Jersey may be next in line for installation of the new equipment, although he hesitated to say which bridge will be first to receive it. The Bayonne Bridge in New Jersey and the Verrazano Narrows Bridge in New York are possible candidates.

The sensors are microwave devices that have no direct contact with the water and should provide trouble-free operation, Edwing said. The sensor data is updated every six minutes because of changes in tide level, vehicle traffic and temperature — all variables having an effect on the air gap.

Image Credit: Courtesy National Oceanic & Atmospheric Administration

Workers install a sensor on the bridge over the canal at Reedy Point in Deleware.

NOAA is adding the air-gap sensors to its Physical Oceanographic Real-Time System. This suite of measuring devices provides oceanographic and meteorological information such as water level, currents and wind. PORTS arrays are now functioning in 10 locations.

Users can access the air gap and other PORTS information via the Internet or by listening to a recording on a toll-free number for each location.

NOAA views PORTS as a way to help mariners avoid accidents that can take a heavy toll in lives and damage to the environment. The first PORTS installation was in Florida’s Tampa Bay and came in response to the May 1980 ramming of the Sunshine Skyway Bridge. That accident resulted in 35 deaths.

PORTS installations are now in place in San Francisco, New York/New Jersey, Houston/Galveston, Tampa Bay, Chesapeake Bay, Narragansett Bay, Soo Locks, Los Angeles/Long Beach, the Delaware River and Bay, and Anchorage, Alaska.

All are accessible online at The website also provides toll-free telephone numbers for the individual PORTS locations.

By Professional Mariner Staff