The 210 Stations That Watch America's Water Levels, Some Since the 1850s

Some of the instruments that measure the height of the sea around the United States have been doing it since the 1850s. They belong to the National Water Level Observation Network, known as NWLON: a permanent system of 210 continuously operating stations spread along the coasts of the U.S. and its territories. Government agencies and businesses alike treat it as the place to go for water level data, whether they are steering ships, planning recreation or managing coastal ecosystems.

An NWLON station in San Francisco, California. Credit: NOAA.

More than the tide

Each station records the water level, and the stations also measure other oceanographic and weather conditions, such as water temperature and wind speed. The data flows in 24 hours a day, seven days a week, and NOAA uses it in real time to keep navigation safe.

The same measurements feed NOAA's nowcast and forecast models, which describe what the water is doing now and what it is likely to do next. Those models can sharpen warnings for tsunamis and storm surges. The network is also the basis for the tide predictions NOAA publishes every year.

A long memory

Because some stations have been collecting data since the 1850s, the network holds a historical record as well as a live feed. Scientists use that history to calculate how local mean sea level is changing and to understand when and why unusually high tides occur. A station that has watched the same harbor for generations turns ordinary readings into a trend.

Who runs it

NWLON is managed by NOAA's Center for Operational Oceanographic Products and Services. Its work reaches well beyond oceanography: accurate water levels matter to anyone who navigates, builds, restores or preserves anything along the coast.

Sources

Based on "How does NOAA monitor water levels around the nation?" from NOAA's National Ocean Service, a work of the United States government in the public domain.