First, researchers from NASA and Virginia Tech used satellite data to measure the altitude and speed of potentially dangerous floods traveling along U.S. rivers. The three waves they tracked were probably caused by extreme rainfall and loose ice jam. Although there is currently no database to compile satellite data on river flooding, the new study highlights the potential of space observations to help hydrologists and engineers, especially those working in riverside networks, with limited levee and flood control structures such as levees and flood pools.

Unlike waves that are usually driven by wind and tides and rolling to shore on a stable clip, river waves (also known as flooding or wandering waves) are temporary currents that extend to hundreds of miles. Often caused by rainfall or seasonal snow melt, they are essential for driving nutrients and organisms down the river. But they can also pose dangers: Extreme rivers triggered by prolonged downpours or dam rupture can cause flooding.

"Waves are well known on surfing and sailing, but rivers are the arteries of the Earth. We want to know their dynamics." Cedric David, a hydrologist at NASA's Jet Propulsion Laboratory in Southern California, and is also a co-author of a new study published in a geophysical research letter on May 14.

In search of a river for doctoral research, Virginia Tech lead author Hana Thurman turned to the spacecraft launched in 2022. The SWOT (surface water and oceanic topography) satellite is a collaboration between NASA and the French space agency CNES (Center Centry National D'études d'étudesspatiales). It used its sensitive KA band radar interferometer (Karin) to investigate the height of almost all Earth's surface water. The instrument maps the height and width of the water body by bounced the microwave from the surface and timing the signal back how long.

"In addition to monitoring the total storage of water in lakes and rivers, we also amplify the impact of dynamics and impact," said Nadya Vinogradova Shiffer, SWOT program scientist at NASA's headquarters in Washington.

Thurman knows that SWOT helped scientists track sea level rise near the coast, spotted tsunami Slosh and map the seabed, but can she identify river height anomalies in the data, indicating this moving wave?

She found that the mission captured three clear river waves, including one that popped up on the Yellowstone River in Montana in 2023. As the satellite passed overhead, it observed the summit of the 9.1-foot-high mountain peak (2.8 meters high), flowing towards the Missouri River in North Dakota. It is divided into a dramatic 6.8-mile (11 km) long peak, followed by a more pulling tail. Thurman said the details are excitingly seen from orbit and illustrate the unique high spatial resolution of the Kalin instrument.

She scouted through the optical Sentinel 2 image of the area, and she determined that the waves might have been caused by ice jam upstream and release of ice cream that suppresses water.

Thurman and the other two rivers found by the team were triggered by rainfall runoff. Starting from January 25, 2024, on the Colorado River south of Austin, Texas, SWOT began to discover that it was related to the largest flooding in that part of the river. It has a height of more than 30 feet (9 meters), a length of 166 miles (267 kilometers), travels about 3.5 feet (1.07 meters) per second, lasts 250 miles (400 kilometers) before being discharged into Matagorda Bay.

Another wave originated in March 2024 on the Ocmulgee River near Macon, Georgia. The size is over 20 feet (6 meters) high, extending over 100 miles (165 kilometers) and traveling time is over 124 miles (2004 miles) per second.

"We are learning more about the shape and speed of wandering waves and how they extend along the long river," Thurman said. "Will this help us answer such as the speed at which floods get here, and the infrastructure is at risk?"

Engineers and water managers measuring river waves have long relied on river meters, which estuaries record water height and estimated emissions at fixed points along the river. In the United States, the flowmeter network is maintained by agencies including the U.S. Geological Survey. They are more sparse in other parts of the world.

"Satellite data are complementary because it can help fill the gap," said George Allen, a hydrologist and remote sensing expert at Virginia Tech.

If the flow meter is like a passing pass clock, the SWOT is like a traffic helicopter holding a snapshot of the highway.

Allen said the wave velocity that SWOT helped determine is similar to that calculated using only gauge data, indicating how satellites can help waves monitor waves in rivers without metering. Knowing where the river is and why development can help scientists track changing patterns of flooding around the world.

SWOT orbits the Earth multiple times a day, and at some stage of its life cycle approximately 55% of large-scale flooding will be observed. “If we see something in the data, we can say something,” David said of the potential for SWOT to have dangerous flooding in manufacturing. “We have been standing on the banks of rivers for a long time, but we have never seen them like we are now.”

The SWOT satellite was jointly developed by NASA and CNES and was donated by the Canadian Space Agency (CSA) and the British Space Agency. NASA's JET Propulsion Laboratory is run by Caltech in Pasadena, California, leading the U.S. component of the project. For flight system payloads, NASA provides KA band radar interferometer (KARIN) instruments, GPS science receivers, laser reversers, two-beam microwave radiometers and NASA instruments operated. Satellite system integrated Doppler orbitography and radiation, dual-frequency Poseidon Altimeter (developed by Thales Alenia Space), Karin Radio-Roady-doadigen frequency subsystem (supported by Thales Alenia Space and UK space agents), satellite platforms, satellite platforms and ground operations. CSA provides Karin high power transmitter components.

Jane Lee/Andrew King
Jet Propulsion Laboratory in Pasadena, California.
818-354-0307 / 626-379-6874
Written by Sally Younger
2025-074