Unlike ocean waves, which are ordinarily driven by wind and tides, and roll to shore at a steady clip, river waves (also called flood or flow waves) are temporary surges stretching tens to hundreds of miles.
But they can also pose hazards: Extreme river waves triggered by a prolonged downpour or dam break can produce floods.
Measuring Speed and Size To search for river waves for her doctoral research, lead author Hana Thurman of Virginia Tech turned to a spacecraft launched in 2022.
She found that the mission had caught three clear examples of river waves, including one that arose abruptly on the Yellowstone River in Montana in April 2023.
The other two river waves that Thurman and the team found were triggered by rainfall runoff.
The height and velocity of potentially dangerous flood waves moving down the U.S. were measured for the first time by NASA and Virginia Tech researchers using satellite data. S. rivers. . The three waves they observed were probably brought on by a loosened ice jam and heavy rain. The new study emphasizes how space-based observations can help hydrologists and engineers, particularly those working in communities along river networks with limited flood control structures like levees and flood gates, even though there isn’t currently a database that gathers satellite data on river flood waves.
In contrast to ocean waves, which are typically influenced by wind and tides and roll steadily to shore, river waves—also known as flood or flow waves—are transient surges that can last anywhere from tens to hundreds of miles. They are necessary to transport nutrients and organisms down a river and are usually brought on by rainfall or seasonal snowmelt. However, they can also be dangerous: Floods can be caused by extreme river waves brought on by a protracted downpour or dam failure.
While sailing and surfing are familiar with ocean waves, rivers are the planet’s lifeblood. Coauthor of a recent study published May 14 in Geophysical Research Letters, Cedric David, a hydrologist at NASA’s Jet Propulsion Laboratory in Southern California, stated, “We want to understand their dynamics.”.
measuring both size and speed.
The lead author, Hana Thurman of Virginia Tech, used a spacecraft launched in 2022 to look for river waves for her doctoral research. A partnership between NASA and the French space agency CNES (Centre National d’Études Spatiales) produced the SWOT (Surface Water and Ocean Topography) satellite. It is using its sensitive Ka-band Radar Interferometer (KaRIn) to survey the height of almost all of the fresh and salty surface waters on Earth. By bouncing microwaves off the surface and measuring the time it takes for the signal to return, the device maps the width and elevation of bodies of water.
“We focus on the dynamics and effects of water movement and change in addition to tracking the overall amount of water stored in lakes and rivers,” stated Nadya Vinogradova Shiffer, SWOT program scientist at NASA Headquarters in Washington.
Thurman was aware that SWOT has aided scientists in mapping the seafloor, detecting tsunami slosh, and tracking rising sea levels close to the coast. However, could she spot anomalies in the data related to river height that would indicate a wave in motion?
Three distinct instances of river waves, including one that suddenly appeared on the Yellowstone River in Montana in April 2023, were captured by the mission, she discovered. A 9-foot-one-foot (2-meter-tall) crest was seen flowing toward the Missouri River in North Dakota as the satellite passed overhead. It was separated by a striking peak that was 6 inches (8 kilometers) long, followed by a longer tail. The KaRIn instrument’s exceptionally high spatial resolution is demonstrated by these details, which are thrilling to observe from orbit, Thurman said.
Investigating the area using optical Sentinel-2 imagery, she concluded that the wave was probably caused by pent-up water being released when an ice jam broke apart upstream.
Thurman and the team discovered two additional river waves that were caused by runoff from rainfall. One was discovered by SWOT beginning in January. the biggest flood of the year on that portion of the Colorado River south of Austin, Texas, on May 25, 2024. It was more than thirty feet (9 meters) high and 166 miles (267 kilometers) long. It traveled more than 250 miles (400 kilometers) at a speed of about three and a half feet (1 and a half meters) per second before emptying into Matagorda Bay.
The other wave began in March 2024 on the Ocmulgee River close to Macon, Georgia. Standing more than 20 feet (6 meters) tall and spanning more than 100 miles (165 kilometers), it covered more than 124 miles (200 kilometers) at a speed of roughly one foot (0.33 meters) per second.
Thurman explained, “We’re learning more about the shape and speed of flow waves, and how they change along long stretches of river.”. “That could help us answer questions like whether infrastructure is at risk and how quickly a flood could arrive.”.
complementary observations.
Stream gauges, which record water height and estimate discharge at fixed points along a river, have long been used by engineers and water managers to measure river waves. The U.S. government is one of the agencies responsible for maintaining stream gauge networks. A. Geological Survey. Other regions of the world have fewer of them.
“Satellite data is complementary because it can help fill in the gaps,” said George Allen, a Virginia Tech hydrologist and remote sensing specialist who oversaw the study.
SWOT is similar to a traffic helicopter that takes pictures of the highway, if stream gauges are similar to toll booths that clock cars as they pass.
Allen stated that the wave speeds determined by SWOT were comparable to those determined solely by gauge data, demonstrating how the satellite could assist in wave monitoring in river basins without gauges. Scientists can monitor shifting flood patterns globally by understanding where and why river waves form.
Around 55% of large-scale floods are predicted to be observed by SWOT, which orbits the Earth several times every day, at some point during their life cycle. David stated that SWOT analysis has the ability to identify potentially harmful floods in the making. “If we see something in the data, we can say something,” he said. Even though we have been standing on the banks of our rivers for a while, we have never seen them as we do now. “”.
Learn more about SWOT analysis.
NASA and CNES collaborated to develop the SWOT satellite, with assistance from the UK Space Agency and the Canadian Space Agency (CSA). The United States is led by NASA’s Jet Propulsion Laboratory, which is run by Caltech in Pasadena, California. S. . part of the undertaking. NASA provided the Ka-band radar interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations for the flight system payload. CNES supplied the Doppler Orbitography and Radioposition Integrated by Satellite system, the dual frequency Poseidon altimeter (created by Thales Alenia Space), the KaRIn radio-frequency subsystem (co-developed with Thales Alenia Space and assisted by the UK Space Agency), the satellite platform, and ground operations. CSA provided the KaRIn high-power transmitter assembly.
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