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. Extreme rainfall and a loosened ice jam were probably the causes of the three waves they tracked. Although there isn’t a database that gathers satellite data on river flood waves yet, the new study shows how useful space-based observations can be for hydrologists and engineers, particularly those who work in communities along river networks with few flood control features like levees and flood gates.
River waves (also known as flood or flow waves) are transient surges that can extend tens to hundreds of miles, in contrast to ocean waves, which are typically driven by wind and tides and roll to shore at a steady clip. Usually brought on by precipitation or seasonal snowmelt, they are vital for moving organisms and nutrients down a river. They can be dangerous, though, as extreme river waves brought on by a protracted downpour or dam failure can result in flooding.
Rivers are the planet’s lifeblood, but ocean waves are well-known from sailing and surfing. “We are interested in comprehending their dynamics,” stated Cedric David, a hydrologist at NASA’s Jet Propulsion Laboratory in Southern California and a coauthor of a recent study that was published in Geophysical Research Letters on May 14.
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. NASA and the French space agency CNES (Centre National d’Études Spatiales) collaborated to create the SWOT (Surface Water and Ocean Topography) satellite. With the use of its sensitive Ka-band Radar Interferometer (KaRIn), it is surveying the elevation 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 water bodies.
Nadya Vinogradova Shiffer, SWOT program scientist at NASA Headquarters in Washington, stated, “We zoom in on dynamics and impacts of water movement and change in addition to monitoring total storage of waters in lakes and rivers.”.
Thurman knew that SWOT has been used to map the seafloor, detect tsunami slosh, and track rising sea levels close to the coast. But could she spot anomalies in river height in the data that would indicate a wave in motion?
She discovered that three distinct instances of river waves, including one that suddenly appeared on the Yellowstone River in Montana in April 2023, had been captured by the mission. A 9.1-foot (2.8-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.
Using optical Sentinel-2 imagery of the region, she deduced that the wave was probably caused by pent-up water being released when an ice jam broke apart upstream.
Rainfall runoff was responsible for the other two river waves that Thurman and his team discovered. Beginning in January, SWOT identified one. 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 30 feet (9 meters) high and 166 miles (267 kilometers) long. It traveled more than 250 miles (400 kilometers) at a speed of about 3:05 feet (1:07 meters) per second before emptying into Matagorda Bay.
In March 2024, the other wave formed 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 stated, “We are gaining a better understanding of the form, velocity, and evolution of flow waves over extended river segments.”. “That could help us answer questions like whether infrastructure is at risk and how quickly a flood could arrive.”.
Observations in harmony.
Stream gauges, which measure water height and estimate discharge at fixed points along a river, have long been used by engineers and water managers to measure river waves. In the US, organizations such as the U.S. Coast Guard maintain stream gauge networks. S. . Geological Survey. In other regions of the world, they are less common.
The study’s supervisor, George Allen, a hydrologist and remote sensing specialist at Virginia Tech, stated that satellite data is complementary because it can help close the gaps.
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.
“The satellite could help monitor waves in river basins without gauges,” Allen said, pointing out that the wave speeds that SWOT helped determine were comparable to those computed using gauge data alone. Scientists can track shifting flood patterns globally by understanding the location and causes of river wave development.
About 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. Regarding SWOT’s ability to identify potentially harmful floods in the making, David stated, “If we see something in the data, we can say something.”. We have stood on the banks of our rivers for a long time, but we have never seen them as we do now. “”.
Learn more about SWOT.
With assistance from the UK Space Agency and the Canadian Space Agency (CSA), NASA and CNES collaborated to develop the SWOT satellite. Leading the U.S. is NASA’s Jet Propulsion Laboratory, which is run by Caltech in Pasadena, California. A. a part of the project. 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 provided the satellite platform, ground operations, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the Doppler Orbitography and Radioposition Integrated by Satellite system, and the KaRIn radio-frequency subsystem (developed with Thales Alenia Space and assistance from the UK Space Agency). CSA supplied the high-power KaRIn transmitter assembly.
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