NASA satellite records unprecedented river waves in the United States

Yahoo

26-05-2025

SAN DIEGO (FOX 5/KUSI) — NASA's U.S.-French Surface Water and Ocean Topography (SWOT) satellite, which was launched in 2022 from Vandenberg Space Force Base, has spotted large-scale river waves for the first time, the NASA Jet Propulsion Laboratory (JPL) in Southern California has announced.
The river waves, which, unlike ocean waves, are temporary surges of water, stretched from 47 to 166 miles long as they traveled down rivers in Montana, Texas, and Georgia, the SWOT satellite recorded.
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The three large waves measured by the SWOT satellite from 2023 to 2024 were believed to be caused by extreme rainfall and a loosened ice jam, NASA reports, with the largest measuring over 30-feet-tall, creating potentially hazardous flood waves traveling down U.S. rivers.
Ocean waves are primarily driven by wind and the gravitational pull of the moon and sun — tides – and move across the ocean until they crash to shore. According to NASA, river waves are temporary surges that can stretch tens to hundreds of miles, and are typically caused by rainfall or seasonal snowmelt. The waves can be beneficial, by shuttling nutrients and organisms down a river. But extreme river waves are usually triggered by a prolonged downpour or dam break and can cause floods.
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'Ocean waves are well known from surfing and sailing, but rivers are the arteries of the planet. We want to understand their dynamics,' said Cedric David, a hydrologist at NASA's Jet Propulsion Laboratory in Southern California and a coauthor of a new study published May 14 in Geophysical Research Letters.
Since 2022, the SWOT satellite has surveyed the height of nearly all of Earth's surface waters, both fresh and salty, using its sensitive Ka-band Radar Interferometer (KaRIn), which maps the elevation and width of water bodies by bouncing microwaves off the surface and timing how long the signal takes to return.
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Lead author Hana Thurman of Virginia Tech and team used SWOT data to search for river waves for her doctoral research.
Thurman and team measured SWOT data that recorded the first wave on the Yellowstone River in Montana in April 2023. The satellite recorded the wave rise abruptly to 9.1 feet, and flow toward the Missouri River in North Dakota. It then divided into a 6.8-mile-long peak followed by a more drawn‐out tail.
Through optical Sentinel-2 imagery of the area, Thurman was able to determine that the wave likely resulted from an ice jam breaking apart upstream and releasing pent-up water.
The other two river waves were found to be caused by rainfall runoff.
On Jan. 25, 2024, on the Colorado River south of Austin, Texas, a river wave over 30-feet-tall and and 166 miles long traveled around 3.5 feet per second for over 250 miles before discharging into Matagorda Bay, and was associated with the largest flood of the year on that section of river, according to NASA.
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The third wave originated on the Ocmulgee River near Macon, Georgia, in March 2024. The SWOT satellite measured it at over 20-feet-tall and extending more than 100 miles, traveling about a foot per second for more than 124 miles.
'We're learning more about the shape and speed of flow waves, and how they change along long stretches of river,' Thurman said. 'That could help us answer questions like, how fast could a flood get here and is infrastructure at risk?'
The study is helping engineers and water managers measure river waves in ways never before possible, who have long relied on stream gauges. Also, knowing where and why river waves develop can help scientists track changing flood patterns around the world.
'Satellite data is complementary because it can help fill in the gaps,' said study supervisor George Allen, a hydrologist and remote sensing expert at Virginia Tech.
Orbiting Earth multiple times each day, SWOT is expected to observe some 55% of large-scale floods at some stage in their life cycle. 'If we see something in the data, we can say something,' David said of SWOT's potential to flag dangerous floods in the making. 'For a long time, we've stood on the banks of our rivers, but we've never seen them like we are now.'
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NASA also used SWOT to measure how big the lake was that briefly formed in Death Valley in April 2024.
The SWOT satellite was jointly developed by NASA and the French space agency CNES (Centre National d'Études Spatiales), with contributions from the Canadian Space Agency (CSA) and the UK Space Agency.
NASA's Jet Propulsion Laboratory, managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project.
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