The researchers developed a new method called Acoustic Mapping Velocimetry (AMV) to estimate how much sand is moving in big rivers. They used sound and images to track the sand moving on the riverbed. By studying the Ohio and Mississippi rivers, they found that AMV can accurately measure how sand moves in the water. They also discovered that small sand formations on top of bigger ones play a role in moving sediment. This new technique can help scientists better understand how sand moves in large rivers where traditional methods don't work well.