Floods transport huge amounts of sediment as fast-moving rivers and streams can pick up and move larger particles more easily than slow-moving waters. They also collect runoff from lands that are usually above the water line.
The multi-day rainfall accumulations that hit southern Louisiana (more than 20 inches in some places) stemmed from an unusual storm pattern similar to a tropical depression, except that surface winds were light. The system was extremely slow moving, dropping 600 percent of normal rain over a seven-day period, according to the Lower Mississippi River Forecast Center of the U.S National Weather Service.
NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Caption and image cropping by Adam Voiland.