As water flows out of the stream's channel, it immediately slows down. The material carried by the stream, sediment such as gravel, sand, silt, and clay, is deposited on the floodplain. Large particles are deposited first, and much of this material is laid down alongside both banks. This process, repeated over and over, forms low ridges or mounds known as natural levees. As flooding continues, sediments are lifted over the levees and deposited as noted in the photograph. These areas often the sites of farming because the sediments deposited tends to be very fertile.

Floodwaters bring fine silt-like sediments over the levees. Why does the water tend to carry such particles rather than sand or gravel?