What are natural embankments made of silt that build up at the sides of a river called?

Natural embankments made of silt that accumulate at the sides of a river are referred to as levées. These formations typically arise during flood events when the river overflows its banks. As the water slows down upon leaving the river channel, it loses energy and deposits sediment, which gradually builds up over time to create these elevated structures. Levées help contain river flows and can influence the development of the surrounding landscape, playing a crucial role in the river's ecosystem and flood management.

The other options do not accurately describe this specific landform. Dikes are man-made barriers constructed to control or prevent flooding, clouds are formations in the atmosphere, and barriers generally refer to structures designed to block or obstruct movement or flow of a resource, which does not specifically relate to silt deposits alongside rivers. Understanding levées is important in river studies, particularly in discussing sediment transport and floodplain management.