What is the term for the transport of large boulders rolling along the riverbed?

The transport of large boulders rolling along the riverbed is referred to as traction. This process involves heavier sediment which cannot be lifted and carried through the water column; instead, it is moved along the bottom of the river as the flow of water pushes against it. The continuous movement and scraping of these large materials along the riverbed can help shape the river's landscape and contribute to processes like erosion and sediment deposition.

In contrast, the other transport methods refer to different sizes and types of sediment movement. Suspension involves lighter particles that can be carried within the water itself, while saltation describes the bouncing movement of smaller particles that are momentarily lifted and then fall back to the riverbed. Solution refers to the dissolved state of minerals in the water, which is another way that materials can be transported, but is not relevant to the movement of large boulders. Thus, traction specifically addresses the movement of boulders as they roll along the riverbed.