What is a key characteristic of a graded stream system?

A graded stream system is characterized by a state of dynamic equilibrium where the sediment load transported by the stream is balanced with the energy available in the flow. This means that on average, the stream neither erodes material from its banks or bed nor deposits sediment along its course. Instead, it maintains a consistent profile where the processes of erosion and deposition are effectively in balance. In such systems, the stream has reached an adjustment where it can transport sediment without accumulating excess material or suffering from excessive erosion, leading to a generally stable shape and channel gradient.

This balance allows graded streams to transport sediments efficiently, which is a key aspect of their function in the landscape. The other options imply conditions where the stream is either actively eroding, solely depositing material, or flowing at a high velocity, none of which accurately describe the sustained equilibrium of a graded stream system.