Final answer:
In a river system, the riser or bluff refers to a steep slope that separates a modern floodplain from adjacent terraces.
Step-by-step explanation:
In a river system, the riser or bluff is a steep slope separating a modern floodplain from adjacent terraces. This feature is an essential part of a river's morphology and is often found where the river has cut down into its valley, leaving a marked elevation between the level of the floodplain and older terraces. Major river systems, like the Mississippi, exhibit these features, which show the historical paths and stages of the river's development.
Among the features associated with river systems are cut banks, point bars, levees, oxbow lakes, and flood plains. Each of these features contributes to the dynamic nature of river ecosystems and shapes the surrounding landscapes.