What primarily characterizes the upper course of a river?

The upper course of a river is primarily characterized by steep gradients and waterfalls due to the elevation of the land as the river begins its journey from its source. In this section, the river is often narrow and flows rapidly as it descends from higher altitudes, eroding the landscape and creating features like gorges and rapids. The steep slopes facilitate faster water movement, which is essential for the erosion processes that shape the riverbed and surrounding landscape.

This contrasts with the characteristics of other river courses. For instance, the flat terrain and rich soil typically associated with the river's lower course allow for extensive floodplains and agriculture, while meandering bends and wide channels are more common in the middle course where the river has more energy and begins to transport sediment. Deep valleys and deltas are found at the river's mouth, where it meets larger bodies of water, and sediment deposition occurs extensively. Hence, the upper course's unique features are a result of its initial stage of geography and hydrodynamics, validating its classification with steep gradients and waterfalls.