Which observation led to the concept of a graded stream?

The concept of a graded stream is linked to the understanding of how streams adjust their profiles in response to changes in base level. A graded stream is one that has reached a state of equilibrium where it efficiently transports sediment and water, and its slope reflects the balance between the energy of flow and the sediment load.

When base level changes—such as rising due to sediment deposition or falling due to erosion—the stream must readjust its profile to maintain its balance. This adjustment can manifest in changes to gradient, width, and depth to achieve a new equilibrium. This dynamic process is essential for understanding river morphology and sediment transport.

In contrast, studying the formation of lakes, evaluating sediment reach in valleys, and analyzing rainfall patterns do not specifically address the equilibrium adjustments in stream profiles in relation to base level. While these factors can influence surface water and sediment dynamics, they are not the primary observations that led to the development of the graded stream concept.