In the upper course of a river, the primary factor that influences the shape of the river valley is erosion. This stage of a river is characterized by steep gradients and fast-flowing water, which are effective in cutting through the landscape. The process of erosion shapes the valley as the river slices into the land, often creating features such as V-shaped valleys, steep-sided banks, and even narrow gorges.
During this phase, the river mainly erodes the substrate, primarily through processes like hydraulic action and abrasion. The power of the water moving quickly allows it to remove material from the riverbed and banks, effectively widening and deepening the valley over time. This results in the characteristic shape associated with a river's upper course, as opposed to the flatter, broader valleys that are typically formed in the middle and lower courses where deposition becomes more significant.
In contrast, deposition typically occurs in the middle or lower parts of a river, where the flow slows down, allowing sediments to settle. Meandering is a characteristic of mature rivers found in the middle course, shaped by erosion and deposition along the banks, while human activity may alter river valleys but does not primarily influence their natural shape, especially in the upper course.