The way rivers meander and connect with other rivers and streams is shaped by a range of environmental factors. One interesting aspect of river geography is the formation of tributaries, particularly when they occur predominantly on one side of a river. The steepness of the surrounding landscape is a key factor that can lead to this unusual pattern.
What are tributaries?
Tributaries are smaller streams or rivers that flow into a larger river or stream. Tributaries do not flow directly into the sea. Instead, tributaries feed into another body of water, helping to form a network of connected waterways known as a river system or watershed.
Understanding slope dynamics and river formation
The slope of a landscape—how steep or gentle it is—plays a critical role in the behavior and formation of rivers. Steeper slopes cause water to flow more rapidly, strengthening its ability to erode the surrounding land and carve out channels that form the tributaries.
Example: Tributaries of Des Lacs River
This photograph taken from the International Space Station captures a section of the Des Lacs River as it meanders through the Des Lacs Valley in northwestern North Dakota. Although both sides of the river feature cliffs, the cliffs on the south side have significantly darker shadows in the photo due to their much steeper incline.
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This section of the Des Lacs River is a good example of how slope steepness influences the formation of tributaries. In this section of the river, tributaries found only on the south side that feed into the Des Lacs River along this stretch of the valley. These smaller streams contribute to the river’s flow as it continues its journey.
On the north side of the river, the cliffs mark the boundary of a gently rolling landscape known as prairie potholes. Prairie potholes are small, shallow wetlands scattered across the northern Great Plains of North America, primarily formed by glacial activity thousands of years ago. The cliffs on this side are relatively low in gradient, resulting in less gravitational pull and, consequently, less erosive power.
In contrast, the cliffs on the south side of the river are significantly steeper. The steeper slope on the southern side generates a stronger gravitational force, which enhances the erosive power of water as it flows down. This increased erosion enables the formation of more pronounced channels, allowing tributaries to carve their way into the valley.
This dynamic illustrates how variations in topography can lead to the asymmetric development of a river’s tributary network, with tributaries more likely to form where the landscape is steeper and erosion more intense.
Eventually, the Des Lacs River joins the Mouse River, becoming one of its tributaries. The Mouse River, in turn, winds its way northward, crossing the U.S.-Canada border before ultimately emptying into Hudson Bay, making it part of a larger network of waterways that drain into the Arctic Ocean.
More river articles
Fonte : National Geographic
