What does tributaries?
A tributary is a freshwater stream that contributes its flow to a larger stream or river, known as the mainstem. The location where a tributary merges with the mainstem is referred to as the confluence. Tributaries, also known as affluents, do not discharge directly into the ocean. Instead, they play a crucial role in the formation of larger river systems by draining water from various watersheds and delivering runoff and snowmelt to the main river.
The Formation of Major Rivers
Most significant rivers are composed of numerous tributaries, each draining a distinct watershed. For instance, the Missouri River boasts a vast watershed formed by the watersheds of multiple tributaries that extend from Alberta and Saskatchewan in Canada through seven states in the Upper Midwest of the United States. The Missouri River is the largest tributary of the Mississippi River, where they converge at a confluence in St. Louis, Missouri. The Mississippi River watershed ranks as the fourth-largest globally, showcasing the extensive network of tributaries that contribute to its flow.
Left-Bank and Right-Bank Tributaries
Geographers classify tributaries based on their position relative to the mainstem. A tributary is designated as a left-bank tributary or right-bank tributary depending on which side it enters the river when viewed from a downstream perspective. This classification is essential for understanding the hydrology of river systems. For example, the Euphrates River, the longest river in southwestern Asia, receives water from several smaller streams originating in eastern Turkey. Among these, the Balikh River is a left-bank tributary, while the Sajur River is a right-bank tributary.
Naming Conventions: Forks of Rivers
In some cases, tributaries share the same name as the river they feed into, referred to as forks. These forks are typically distinguished by their flow direction into the mainstem. A notable example is the Shenandoah River, which flows through West Virginia and Virginia. It features two significant tributaries: the North Fork and the South Fork, which converge at a confluence in Harpers Ferry, West Virginia.
Distributaries: The Opposite of Tributaries
Contrasting with tributaries are distributaries, which branch off from the mainstem and flow away from it. This process, known as river bifurcation, creates new channels that can lead to different water bodies. A prime example is found at the Continental Divide in Wyoming, where North Two Ocean Creek bifurcates into Pacific Creek and Atlantic Creek, with each stream flowing into its respective ocean.
Classifying Tributaries
Geographers and potamologists (scientists who study rivers) use two main methods to classify tributaries:
Source Proximity
This method organizes tributaries based on their distance from the river’s source or headwaters. For instance, the earliest tributaries of the Rhine River include the Thur River in Switzerland and the Ill River in Austria. The Rhine, one of Europe’s longest rivers, originates in the Alps and flows into the North Sea.
Flow Ranking
Tributaries can also be ranked by their flow capacity, with smaller streams assigned lower numbers and larger tributaries receiving higher numbers. For example, the Tshuapa and Kasai Rivers are both left-bank tributaries of the Congo River, the world’s deepest river, with the Tshuapa being smaller and thus ranked lower than the Kasai.
The Importance of Watersheds
The most significant landform component of a tributary system is the watershed, also known as a drainage basin. Each watershed collects precipitation and snowmelt within its geographical area, starting from mountain summits and extending down to plains, ultimately leading to oceans or seas. Some of this water seeps into the ground, replenishing aquifers, which are underground water reservoirs. Multiple watersheds can exist within a larger watershed, collectively draining surface water from the landscape.
Within each nested watershed lies a river system, which consists of streams that converge to form a mainstem river. The term river refers to a natural watercourse that follows a permanent path, typically within a valley, while a stream describes a temporary water flow toward a valley. The junction where a stream meets a river is called the confluence.
Human Impact on Tributaries
Human activities often lead to pollution in tributaries, which subsequently affects the mainstem. The runoff and contaminants from tributaries contribute to the overall water quality of the river. Generally, rivers with tributaries draining undeveloped or non-agricultural land tend to be less polluted than those fed by tributaries in urban or agricultural areas.
Interestingly, the degree of pollution in rivers is more influenced by development than by the river’s size. For example, the Amazon River, which has the largest drainage basin globally, remains relatively clean due to its tributaries flowing through pristine regions of the Andes Mountains and rainforests. In contrast, the Hudson River, which traverses one of the world’s most densely populated urban areas, is significantly more polluted, highlighting the impact of human activity on water quality.
Conclusion
Tributaries are vital components of river systems, contributing to the flow and health of larger rivers. Understanding their classification, the role of watersheds, and the impact of human activity is essential for managing and protecting freshwater resources. By recognizing the significance of tributaries, we can better appreciate their role in maintaining ecological balance and ensuring clean water for future generations.
Reference
1.Tributary
https://education.nationalgeographic.org/resource/tributary/
2.Tributary | Definition, Landforms & Examples
https://study.com/learn/lesson/tributary-landform-examples.html
