What is a Drainage Basin?

A drainage basin is a naturally occurring extent of land which serves as a funnel to channel precipitation and excess water to a nearby river or stream. They are also known as catchments, catchment basins, watersheds, or water basins. Drainage basins are separated by geographical boundaries such as mounds, hills, ridges, or mountains, that are known as water or drainage divides. The divides aid with determining the direction of the flow of the water, whereas landscape, weather, soil type, and plant life will influence the content and movement of the flow.

When first formed, a drainage basin can adopt one of many different patterns that is easily recognizable on a map or from an aerial view. When draining precipitation, also known as runoff, basins flow in a hierarchical pattern. Smaller sub-drainage basins combine to form larger basins. Generally, smaller basins contribute to streams, whereas larger basins contribute to rivers. Patterns formed by these drainage basins oftentimes offer insight about the landscape on which they flow.

Radial drainage basin patterns occur around a central, high point such as a hill or a mound. The streams flow downward from the highest point. Similar to the radial pattern is the parallel pattern that forms in rocky areas where the water flows uniformly in the one direction. When there are fractures in the massive rock on which the water flows, such as fault lines or joints, the drainage patterns assume right angles and form a rectangular pattern.

If the drainage basin is located in an area where the rock is uprooted or has an upward tilt, then the stream will take on a trellised pattern and flow along the weaker areas of the rock formation. Opposite of the trellised pattern is the annular pattern in which the stream channels possess a common center, such as a depression or crater, and flow along the weaker beds of rock. Dendritic patterns, which resemble the meandering veins of a leaf, occur in areas where there is erodible sediment, as found in shallow streams or rivers.

Deranged drainage basin patterns are formed when the terrain on which the water flows has been only recently formed or revealed. Pockets of water form along the bends of the streams which have not had a chance to fully mature. This type of pattern is usually found in areas where there's been a recent, natural event such as some kind of volcanic activity. In these instances, over time, the stream will mature and its flow will progress.