Drainage system
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A drainage system is the pattern formed by the streams, rivers, and lakes in a particular watershed. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land.
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Types of drainage system
There are several different types of drainage system:
Dendritic drainage systems
Dendritic drainage systems are the most common form of drainage system in the world. They consists of a main river with tributaries with their own tributaries. From above, it looks like a tree or a river delta in reverse. Examples include the Amazon River and the Mississippi River.
Parallel drainage system
A parallel drainage system is a pattern of rivers caused by steep slopes with some relief. Because of the steep slopes, the streams are swift and straight, with very few tributaries. Regions with mountain ranges sometimes have this drainage system.
Trellis drainage systems
Trellis drainage systems tend to occur where there is strong structural control over streams as a result of geology. Streams tend to run parallel to structures in the bedrock with minor tributaries coming in at right angles.
Mt_Taranaki_Drainage_System.jpg
Radial drainage system
A radial drainage system features a pattern of waterways which flow away from a central high point in all directions. This may be visulised as appearing like the spokes of a wheel. Most small islands, and especially volcanic ones have this pattern. A fine example can be shown in the rivers of Taranaki, on the west coast of New Zealand's North Island.
Rectangular drainage system
Rectangular drainage systems are arranged around faulted ground.
Annular drainage system
Annular drainage systems are arranged in ring-shaped patterns around a central basin.
Deranged drainage system
A deranged drainage system is a drainage system in watersheds where there is no coherent pattern to the rivers and lakes. It happens in areas where there has been much geological disruption. The classic example is the Canadian Shield. During the last ice age, the topsoil was scraped off, leaving mostly bare rock. The watersheds are young and are still "sorting themselves out". Eventually the system will stabilize. This is why there are so many lakes in Canada.