Deranged drainage

Drainage system (Geomorphology)

In geomorphology, 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.

Types of drainage system (geomorphology)

Drainage systems fall into one of several categories, depending on the topography and geology of the land:

Dendritic drainage system

Dendritic drainage systems are the most common form of drainage system. The term dendritic comes from the Greek word "dendron", meaning tree, due to the resemblance of the system to a tree. In a dendritic system there is one main river (like the trunk of a tree), which was joined and formed by many smaller tributary rivers. They develop where the river channel follows the slope of the terrain. Dendritic systems form in V-shaped valleys; as a result, the rock types must be impervious and non-porous.

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, and all flow in the same direction. This system forms on uniformly sloping surfaces, for example, rivers flowing southeast from the Aberdare Mountains in Kenya.

Trellis drainage system

Trellis systems form in areas of alternating geology, particularly chalk and clay. The main river (the consequent) flows straight down hill. Subsequent streams develop perpendicular to the consequent along softer rock and erode it away, forming vales. The consequent river then cuts through the escarpments of harder rock. Obsequent streams flow down the dip slope of the escarpments to join the subsequent streams.

Rectangular drainage system

This develops on a strongly jointed rocky terrain. The rectangular drainage pattern is found in regions that have undergone faulting. Streams follow the path of least resistance and thus are concentrated in places where exposed rock is the weakest. Movement of the surface due to faulting off-sets the direction of the stream. As a result, the tributary streams make shape bends and enter the main stream at high angles.

Radial drainage system

Rivers radiate outwards from a central point, e.g. a volcanic cone or from a mountain range batholith,radial drainage is often found on steep mountainous terrain.

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 melting of the glaciers left land with many irregularities of elevation, and a great deal of water to collect in the low points, explaining the large number of lakes which are found in Canada. The watersheds are young and are still "sorting themselves out". Eventually the system will stabilize.

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