Hydrological Cycle

[Note: In the above explanation, the cycle was broken into stages to explain the various terms. However, the hydrological cycle is continuous and has no specific starting or ending point.]

Drainage Basin

A drainage basin, also called catchment area refers to the area of the land drained by a river and its tributaries.

Drainage basins are separated from one another by a watershed, a boundary that lies along the crest of hills and ridges.

The source of a river in a drainage basin is where it starts, whereas the mouth refers to where the river ends, where the water is usually discharged into a lake, sea or ocean.

The path taken by the river as it goes from the source to the mouth is called the course. A river may be joined by tributaries (smaller rivers) along its course.

Drainage Density

Drainage density refers to the length of a river per unit area in a drainage basin. It is calculated by dividing the total length of the river and its tributaries by the total area.

Drainage Patterns

The drainage pattern of a basin refers to the arrangement of the river and its tributaries. There are different drainage patterns that are formed in different areas.

1. Dendritic patternThe tributaries join the main river at acute angles, forming a pattern that looks like the branches of a tree. The name ‘dendritic’ has its origins in the Greek word ‘dendron’, meaning tree. This type of pattern usually develops in areas with one type of rock or rocks of equal resistance to erosion, so that there is even erosion throughout.

2. Trellis pattern

In areas with alternating bands of resistant and less resistant rocks lying at right angles to the main river, the drainage is of trellis pattern. In a trellis pattern, the tributaries flow along the less resistant rocks and join the main river at right angles.

3. Radial pattern

In a radial pattern, river flow down outwards, in all directions from a central high point, such as the crater of a volcanic cone.

4. Centripetal pattern

Rivers that flow inwards to a central depression form a drainage pattern called the centripetal pattern. Such a pattern is more likely to develop in inland basins.