In geomorphology, the drainage systems, which are also known as a stream or river systems, are the patterns formed by the streams, rivers, and lakes in a particular drainage basin. 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. Geomorphologists and hydrologists often view streams as part of drainage basins (and sub-basins). This is the topographic region from which a stream receives runoff, throughflow, and its saturated equivalent, groundwater flow. The number, size, and shape of the drainage basins vary and the larger and more detailed the topographic map, the more information is available.
Drainage Basin: A land area surrounded by divides that contribute water to a river, is called a drainage basin.
Divide: It is a ridge of high ground that separates two drainage basins. Divides range in size from a ridge separating two small gullies to continental divides which divide continents into large drainage basins.
River Capture: River capture is a process by which a part of the drainage of one river is diverted into another. Due to greater discharge, slope or other factors, the stream on one side of a divide may erode its valley more actively than the stream on the opposite side. While strengthening its valley head-ward, it may reach the less active river by breaking down the divide between the two and divert a part or all of its drainage into its own channel. The river capture commonly occurs in the youth stage. It becomes less common as streams grow larger and is rare in large rivers.
Although all drainage networks branch in the same way, the shape of their patterns varies greatly from one kind of terrain to another, depending upon the rock type of structure. The chief drainage patterns are (i) dendritic, (ii) trillis, (iii) rectangular, and (iv) parallel.
- Dendritic Pattern:
In dendritic pattern the streams show a branching tree-like arrangement. This pattern develps in terrains covered with uniform rock types, such as horizontal sedimentary rocks or massive igneous or metamorphic rocks.
- Trellis Pattern:
A trellis drainage pattern is one in which major streams are parallel and short tributaries join the main stream at nearly right angle. This type of drainage pattern develops in regions containing folded or tilted strata. Here the main stream develops in the strike valleys cut into the soft rocks, while tributaries flow down the resistant ridges.
Differential weathering of faults or joint systems in bedrocks localizes the stream flow producing a more ordered rectangular drainage. In a rectangular drainage pattern angular deflection of stream courses are apparent.
- Radial Pattern:
In a radial drainage pattern, in which consequent streams radiate or diverge outward, like the spokes of a wheel, from a high central area; it is best developed on the slopes of a young, unbreached domal structure or of a volcanic cone.
- Parallel Pattern:
A parallel drainage pattern is a system of river channel or stream caused by steep slopes with minor relief. As the stream channel is very steep therefore, the flow of water is very swift and fast. The swift flow of water is straight without any curves and zigzags. Each strand of the stream runs parallel to the other stand.