DRAINAGE BASINS AND PATTERNS - GEOLOGICAL WORK OF RIVER - ENGINEERING GEOLOGY (StudyCivilEngg.com)

DRAINAGE BASINS AND PATTERNS

GEOLOGICAL WORK OF RIVER

SUBJECT : ENGINEERING GEOLOGY

• A drainage basin is a limited clearly defined area developed by major river and its tributaries. The divides marking the boundaries between the drainage basins are usually the dominant morphological features e.g. any major mountain range.
• The water can run off to two sides at uneven velocities controlled by local gradients. In addition, there are also local divides found between various tributaries to the principal river right upto the smallest creeks. Thus, on satellite imageries or on small scale top sheet a river system gives rise to a tree like branched system; growth of which is controlled by several factors including physical properties of rock, structure and climate.
• Based on the geometry of tree like branched system on local or regional scale several drainage patterns are recognised. Some of them are summarised in below table
• Dendritic Type is the most frequently developed pattern belongs to the river systems essentially controlled by the bedrock. The main river corresponds to the trunk of a tree, the tributaries of various orders to its branches and twigs. This pattern is called dendritic pattern. In this, the tributaries join the subsequent streams at highly diverse angles.
• Trellis or angular pattern is governed by the succession of escarpments and intervening valleys parallel to the bedding resulting from the differences in weathering and erodibility of these alternations of lithology. The pattern is also developed in areas where horizontal homogeneous massive rocks are cut by parallel fracture zones and intersecting major fault. As a result, the main river follows the easily eroded major fault while the tributaries are controlled by the fracture zones

Significance of Basic Drainage Patterns

Basic Drainage Patterns

• Radial and Annular patterns are found in areas of domes, basins, volcanoes, and granite domes. In the areas of ascent, erosion selectively carves out the harder rocks. Over the rock sequences dipping away from the center a circular topography is developed with concentric valleys and ridges. The consequent streams here flow away radially over the bedding surfaces. They end in the larger subsequent streams which follow the circular strike of the ring structures until they reach a cross cutting gorge through which they flow out and away from ring structures.
• Drainage pattern of the radial or similar types can also be found around plunging axes of anticlines and synclines.

Rivers of High Plateaus and Table Lands

These streams may be considered as a special type of mountain rivers. In this system, the river either adjust themselves to the topography and to the geological structures or they form the topography in accordance with the sequence exposed. Following types are recognised

• Consequent streams following the natural slope of the land surface.
• Subsequent streams flowing into the consequent streams from the sides at right angles to dip and parallel to strike.
• Resequent streams as tributaries to the subsequent streams more or less parallel to the main consequent stream.
• Obsequent streams flowing against the dip of the beds.
• Insequent streams which show no clearcut relation to the dip of the beds.

Development of consequent valley system over an initial  landscape

With later erosion subsequent streams become  prominent. 

C — consequent

S — subsequent

R — Resequent 

O — Obsequent rivers and valleys 

FAQs COVERED IN THIS POST

What are the drainage basins in ground work of river?

What are the patterns in ground work of river?

What is Dendritic Type of pattern?

What is Trellis Pattern?

What are different types of basic drainage patterns?

What are different types of streams?

What are consequent streams?

What are subsequent streams?

What are resequent streams?

What are obsequent streams?

What are insequent streams?

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