Dendritic drainage pattern

Topic: Drainage System of India: Rivers, Basins and Patterns · NCERT: Class 11, Ch 3 "Drainage System"

Meaning

A dendritic drainage pattern is a tree-like river pattern: the main river is the trunk, and its tributaries (smaller streams that join a bigger river) are the branches. They join the main river at acute angles (angles less than 90°). The name comes from the Greek word dendron, meaning "tree".

It is the most common stream pattern in the world [3]. In India it is the pattern of the rivers of the northern plain. The pattern also tells us something about the rock below: a dendritic pattern means the ground is uniform.

Explanation

What decides any drainage pattern

• A drainage pattern is the shape that a river and all its tributaries make on a map.
• Three things decide this shape:
• Slope: which way the land tilts and how steep it is.
• Rock structure: whether the rock is the same everywhere, or has folds, faults, joints, hard bands and soft bands.

• History: how old the land surface is, and whether it has been uplifted, folded or glaciated.

• A river follows weakness in the rock.

• Over time a river adjusts to the rock under it.
• It cuts its valley along weak rock and weak lines, such as faults and joints.

• So the drainage pattern shows the hidden geology [2].

• NCERT names four patterns: dendritic, radial, trellis and centripetal [2].

How a dendritic pattern forms (cause → process → result)

• Cause: uniform ground.
• The rock or sediment is about the same everywhere.

• It has no big weak lines, such as faults or joints, to steer the streams [3].

• Process: streams branch freely.

• The slope is gentle.
• Since no direction is easier than any other, small streams grow and branch out in every direction.

• Each small stream meets a bigger one at a narrow, acute angle. That bigger stream then meets the main river the same way.

• Result: a tree or leaf shape.

• The map looks like the branches of a tree or the veins of a leaf [3].

Parts and key features

• Trunk: the main river.
• Branches: tributaries of different sizes, with smaller streams joining bigger ones.
• Angle of joining: always acute, never at right angles.
• Spread: the streams spread out irregularly, with no fixed direction.
• Underlying material: uniform rock or sediment. In India this is thick, even layers of alluvium (fine sand, silt and clay laid down by rivers).

Conditions it needs

• Uniform rock or sediment, with no strong change from hard to soft bands.
• No major faults, joints or folds controlling the flow [3].
• A gentle slope.
• If these conditions fail, other patterns form instead. Folded hard and soft bands give trellis drainage. Crossing faults and joints give rectangular drainage [2].

Where it occurs

• India: rivers of the northern plain.
• The classic example is the Ganga–Yamuna system on the Indo-Gangetic plain.

• The plain is made of thick, even layers of alluvium. This uniform ground lets the tributaries branch freely, like a tree.

• World: it is the most common stream pattern on Earth. It appears wherever rock or sediment is uniform and free of major weak lines [3].

• Contrast inside India, which helps to place it on a map:
• Folded Himalayas and the Singhbhum belt (Jharkhand): trellis, not dendritic.
• Amarkantak plateau (Maikala range, Madhya Pradesh): radial.
• Vindhyas and the Chambal area: rectangular, in parts.
• Western Ghats (short rivers to the Arabian Sea): parallel.

Don't confuse with

• Trellis pattern: forms on folded rock with alternating hard and soft bands, and its secondary streams join at right angles (folded Himalayas, Singhbhum). Dendritic forms on uniform rock, with acute-angle joins. This is NCERT's exam pair.
• Rectangular pattern: has sharp right-angle bends caused by faults and joints that cross at about 90° [2] (Vindhyas, Chambal). Dendritic has no such control.
• Radial pattern: rivers flow outward in all directions from one high centre, like the spokes of a wheel (Amarkantak). In dendritic drainage, tributaries come together into one trunk river.
• Parallel pattern: many short streams run side by side down a steep, even slope (Western Ghats). Dendritic forms on a gentle slope and branches in every direction.

Prelims Hooks

• Dendritic = tributaries join the main river at acute angles (less than 90°), not at right angles.
• Condition: uniform rock or sediment, no major faults or joints, and a gentle slope [3].
• Indian example: the rivers of the northern plain (the Ganga–Yamuna system on the alluvial Indo-Gangetic plain).
• It is the most common drainage pattern in the world, and looks like tree branches or leaf veins [3].
• NCERT lists four patterns: dendritic, radial, trellis, centripetal [2]. Rectangular, annular, parallel and deranged come from wider geomorphology texts.
• Trap: "right-angle joins on folded hard and soft rock" describes trellis, and "right-angle bends along faults and joints" describes rectangular. Neither is dendritic.

Mains Points

• The pattern records the geology (GS-I).
• A dendritic pattern shows uniform alluvium in the northern plain.
• A trellis pattern shows folded Himalayan and Singhbhum rocks. A rectangular pattern shows the jointed, faulted Vindhyan rocks.

• So reading the drainage pattern helps in mapping rock structure, faults and mineral belts.

• Flood behaviour (GS-III, disasters).

• Dendritic plains rivers gather water from many branching tributaries over a wide, gentle area.
• This gives wide, slow floods. The short parallel rivers of the Western Ghats instead give quick, steep run-off.

• Flood planning on the Ganga plain must therefore cover the whole basin, not just the main channel.

• Infrastructure planning (GS-III).

• The drainage pattern affects where dams, canals and interlinking projects (such as Ken–Betwa) can be placed.
• On a dendritic plain, the many joining tributaries and the low slope shape where canals and embankments are built.

Related concepts

• Drainage pattern
• Radial drainage pattern
• Trellis drainage pattern
• Centripetal drainage pattern
• Amarkantak plateau

Read more

• Drainage patterns