Drainage System

Just as the veins of a leaf reflect its growth pattern, the rivers and streams that flow across our land trace the long story of the Earth’s surface. The study of a drainage system is not merely about rivers—it’s a glimpse into the earth’s geological history, tectonic behaviour, and climatic responses over millennia.

The drainage system refers to the origin and development of streams and rivers through geological time. It explains how rivers begin, evolve, and carve their paths, adjusting to landforms and underlying structures. On the other hand, drainage pattern is more about how rivers are arranged in space—their shapes and alignments on the surface—which are dictated by the terrain’s topography, rock types, and climate conditions.

Types of Drainage Systems

Drainage systems are broadly classified into sequent and insequent types, depending on how they relate to geological structures.

1. Sequent Drainage System

This type of system shows clear alignment with regional slope and geological structure. It evolves naturally over time, as rivers align themselves with structural features like folds, faults, and beds.

• Consequent Rivers:

  • These are the earliest rivers to emerge in a newly uplifted region. They flow in the direction of the natural slope of the land.
  • Example: The Ganga and Yamuna, which flow eastward along the general slope of the northern plains.

• Subsequent Rivers:

  • These are tributaries that form later, often cutting along weaker rock zones like joints and faults. They tend to flow perpendicular to consequent rivers.
  • Example: The Asan River, which joins the Yamuna.

• Obsequent Rivers:

  • These streams flow in a direction opposite to that of the original slope due to later tectonic changes.
  • Example: Certain sections of the Indus River, which now flows westwards, opposite to the general slope of the Himalayas.

2. Insequent or Inconsequent Drainage System

These river systems are not guided by structure or slope. They often look random and seem unrelated to the landscape. They may cross rock types and slopes, reflecting older paths or sudden disruptions.

• Antecedent Rivers:

  • These are rivers that existed before a tectonic uplift occurred. When land rises (as in mountain building), such rivers maintain their original course by cutting deep gorges or valleys through the rising terrain.
  • Examples: The Indus, Sutlej, Kali, Kosi, and Brahmaputra. The Arun River in Nepal flows through deep gorges, proving it existed before the uplift of the Himalayas.

• Superimposed Rivers:

  • These rivers evolved on a younger surface like a lava plateau, then later cut through older structures as erosion removed the overlying material. The river retains its original direction, even if the older rocks below are harder or folded.
  • Example: Rivers like Subarnarekha and Son in the Deccan Trap region. After the lava cooled and eroded away, rivers cut across ancient structures beneath.

Drainage Patterns

The form or pattern that rivers take on the land depends largely on rock type, structure, slope, and climate. Some of the most common drainage patterns in India and globally include:

1. Dendritic Pattern

• Resembles the branches of a tree.
• Formed in areas with uniform rock structure and gentle slope.
• Tributaries join the main river at acute angles.
• Example: Seen in most of the Peninsular rivers like Godavari, Krishna.

2. Trellis Pattern

• Appears like a garden trellis (a lattice).
• Develops in areas of alternate hard and soft rocks, often in folded mountains.
• Tributaries run parallel and meet the main river at nearly right angles.
• Example: Rivers in the Vindhyan ranges.

3. Rectangular Pattern

• Develops in regions where there are faults and fractures.
• Streams bend sharply and meet at high angles due to structural controls.
• Example: Found in the Chambal basin and some regions of Bundelkhand.

4. Radial Pattern

• Streams radiate outward from a central elevated point like a volcano or dome.
• Common in conical hills or volcanic peaks.
• Example: Drainage around Mount Girnar (Gujarat) and Nilgiris.

5. Centripetal Pattern

• Opposite of radial; rivers converge into a central basin or depression.
• Seen in arid regions where there is interior drainage.
• Example: Drainage in Rajasthan’s inland basins like Sambhar Lake.

6. Deranged Pattern

• Results from disruption of a previous drainage system by glaciation, tectonic uplift, or lava flows.
• Streams are irregular, with marshes, lakes, and disconnected channels.
• Example: Glaciated regions like parts of Canada or northern Europe.

River Capture (Stream Piracy)

One of the most fascinating geomorphic processes is river capture. It is the phenomenon where one river diverts or captures the headwaters of another river, extending its basin and flow.

This typically happens through:

• Headward erosion: when a river cuts upstream into the source of a nearby river.
• Lateral erosion or meander encroachment: when bends from different rivers meet.
• Tectonic uplift: can divert water from one river system to another.

Key Terms:

• Capturing River / Captor: the aggressive river that extends its course.
• Captured River: the river that loses part of its water and catchment.

Ideal Conditions for River Capture:

• Steeper gradient and higher velocity in the captor stream.
• Narrow valleys and soft rocks, allowing faster erosion.
• Greater water volume enhancing erosion potential.
• A mature or youthful landscape where erosion is active.

Indian Example:

• The Bhagirathi and Vishnu Ganga (tributaries of the Ganga) are believed to have captured tributaries of the Sutlej.
• This shows how Himalayan uplift and aggressive headward erosion shaped modern river networks.

Conclusion

India’s rivers have not only nurtured civilizations but also recorded the silent story of landforms, tectonic activity, and climatic shifts. From the mighty antecedent Ganga cutting across the Himalayas to the superimposed rivers of the Deccan, our drainage systems reflect both ancient evolution and ongoing change. Understanding them is crucial not just for geography but also for flood management, hydroelectric development, and ecological planning.

---

PDF File:

No PDF attached

---

Subject: Geography

← Back