Classification of Drainage System Based on Geological Adjustment

When a river flows across a region, its path is not random. It is often influenced by the land’s initial slope, rock type, geological structure, and subsequent land changes. Based on how streams adjust themselves to the surface and underlying geological structure, drainage systems are broadly classified into:

1. Sequent (or Concordant) Drainage System – Streams that adjust according to the regional slope and geological structure.
2. Insequent (or Discordant) Drainage System – Streams that do not adjust to the regional slope or geological structure.

1. Sequent (Concordant) Drainage System

In this system, streams align themselves naturally with the regional slope or geological structure. It means the river’s path is in harmony with the landscape and rock formations. This type of system has four sub-categories based on the time and direction of river flow:

a. Consequent River (Dip Stream)

👉 Consequent Rivers are the first streams to develop in a region when new land surfaces are exposed (like after volcanic eruption or mountain formation).

• These rivers follow the natural slope of the land.
• As they develop first, they create a master path for other smaller streams.
• They are also known as Dip Streams as they flow according to the initial slope of the land.
• In folded mountain regions, if the river flows along the depression (synclinal trough), it is called a Synclinal Consequent River.

💡 Example: Most of the rivers originating from the Himalayas (like Ganga, Yamuna) initially behaved as consequent rivers following the natural slope towards the plains.

b. Subsequent River

👉 As time passes and the consequent river establishes its course, smaller streams start to develop perpendicular to the main river. These are called Subsequent Rivers.

• They form after the master consequent river and typically erode the softer rocks along anticlines (ridges).
• They develop their path based on structural weaknesses in the land (like faults, cracks, or softer rock layers).
• They typically join the consequent river at a right angle (perpendicularly).

💡 Example: Chambal River (which flows perpendicular to the Yamuna).

c. Obsequent River

👉 These are opposing rivers that flow in the opposite direction to the master consequent river.

• Over time, erosion and land modification may cause the water to flow in the reverse direction of the initial slope.
• This mainly happens in highly eroded landscapes or uplifted regions.

💡 Example: Sun Kosi River (in Nepal) flows opposite to the master consequent Ganga River.

d. Resequent River

👉 Resequent Rivers are those that flow in the same direction as the master consequent but form at a much later time due to continuous erosion and denudation.

• Over time, denudation (erosion) changes the landscape — anticlines may turn into valleys, and synclines may turn into ridges.
• These rivers then begin to flow along the new slope but still in the same direction as the original consequent river.
• This phenomenon is known as inversion of relief (where anticlines become valleys and synclines become ridges).

💡 Example: Betwa River, which initially formed later but flows in the same direction as the master river (Yamuna).

2. Insequent (Discordant) Drainage System

This system includes rivers that do not follow the natural slope or geological structure of the land. They either maintain their old path despite land changes or cut through various geological formations irrespective of structure. There are two major types:

a. Antecedent River (Pre-existing River)

👉 This is a very interesting concept! Imagine a river that existed before a mountain was formed. Now, as the land starts uplifting, the river does not change its course but instead cuts through the rising land by eroding it continuously. This river is called an Antecedent River.

• It originates before the upliftment of land.
• As the land rises, the river keeps cutting through the rising rock at the same pace, creating deep valleys or gorges.
• However, if the land upliftment is too rapid, the river may be diverted.

💡 Example:

• Indus River in Ladakh (cutting through Ladakh and Zaskar ranges).
• Brahmaputra River cutting through the Himalayas.

b. Superimposed River (Epigenetic or Superinduced River)

👉 This is another fascinating concept. Imagine a river flowing on a flat layer of soft rock. Over time, as the river cuts deeper, it eventually reaches a hard rock layer below but continues to flow as if the hard rock never existed. This happens because the river has already established its flow path and does not get influenced by the new underlying rock.

• It originates on a higher surface of a different rock type and eventually cuts down to harder rocks without adjusting its course.
• The river appears unrelated to the current rock structure.
• This is called a Superimposed Drainage System.

💡 Example:

• Damodar River in Jharkhand.
• Subarnarekha River in Odisha.

✅ Difference Between Antecedent and Superimposed River

✅ Summary (Golden Points):

1. Sequent Drainage System – Rivers adjust to the initial slope and structure of the land.
   • Consequent Rivers – First to form, follow initial slope.
   • Subsequent Rivers – Form later, erode weaker rocks, flow perpendicular to the master river.
   • Obsequent Rivers – Flow opposite to the master consequent river.
   • Resequent Rivers – Flow in the same direction as the master river but originate later due to erosion.
2. Insequent Drainage System – Rivers do not adjust to the slope or geological structure.
   • Antecedent Rivers – Formed before land upliftment, maintain their course by cutting through uplifted rocks.
   • Superimposed Rivers – Originated on a different rock layer, later cut through harder rock without changing path.

💯 Simple Way to Remember

• Consequent – The FIRST river, following the natural slope.
• Subsequent – The follower rivers, cutting weaker rocks.
• Obsequent – Opposite to the master river.
• Resequent – Same direction as the master river but formed later.
• Antecedent – “I was here before!” (River existed before land upliftment).
• Superimposed – “I don’t care what’s below!” (River flows despite a harder rock below).

👉 This classification helps geologists understand the evolution of landforms and how rivers shape landscapes over millions of years. It also explains why some rivers cut through mountains while others follow natural slopes.