1.5 - Geography Notes 38

Elaborate Notes

DRAINAGE SYSTEM OF INDIA

The drainage system of India provides a framework for understanding the geomorphological structure and hydrological characteristics of the subcontinent. The control of relief features is paramount, leading to a primary classification into the Himalayan rivers and the Peninsular rivers. These two systems are distinct in their origin, nature, and geomorphic work.

Evolution of Himalayan Drainage System

The modern Himalayan drainage system is a result of a complex geological history intricately linked to the Himalayan orogeny. The most widely accepted framework for its evolution is the Indobrahma or Siwalik River Theory.

The Indobrahma River Theory: This theory was first proposed by geologists like E. H. Pascoe (1919) and further elaborated upon by G. E. Pilgrim (1919) and M. S. Krishnan. It postulates the existence of a single, mighty, longitudinal river during the Miocene to Pliocene epochs (about 5-24 million years ago).
- This river, called the Indobrahma or Siwalik River, flowed from the northeastern region of Assam, all along the southern foothills of the newly formed Himalayas (the Siwaliks), and drained westwards into the Gulf of Sindh (present-day Arabian Sea).
- Evidence: The primary evidence for this theory lies in the remarkable continuity and lithological similarity of the Siwalik deposits, which are fluvial in origin (river-deposited). These deposits consist of thick layers of sand, clay, and conglomerates, stretching from the Potwar Plateau in Pakistan to the Brahmaputra valley. Paleontological studies of fossils found within these deposits also support a continuous fluvial environment.
Dismemberment of the Indobrahma: The singular Indobrahma system was dismembered into the present-day three major river systems (Indus, Ganga, and Brahmaputra) due to significant plate-tectonic and geomorphic events during the late Pliocene and Pleistocene epochs.
1. Higher Uplift of the Western Himalayas: Continued collision of the Indian and Eurasian plates led to a pronounced uplift in the western part of the Himalayas, including the Potwar Plateau. This acted as a water divide, blocking the westward path of the river.
2. Rising of Potwar Plateau and Delhi Ridge: The uplift of the Potwar Plateau (west of the present-day Yamuna) and the Aravalli-Delhi ridge acted as a crucial water divide between the Indus and Ganga drainage systems. The main river was forced to find new outlets.
3. Downthrusting of Malda Gap: Subsidence or “downthrusting” of the land between the Rajmahal Hills (part of the Peninsular block) and the Garo Hills (Meghalaya Plateau) created the Malda Gap or Garo-Rajmahal Gap. This event provided a new, shorter southeasterly course for the eastern part of the Indobrahma river to flow into the Bay of Bengal, thus creating the Ganga and Brahmaputra river systems as we know them. The Brahmaputra, which previously flowed west, took a sharp southward turn at the eastern Himalayan syntaxis and flowed through this gap.

This tripartite dismemberment resulted in the formation of:

The Indus system with its five major tributaries in the west.
The Ganga system, capturing the central portion of the old river and flowing southeast into the Bay of Bengal.
The Brahmaputra system in the east, which reversed its course to join the Ganga.

Peninsular Drainage System

The Peninsular drainage system is significantly older than the Himalayan system and is a product of the long geological history of the stable Peninsular block. Its present form is a result of key tectonic events that occurred over millions of years.

Submergence of the Western Flank: During the early Tertiary period (around 60-65 million years ago), a major faulting and subsidence event occurred along the western coast of the peninsula. The western part of the Peninsular block, including the original symmetrical drainage divide, subsided below sea level.
- This event formed the Western Ghats as a prominent escarpment, not a true fold mountain range.
- It drastically altered the drainage. Rivers that originally flowed westwards over a longer course were truncated, resulting in the present-day short, swift, and straight-flowing rivers of the Western Ghats (e.g., Sharavathi, Periyar). The symmetrical pattern was lost.
Upliftment of the Himalayas and Peninsular Tilt: The immense pressure exerted by the northward-moving Indian plate during the Himalayan orogeny caused a “flexure” or bending of the Peninsular block.
- This led to the formation of a long, linear trough or foredeep south of the Himalayas, which was subsequently filled by alluvial deposits, forming the Indo-Gangetic plains.
- Crucially, this process caused the northern part of the Peninsula (north of the Vindhyas) to subside slightly and tilt northwards. This explains why rivers like the Chambal, Betwa, and Son, originating in the Peninsula, flow north to join the Yamuna-Ganga system.
- The same tectonic stress deepened the existing rift valleys, particularly the E-W trending Narmada and Tapi rifts, which existed as lines of weakness in the crust.
Slight Tilting from North-West to South-East: In conjunction with the above events, the Peninsular block as a whole experienced a slight tilt from the northwest to the southeast.
- This general tilt dictated the direction of flow for most major Peninsular rivers like the Mahanadi, Godavari, Krishna, and Cauvery.
- These rivers consequently established their courses towards the Bay of Bengal, creating large deltas on the east coast.

Difference between Himalayan and Peninsular Drainage

Feature	Himalayan Drainage	Peninsular Drainage
Origin & Source	Originate in the young, tectonically active Himalayan mountains. Sourced from both glaciers (snowmelt) and rainfall.	Originate in the ancient, tectonically stable Peninsular Plateau. Sourced almost exclusively from rainfall (monsoonal).
Nature of Flow	Perennial: Receive a continuous supply of water from both glacial melt in summer and monsoonal rains.	Seasonal/Ephemeral: Flow is dictated by monsoon rainfall, leading to significant reduction in discharge during dry seasons.
Stage of River	Predominantly in their youthful stage in the mountains, characterized by intense vertical erosion.	Predominantly in their mature and old stages, having reached their base level of erosion over a long geological period.
Valleys	Carve deep, steep-sided V-shaped valleys, gorges, and canyons (e.g., the Indus Gorge near Bunji).	Flow through broad, shallow, graded valleys. They are not U-shaped; U-shaped valleys are formed by glaciers.
Course & Meandering	Have long, sinuous courses. They meander extensively in the plains due to high sediment load and gentle gradients.	Have shorter, more defined courses. Meandering is low due to hard rock terrain and lower sediment load.
Basin & Catchment	Possess very large, extensive basins and catchment areas (e.g., the Ganga basin covers over 8 lakh sq. km).	Have comparatively smaller basins and catchment areas.
Delta Formation	Form some of the world’s largest deltas (e.g., the Ganga-Brahmaputra Delta or Sundarbans).	Form smaller deltas (e.g., Mahanadi, Krishna-Godavari). Many west-flowing rivers form estuaries instead of deltas.
Navigability	Navigable over long stretches in their middle and lower courses across the plains (e.g., Ganga from Prayagraj).	Limited navigability due to seasonal flow, waterfalls, and hard rocky beds.
River Type	Feature numerous antecedent rivers, which predate the uplift of the Himalayas and have cut through them.	Primarily consequent rivers, which follow the general slope of the land. No major antecedent rivers exist.
Drainage Pattern	Mainly dendritic in the plains due to uniform alluvial soil. In the Himalayas, trellis patterns can be seen.	Exhibit various patterns like trellis, rectangular, and radial, reflecting the control of the underlying hard rock structure.

Antecedent Rivers: These rivers existed before the landform they cut across was uplifted. The Indus, Brahmaputra, Sutlej, Ghagra, Gandak, and Kosi are classic examples, as they maintained their courses by cutting deep gorges through the rising Himalayas.
Consequent Rivers: These rivers follow the initial slope of the land. The Ganga and Yamuna are consequent in the plains, as are most peninsular rivers like Godavari and Krishna, which follow the SE tilt of the plateau.

DRAINAGE PATTERNS

A drainage pattern is the spatial arrangement of a stream and its tributaries, which is often a direct reflection of the region’s topography, lithology, and geological structure.

(a) Dendritic Pattern:
- Description: This is the most common pattern, resembling the branching of a tree or the veins on a leaf. Tributaries join the main stream at acute angles.
- Geological Control: It develops on terrain with uniform lithology (rock type) and a gentle slope, where the geological structure exerts little to no control on the river’s path.
- Example: The rivers of the Indo-Gangetic plains, like the Ganga and its tributaries (Yamuna, Ghaghara), exhibit a classic dendritic pattern on the flat, homogenous alluvial deposits.
(b) Rectangular Pattern:
- Description: The main stream and its tributaries display a pattern of right-angled bends.
- Geological Control: It is indicative of strong structural control. It develops in regions that are heavily jointed or faulted, where the river follows the path of least resistance along these lines of weakness.
- Example: Found in the hard, crystalline rock regions of the Peninsular Plateau. Rivers in the Vindhyan mountains of India follow this pattern.
(c) Trellis Pattern:
- Description: The primary tributaries flow parallel to each other, and secondary tributaries join them at right angles. The overall pattern resembles a garden trellis.
- Geological Control: This pattern typically develops in regions of alternating bands of hard and soft rock that are folded or tilted. The main river cuts across the hard rock ridges (as a consequent stream), while tributaries develop along the softer rock bands (as subsequent streams).
- Example: The rivers originating from the Chota Nagpur Plateau, such as the Damodar valley, show this pattern. The Narmada and Tapi rivers, confined within their rift valleys with tributaries joining at right angles from the Vindhyas and Satpuras, also exhibit a trellis pattern.
(d) Radial Pattern:
- Description: Streams flow outwards in all directions from a central high point, like the spokes of a wheel.
- Geological Control: This pattern develops on elevated landforms such as domes, volcanoes, or plateaus.
- Example: The rivers originating from the Amarkantak Plateau are a prime example. The Narmada flows west, the Son flows north-east, and the Mahanadi (or its tributaries like Hasdeo) flows south/southeast from this single elevated point. The Hazaribagh Plateau is another example.
(e) Parallel Drainage:
- Description: A pattern of rivers flowing nearly parallel to each other, following a pronounced slope.
- Geological Control: It is found on steep, uniform slopes or in areas with parallel, elongated landforms.
- Example: The numerous short, swift rivers originating on the western slopes of the Western Ghats and draining into the Arabian Sea exhibit a parallel drainage pattern.

MAPPING OF THE RIVERS

Indus River System

Course: The Indus, known as ‘Sindhu’ in ancient texts, is a trans-Himalayan river. It flows through China (Tibet), India, and Pakistan.
Origin: It originates from the Bokhar Chu glacier near Manasarovar Lake in the Kailash Range, Tibet.
Tributaries in India:
- Right-Bank Tributaries: Shyok, Nubra (a tributary of Shyok, originating from the Siachen Glacier), Gilgit, Hunza, Swat, and Kabul (which joins in Pakistan).
- Left-Bank Tributaries: The five major rivers of Punjab (Panjnad): Jhelum, Chenab, Ravi, Beas, and Sutlej. Zanskar is another important left-bank tributary in Ladakh.

Jhelum

Origin: Rises from a spring at Verinag, situated at the foot of the Pir Panjal range in the Kashmir Valley.
Course: It flows northwards through the Kashmir Valley, a structural basin. It passes through Srinagar and feeds the Wular Lake, India’s largest freshwater lake.
Unique Feature: Jhelum exhibits prominent meanders in its youthful stage while flowing through the Kashmir valley. This is a unique geomorphic feature, caused by the river flowing over older lacustrine (lake) deposits that form the flat valley floor, which acts as a local, temporary base level for the river.
Confluence: It joins the Chenab at Jhang in Pakistan.

Chenab

Origin: Formed by the confluence of two headstreams, the Chandra and the Bhaga, which meet at Tandi in the Lahaul-Spiti region of Himachal Pradesh.
Headstreams’ Sources: The Chandra originates from a glacier near Chandra Tal lake, and the Bhaga from the Suraj Tal lake. Both are located near the Bara Lacha La pass. The Barashigri glacier feeds the Chandra river.
Course: It is the largest tributary of the Indus by volume.

Ravi

Origin: Rises west of the Rohtang Pass in the Kullu Hills of Himachal Pradesh.
Ancient Name: Known as Parushni in the Vedas and Iravati in later Sanskrit texts.
Course: It flows through the Chamba valley and forms a part of the Indo-Pak border before entering Pakistan and joining the Chenab.

Beas

Origin: Rises from the Beas Kund near the Rohtang Pass in Himachal Pradesh.
Unique Feature: The Beas is the only major tributary of the Indus system that flows entirely within Indian territory.
Confluence: It joins the Sutlej at Harike in Punjab, a Ramsar wetland site of international importance.

Sutlej

Origin: Originates from Rakas Lake (Rakshastal), which is connected to Manasarovar Lake in Tibet. Rakas Lake is known for its salty water. It is an antecedent river.
Ancient Name: Known as Satadru in the Vedas.
Course: It enters India through the Shipki La pass in Himachal Pradesh and cuts a deep gorge. It is a very important river for irrigation in the Punjab plains (Bhakra-Nangal Project).
Confluence: It receives the combined waters of the Ravi, Chenab, and Jhelum before finally joining the Indus. It meets the Beas at Harike.

Prelims Pointers

Indobrahma/Siwalik River: A single mighty river believed to have flowed from east to west along the Himalayan foothills in the Miocene-Pliocene period.
Dismemberment of Indobrahma River (Causes):
1. Uplift of the Potwar Plateau.
2. Formation of the Delhi Ridge as a water divide.
3. Downthrusting of the Malda Gap (between Rajmahal and Garo Hills).
Evolution of Peninsular Drainage (Causes):
1. Submergence of the western flank of the peninsula.
2. Himalayan uplift causing tilting and foredeep formation.
3. Overall tilt of the peninsular block from North-West to South-East.
Himalayan Rivers Source: Glaciers (snowmelt) and rainfall (Perennial).
Peninsular Rivers Source: Rainfall only (Seasonal).
Himalayan River Valleys: V-shaped valleys, deep gorges.
Peninsular River Valleys: Broad, shallow, graded valleys.
Antecedent Rivers (Himalayan): Indus, Sutlej, Brahmaputra, Kosi, Ghagra, Gandak.
Consequent Rivers (Peninsular): Godavari, Krishna, Cauvery, Mahanadi. Ganga and Yamuna are consequent in the plains.
Drainage Patterns and Examples:
- Dendritic: Ganga system in the northern plains.
- Rectangular: Rivers in the Vindhyan mountains.
- Trellis: Narmada and Tapi in their rift valleys.
- Radial: Rivers from Amarkantak Plateau (Narmada, Son).
- Parallel: West-flowing rivers from the Western Ghats.
Indus River Origin: Bokhar Chu glacier near Manasarovar Lake, Tibet.
Jhelum River Origin: Spring at Verinag, Kashmir.
Jhelum and Wular Lake: Jhelum river flows through and feeds Wular Lake.
Chenab River Formation: Confluence of Chandra and Bhaga rivers at Tandi, Himachal Pradesh.
Chandra River Source: Chandra Tal (fed by Barashigri glacier).
Bhaga River Source: Suraj Tal.
Ravi River Origin: West of Rohtang Pass, Kullu Hills.
Beas River Origin: Beas Kund near Rohtang Pass.
Beas River Fact: Flows entirely within India.
Sutlej River Origin: Rakas Lake (Rakshastal), Tibet.
Confluence of Beas and Sutlej: At Harike in Punjab.
Nubra River: A tributary of the Shyok River, originating from the Siachen Glacier.

Mains Insights

Himalayan vs. Peninsular Rivers: A Geopolitical and Socio-Economic Comparison

Resource Management and Disputes:
- Himalayan System: The perennial nature makes these rivers vital for the agrarian economy of the northern plains (the ‘granary of India’). However, their transboundary nature is a source of geopolitical friction.
  - Cause-Effect: The Indus Water Treaty (1960) with Pakistan is a classic example of water-sharing diplomacy. China’s dam-building activities on the Brahmaputra (Yarlung Tsangpo) raise strategic concerns for India and Bangladesh regarding water security and potential weaponization of water.
- Peninsular System: Seasonal flow leads to water scarcity in the dry season, creating intense inter-state disputes.
  - Example: The Cauvery water dispute between Karnataka and Tamil Nadu, and the Krishna water dispute among Maharashtra, Karnataka, and Andhra Pradesh, are long-standing issues that highlight the challenges of managing water in a water-stressed region.
Economic Potential and Hazards:
- Himalayan System: High gradient in the upper reaches offers immense hydroelectric potential. The fertile alluvial plains deposited by them support high population density. However, they are prone to devastating floods (e.g., Kosi - ‘Sorrow of Bihar’), bank erosion, and frequent course changes, posing significant disaster management challenges.
- Peninsular System: While hydroelectric potential exists (e.g., Koyna Dam), it’s comparatively less than the Himalayan system. These rivers are less prone to flooding on the same scale, but water deficit impacts agriculture, leading to farmer distress and the need for ambitious projects like river interlinking.

Plate Tectonics and the Dynamic Geography of India

River Evolution as evidence of Tectonic Activity:
- The evolution of both the Himalayan and Peninsular drainage systems serves as a powerful illustration of the continuing impact of plate tectonics. The concept of antecedent drainage in the Himalayas is direct proof that rivers like the Sutlej and Brahmaputra are older than the mountain ranges they cut through, indicating continuous and rapid uplift.
- This dynamism makes the Himalayan region geologically fragile and susceptible to earthquakes, landslides, and flash floods (e.g., the 2013 Kedarnath tragedy), a crucial perspective for GS Paper III (Disaster Management).
Debate on Peninsular Stability:
- While the Peninsular Plateau is considered a stable craton, its drainage evolution (faulting of the west coast, formation of rift valleys, and tilting) proves it is not inert.
- Historiographical Viewpoint: Traditionally viewed as a stable shield, evidence from neo-tectonic activities (e.g., Koyna Earthquake, 1967; Latur Earthquake, 1993) has forced geologists to reconsider this notion. The rejuvenation of Peninsular rivers in certain sections, evidenced by incised meanders, also points towards localized uplifts. This perspective is vital for infrastructure planning and seismic zonation.

Drainage Patterns as a Geomorphological Diagnostic Tool

Interpreting Landforms: The analysis of drainage patterns provides deep insights into the underlying geology and geomorphic history of a region, which is a core concept in GS Paper I (Geography).
- Cause-Effect Relationship: A dendritic pattern suggests a lack of structural control and homogenous rock type, typical of plains or plateaus with horizontal strata. In contrast, a trellis or rectangular pattern immediately signals the presence of folded, faulted, or jointed rock structures that control the erosional pathways.
- Application: This knowledge can be used in resource mapping (e.g., identifying fault lines which might be zones for mineralisation or groundwater accumulation) and land-use planning (e.g., avoiding construction on structurally weak zones indicated by the drainage pattern). For example, the radial pattern on the Amarkantak plateau points to it being an uplifted block, which has implications for understanding mineral distribution in the region.

GS Notes