Drainage pattern in Peninsular India is a result of its geological structure and topography. Elaborate.

Geological Structure of the Peninsular Plateau

The Peninsular Plateau is primarily composed of Archaean rocks – granite, gneiss, and schist – which are highly resistant to erosion. However, interspersed within these hard rocks are zones of softer sedimentary formations and basaltic lava flows. Key structural features include:

• Faults and Fractures: These weaknesses in the rock structure have provided pathways for river courses.
• Joints: Regularly spaced fractures contribute to block-like disintegration and influence drainage alignment.
• Basaltic Trap Regions: The Deccan Trap region, formed by volcanic activity, exhibits a distinct drainage pattern due to its porous and layered structure.
• Horst and Graben Structures: These uplifted (horst) and subsided (graben) blocks influence river flow direction and create localized drainage basins.

Drainage Patterns and their Geological Basis

The Peninsular Plateau displays a variety of drainage patterns, each reflecting the underlying geological conditions:

1. Dendritic Drainage Pattern

This is the most common pattern, resembling the branching of a tree. It develops in areas with uniform rock resistance and topography. The rivers originate from highlands and flow down the slopes. Example: The upper reaches of the Godavari and Krishna rivers exhibit a dendritic pattern.

2. Radial Drainage Pattern

Rivers radiate outwards from a central high point. This pattern is typically found in dome-shaped or conical hills. Example: The rivers originating from the Mahabaleshwar hills in the Western Ghats display a radial pattern.

3. Trellis Drainage Pattern

This pattern develops in areas with alternating bands of hard and soft rocks. The rivers follow the softer rocks, while tributaries join them at right angles. Example: The Vindhyan Range exhibits a trellis pattern where rivers flow through the softer sandstone layers.

4. Rectangular Drainage Pattern

Similar to trellis, but with more pronounced right-angled bends. This occurs in areas with well-defined joint patterns. Example: Parts of the Chambal River basin show a rectangular pattern due to the presence of extensive jointing in the rocks.

5. Barbed Drainage Pattern

This pattern is less common and indicates river capture, where a tributary river is diverted by a more powerful river. Example: Some tributaries of the Narmada River exhibit a barbed pattern, suggesting capture by the Narmada.

6. Annular Drainage Pattern

This pattern develops around a dome-shaped structure, where rivers flow in a circular manner. Example: Though not a perfect example, the drainage around some isolated hills in the Eastern Ghats shows tendencies towards an annular pattern.

Regional Variations and Specific Examples

The drainage patterns vary across different regions of the Peninsular Plateau:

• Western Ghats: Radial and dendritic patterns dominate due to the steep slopes and varied rock types.
• Deccan Trap: The rivers flow through basaltic fissures, often forming waterfalls. The Godavari, Krishna, and Cauvery rivers flow through this region.
• Chota Nagpur Plateau: Dendritic and radial patterns are common, with rivers like the Damodar and Subarnarekha flowing through this area.
• Eastern Ghats: A less defined drainage pattern due to the fragmented nature of the hills and the presence of more weathered rocks.

River Basin	Dominant Drainage Pattern	Geological Influence
Godavari	Dendritic	Uniform rock resistance in the upper reaches, basaltic trap in the lower reaches.
Krishna	Dendritic	Similar to Godavari, with influence from Deccan Trap.
Narmada	Radial & Dendritic	Rift valley setting, fractured rocks.
Mahanadi	Dendritic	Eastern Ghats influence, sedimentary formations.