Understanding Drainage Patterns and Structural Control

Drainage patterns are the characteristic arrangements of streams in a drainage basin. These patterns are often influenced by the underlying geology, specifically the 'parent structure' (like rock type, faults, folds, and dip). Some patterns develop in direct response to this structure, while others form more independently.

Types of Drainage Patterns

• Consequent Drainage: Develops directly on and follows the initial slope of the land surface, typically dipping in the same direction as the underlying strata. It is controlled by the initial slope and structure.
• Subsequent Drainage: Develops after the consequent streams, usually along zones of less resistant rock or structural lines (like faults or joints) that cut across the initial slope. It is structurally controlled.
• Insequent Drainage: This pattern develops *independently* of the underlying geological structure. It often arises on homogeneous rock formations or follows minor irregularities in the terrain, not dictated by the major structural features.
• Resequent Drainage: Develops in the same direction as the consequent drainage (following the dip) but appears later, often as tributaries to the consequent streams. It is also structurally controlled.

Identifying Non-Structure Controlled Patterns

The question asks for the drainage pattern *not* controlled by the parent structure. Based on the definitions:

• Consequent, Subsequent, and Resequent patterns are all significantly influenced or determined by the underlying geological structure.
• Insequent drainage develops without strict adherence to the major structural trends, forming on its own based on local topography or rock resistance variations.

Therefore, the drainage pattern not controlled by the parent structure is the Insequent pattern.