Which factor does NOT contribute to the formation of river meanders?

The correct option is High velocity of streams flowing over steep gradients..

Explanation

Meanders are loop-like channel patterns that develop primarily in the mature and old stages of a river's course. They are not landforms in themselves but are associated with the formation of erosional and depositional features. Their formation is driven by the fluid dynamics of running water on gentle slopes where lateral erosion dominates over vertical down-cutting.

Analysis of Factors:

• Propensity of water flowing over gentle gradients to work laterally. Propensity of water flowing over gentle gradients to work laterally: This is a contributing factor. On gentle gradients, the river lacks the velocity for significant vertical erosion (down-cutting). Instead, irregularities in the channel cause the water to swing laterally, eroding the banks and creating curves.
• Unconsolidated nature of alluvial deposits making up the banks. Unconsolidated nature of alluvial deposits making up the banks: This is a contributing factor. Soft, unconsolidated alluvial banks are easily eroded by the lateral force of the water, allowing the river channel to shift and the bends to accentuate into meanders.
• Coriolis force acting on the fluid water. Coriolis force acting on the fluid water: This is a contributing factor. The Coriolis force, caused by the earth's rotation, acts on the moving fluid, causing a slight deflection (to the right in the Northern Hemisphere). This deflection contributes to the development of the curved path necessary for meandering.
• High velocity of streams flowing over steep gradients. High velocity of streams flowing over steep gradients: This is NOT a contributing factor. High velocity on steep gradients (typical of the youthful stage) results in high kinetic energy focused on vertical erosion (down-cutting). This leads to the formation of V-shaped valleys, gorges, and canyons rather than the lateral swinging required for meanders.

Key Takeaway:

River meanders form due to lateral erosion on gentle gradients, aided by unconsolidated banks and the Coriolis force. Steep gradients and high velocities promote vertical erosion, preventing meander formation.