River behaviour: Meandering of a river is most commonly associated with which stage of the river’s course?

Introduction / Context:
Rivers evolve from steep youthful reaches to low-slope mature floodplains and finally deltaic or estuarine environments. Meanders arise where slopes are gentle and lateral erosion exceeds vertical incision.

Given Data / Assumptions:

• Typical alluvial river on a low gradient floodplain.
• No rigid bedrock constraints (which would limit planform change).

Concept / Approach:
Meandering is driven by secondary currents and bank erosion on outer bends, with deposition on inner bends, forming point bars. This mechanism is most active in the mature (trough) stage where the river develops a wide floodplain and the energy is preferentially used for lateral migration rather than downcutting.

Step-by-Step Solution:
Identify river stage with low gradient and broad floodplain: mature stage.Recognize meander formation due to alternating helical flows and bank erodibility.Select the corresponding option: trough (mature/floodplain) stage.

Verification / Alternative check:
Geomorphology references consistently show meanders and oxbow lakes forming in mature/alluvial plains; youthful rocky gorges show straight, confined channels.

Why Other Options Are Wrong:

• (a) Rocky youthful stage: dominated by vertical incision, not meandering.
• (b) Delta stage: distributary network and deposition at the mouth dominate planform.
• (c) Boulder stage: steep, coarse-bed torrents with limited lateral migration.

Common Pitfalls:
Assuming all lowland rivers are deltaic; mixing the concepts of braiding (high sediment load, wide shallow channels) with meandering.

Final Answer:
Trough (mature/floodplain) stage