Fluvial geomorphology: The process of meandering in alluvial rivers primarily arises due to which combined set of factors?

Introduction / Context:
River meandering is a hallmark of alluvial channels and is central to river engineering, river training works, and the design of hydraulic structures. Understanding the drivers of meandering helps engineers plan guide banks, spurs, and bank protections to stabilize alignments near barrages, bridges, and canal offtakes.

Given Data / Assumptions:

• Alluvial river with mobile bed and banks.
• Natural planform evolution without artificial straightening.
• Typical ranges of discharge and sediment supply.

Concept / Approach:
Meanders result from feedback between flow, sediment transport, and bank erodibility. Non-uniform velocity distribution creates zones of higher shear on outer bends (erosion) and lower shear on inner bends (deposition). Sediment size and load influence transport thresholds and bar formation, while bank material (cohesion and roughness) controls resistance to erosion.

Step-by-Step Solution:
1) Identify drivers: (a) sediment load and size distribution, (b) hydraulics governed by discharge/velocity/shear, (c) material properties of bed and banks.2) Recognize feedback: outer-bank erosion and inner-bank deposition amplify curvature.3) Conclude that meandering is not due to a single parameter but the combined action of all three.

Verification / Alternative check:
Empirical observations across alluvial rivers show meanders develop where banks are erodible, sediment is available for transport, and flow has sufficient energy to rework the planform. Reducing any one can dampen meander growth.

Why Other Options Are Wrong:

• Solely sediment load: without hydraulic forcing and weak banks, meanders do not propagate.
• Solely discharge/hydraulics: with resistant banks, channels can remain straight despite high flows.
• Solely erodibility: requires hydraulic action and sediment movement to form bends.
• None of the above: contradicted by field and theory.

Common Pitfalls:

• Attributing meanders to “Coriolis effect” in engineering practice—local hydraulics dominate.
• Ignoring cohesive strength of banks in meander migration rates.

Final Answer:
All of the above.