Which factors significantly affect the shapes of alluvial channels?

The correct choice highlights the critical role of sediment size, channel gradient, and discharge in shaping alluvial channels.

Sediment size is fundamental because it influences how easily materials can be transported by flowing water. Larger sediment particles require more energy to move, typically found in higher gradient areas, whereas finer particles can be more easily carried in lower gradient zones.

Channel gradient, or slope, affects the velocity of water flow. A steeper gradient increases water speed, which in turn can lead to more erosion and a more defined channel shape. Conversely, a gentle gradient tends to create wider channels with more meandering patterns as the water flow slows down and allows sediment deposition.

Discharge, the volume of water flowing through the channel, is also vital. Higher discharge usually intensifies the water's capacity to transport sediment, leading to wider and deeper channels. Changes in discharge can shift alluvial channels from one shape to another by altering flow dynamics and sediment transport mechanisms.

All these factors interact dynamically, making them fundamental in determining the overall morphology of alluvial channels.