Alluvial river-channel motion and patterns

Alluvial river planforms tell us about the processes of channel change that they undergo.

Learning Goals

• Know the names of typical alluvial-river planforms: straight, meandering, braided, and anastomosing
• Connect these with the processes of river-channel motion and change: lateral migration and avulsion

Channel patterns and dynamics

Why do rivers meander?

Laboratory experiments

Laboratory experiments are among the best ways to study and analyze river behaviors. They allow us to demonstrate river-channel change over time scales that we can watch – instead of needing centuries of repeat maps!

The following experiments compare meandering and braided systems; the meandering river forms because cohesive sediment is used to create the surface into which it carves its course. The cohesionless sand in the braided-river case promotes unconfined flow and what is thermed the “braiding instability” – which leads to this form of river.

Note: the version with overhead images, below, has the meandering river on the bottom instead of the top.

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