Stream competency is defined as which?

• A. The size of particles a stream can carry
• B. The total amount of sediments a river can transport
• C. The rate of flow of the stream
• D. The depth of the stream channel

Answer: (A)

Competency is the maximum size of sediment that a stream can move under its present flow conditions. It reflects how energetic the water is: higher velocity and shear stress allow the stream to entrain and transport larger grains. As discharge increases, the stream can carry bigger particles, so competency rises with flow intensity. This concept focuses on the size of the particle that can be mobilized, not how much sediment in total or how fast the water is moving overall.

This differs from capacity, which describes the total amount of sediment a stream can transport, including all sizes, not just the largest one. The rate of flow relates to how much water passes a point (discharge) and influences both competency and capacity but is not, by itself, what competency measures. The depth of the channel is a geometric property of the cross-section and does not define the largest movable particle size.

So, the best description is the largest particle size a stream can carry under current flow conditions.