What kind of streambed would cause the most friction?

A shallow streambed that is rough and rock.

Answer:-

A shallow streambed causes the most friction

Explanation:-

A streambed is the channel bottom of a water body like a river. Stream velocity is greatest in midstream near the surface and is slowest along the stream bed and banks due to friction.

The greater the cross-sectional area in comparison to the perimeter, the stream will be more freely flowing because less of the water in the stream is in proximity to the frictional bed.

Hence a shallow streambed would cause the most friction having the least cross sectional area.