Theory 34/Transport & flow/River flow
River Resistance Is Roughness Against Depth
The claim
Flow resistance in a river is set by the ratio of bed roughness to flow depth, so a shallow river is far rougher than a deep one with the same bed.
01Mechanism
Roughness elements protrude into the flow and generate turbulence; the ratio sets how much.
02Prediction
Resistance should track the ratio.
03Refutation
Resistance tracking grain size would remove depth.