Which of the following does Manning's n not directly represent?

• A. Channel roughness.
• B. Channel slope.
• C. Discharge.
• D. Channel geometry.

Answer: (C)

Manning's n is a roughness coefficient that represents friction from the channel surface—the bed, banks, vegetation, and other irregularities that impede flow. It does not directly represent discharge; in Manning's equation, discharge is determined by combining n with the cross-sectional area, hydraulic radius, and slope: Q = (1/n) A R^(2/3) S^(1/2). So n captures how rough the channel is, while discharge is the outcome of that roughness together with geometry and slope. Channel slope and channel geometry influence discharge through the S, A, and R terms, whereas discharge itself is not what n directly represents.