Stream and catchment roughness
The hydraulic equations used to describe flows and their characteristics include various roughness factors such as Manning's n, Chezy's C and the Colebrook-White e or k factor. The rougher the pipe or channel, the greater the friction losses and slopes for hydraulic grade lines.
In open channels, increasing roughness usually results in higher water levels and slower flow velocities (complications might occur due to sub- and supercritical water surface profiles).