Hydraulic roughness is the measure of the amount of frictional resistance water experiences when passing over land and channel features.
The coefficient is critical in hydraulic engineering, floodplain management, and sediment transport studies.
Biological factors have the greatest overall effect on Manning's n; key influences include bank stabilization by vegetation, height of grass and brush across a floodplain, and stumps and logs creating natural dams are the main observable influences.
Additionally, seasonal changes in vegetation density and growth can cause fluctuations in Manning's n values.
Textural fining of stream beds can affect more than just salmon spawning habitats, “bar and wood roughness create a greater variety of textural patches, offering a range of aquatic habitats that may promote biologic diversity or be of use to specific animals at different life stages.”[5]