Commonly referred to as Manning's “n” coefficients, these coefficients are used in the hydraulic calculations to reflect the resistance to flow in the channel and overbanks. Resistance to flow is typically due to the composition of surfaces (cement vs boulders, etc.) and type of vegetation that is present in these areas. This section lists the range of Manning's “n” coefficients used in the study for the channel and overbanks.

Example of how the Manning's “n” coefficients may be used in a FIS

Channel and overbank roughness coefficients (Manning's “n”) were assigned by field inspection, photographs, and textbook resources (References 6 and 7).

In Sampleville, the “n” coefficients for the Mud River and Mud River East Channel range from 0.025 to 0.028 for the channel and 0.038 to 0.055 for the overbanks. For Sandy Creek, the “n” coefficients range from 0.035 to 0.040 for the channel and from 0.040 to 0.065 for the overbanks. For Southside Road Drainage Ditch, the channel “n” coefficient is 0.035 and the overbank “n” coefficient is 0.04.

Select USGS Surface-Water Field Techniques, available at https://wwwrcamnl.wr.usgs.gov/sws/fieldmethods/Indirects/nvalues/index.htm to see examples of some typical channels whose roughness coefficients are known.