Guide for selecting roughness coefficient "n" values for channels

The purpose of this group of pictures, selected from Technical Bulletin 129, "Flow of Water in Drainage Channels" by C.E. Ramser, is to illustrate the wide range of the roughness coefficient "n" of Manning's formula for channel velocities related to actual channel conditions. Study of the pictures and information shown should assist in selecting realistic values of "n" for both present and future constructed channels.