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USGS Water-Supply Paper 1849 by H.H. Barnes, 1967. Has upstream and downstream color photographs and channel cross-sections for 50 stream channels where Manning's n has been determined. n ranges from 0.024 to 0.075. Useful for helping to estimate n from visual inspection.
Web-reformatted and metricated version of USGS Water-Supply Paper 2339 by G.J. Arcement & V.R. Schneider, 1989. Classic paper for estimating Manning's n from physical observation of channel and floodplain characteristics. This web-formatted version taken from the Federal Highway Administration website is not as satisfactory as the original paper.
US Army Corps of Engineers Document EM1110-2-1601, Ch.5, 1994.