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Introduction
 timedistribution of runoff depends on flow velocity over
every part of the watershed
 at most points velocity must be estimated, generally using
Manning's Equation:

(1) 
 for metric units, use constant = 1 (rather than 1.49)
Determining
Several approaches to choosing a roughness coefficient:
 Choose from similar settings shown in photographic guides
 Choose from tabulated values for various settings
(Figs. 13)
 ``Cowan Method'' (Fig. 4):
 pick basic coefficient value (Fig. 5)
 sequentially adjust value for variables that increase
turbulence in flow:
 channel irregularity (Fig. 6)
 crosssection variation
(Fig. 7)
 obstructions (Fig. 8)
 vegetation (Fig. 9)
 channel meandering (Fig. 10)
Standard Values for
Figure 1:
Recommended design values for Manning Roughness Coefficient
(McCuen, 2004).

Standard Values for (cont.)
Figure 2:
Recommended design values for Manning Roughness Coefficient (cont.)
(McCuen, 2004).

Standard Values for (cont.)
Figure 3:
Recommended design values for Manning Roughness Coefficient (cont.)(McCuen, 2004).

Next: Cowan's Method for Estimating
Up: Manning's Roughness Coefficient
Previous: Manning's Roughness Coefficient
GEOS 5313 Lecture Notes, Spring 2007
Dr. T. Brikowski, UTD. All rights reserved.