iemisc (version 0.9.9)

n: Manning's n for natural channels

Description

This function computes Manning's n for natural channels.

Usage

n(nb = NULL, n1 = NULL, n2 = NULL, n3 = NULL, n4 = NULL, m = NULL)

Value

n as Manning's n for a natural channel as a numeric vector.

Arguments

nb

numeric vector that contains "the base value for a straight, uniform channel", if needed

n1

numeric vector that contains "correction for surface irregularities", if needed

n2

numeric vector that contains "correction for variations in the shape and size of the cross section", if needed

n3

numeric vector that contains "correction for obstructions", if needed

n4

numeric vector that contains "correction for vegetation and flow conditions", if needed

m

numeric vector that contains "correction factor for channel meandering", if needed

Details

"Roughness values for channels and flood plains should be determined separately. The composition, physical shape, and vegetation of a flood plain can be quite different from those of a channel." Source: USGS.

The equation to find Manning's n for natural channels is expressed as

$$n = \left(n_b + n_1 + n_2 + n_3 + n_4\right)m$$

n

Manning's n

\(n_b\)

"the base value for a straight, uniform channel"

\(n_1\)

"correction for surface irregularities"

\(n_2\)

"correction for variations in the shape and size of the cross section"

\(n_3\)

"correction for obstructions"

\(n_4\)

"correction for vegetation and flow conditions"

m

"correction factor for channel meandering"

Source: Sturm page 114.

References

1. Terry W. Sturm, Open Channel Hydraulics, 2nd Edition, New York City, New York: The McGraw-Hill Companies, Inc., 2010, page 114.

2. Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains, United States Geological Survey Water-supply Paper 2339 Metric Version

3. George J. Arcement, Jr., and Verne R. Schneider, United States Geological Survey Water-Supply Paper 2339, "Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains", 1989, http://pubs.usgs.gov/wsp/2339/report.pdf.

See Also

nc1 for Horton method for composite Manning's n, nc2 for Einstein and Banks method for composite Manning's n, nc3 for Lotter method for composite Manning's n, and nc4 for Krishnamurthy and Christensen method for composite Manning's n.

Examples

library("iemisc")
# Example from Table 4. from the USGS Reference text page 35
n(nb = 0.025, n4 = 0.005, m = 1.00)