# nc3: Lotter method for composite Manning's n In iemisc: Irucka Embry's Miscellaneous Functions

## Description

This function computes the composite Manning's n using the Lotter method.

## Usage

 1 nc3(P, n, R) 

## Arguments

 P numeric vector that contains "wetted perimeter of any section i" n numeric vector that contains "Manning's n of any section i" R numeric vector that contains "hydraulic radius of any section i"

## Details

"A composite value of Manning's n for a single channel; that is, for the main channel only of a compound channel or a canal with laterally varying roughness."

The equation to find Manning's composite n using the Lotter method is

n_c = \frac{PR^\frac{5}{3}}{∑ \limits_{i=1}^N \frac{P_i R_i^\frac{5}{3}}{n_i}}

n_c

Manning's composite n

P

"wetted perimeter of the entire cross section"

R

"hydraulic radius of the entire cross section"

P_i

"wetted perimeter of any section i"

R_i

"hydraulic radius of any section i"

n_i

"Manning's n of any section i"

N

"total number of sections into which the wetted perimeter and hydraulic radius are divided"

## Value

numeric vector that contains nc3 as Manning's composite n.

## References

1. Terry W. Sturm, Open Channel Hydraulics, 2nd Edition, New York City, New York: The McGraw-Hill Companies, Inc., 2010, page 118-119.

n for Manning's n for natural channels, nc1 for Horton method for composite Manning's n, nc2 for Einstein and Banks method for composite Manning's n, and nc4 for Krishnamurthy and Christensen method for composite Manning's n.
 1 2 library("iemisc") nc3(n = c(0.0024, 0.035), P = c(23.65, 36.08), R = c(2.02, 6.23))