FLOOD05012

• County: Statewide
• Basin: Statewide
• Title: Verification of Roughness Coefficients for Selected Natural and Constructed Stream Channels in Arizona
• Date: 1/1/1998
• Prepared For: Maricopa County Arizona
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

Verification of Roughness Coefficients for
Selected Natural and Constructed Stream
Channels in Arizona

By Jeff V. Phillips and Todd L. Ingersoll

ABSTRACT

Physical and hydraulic characteristics are
presented for 14 river and canal reaches in Arizona
for which 37 roughness coefficients have been
determined. The verified roughness coefficients,
which ranged from 0,017 to 0.067, were computed
from discharges, channel geometry, and water-
surface profiles measured at each of the sites. The
reaches studied cover a wide range of channel
conditions including alluvial channels, boulder
channels, constructed channels, and channels con-
taining varying amounts of riparian vegetation.
The information given for each stream segment
includes bed and bank descriptions, data tables
showing channel and hydraulic components, a
plan view, a representative cross-section plot, and
color photographs that can be used as a compari-
son standard to aid in determining roughness coef-
ficients for similarly characterized channels.
Relations derived from the data presented
relate Manning's roughness coefficient (n) to vari,
ous hydraulic components. For gravel-bed
streams, verified roughness coefficients are related
to median grain size of the bed material and
hydraulic radius resulting in an equation that can
be used to transfer results to sirnilar dryland chan-
nels. The equation developed for base values of n
for gravel-bed channels in Arizona is significantly
different from similarly derived equations for
other regions of the United States and the world,
Another equation was developed to quantify the
magnitude of the vegetation component of

Manning's roughness coefficient for channels III
which vegetation is present.

INTRODUCTION

The U.S. Geological Survey, in cooperation with
the Flood Control District of Maricopa County, has
been studying the hydraulic effects associated with
channel,roughness elements in streams in Arizona.
Manning's roughness coefficient, n, commonly is used
to represent flow resistance for hydraulic computations
of flow in open channels, The procedure for selecting n
values is subjective and requires judgment and skill
that is developed primarily through experience, The
expertise necessary for proper selection of roughness
coefficients can be obtained, in part, by examining
characteristics of channels that have known or verified
coefficients. The roughness coefficient can be verified
by computations made using data from streamflow
measurements and from measurements of the physical
features of the channeL Photographs of channel
segments where n values have been verified can be
used as a comparison standard to aid in assigning n
values to similar channels,
Verified values of Manning's n have been
presented for streams that represent a wide range of
channel conditions in the United States and other
countries throughout the world. Past investigations
include verified roughness coefficients for 50 selected
stream channels in the United States (Barnes, 1967),21
high'gradient streams in Colorado (Jarrett, 1985), IS
flood plains in the southeastern United States
(Arcement and Schneider, 1989), 78 rivers and canals
in New Zealand (Hicks and Mason, 1991), 11 gravel,
bed streams in California (Limerinos, 1970),67 gravel-

Abstract