STREAM SYSTEMS TECHNOLOGY CENTER
To Aid in Securing Favorable Conditions of Water Flows
April 1995
A Video Guide to Field Identification of Bankfull
Stage in the Western United States
Bankfull stage is often difficult to iden­
tify in the field. The video, A Guide
to Field Identification of Bankfull
Stage in the Western United States,
produced by the Rocky Mountain For­
est and Range Experiment Station,
Stream Systems Technology Center,
discusses key steps and demonstrates
techniques that can be used to consis­
tently identify bankfull levels for a
variety of different streams and rivers
in the western United States.
Technical presenters include:
· Luna B. Leopold - Emeritus
Professor of Geology, University
of California, Berkeley
· William W. Emmett - Research
Hydrologist (Retired), U.S.
Geological Survey, Water Re­
sources Division
· Hilton L. Silvey - Consulting
Hydrologist, Western Hydrology
· David L. Rosgen - Consulting
Hydrologist, Wildland Hydrol­
ogy Consultants
Bankfull discharge is important be­
cause the bankfull stage is the level at
which water begins to flow over the
floodplain. When water flows over the
floodplain, then it is by definition a
flood. Bankfull discharge is also im­
portant because of its role in forming
the physical dimensions of the chan­
nel. Flows near bankfull stage move
the most sediment over the long-term
and the processes of sediment trans­
port and deposition are most active in
forming the channel.
STREAM NOTES is produced quarterly by the Stream
Systems Technology Center, Fort Collins, Colorado.
The 31-minute video focuses on iden­
tification of bankfull stage as one of
the important field observable charac­
teristics of rivers. In the video, Luna
Leopold defines bankfull stage and
discusses the importance of bankfull
discharge. Bill Emmett and Lee Silvey
demonstrate a procedure in the field
to consistently identify or estimate
bankfull levels using available data and
indicators. The video briefly touches
on various applications of bankfull
determinations in design, construction,
planning, and resource management.
Ideas and opinions expressed are not necessarily Forest
Service Policy. Trade names do not constitute
endorsement by the USDA Forest Service.
The video emphasizes identification of
the relatively flat depositional surface
of the floodplain over a reach of stream
channel as the best way to identify
bankfull stage. The use of supplemen­
tary indicators, such as the top of point
bars, edge of perennial vegetation, and
slope breaks, are only recommended
for determining bankfull stage when
floodplains are absent or poorly ex-
The PRIMARY AIM is to exchange technical ideas and
transfer technology among scientists working with
wildland stream systems.
CONTRIBUTIONS are voluntary and will be accepted
at any time. They should be typewritten, single-spaced,
limited to two pages in length. Graphics and tables
are encouraged.
Phone: (303) 498-1731
FAX: (303) 498-2306
DG: STREAM:S28A
e-mail: /s=stream/oul=s28a
@mhs-wa.attmail.com
IN THIS ISSUE
• Video on Field
Identification of
Bankfull Stage
• Ask Doc Hydro
— Velocity Floats
• New Area Code and
E-Mail Address for
STREAM TEAM
Finding bankfull stage in the
field requires a rigorous and
complete observation process
demonstrated for various
stream types in Wyoming and
Colorado. The video points out
that floodplains do not exist
along all stream channels and
that they are most prominent
along low-gradient streams.
In steep-gradient channels,
floodplains may be intermit­
tent, on alternate sides of me­
ander bends, or completely ab­
sent. Consequently, identifica­
tion of bankfull stage in steep
gradient channels is difficult.
In these channels, other indica­
tors may serve as surrogates to
identify bankfull stage. Only
use surrogates, however, if they
have been verified for the local
area of interest through direct
Dr. Luna Leopold discusses the importance of bankfull discharge on the New Fork
observation to establish that the
River near Boulder, Wyoming.
inundation level of the surro­
gate indicators occurs simulta­
pressed. Zeroing in on the flat depositional features of the neously with the inundation of the floodplain.
floodplain, will greatly improve consistency among field
The video presents several side-by-side comparisons of
personnel in field identification of bankfull stage.
channels at low flow compared to what they look like when
The video advocates the use of regional relationships be­ filled to bankfull.
tween bankfull discharge and channel characteristics, such
Bill Putnam, Watershed Program Manager, Region 1, co­
as those found in the book Water in Environmental Plan­
ning by Dunne and Leopold, as a good beginning point to ordinated the video production. Lee Silvey, consultant with
help determine where to look for the floodplain and bankfull Western Hydrology, provided technical coordination and
arranged the field shooting schedule.
stage in specific geographic regions of the country.
Dave Rosgen discusses the selection of stream reaches for
making the determination and the importance of recogniz­
ing common geomorphic features, including abandoned
floodplains and terraces. It is especially critical not to con­
fuse the level of the low terrace, located at approximately 2
to 4 feet above the present stream, with that of the flood­
plain and to be able to recognize disturbed and incised chan­
nels.
Closed captioned copies of the 31-minute VHS format vid­
eos have been mailed to hydrologists and fishery biologists
on the National Forests, Forest Service Research Stations,
and Stream Systems Technology Center cooperators. Cop­
ies are available from the Stream Systems Technology Cen­
ter.
STREAM SYSTEMS TECHNOLOGY CENTER
Since surface velocity (Vsurf) is higher than mean velocity
(Vmean), a correction factor (k) must be applied:
Vmean = k Vsurf
I need to measure discharge this runoff season in streams
that are too deep to safely wade and where there are no
bridges. Do you have any advice about using floats to
measure discharge?
Floats provide a quick way to measure water velocity and
requires little time or equipment. Estimates may not be
very accurate, but they may suffice for events such as ma­
jor floods . Discharge measurements made with floats are
only accurate within plus or minus 10% under ideal condi­
tions. Errors up to 25% may occur in non-uniform sections
or where wind is excessive.
The ideal float should move at the same velocity as the water
at the stream’s surface. Objects such as oranges are pre­
ferred since they are highly visible, float low in the water,
are not subject to wind disturbance, are environmentally
expendable, and are relatively low in cost.
Select straight reaches with a minimum of turbulence. Mark
distance along the bank and record the time with a stop­
watch. Introduce floats above the measurement section so
they can reach stream velocity before they get to the mea­
surement section. Make several runs b and calculate the
average velocity. When stream width exceeds 25 feet, di­
vide the stream into 3 subsections and measure each sepa­
rately. Ideally, the reach should contain a measured crosssection, especially if calculating discharge.
The commonly used value for the correction factor is 0.85.
Values of k generally range from 0.80 for rough beds to
0.90 for smooth artificial channels. Robert Jarrett of the
U.S. Geological Survey in Denver has calculated values as
low as 0.67 for mountain streams. Consequently, apply a
correction factor to mountain streams with caution.
For a scholarly discussion on the use of oranges for mea­
suring velocity see:
B.A. Christensen, 1994. Velocity Measurements by
the “One-Orange Method.” American Society of
Civil Engineers, Symposium Proceedings, Funda­
mentals and Advancements in Hydraulic Measure­
ments and Experimentation, Buffalo, New York,
August 2-4, 1994.
Dr. Christensen, Professor of Hydraulics, Department of
Civil Engineering, University of Florida in Gainesville,
Floride states that sophisticated instrumentation is not al­
ways necessary, nor even desirable, for the measurement
of mean velocity, discharge, and other hydraulic parameters.
Dr. Christensen’s simple procedure, explained in precise
mathematical detail, is based on the rising buoyant body
method, meaning that the orange is released from the bot­
tom of the channel. A similar procedure, using a cloud of
small air bubbles instead of a buoyant body (orange) was
proposed by the author in 1985. Field application of the
one-orange method requires significantly less equipment.
One final note: Always make the velocity or discharge
measurement before lunch!
STREAM SYSTEMS TECHNOLOGY CENTER
— Notice —
New Area Code and
E-Mail Address:
The telephone area code for the Stream Systems Technol­
ogy Center has changed from 303 to 970. The new
numbers for STREAM are:
Phone: (970) 498-1731 and
FAX: (970) 498-2306 (3 or less pages)
FAX: (970) 498-1660 (more than 3 pages)
Please make a note of these changes.
We are also pleased to introduce
our Internet E-Mail address:
/s=stream/ou1=s28a
@mhs-fswa.attmail.com
Editorial Policy
To make this newsletter a success, we need voluntary con­
tributions of relevant articles or items of general interest.
YOU can help by taking the time to share innovative ap­
proaches to problem solving that you may have developed.
Please submit typed, single-spaced contributions limited to
two pages. Include graphics and photos that help explain
ideas.
We reserve editorial judgments regarding appropriate rel­
evance, style, and content to meet our objectives of im­
proving scientific knowledge.
Send all contributions to:
Stream Systems Technology Center,
Attention: STREAM NOTES Editor.
USDA policy prohibits discrimination because of race, color, national origin, sex, age, religion, or handicapping condition. Any person
who believes he or she has been discriminated against in any USDA-related activity should immediately contact the Secretary of Agricul­
ture, Washington, DC 20250.
STREAM SYSTEMS TECHNOLOGY CENTER
USDA Forest Service
Rocky Mountain Station
240 West Prospect
Fort Collins, CO 80525
APRIL 1995
IN THIS ISSUE
• Video on Field
Identification of
Bankfull Stage
• Ask Doc Hydro
— Velocity Floats
• New Area Code and
E-Mail Address for
STREAM TEAM
BULK RATE
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