Transcript Slide 1

National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
A tool from the NCED
Stream Restoration
Toolbox:
The Gravel River
Bankfull Channel
Estimator
Gary Parker, 10/2004
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
The Stream Restoration Toolbox
The Stream Restoration Toolbox consists of current basic research cast into the form of
tools that can be used by practitioners. The details of a tool are presented through a
PowerPoint presentation, augmented by embedded Excel spreadsheets or other commonly
available applications. The toolbox is a vehicle for bringing research findings into practice.
While many tools are being developed by NCED Researchers, the opportunity to contribute
a tool to the Toolbox is open to the community. For more information on how to contribute
please contact Jeff Marr at [email protected].
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
Statement of liability and usage
This tool is provided free of charge. Use this tool at your own risk. In offering this tool, the
following entities and persons do not accept any responsibility or liability for the tool’s use by
third parties:
• The National Center for Earth-surface Dynamics;
• The universities and institutions associated with the National Center for Earth-surface
dynamics; and
•The authors of this tool.
Users of this tool assume all responsibility for the tool results and application thereof. The
readers of the information provided by the Web site assume all risks from using the
information provided herein. None of the above-mentioned entities and persons assume
liability or responsibility for damage or injury to persons or property arising from any use of
the tool, information, ideas or instruction contained in the information provided to you.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
Title Page
Tool Title: The Gravel River Bankfull Channel Estimator
Tool Author: Gary Parker
Author e-mail: [email protected]
Version: 2.0
Associated files:
1) BankfullChannelEstimator_v2.ppt
2) ToolboxGravelBankfullData.xls
Date: October 2006
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
Outline of this Document
• Introduction
• This Tool is for Gravel-Bed Streams
• This Tool Addresses Single-Thread Rather Than Multiple-Thread Rivers
• This Tool Addresses Mobile-Bed Rather Than Threshold Channels
• Bankfull Parameters
• Bankfull discharge
• Bankfull channel width
• Bankfull channel depth
• Channel slope
• Surface median size
• Dimensionless Parameters
• What the Data Say
• A Worked Example of River Restoration
• Original Channel
• Restoration Scheme
• Appendix: Sediment Size Distributions In Gravel-Bed Streams
• References
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CAVEAT
This tool is provided free of charge.
Use this tool at your own risk.
In offering this tool, none of the following accept responsibility or liability for
its use by third parties:
• the National Center for Earth-surface Dynamics;
• any of the universities and institutions associated with the National Center
for Earth-surface dynamics; or
• any of the authors of this tool.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
The Gravel River Bankfull Channel
Estimator
This tool consists of a set of regression relations for predicting
bankfull geometry of mobile-bed single-thread gravel bed
streams in terms of bankfull discharge and bed surface
median grain size.
These relations can be used to a) help optimize the design of a
restored channel to be as close as possible to its natural
bankfull geometry, and b) help speed along the development
toward this geometry by providing guidelines for
preconstruction.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
RIVERS ARE THE AUTHORS OF THEIR OWN GEOMETRY
• Given enough time, rivers construct their own channels.
• A river channel is characterized in terms of its bankfull geometry.
• Bankfull geometry is defined in terms of river width and
average depth at bankfull discharge.
• Bankfull discharge is the flow discharge when the river is just
about to spill onto its floodplain.
• A river restoration scheme is likely to become more successful in
a shorter amount of time if it takes into account the natural
bankfull geometry of a channel.
• This tool helps predict bankfull geometry for single-thread gravelbed rivers with definable floodplains that actively move
the gravel on their beds from time to time.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
THIS TOOL IS FOR GRAVEL-BED STREAMS
Raging River, Washington,
USA: a gravel-bed river
Little Wekiva River,
Florida, USA: a sandbed river.
This tool addresses gravel-bed streams. Typical gravel-bed streams
have bed surface median sizes Ds50 in the range from 8 to 256 mm.
Boulder-bed streams have median sizes in excess of 256 mm. Sand9
bed streams have median sizes between 0.062 and 2 mm.
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
THIS TOOL ADDRESSES SINGLE-THREAD RATHER
THAN MULTIPLE-THREAD RIVERS
Raging River, Washington,
USA: a single-thread
gravel-bed river
Sunwapta River, Canada: a
multiple-thread (braided)
gravel-bed river
This tool addresses single-thread streams. A single-thread stream has
a single definable channel, although mid-channel bars may be present.
A multiple-thread, or braided stream has several channels that intertwine
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back and forth.
National Center for Earth-surface Dynamics
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THIS TOOL ADDRESSES MOBILE-BED RATHER THAN
THRESHOLD CHANNELS
Raging River, Washington,
USA: a mobile-bed river
Trinity Dam on the Trinity River,
California, USA. A threshold channel
forms immediately downstream.
This tool addresses mobile-bed gravel streams. Such streams are
competent to modify their beds because they mobilize all or nearly all
gravel sizes on the bed from time to time during floods. Threshold
channels are defined in the next slide.
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National Center for Earth-surface Dynamics
Stream Restoration Program
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THRESHOLD CHANNELS
Threshold gravel-bed channels
are channels which are barely not
able to move the gravel on their
beds, even during high flows.
These channels form e.g.
immediately downstream of dams,
where their sediment supply is cut
off. They also often form in urban
settings, where paving and
revetment have cut off the supply
of sediment. Threshold
channels are not the authors of
their own geometry. The
relations presented in this tool do
not apply to them.
Trinity Dam on the Trinity River,
California, USA. A threshold
channel forms immediately
downstream.
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National Center for Earth-surface Dynamics
Stream Restoration Program
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PARAMETERS USED IN THIS TOOL
This tool uses the following parameters:
1. Bankfull discharge Qbf in cubic meters per second (m3/s) or cubic
feet per second (ft3/s);
2. Bankfull channel width Bbf is meters (m) or feet (ft);
3. Bankfull cross-sectionally averaged channel depth Hbf in meters (m)
or feet (ft);
4. Down-channel slope S (meters drop per meter distance or feet drop
per feet distance).
5. Bed surface median grain size Ds50. This parameter is usually
measured in millimeters (mm); the value must be converted to
meters or feet in using the tool presented here.
These parameters are defined before the tool is introduced. If you are
familiar with the parameters, click the hyperlink to jump to the tool.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
BANKFULL PARAMETERS: THE RIVER AND ITS
FLOODPLAIN
floodplain
A river constructs its own
channel and floodplain.
channel
At bankfull flow the river is on the verge of spilling out onto its
floodplain.
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National Center for Earth-surface Dynamics
Stream Restoration Program
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THE DEFINITION OF BANKFULL DISCHARGE Qbf
Let  denote river stage (water surface elevation in
meters or feet relative to an arbitrary datum) and Q
denote volume water discharge (cubic meters or feet
per second). In the case of rivers with floodplains, 
tends to increase rapidly with increasing Q when all the
flow is confined to the channel, but much less rapidly
when the flow spills significantly onto the floodplain.
The rollover in the curve defines bankfull discharge Qbf.
The floodplain is
often somewhat
poorly-developed in
mountain gravel-bed
streams. Bankfull
stage, however, can
often still be
determined by direct
field inspection.

Qbf
Q
Minnesota River and flooded
floodplain, USA, during the
record flood of 1965
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National Center for Earth-surface Dynamics
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CHARACTERIZING BANKFULL DISCHARGE Qbf
• Bankfull discharge Qbf is used as a shorthand for the characteristic flow
discharge that forms the channel.
• One way to determine it is by means of direct measurement of the flow in a river.
Since bankfull flow is not frequent, this method may be impractical in a river
restoration scheme.
• Another way to estimate it is from a stage-discharge curve, as described in the
previous slide. In order to implement this, the river must be gaged near the
reach of interest.
• Another way is to estimate it using stream hydrology. It has been found that in gravelbed streams bankfull flow is often reasonably estimated in terms of a peak
flood discharge with a recurrence of 2 years (e.g. Williams, 1978 ). This
corresponds to a flow discharge that has a 50% probability of occurring in any
given year.
• When none of the above methods can be implemented, Qbf can be estimated from
bankfull channel characteristics using the tool
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BankfullDischargePredictor.ppt of this toolbox.
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CHARACTERIZING BANKFULL CHANNEL GEOMETRY:
BANKFULL WIDTH Bbf AND BANKFULL DEPTH Hbf
Bankfull geometry is here defined in terms of the average characteristics
of a channel cross-section at bankfull stage, i.e. when the flow is at
bankfull discharge. Here the key parameters are:
bankfull width Bbf and
cross-sectionally averaged bankfull depth Hbf.
These parameters should be determined from averages of values
determined at several cross-sections along the river reach of interest.
Bbf
Hbf
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CAVEAT: NOT ALL RIVERS HAVE A DEFINABLE
BANKFULL GEOMETRY!
Rivers in bedrock often have no
active floodplain, and thus no
definable bankfull geometry.
Highly disturbed alluvial rivers are
often undergoing rapid
downcutting. What used to be the
floodplain becomes a terrace that
is almost never flooded. Time is
required for the river to construct a
new equilibrium channel and
floodplain.
Wilson Creek, Kentucky: a
bedrock stream. Image
courtesy A. Parola.
Reach of the East
Prairie Creek,
Alberta, Canada
undergoing rapid
downcutting due to stream straightening. Image
courtesy D. Andres.
The relations presented in this tool do not apply to bedrock streams, or disturbed
alluvial streams with no active floodplain. They may, however, be used to estimate
characteristics of the ultimate equilibrium alluvial channel that will evolve in time. 18
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
FIELD MEASUREMENT OF BANKFULL CHANNEL
GEOMETRY
Not all field channels have definable bankfull geometries. Even when a
channel does have a definable bankfull geometry, some experience and
judgement is required to measure it. In the future a worked example
complete with photographs and data files will be added to the toolbox.
Until this is done, the user is urged to spend some time to determine how
bankfull geometry should be determined.
Bbf
Hbf
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CHARACTERIZING BED SEDIMENT IN GRAVEL-BED
STREAMS: MEDIAN SURFACE SIZE Ds50
Armored surface
Gravel-bed streams usually show a
surface armor. That is, the surface
layer is coarser than the substrate
below.
substrate
Bed sediment of the River Wharfe,
U.K., showing a pronounced surface
armor. Photo courtesy D. Powell.
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National Center for Earth-surface Dynamics
Stream Restoration Program
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SURFACE AND SUBSTRATE MEDIAN SIZES
Here the surface median size is denoted as Ds50 and the substrate median
size is denoted as Dsub50. The surface is said to be armored when Ds50/Dsub50
> 1.
This ratio also provides a rough estimate of ability of the stream to move its
own gravel. Low values of Ds50/Dsub50 (e.g. < 1.3, i.e. relatively weak
armoring) are generally indicative of relatively high mean annual sediment
transport rates, whereas high values of Ds50/Dsub50 (e.g. > 4, relatively strong
armor) are generally indicative of relatively low mean annual sediment
transport rates (Dietrich et al., 1989).
Notes on bed sampling, grain size distributions and the determination of
median sediment size are given in and Appendix (slides 35-41) toward the
end of this presentation. To jump to them click the hyperlink bed sampling.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CHARACTERIZING DOWN-CHANNEL SLOPE S
Down-channel bed slope should be determined from a survey of the long
profile of the channel centerline. The reach chosen to determine bed slope
should be long enough to average over any bars and bends in the channel,
which are associated with local elevation highs and lows.
plan view
A
B
A
bed
elevation
S
long profile of centerline bed elevation
down-channel distance
B
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National Center for Earth-surface Dynamics
Stream Restoration Program
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CHANNEL SLOPE VERSUS VALLEY SLOPE
Valley walls
B
Channel
A
In the figure to the left, down-channel bed
slope S is the difference in bed elevation from A
to B divided by the along-channel distance from
A to B (red line). Down-valley bed slope Sv is
the difference in elevation from A to B divided by
the along-valley distance from A to B (blue line).
The ratio between the down-channel distance
from A to B and the down-valley distance from A
to B is known as channel sinuosity . For a
channel that is parallel to the valley (essentially
straight)  = 1. Gravel-bed rivers tend to have
sinuosities ranging from about 1.2 to 1.8, with
lower values generally at higher slopes.
The relation between downchannel slope S and
down-valley slope Sv is given as
S   Sv
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
SINGLE-THREAD GRAVEL-BED RIVERS HAVE
CONSISTENT BANKFULL GEOMETRIES!
This is illustrated here using data from four sources:
• 16 streams flowing from the Rocky Mountains in Alberta, Canada
(Kellerhals et al., 1972);
• 23 mountain streams in Idaho (Parker et al., 2003);
• 23 upland streams in Britain (mostly Wales) (Charlton et al. 1978);
• 10 reaches along the upper Colorado River, Colorado (Pitlick and
Cress, 2002) (Each reach represents an average of several
subreaches.)
The original data for Qbf, Bbf, Hbf, S and Ds50 for each reach can be
found in the companion Excel file, ToolboxGravelBankfullData.xls.
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National Center for Earth-surface Dynamics
Stream Restoration Program
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RANGE OF PARAMETERS
Among all four sets of data, the range of parameters is as given below:
Bankfull discharge
Qbf (in meters3/sec)
2.7 ~ 5440
Bankfull width
Bbf (in meters)
5.24 ~ 280
Bankfull depth
Hbf (in meters)
0.25 ~ 6.95
Channel slope
S
0.00034 ~ 0.031
Surface median size
Ds50 (in mm)
27 ~ 167
These ranges approximate the range of applicability of the relations
presented in this tool.
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
DIMENSIONLESS PARAMETERS
The universality of bankfull characteristics of single-thread gravel-bed
rivers is expressed with the use of dimensionless parameters.
Dimensionless bankfull depth, width and discharge are defined as
~ g1/ 5Hbf
H
Qbf2 / 5
~ g1/ 5Bbf
, B  2/5
Qbf
ˆ 
, Q
Qbf
gDs50 Ds250
where g denotes the acceleration of gravity.
These parameters can be computed in either SI or English. When using
SI units, Hbf, Bbf and Ds50 should be in meters (convert Ds50 from mm),
Qbf should be in cubic meters per second, and g should take a value of
9.81 meters/sec2. When using English units, Hbf, Bbf and Ds50 should be
in feet (convert Ds50 from mm), Qbf should be in cubic feet per second,
and g should take a value of 32.2 ft/sec2.
Note that down-channel bed slope S is already dimensionless (meter
drop per meter distance or feet drop per feet distance).
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
WHAT THE DATA SAY
The four data sets tell a consistent story of bankfull channel characteristics.
100
~
B
Dimensionless width
Britain width
Alberta width
Idaho width
Colorado width
Britain depth
Alberta depth
Idaho depth
Colorado depth
Britain slope
Alberta slope
Idaho slope
Colorado slope
Btilde, Htilde, S
10
~
H
1
~ ~
B, H, S
0.1
Dimensionless depth
S
0.01
0.001
Down-channel bed slope
0.0001
1.0E+02
1.0E+03
1.0E+04
1.0E+05
ˆ
Q
Qhat
1.0E+06
1.0E+07
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National Center for Earth-surface Dynamics
Stream Restoration Program
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REGRESSION RELATIONS FOR BANKFULL CHANNEL
CHARACTERISTICS
~
~
ˆ 0.00004 , B
ˆ 0.0661
H  0.3785Q
 4.698Q
To a high degree of approximation,
1.E+02
~
B
Bdimtilde, Hdimtilde, S
y = 4.6977x0.0661
~ ~
B, H, S
ˆ 0.3438
, S  0.1003Q
~ ~
H  Hc  0.3785
1.E+01
~
H
y = 0.3785x4E-05
1.E+00
Bdimtilde
Hdimtilde
S
Power (Hdimtilde)
Power (Bdimtilde)
Power (S)
1.E-01
y = 0.1003x-0.3438
1.E-02
S
1.E-03
1.E-04
1.E+02
1.E+03
1.E+04
1.E+05
ˆ
Qdim
Q
1.E+06
1.E+07
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National Center for Earth-surface Dynamics
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WHY DOES THE RELATION FOR SLOPE SHOW THE
MOST SCATTER?
1.E+02
~
B
Bdimtilde, Hdimtilde, S
y = 4.6977x0.0661
~ ~
B, H, S
1.E+01
~
H
y = 0.3785x4E-05
1.E+00
Bdimtilde
Hdimtilde
S
Power (Hdimtilde)
Power (Bdimtilde)
Power (S)
1.E-01
y = 0.1003x-0.3438
1.E-02
S
1.E-03
1.E-04
1.E+02
1.E+03
1.E+04
1.E+05
Qdim
ˆ
Q
1.E+06
1.E+07
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National Center for Earth-surface Dynamics
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WHY DOES THE RELATION FOR SLOPE SHOW THE
MOST SCATTER?
• Rivers can readjust their bankfull depths and widths over short
geomorphic time, e.g. hundreds to thousands of years.
• Readjusting river valley slope involves moving large amounts of sediment
over long reaches, and typically requires long geomorphic time (tens of
thousands of years or more).
• As a result, valley slope can often be considered to be an imposed
parameter that the river is not free to adjust in short geomorphic time. This
concept should be used in most river restoration projects.
• Varying the channel sinuosity  allows for some variation in channel
slope S at the same valley slope Sv.
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National Center for Earth-surface Dynamics
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THE TOOL CONSISTS OF THREE RELATIONS
Qbf2 / 5
Hbf  0.3785 1/ 5
g
2/5
bf
1/ 5
Q
Bbf  4.698
g


Q
bf


 gD D2 
s 50
s 50 



Q
bf

S  0.1003
 gD D2 
s 50
s 50 

0.0661
0.3438
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Caution: use these relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
TOOL IMPLEMENTATION: BANKFULL GEOMETRY
PREDICTED FROM THE REGRESSION RELATIONS
Stop the slide show and double-click to activate the Excel spreadsheet.
The spreadsheet is then live: you can change input as you please.
Input
Bankfull discharge
Surface median size
Calculated
SI
Qbf
Ds50
Ds50
Dimensionless discharge Qhat
Output
Bankfull depth
Bankfull width
Estimated channel slope
Hbf
Bbf
S
English
3
200.0 m /s
66.0 mm
3
7060.0 ft /s
66.0 mm
0.066 m
5.71E+04
0.217 ft
5.70E+04
1.996 m
51.1 m
0.0023
6.547 ft
167.6 ft
0.0023
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Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
A WORKED EXAMPLE OF RIVER RESTORATION
A reach of river had the following characteristics before intervention.
Qbf = 600 m3/s (2-year flood)
Bbf = 96 m
Hbf = 2.9 m
S = 0.00015
Ds50 = 46 mm
A dam was constructed on the reach. As a result all flood flows were cut off, and
the channel was turned into a threshold channel.
As part of a river restoration scheme, annual flooding is to be restored using
controlled reservoir releases. No gravel is to be fed in immediately downstream of
the dam, so that reach will remain a threshold channel. Gravel of similar size to that
which prevailed in the channel enters the stream at the first major tributary. The
effective 2-year recurrence flood of the restoration scheme is 220 m3/s. Compute
the bankfull characteristics of the restored mobile-bed channel downstream of the
first tributary.
33
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
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WORKED EXAMPLE contd.
In this example, the original bankfull discharge was 600 m3/s. The
intervention of a dam cut off all flood flows. The restoration scheme brings
back a 2-year flood of 220 m3/s. Using this value as the new bankfull
discharge, it is apparent that the channel must shrink to fit it. That is, both
bankfull width Bbf and bankfull depth Hbf must reduce over time to fit the
reduced bankfull discharge.
In nature, this is accomplished by means of sediment deposition,
augmented by vegetal encroachment. In time, a smaller but
morphologically (and presumably ecologically) healthy channel should
evolve. This natural process may take decades or centuries. A river
restoration scheme can speed the evolution to this new state by partially
pre-installing the new channel.
34
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CALCULATIONS FOR THE ORIGINAL CHANNEL
Stop the slide show and double-click to activate the Excel spreadsheet.
The spreadsheet is then live: you can change input as you please.
Input
Bankfull discharge
Surface median size
Calculated
SI
Qbf
Ds50
Ds50
Dimensionless discharge Qhat
Output
Bankfull depth
Bankfull width
Estimated channel slope
Hbf
Bbf
S
English
3
600.0 m /s
46 mm
3
21188.8 ft /s
46 mm
0.046 m
4.22E+05
0.150919 ft
4.22E+05
3.097 m
90.5 m
0.0012
10.161 ft
296.905 ft
0.0012
35
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
COMPARISON BETWEEN THE OBSERVED ORIGINAL
CHANNEL AND THAT COMPUTED FROM THE
REGRESSION RELATIONS
Parameter
Observed
Regression
Bbf (m)
96
90.5
Hbf (m)
2.9
3.1
S
0.00015
0.00012
The values predicted from the regression relations are similar to the observed
values, at least within the scatter of the data used to determine them.
36
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
CALCULATIONS FOR RESTORATION SCHEME
Double-click to activate the Excel spreadsheet.
The spreadsheet is live: you can change input as you please.
Input
Bankfull discharge
Surface median size
Calculated
SI
Qbf
Ds50
Ds50
Dimensionless discharge Qhat
Output
Bankfull depth
Bankfull width
Estimated channel slope
Hbf
Bbf
S
English
3
220.0 m /s
46 mm
3
7770.0 ft /s
46 mm
0.046 m
1.55E+05
0.150919 ft
1.55E+05
2.073 m
56.7 m
0.0016
6.802 ft
186.014 ft
0.0016
37
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
BANKFULL CHARACTERISTICS OF THE RESTORED
CHANNEL
Parameter
Regression
original
(before
intervention)
90.5
Regression
after
restoration
Bbf (m)
Observed
original
(before
intervention)
96
Hbf (m)
2.9
3.1
2.1
S
0.00015
0.00012
0.00016
56.7
38
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
BANKFULL CHARACTERISTICS OF THE RESTORED
CHANNEL contd.
Parameter
Observed
original (before
intervention)
Regression
original (before
intervention)
Regression
after restoration
Bbf (m)
96
90.5
56.7
Hbf (m)
2.9
3.1
2.1
S
0.00015
0.00012
0.00016
The restored bankfull channel should have 63% of the original width and 68% of the
original depth. These percentages should be applied to the values for the original
channel (rather than those predicted from the regression relations) if they are known.
It may take decades or centuries for the new channel to evolve on its own;
channel modification can help speed the evolution to the new
dimensions by providing a head start.
39
Caution: use the relations subject to the caveats of Slides 5, 6, 7, 8 and 14!
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
SINUOSITY OF THE RESTORED CHANNEL
Parameter
Observed
original (before
intervention)
Regression
original (before
intervention)
Regression
after restoration
S
0.00015
0.00012
0.00016
Valley slope Sv is assumed to be constant. As a result, the relation
between sinuosity and slope is
ar So

o Sar
where the subscripts “o” and “ar” denote “original” and “after restoration.”
The numbers in the above table give:
ar
 0.75
o
Thus the restored channel should be somewhat less sinuous than
40
the original channel before intervention.
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
FURTHER CAVEATS
1. It is not possible to restore a stream in a meaningful way by supplying it
with a discharge that is constant the year round. Channel and floodplain
formation, cleaning of the gravel bed and renewal of the riparian
ecosystem all require both flood and low flows.
2. A restored flood regimen should not consist of only a very brief spike.
The restored flood hydrograph should have a duration that is at least
somewhat similar to the original one before intervention. If the flood
hydrograph is too short it will be insufficient to a) overturn the gravel and
b) rip out excessive encroaching vegetation.
3. The flood regimen should not be restored without a gravel supply. If the
gravel supply of the first major tributary downstream of a dam is
insufficient, or too fine, it may be necessary to feed gravel in addition to
restoring flood flows. A threshold channel will develop or be maintained
on any reach that has no gravel supply.
41
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
APPENDIX: SEDIMENT SIZE DISTRIBUTIONS IN GRAVELBED STREAMS
Armored surface
Implementation of the regression relations requires a
knowledge of the median size of the surface armor
Ds50. This value must be determined by sampling the
bed. In order to characterize the bed sediment of the
stream the surface and substrate should be sampled
separately. The results of sampling are plotted in
terms of percent finer versus grain size (mm) as
illustrated below.
100
90
80
Percent Finer
substrate
Bed sediment of the River Wharfe,
U.K., showing a pronounced surface
armor. Photo courtesy D. Powell.
70
60
Substrate
Surface
50
40
30
20
10
0
0.1
1
10
D (mm)
100
1000
42
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
WOLMAN COUNT OF SURFACE SEDIMENT
The simplest way to sample a gravel bed surface is by means of a Wolman
count (Wolman, 1954). The gravel surface is paced, and at set intervals a
particle next to the toe of one’s foot is sampled. The sampling should be
chosen so as to capture the spatial variation in bed texture. Grain size is
characterized in terms of the b-axis of a grain (middle axis as measured
with a caliper) or the size of the smallest square through which the grain
will fit. A series grain size ranges is set for estimating the grain size
distribution. In analyzing a Wolman sample, it is necessary to determine
the number of grains in each range. These numbers are used to
determine the grain size distribution. A sample calculation is given in the
live spreadsheet of the next slide.
Wolman sampling is not practical for sand-sized or smaller grains. More
specifically, grains finer than about 4 mm should not be included in a
sample. It should be understood that this method misses the finer grains
43
in the surface.
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
GRAIN SIZE DISTRIBUTION FROM WOLMAN COUNT
Percent Finer
The live
spreadsheet to the
right shows a
worked example
for a Wolman
count. Stop the
slide show and
double-click to
activate it. It is
customary to plot
grain size on a
logarithmic scale
when presenting
grain size
distributions.
Measured
Computed
Range mm No. of grains Percent
Size mm Percent finer
128-256
46
24.21%
256
100.00%
64-128
48
25.26%
128
75.79%
32-64
37
19.47%
64
50.53%
16-32
26
13.68%
32
31.05%
8-16
27
14.21%
16
17.37%
4-8
6
3.16%
8
3.16%
4
0.00%
Total no.
190 100.00%
100%
80%
60%
40%
20%
0%
1
10
100
Grain Size mm
1000
44
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
KLINGEMAN SAMPLE OF SURFACE SEDIMENT
The methodology for a Klingeman sample of the surface sediment is
outlined in Klingeman et al. (1979). A circular patch of sediment is specified
on the bed. The largest grain that shows any exposure on the bed surface
is located and removed. All of the bed material (including sand) is then
sampled down to the level of the bottom of the hole created by removing
the largest grain. The resulting sample is analyzed by mass (weight) rather
than number.
A Klingeman sample captures the sand as well as the gravel in the surface
layer. Sampling is, however, more laborious than that required for a
Wolman sample. In addition, several Klingeman samples at different
locations may be needed to characterize the spatial variability of the
surface sediment. A sample calculation is given in the live spreadsheet of
the next page.
45
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
KLINGEMAN SAMPLE OF SURFACE SEDIMENT contd.
18
16
12
13
5
7
2
3
6
2
84
Computed
Percent
Size mm Percent finer
21.43%
256
100.00%
19.05%
128
78.57%
14.29%
64
59.52%
15.48%
32
45.24%
5.95%
16
29.76%
8.33%
8
23.81%
2.38%
4
15.48%
3.57%
2
13.10%
7.14%
1
9.52%
2.38%
0.5
2.38%
kg
0.25
0.00%
100%
Percent Finer
The live spreadsheet to
the right shows a
worked example for a
Klingeman sample.
Stop the slide show and
double-click to activate
it.
Measured
Range mm Mass kg
128-256
64-128
32-64
16-32
8-16
4-8
2-4
1-2
0.5-1
0.25-5
Total mass
50%
0%
0.1
10
Grain Size mm
1000
46
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
BULK SAMPLE OF SUBSTRATE
The substrate may be sampled in bulk. The surface layer is first carefully
stripped off down to the depth of the bottom of the largest particle exposed
on the surface. A bulk sample (e.g. cubical) volume of substrate is then
excavated. According to the guidelines of Church et al. (1987), the mass
(weight) of the sample should be at least 100 times the mass (weight) of the
largest grain contained in the sample. Several such samples may be
needed to characterize the spatial variability of the substrate.
The sample is analyzed in terms of mass (weight) rather than number.
47
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
MEDIAN SIZE
It is useful to characterize a sample in terms of its median size D50, i.e. the
size for which 50% of the material is finer. To do this, find the grain sizes D1
and D2 such that the percentage content F1 is the highest value below 50%
and the percentage content F2 is the lowest percentage above 50%. The
median size D50 is then estimated by log-linear interpolation as:

n(D2 )  n(D1)(50  F )
D50  expn(D1 ) 
1 
F

F


2
1
For example, in the Klingeman sample of slide 13:
D1 = 32 mm, F1 = 45.24%, D2 = 64 mm and F2 = 59.52%. The calculation
of D50 is illustrated in terms of the live spreadsheet below. Stop the slide
show and double-click to activate it.
Input
D1
D2
F1
F2
32 mm
64 mm
45.24
59.52
Output
D50
40.3 mm
48
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
REFERENCES
Charlton, F. G., Brown, P. M. and R. W. Benson 1978 The
hydraulic geometry of some gravel rivers in Britain. Report INT 180,
Hydraulics Research Station, Wallingford, England, 48 p.
Church, M. A., D. G. McLean and J. F. Wolcott 1987 River bed gravels: sampling
and analysis. In Sediment Transport in Gravel-bed Rivers, Thorne, C. R.,
J. C. Bathurst, and R. D. Hey, eds., John Wiley & Sons, 43-79.
Dietrich, W. E., J. W. Kirchner, H. Ikeda and F. Iseya 1989 Sediment supply and
the development of the coarse surface layer in gravel-bedded rivers.
Nature, 340, 215-217.
Ferguson, R. I. 1987 Hydraulic and sedimentary controls of channel pattern. In
Rivers: Environment and Process, K. Richards. ed., Blackwell, Oxford,
129-158.
Kellerhals, R., Neill, C. R. and D. I. Bray 1972 Hydraulic and
geomorphic characteristics of rivers in Alberta. River Engineering
and Surface Hydrology Report, Research Council of Alberta, Canada,
No. 72-1.
49
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
REFERENCES contd.
Klingeman, P. C., C. J. Chaquette, and S. B. Hammond 1979 Bed Material
Characteristics near Oak Creek Sediment Transport Research Facilities,
1978-1979. Oak Creek Sediment Transport Report No. BM3, Water
Resources Research Institute, Oregon State University, Corvallis, Oregon,
June.
Parker, G., Toro-Escobar, C. M., Ramey, M. and S. Beck 2003 The effect of
floodwater extraction on the morphology of mountain streams. Journal of
Hydraulic Engineering, 129(11).
Parker, G. 2004 Quasi-universal relations for bankfull hydraulic geometry of singlethread gravel-bed rivers . In preparation.
Pitlick, J. and R. Cress 2002 Downstream changes in the channel of a large
gravel bed river. Water Resources Research 38(10), 1216,
doi:10.1029/2001WR000898, 2002.
Williams, G. P. 1978 Bankfull discharge of rivers. Water Resources Research,
14, 1141-1154.
Wolman, M.G. 1954. A method of sampling coarse river bed material.
Trans. Am. Geophys. Union, 35, 951–956.
50
National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
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National Center for Earth-surface Dynamics
Stream Restoration Program
Enabling Landscape Sustainability
Want more information?
For more information on this tool or the NCED Stream
Restoration Toolbox please contact the author of this tool,
Gary Parker, or the NCED Stream Restoration Project
Manager, Jeff Marr at [email protected]
National Center for Earth-surface Dynamics
2 3rd Ave SE,
Minneapolis, MN 55414
612.624.4606
52