Hydraulics for Hydrographers
Channel Dynamics and Shift Corrections
AQUARIUS Time-Series Software™
Aquatic Informatics Inc.
Preview
Concepts, terms and definitions
Fluvial Processes
Hydraulic Geometry
EcoHydraulics
Shift Corrections
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Fluvial Processes
Mechanics of transport
Solution
Flotation
Suspension
Saltation
Traction
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Suspended Load
For a sediment particle to be held in
suspension, the settling velocity must be less
than or equal to the turbulent velocity
As discharge increases, the suspended load
increases at a more rapid rate than the
discharge.
The enhanced concentration is due to erosion
of the drainage basin, not of scouring of the
channel.
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Revised Universal Soil Loss Equation
A  R  K  LS  P  C
Where A = soil loss; R is rainfall erosivity; K is soil
erodibility; LS is topography (length of slope and
slope); P is a conservative practices factor; and C is
a cover factor
Most sediment originates from the landscape
Understanding the landscape upstream of your
gauge can help in interpreting Shift Corrections
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Stoke’s Law for settling
velocity of supended particles
Vs 
2(  p   f ) gr
2
9m
Where: Vs is settling velocity; ρp is density of
the particle; ρf is density of the fluid; g is
gravity; r is radius of particle; and m is viscosity
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Bed Load: Saltation and Traction
Saltation refers to low extended trajectories of
sediment particles of particles with less mass
than the tractive force.
Traction is the movement of larger particles by
rolling or sliding
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Sixth power law
The radius of the largest particle that can be
set in motion by a given velocity is:
r  kv
3
6
Where r is radius; k is a constant that includes
gravity and grain density; and v is flow velocity
Therefore a small increase in velocity can have
a large increase in the size of particle that can
be moved
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Hydraulic lift and the critical tractive
force
The steep gradient of velocity near the stream
bed lowers the pressure on the top of particles
resulting in hydraulic lift
The column of water supported by a particle
exerts as critical tractive force:
Ft  gds
Where Ft is critical tractive force;  is density of
water; g is gravity; d is depth of water; and s is
the gradient of the stream
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Erosion, transport and deposition
10
Erosion
velocity (m/s)
1
0.1
Transport
Deposition
0.01
0.001
0.001
0.01
0.1
1
10
100
Diameter (mm)
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Fluvial Landforms
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Dynamic equilibrium
2000
hypsometric integral = 0.45
elevation (m)
1500
1000
500
0
0
10
20
30
40
50
60
70
80
90
100
% of basin area
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Hydraulic Geometry
Q  AV  WDV
w  aQ
d  cQf
b
v  kQ
a  c  k  1.0
b  f  m  1.0
m
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Hydraulic Geometry
Channels with resistant bank-forming material
such as cohesive silts have large values for ‘f’
and low values for ‘b’
Whereas channels with weak bank forming
material such as sand have low values for ‘f’
and high values for ‘b’
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Hydraulic geometry
Velocity (m/s)
10
1
v  0.024  Q
0.1
Depth (m)
100
d  0.781  Q
10
0.303
w  53.542  Q
1
1000
Width (m)
0.595
0.103
100
10
100
1000
Discharge (m3/s)
10000
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Velocity Residuals (m/s) Depth Residuals (m)
Width Residuals (m)
Hydraulic Geometry
20
10
0
-10
-20
1.0
0.0
-1.0
0.4
0.2
0
-0.2
-0.4
10/3/54
8/28/76
Discharge (m3/s)
7/24/98
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EcoHydraulics
Beavers
=leaky weirs
Vegetation
Biofilms
Submergent
Emergent
Riparian and
LWD
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EcoHydraulics
Stage data are more
indicative of reach
storage than of discharge
Beavers regulate flow to
control water table (e.g.
To expand riparian zone)
or to regulate water level
(e.g. For protection of
lodge entrance from
predators)
S
Qo  Qi 
dt
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Beaver Dams
Simplistic Hydraulic solutions are invalid
Hydrologic solutions include:
Estimation of flow from representative gauged basins (e.g.
using Empirical modeling toolbox)
Interpolation between measurements with adjustments
for runoff processes (e.g. using Data Correction Toolbox)
Use of rainfall-runoff modeling (e.g. using custom
toolboxes)
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River ice
The effects of river ice are discussed in the
lesson “River Ice Processes and Dynamics”
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Biofilms
Biofilms are thin layers of algae that form
under favourable conditions
They are ‘slippery’ - affecting the coefficient in the
rating equation - use a time-based to the right.
If thick enough - the dominant effect may be on
PZH, which can be temporarily be handled with a
time-based shift to the left.
Note: Rock Snot (Didymosphenia geminata) is transferred from watershed to
watershed on waders – clean your waders between measurements if you don’t want to
be responsible for its spread
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Submergent Lotic Vegetation
Vegetation that does not break the water
surface affects both the PZH and the HeadArea relation
Note that the effect varies with stage – because
high velocities flatten the weeds. At low velocities
the weeds have a greater effect on PZH and the
Head-Area relation.
Use a time-based knee-bend shift to the left
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Emergent Lentic Vegetation
In addition to all the effects of submergent
vegetation – Emergent vegetation (e.g. lily
pads) affect the wetted perimeter fundamentally altering the Hydraulic Radius
upon which the rating curve is based.
Use a time-based, truss shift to the left.
Knowing the timing of emergence is crucial.
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Riparian vegetation - overhanging
Riparian vegetation competes for sunlight in forests
by growing out over the stream channel
Overhanging vegetation may only come in contact
with the water during high flows
Overhanging vegetation affects wetted perimeter, and will
result in an abrupt stage change at time of contact
Use an upside down knee-bend shift to the left
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Riparian Vegetation – floating LWD
Sweepers alter the wetted perimeter, PZH,
and the Head-Area relation.
Use a time-based shift correction – because they
are floating - the effect is more or less uniform
with respect to stage.
If the sweeper is nasty – full of green branches
etc. –it may not be possible to accurately estimate
discharge using simplistic hydraulic assumptions in
which case hydrologic methods may be required
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Riparian Vegetation – spanning LWD
High water – critical flow
Log spanning streambanks
Abstraction and
obstruction of flow
Stream bed
Normal rating curve
Use a combination of the base rating curve at low-water, hydrologic (coefficient and
exponent are unrelated to base rating curve) estimation from first contact to
submergence of the log and a new rating curve at high water
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Other types of channel dynamics
Variable backwater
•
•
Estuaries
Confluences
Anthropogenic effects - Shopping carts, bicycle
frames etc.
Evaluate the hydraulic parameters affected and shift
according to the type (time-based if the coefficient is
affected; stage-based if the exponent is affected;
time-based, stage-based if PZH is affected)
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Rating Curve Shifts
Natural River Channels are seldom static
(Aggradation/Degradation/ Fill / Ice / Weed Growth)
Even artificial controls are subject to shifts (debris /
algae)
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Fluvial dynamics
velocity (m/s)
10
1
0.1
0.01
0.001
0.001
Transport
0.01
0.1
1
10
100
Diameter (mm)
Aggradation or degradation of the banks generally
affects the exponent, which calls for a stage-based
correction whereas aggradation or degradation of the
bed primarily affects PZH, which usually indicates a
time-based, stage-based correction
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Shifts in AQUARIUS
Can be developed in three ways
Typing in shift points in the Shift Manager
Adjusting points in the Shift Diagram
On the rating curve zoom plots
Shift dates can be specified in
The Shift Manager
The Time Series Pane (Shift Period Bars)
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Shifting by Time
Sometimes Shifts are not static
Weed growth, fill, and scour can take place
gradually
AQUARIUS lets you prorate a shift by leaving
the ‘end date’ unspecified.
An unspecified ‘end date’ shift will pro-rate
into the next shift
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Preview
In the next lesson: ‘River Ice Processes and
Dynamics’ we will look at hydraulic and
hydrologic approaches to estimating winter
streamflow.
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Recommended, on-line,
self-guided, learning resources
USGS GRSAT training
http://wwwrcamnl.wr.usgs.gov/sws/SWTraining/Index.htm
World Hydrological Cycle Observing System (WHYCOS) training material
http://www.whycos.org/rubrique.php3?id_rubrique=65#hydrom
University of Idaho
http://www.agls.uidaho.edu/bae450/lessons.htm
Humboldt College
http://gallatin.humboldt.edu/~brad/nws/lesson1.html
Comet Training – need to register – no cost
http://www.meted.ucar.edu/hydro/basic/Routing/print_version/05stage_discharge.htm#11
Thank you from the AI Team
We hope that you enjoy AQUARIUS!
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