Hydraulics for Hydrographers Channel Dynamics and Shift Corrections AQUARIUS Time-Series Software™...
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Transcript of Hydraulics for Hydrographers Channel Dynamics and Shift Corrections AQUARIUS Time-Series Software™...
Hydraulics for HydrographersChannel Dynamics and Shift Corrections
AQUARIUS Time-Series Software™Aquatic Informatics Inc.
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Concepts, terms and definitionsFluvial ProcessesHydraulic GeometryEcoHydraulicsShift Corrections
Preview
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Mechanics of transportSolutionFlotationSuspensionSaltationTraction
Fluvial Processes
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.
Suspended Load
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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 landscapeUnderstanding the landscape upstream of your gauge can help in interpreting Shift Corrections
Revised Universal Soil Loss Equation
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CPLSKRA
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
Stoke’s Law for settling velocity of supended particles
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9
)(2 2grV fps
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
Bed Load: Saltation and Traction
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The radius of the largest particle that can be set in motion by a given velocity is:
Where r is radius; k is a constant that includes gravity and grain density; and v is flow velocityTherefore a small increase in velocity can have a large increase in the size of particle that can be moved
Sixth power law
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63 kvr
The steep gradient of velocity near the stream bed lowers the pressure on the top of particles resulting in hydraulic liftThe column of water supported by a particle exerts as critical tractive force:
Where Ft is critical tractive force; r is density of water; g is gravity; d is depth of water; and s is the gradient of the stream
Hydraulic lift and the critical tractive force
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gdsFt
Erosion, transport and deposition
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0.001 0.01 0.1 1 10 1000.001
0.01
0.1
1
10
Diameter (mm)
velo
city
(m/s
)
Erosion
Deposition
Transport
Fluvial Landforms
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Dynamic equilibrium
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0 10 20 30 40 50 60 70 80 90 1000
500
1000
1500
2000
% of basin area
elev
ation
(m)
hypsometric integral = 0.45
Hydraulic Geometry
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baQwcQfd
mkQv
WDVAVQ
0.1 kca
0.1 mfb
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’
Hydraulic Geometry
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Hydraulic geometry
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100 1000 10000D ischarge (m 3/s)
10
100
1000
Wid
th (
m)
1
10
100
De
pth
(m
)
0 .1
1
10
Ve
loci
ty (
m/s
)
103.0
303.0
595.0
542.53
781.0
024.0
Qw
Qd
Qv
Hydraulic Geometry
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10/3/54 8/28/76 7/24/98D ischarge (m 3/s)
-0 .4
-0.2
0
0.2
0.4
Ve
loci
ty R
esi
du
als
(m
/s)
-1 .0
0.0
1.0
De
pth
Re
sid
ua
ls (
m)
-20
-10
0
10
20
Wid
th R
esi
du
als
(m
)
Beavers=leaky weirs
VegetationBiofilmsSubmergentEmergentRiparian and LWD
EcoHydraulics
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Stage data are more indicative of reach storage than of dischargeBeavers 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)
EcoHydraulics
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dt
SQQ io
Simplistic Hydraulic solutions are invalidHydrologic 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)
Beaver Dams
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The effects of river ice are discussed in the lesson “River Ice Processes and Dynamics”
River ice
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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.
Biofilms
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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
Vegetation that does not break the water surface affects both the PZH and the Head- Area 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
Submergent Lotic Vegetation
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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.
Emergent Lentic Vegetation
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Riparian vegetation competes for sunlight in forests by growing out over the stream channelOverhanging 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
Riparian vegetation - overhanging
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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
Riparian Vegetation – floating LWD
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Riparian Vegetation – spanning LWD
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Stream bed
Log spanning streambanks
Normal rating curve
Abstraction and obstruction of flow
High water – critical flow
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
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)
Other types of channel dynamics
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Natural River Channels are seldom static (Aggradation/Degradation/ Fill / Ice / Weed Growth)Even artificial controls are subject to shifts (debris / algae)
Rating Curve Shifts
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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
Fluvial dynamics
0.001 0.01 0.1 1 10 1000.001
0.01
0.1
1
10
Diameter (mm)
velo
city
(m/s
)
Transport
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Can be developed in three waysTyping in shift points in the Shift ManagerAdjusting points in the Shift DiagramOn the rating curve zoom plots
Shift dates can be specified inThe Shift ManagerThe Time Series Pane (Shift Period Bars)
Shifts in AQUARIUS
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Sometimes Shifts are not staticWeed growth, fill, and scour can take place graduallyAQUARIUS lets you prorate a shift by leaving the ‘end date’ unspecified.An unspecified ‘end date’ shift will pro-rate into the next shift
Shifting by Time
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In the next lesson: ‘River Ice Processes and Dynamics’ we will look at hydraulic and hydrologic approaches to estimating winter streamflow.
Preview
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Recommended, on-line, self-guided, learning resources
USGS GRSAT traininghttp://wwwrcamnl.wr.usgs.gov/sws/SWTraining/Index.htm
World Hydrological Cycle Observing System (WHYCOS) training materialhttp://www.whycos.org/rubrique.php3?id_rubrique=65#hydrom
University of Idahohttp://www.agls.uidaho.edu/bae450/lessons.htm
Humboldt Collegehttp://gallatin.humboldt.edu/~brad/nws/lesson1.html
Comet Training – need to register – no costhttp://www.meted.ucar.edu/hydro/basic/Routing/print_version/05-stage_discharge.htm#11
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Thank you from the AI TeamWe hope that you enjoy AQUARIUS!