Hydraulics for Hydrographers Channel Dynamics and Shift Corrections

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Hydraulics for HydrographersChannel Dynamics and
Shift Corrections
AQUARIUS Time-Series Software Aquatic
Informatics Inc.
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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

• 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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Stokes Law for settling velocity of supended
particles

• Where Vs is settling velocity ?p is density of
  the particle ?f 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
• 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
• 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

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Erosion, transport and deposition
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Fluvial Landforms
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Dynamic equilibrium
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Hydraulic Geometry
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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
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Hydraulic Geometry
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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)

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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
dont 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 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

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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
Normal rating curve
Stream bed
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
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/s
ws/SWTraining/Index.htm World Hydrological
Cycle Observing System (WHYCOS) training
material http//www.whycos.org/rubrique.php3?id_ru
brique65hydrom University of
Idaho http//www.agls.uidaho.edu/bae450/lessons.ht
m 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/05-stage_discharge.ht
m11
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Thank you from the AI Team We hope that you enjoy
AQUARIUS!