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Hydraulics for Hydrographers Channel Dynamics and Shift Corrections

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Title: Hydraulics for Hydrographers Channel Dynamics and Shift Corrections


1
Hydraulics for HydrographersChannel Dynamics and
Shift Corrections
AQUARIUS Time-Series Software Aquatic
Informatics Inc.
2
Preview
  • Concepts, terms and definitions
  • Fluvial Processes
  • Hydraulic Geometry
  • EcoHydraulics
  • Shift Corrections

3
Fluvial Processes
  • Mechanics of transport
  • Solution
  • Flotation
  • Suspension
  • Saltation
  • Traction

4
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.

5
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

6
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

7
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

8
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

9
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

10
Erosion, transport and deposition
11
Fluvial Landforms
12
Dynamic equilibrium
13
Hydraulic Geometry
14
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

15
Hydraulic geometry
16
Hydraulic Geometry
17
EcoHydraulics
  • Beavers
  • leaky weirs
  • Vegetation
  • Biofilms
  • Submergent
  • Emergent
  • Riparian and LWD

18
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)

19
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)

20
River ice
  • The effects of river ice are discussed in the
    lesson River Ice Processes and Dynamics

21
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
22
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

23
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.

24
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

25
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

26
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
27
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)

28
Rating Curve Shifts
  • Natural River Channels are seldom static
    (Aggradation/Degradation/ Fill / Ice / Weed
    Growth)
  • Even artificial controls are subject to shifts
    (debris / algae)

29
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
30
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)

31
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

32
Preview
  • In the next lesson River Ice Processes and
    Dynamics we will look at hydraulic and
    hydrologic approaches to estimating winter
    streamflow.

33
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
34
Thank you from the AI Team We hope that you enjoy
AQUARIUS!
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