highlights of open channel hydraulics and sediment transport
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HIGHLIGHTS OF OPEN CHANNEL HYDRAULICS AND SEDIMENT TRANSPORT. Dam at Hiram Falls on the Saco River near Hiram, Maine, USA. SIMPLIFICATION OF CHANNEL CROSS-SECTIONAL SHAPE. - PowerPoint PPT PresentationTRANSCRIPT
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
HIGHLIGHTS OF OPEN CHANNEL HYDRAULICS AND SEDIMENT TRANSPORT
Dam at Hiram Falls on the Saco River near Hiram, Maine, USA
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
SIMPLIFICATION OF CHANNEL CROSS-SECTIONAL SHAPE
River channel cross sections have complicated shapes. In a 1D analysis, it is appropriate to approximate the shape as a rectangle, so that B denotes channel width and H denotes channel depth (reflecting the cross-sectionally averaged depth of the actual cross-section). As was seen in Chapter 3, natural channels are generally wide in the sense that Hbf/Bbf << 1, where the subscript “bf” denotes “bankfull”. As a result the hydraulic radius Rh is usually approximated accurately by the average depth. In terms of a rectangular channel,
H
B
channel floodplainfloodplain
H
BH
21
H
H2B
HBRh
3
1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
THE SHIELDS NUMBER:A KEY DIMENSIONLESS PARAMETER QUANTIFYING SEDIMENT MOBILITY
gDRb
3
c
2b
2g
34
~
DR
D
b = boundary shear stress at the bed (= bed drag force acting on the flow per unit bed area) [M/L/T2]
c = Coulomb coefficient of resistance of a granule on a granular bed [1]
Recalling that R = (s/) – 1, the Shields Number * is defined as
It can be interpreted as a ratio scaling the ratio impelling force of flow drag acting on a particle to the Coulomb force resisting motion acting on the same particle, so that
The characterization of bed mobility thus requires a quantification of boundary shear stress at the bed.
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
QUANTIFICATION OF BOUNDARY SHEAR STRESS AT THE BED
2/1fC
u
UCz
U = cross-sectionally averaged flow velocity ( depth-averaged flow velocity in the wide channels studied here) [L/T]
u* = shear velocity [L/T]
Cf = dimensionless bed resistance coefficient [1]
Cz = dimensionless Chezy resistance coefficient [1]
2b
f UC
BH
QU
bu
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
RESISTANCE RELATIONS FOR HYDRAULICALLY ROUGH FLOW
6/1
sr
2/1f k
HC
u
UCz
Keulegan (1938) formulation:
90sks Dnk
s
2/1f k
H11n
1C
u
UCz
where = 0.4 denotes the dimensionless Karman constant and ks = a roughnessheight characterizing the bumpiness of the bed [L].
Manning-Strickler formulation:
where r is a dimensionless constant between 8 and 9. Parker (1991) suggested a value of r of 8.1 for gravel-bed streams.
Roughness height over a flat bed (no bedforms):
where Ds90 denotes the surface sediment size such that 90 percent of the surface material is finer, and nk is a dimensionless number between 1.5 and 3. For example, Kamphuis (1974) evaluated nk as equal to 2.
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
COMPARISION OF KEULEGAN AND MANNING-STRICKLER RELATIONSr = 8.1
Note that Cz does not vary strongly with depth. It is often approximated as a constant in broad-brush calculations.
1
10
100
1 10 100 1000
H/ks
Cz
Keulegan
Parker Version of Manning-Strickler
6/1
sk
H1.8Cz
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
1.00
10.00
100.00
1.00 10.00 100.00
Rb/ks
Cz
ETH 52
Gilbert 116
Parker Version of Manning-Strickler
6/1
s
b
k
R1.8Cz
TEST OF RESISTANCE RELATION AGAINST MOBILE-BED DATA WITHOUT BEDFORMS FROM LABORATORY FLUMES
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
NORMAL FLOW
Normal flow is an equilibrium state defined by a perfect balance between the downstream gravitational impelling force and resistive bed force. The resulting flow is constant in time and in the downstream, or x direction.
Parameters:
x = downstream coordinate [L]H = flow depth [L]U = flow velocity [L/T]qw = water discharge per unit width [L2T-1]B = width [L]Qw = qwB = water discharge [L3/T]g = acceleration of gravity [L/T2] = bed angle [1]b = bed boundary shear stress [M/L/T2]S = tan = streamwise bed slope [1]
(cos 1; sin tan S) = water density [M/L3]
As can be seen from Chapter 3, the bed slope angle of the great majority of alluvial rivers is sufficiently small to allow the approximations
1cos,Stansin
xB
x
gHxBS
bBx
H
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
UHBBqQUHq www Conservation of downstream momentum:
Impelling force (downstream component of weight of water) = resistive force
xBxSgHBsinxgHB b
gHSb
Reduce to obtain depth-slope product rule for normal flow:
NORMAL FLOW contd.
Conservation of water mass (= conservation of water volume as water can be treated as incompressible):
xB
x
gHxBS
bBx
H
gHSu
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
ESTIMATED CHEZY RESISTANCE COEFFICIENTS FOR BANKFULL FLOWBASED ON NORMAL FLOW ASSUMPTION FOR u*
The plot below is from Chapter 3
1
10
100
1 10 100 1000 10000 100000
Grav BritGrav AltaGrav IdaSand MultSand Sing
bfCz
H
50
bf
bfbfbf
bf
bankfull
bf D
HH,
SgHHB
Q
u
UCz
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
Relation for Shields stress at normal equilibrium:(for sediment mobility calculations)
gHSUC 2f
RELATION BETWEEN qw, S and H AT NORMAL EQUILIBRIUM
DR
HS
gDRb
DR
S
g
qC 3/23/12wf
3/12wf
gS
qCH
2/12/1z
2/12/1
f
SHgCSHC
gU or
Reduce the relation for momentum conservation b = gHS with the resistance form b = CfU2:
Generalized Chezy velocity relation
Further eliminating U with the relation for water mass conservation qw = UH and solving for flow depth:
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
ESTIMATED SHIELDS NUMBERS FOR BANKFULL FLOWBASED ON NORMAL FLOW ASSUMPTION FOR b
The plot below is from Chapter 3
25050
bf
50
bf
50
b50bf
DgD
QQ,
DR
SH
gDR
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02 1.E+04 1.E+06 1.E+08 1.E+10 1.E+12 1.E+14
Grav BritGrav AltaSand MultSand SingGrav Ida
Q
50bf
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
RELATIONS AT NORMAL EQUILIBRIUM WITH MANNING-STRICKLER RESISTANCE FORMULATION
6/1
sr
2/1f
3/12wf
k
HC
gS
qCH
RD
S
g
qk 10/710/3
2r
2w
3/1s
Relation for Shields stress at normal equilibrium:(for sediment mobility calculations)
10/3
2r
2w
3/1s
gS
qkH
2/13/26/1
sr
2/12/1
f
SHk
gSH
C
gU
6/1s
r2/13/2
k
g
n
1,SH
n
1U
Manning-Strickler velocity relation(n = Manning’s “n”)
Solve for H to find
Solve for U to find
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
BUT NOT ALL OPEN-CHANNEL FLOWS ARE AT OR CLOSE TO EQUILIBRIUM!
Flow into standing water (lake or reservoir) usually takes the form of an M1 curve.
Flow over a free overfall (waterfall) usually takes the form of an M2 curve.
A key dimensionless parameter describing the way in which open-channel flow can deviate from normal equilibrium is the Froude number Fr: gH
UFr
And therefore the calculation of bed shear stress as b = gHS is not always accurate. In such cases it is necessary to compute the disquilibrium (e.g. gradually varied) flow and calculate the bed shear stress from the relation
2fb UC
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
NON-STEADY, NON-UNIFORM 1D OPEN CHANNEL FLOWS:St. Venant Shallow Water Equations
0x
UH
t
H
Relation for water mass conservation (continuity):
Relation for momentum conservation:
2f
22
UCx
gHx
Hg
2
1
x
HU
t
UH
x = boundary (bed) attached nearly horizontal coordinate [L]y = upward normal coordinate [L] = bed elevation [L]S = tan - /x [1]H = normal (nearly vertical) flow depth [L]Here “normal” means “perpendicular to the bed” and has nothing to do with normal flow in the sense of equilibrium.
xy
H
Bed and water surface slopes exaggerated below for clarity.
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
HYDRAULIC JUMP
subcritical
flow
supercritical
Supercritical (Fr >1) to subcritical (Fr < 1) flow.
1Fr1Fr
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
ILLUSTRATION OF BEDLOAD TRANSPORT
Double-click on the image to see a video clip of bedload transport of 7 mm gravel in a flume (model river) at St. Anthony Falls Laboratory, University of Minnesota. (Wait a bit for the channel to fill with water.) Video clip from the experiments of Miguel Wong.
rte-bookbedload.mpg: to run without relinking, download to same folder as PowerPoint presentations.
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
ILLUSTRATION OF MIXED TRANSPORT OF SUSPENDED LOAD AND BEDLOADDouble-click on the image to see the transport of sand and pea gravel by a turbidity current
(sediment underflow driven by suspended sediment) in a tank at St. Anthony Falls Laboratory. Suspended load is dominant, but bedload transport can also be seen. Video clip from
experiments of Alessandro Cantelli and Bin Yu.
rte-bookturbcurr.mpg: to run without relinking, download to same folder as PowerPoint presentations.
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
PARAMETERS CHARACTERIZING SEDIMENT TRANSPORT
qb = Volume bedload transport rate per unit width [L2/T]qs = Volume suspended load transport rate per unit width [L2/T]qt = qb + qs = volume total bed material transport rate per unit width
[L2/T]qw = Volume wash load transport rate per unit width [L2/T] = water density [M/L3]s = sediment density [M/L3]R = (s/) – 1 = sediment submerged specific gravity [1]D = characteristic sediment size (e.g. Ds50) [L]* = dimensionless Shields number, = (HS)/(RD) for normal flow [1]
Dimensionless Einstein number for bedload transport
Dimensionless Einstein number for total bed material transport
DRgD
qq b
b
DRgD
qq t
t
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
SOME GENERIC RELATIONS FOR SEDIMENT TRANSPORT
BEDLOAD TRANSPORT RELATIONS (e.g. gravel-bed stream)
Wong’s modified version of the relation of Meyer-Peter and Müller (1948)
Parker’s (1979) approximation of the Einstein (1950) relation
TOTAL BED MATERIAL LOAD TRANSPORT RELATION (e.g. sand-bed stream)
Engelund-Hansen relation (1967)
0495.0,97.3q c
5.1
cb
03.0,1)(2.11q c
5.4
c5.1b
2/5
ft )(
C
05.0q
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1D SEDIMENT TRANSPORT MORPHODYNAMICSwith applications to
RIVERS AND TURBIDITY CURRENTS© Gary Parker November, 2004
REFERENCESChaudhry, M. H., 1993, Open-Channel Flow, Prentice-Hall, Englewood Cliffs, 483 p.Crowe, C. T., Elger, D. F. and Robertson, J. A., 2001, Engineering Fluid Mechanics, John Wiley
and sons, New York, 7th Edition, 714 p.Gilbert, G.K., 1914, Transportation of Debris by Running Water, Professional Paper 86, U.S.
Geological Survey.Jain, S. C., 2000, Open-Channel Flow, John Wiley and Sons, New York, 344 p.Kamphuis, J. W., 1974, Determination of sand roughness for fixed beds, Journal of Hydraulic
Research, 12(2): 193-202.Keulegan, G. H., 1938, Laws of turbulent flow in open channels, National Bureau of Standards
Research Paper RP 1151, USA.Henderson, F. M., 1966, Open Channel Flow, Macmillan, New York, 522 p.Meyer-Peter, E., Favre, H. and Einstein, H.A., 1934, Neuere Versuchsresultate über den
Geschiebetrieb, Schweizerische Bauzeitung, E.T.H., 103(13), Zurich, Switzerland.Meyer-Peter, E. and Müller, R., 1948, Formulas for Bed-Load Transport, Proceedings, 2nd
Congress, International Association of Hydraulic Research, Stockholm: 39-64.Parker, G., 1991, Selective sorting and abrasion of river gravel. II: Applications, Journal of
Hydraulic Engineering, 117(2): 150-171. Vanoni, V.A., 1975, Sedimentation Engineering, ASCE Manuals and Reports on Engineering
Practice No. 54, American Society of Civil Engineers (ASCE), New York. Wong, M., 2003, Does the bedload equation of Meyer-Peter and Müller fit its own data?,
Proceedings, 30th Congress, International Association of Hydraulic Research, Thessaloniki, J.F.K. Competition Volume: 73-80.