General Instructions: Modified critical shear stress (Komar, 1987 and 1996) and critical unit discharge
(Bathurst, 1987) approaches to predict sediment entrainment when D > 2 mm (gravels, cobbles, and
boulders)(Komar, 1987 and 1996). If the critical shear stress value for a given particle is less than the channel
boundary shear stress value, the particle will be entrained. If the critical shear stress value for a given particle is
greater than the channel boundary shear stress value, the particle will not be entrained. If the critical unit
discharge value for a given particle is less than the total unit discharge value, the particle will be entrained. If the
critical unit discharge value is greater than the total unit discharge value, the particle will not be entrained.
Highlighted yellow cells are obtained from a flow model (e.g., HEC-RAS) or cross section analayzer (e.g.,
WinXSPro) based on reference reach and design channel characteristics. Blue cells are sediment data
parameters that populate once user enters sediment data (highlighted in green).
Instructions for A, B, C: Table A assesses particle stability in the reference reach. Table B assesses initial
particle stability in the stream simulation design channel based on sediment data obtained from the reference
reach. In Table C, particle sizes are adjusted to obtain similar mobility between the design channel and the
reference-reach channel or a desired stability for the key pieces. In addition to changing particle sizes,
adjustments in channel geometry and channel slope can be made to obtain similar mobility of the channel bed
and/or the desired stabilty of the key pieces.
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Table 4-7. Sediment Properties
Table 4-7. Sediment entrainment properties for different particle
sizes (modified from Julien, 1995). The Shield's parameter is for
the smallest number in the particle-size interval.
angle of Shield's
Particle size Particle size, Di repose, f parameter,
classification (mm) (degrees) t*
very large boulders > 2048 42 0.054
large boulders 1024-2048 42 0.054
medium boulders 512-1024 42 0.054
small boulders 256-512 42 0.054
large cobbles 128-256 42 0.054
small cobbles 64-128 41 0.052
very coarse gravels 32-64 40 0.05
coarse gravels 16-32 38 0.047
medium gravels 8.0-16 36 0.044
fine gravels 4.0-8.0 35 0.042
very fine gravels 2.0-4.0 33 0.039
very coarse sands 1.0-2.0 32 0.029
coarse sands 0.5-1.0 31 0.033
medium sands 0.25-0.50 30 0.048
fine sands 0.125-0.25 30 0.072
very fine sands 0.0625-0.125 30 0.109
coarse silt 0.0313-0.0625 30 0.165
medium silt 0.0156-0.0313 30 0.25
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Crit. q mobility 3.8%
Summary of flow hydraulics and particle mobility/stability for the reference-reach channel (XS4) and stream simulation design channel using the critical unit discharge approach. A.
Reference reach (XS4) hydraulics and particle mobility. B. Preliminary stream simulation design channel (XS7.5D) hydraulics and particle mobility. C. Stream simulation design
channel (XS7.5D) hydraulics and adjusted particle sizes to achieve similar particle mobility as the reference-reach channel.
Hydraulics Particle Mobility/Stability
Critical Unit
Active
Active Critical Discharge
Channel Particle
Channel to Entrain
Width Total Active Total Unit Size Unit
Recur- Dis- Dis- Flood- Chan- Flow Channel Dis- Unit Dis- Range Disharge D84 Particle D84 Particle
rence charge, charge, plain n nel n Width, W t Width, charge, qt charge, qa Channel D16 D50 D84 Measure, for qc-D50 Size, qc-D84 Mobile
3 3
Interval Q (ft /s) Qa (ft /s) Value Value (ft) W a (ft) (ft2/s) a (ft2/s) b slope, Sc (mm) (mm) (mm) bc (ft2/s)d (ft2/s)e (yes/no)
A. Reference reach cross section:
0.06 0.06 0 0.084 2.11 2.11 0.03 0.03 0.0500 16 33 70 0.34 0.87 1.12 no
0.36 0.36 0 0.084 3.26 3.26 0.11 0.11 0.0500 16 33 70 0.34 0.87 1.12 no
0.93 0.93 1 0.084 4.31 4.31 0.22 0.22 0.0500 16 33 70 0.34 0.87 1.12 no
1.84 1.84 2 0.084 5.36 5.36 0.34 0.34 0.0500 16 33 70 0.34 0.87 1.12 no
3.13 3.13 3 0.084 6.31 6.31 0.50 0.50 0.0500 16 33 70 0.34 0.87 1.12 no
4.87 4.87 5 0.084 7.16 7.16 0.68 0.68 0.0500 16 33 70 0.34 0.87 1.12 no
7.11 7.11 7 0.084 7.79 7.78 0.91 0.91 0.0500 16 33 70 0.34 0.87 1.12 no
9.79 9.79 10 0.084 8.36 8.36 1.17 1.17 0.0500 16 33 70 0.34 0.87 1.12 yes
12.89 12.89 13 0.084 8.94 8.94 1.44 1.44 0.0500 16 33 70 0.34 0.87 1.12 yes
16.63 16.63 17 0.084 9.30 9.30 1.79 1.79 0.0500 16 33 70 0.34 0.87 1.12 yes
21 21 21 0.084 9.62 9.62 2.16 2.16 0.0500 16 33 70 0.34 0.87 1.12 yes
25 25 25 0.084 9.93 9.93 2.56 2.56 0.0500 16 33 70 0.34 0.87 1.12 yes
31 31 31 0.084 9.96 10.00 3.11 3.09 0.0500 16 33 70 0.34 0.87 1.12 yes
37 37 37 0.084 10.50 10.00 3.53 3.71 0.0500 16 33 70 0.34 0.87 1.12 yes
44 44 44 0.084 11.17 10.00 3.91 4.37 0.0500 16 33 70 0.34 0.87 1.12 yes
2 51 51 51 0.084 11.85 10.00 4.29 5.09 0.0500 16 33 70 0.34 0.87 1.12 yes
59 59 58 0.084 12.52 10.00 4.67 5.85 0.0500 16 33 70 0.34 0.87 1.12 yes
67 67 66 0.084 13.26 10.00 5.05 6.70 0.0500 16 33 70 0.34 0.87 1.12 yes
75 75 74 0.084 15.15 10.00 4.95 7.50 0.0500 16 33 70 0.34 0.87 1.12 yes
85 85 82 0.084 17.17 10.00 4.95 8.50 0.0500 16 33 70 0.34 0.87 1.12 yes
95 95 91 0.084 18.00 10.00 5.28 9.50 0.0500 16 33 70 0.34 0.87 1.12 yes
100 106 106 100 0.084 18.79 10.00 5.64 10.60 0.0500 16 33 70 0.34 0.87 1.12 yes
118 118 110 0.084 19.29 10.00 6.12 11.80 0.0500 16 33 70 0.34 0.87 1.12 yes
B. Preliminary stream simulation design channel with a channel-bed gradient of 3.78%
0 0 0.028 0.040 4.62 4.62 0.05 0.05 0.0378 16 33 70 0.34 1.19 1.54 no
2 2 0.028 0.040 7.43 7.43 0.21 0.21 0.0378 16 33 70 0.34 1.19 1.54 no
4 4 0.028 0.040 7.51 7.51 0.56 0.56 0.0378 16 33 70 0.34 1.19 1.54 no
8 8 0.028 0.040 7.60 7.60 1.03 1.03 0.0378 16 33 70 0.34 1.19 1.54 no
12 12 0.028 0.040 7.69 7.69 1.58 1.58 0.0378 16 33 70 0.34 1.19 1.54 yes
17 17 0.028 0.040 7.78 7.78 2.22 2.22 0.0378 16 33 70 0.34 1.19 1.54 yes
23 23 0.028 0.040 7.86 7.86 2.92 2.92 0.0378 16 33 70 0.34 1.19 1.54 yes
29 29 0.028 0.040 8.06 7.90 3.66 3.73 0.0378 16 33 70 0.34 1.19 1.54 yes
37 37 0.028 0.040 8.33 7.90 4.43 4.67 0.0378 16 33 70 0.34 1.19 1.54 yes
45 45 0.028 0.040 8.60 7.90 5.23 5.69 0.0378 16 33 70 0.34 1.19 1.54 yes
2 54 54 0.028 0.040 8.87 7.90 6.05 6.78 0.0378 16 33 70 0.34 1.19 1.54 yes
63 63 0.028 0.040 9.14 7.90 6.90 7.96 0.0378 16 33 70 0.34 1.19 1.54 yes
73 73 0.028 0.040 9.40 7.90 7.77 9.20 0.0378 16 33 70 0.34 1.19 1.54 yes
84 83 0.028 0.040 9.81 7.90 8.52 10.52 0.0378 16 33 70 0.34 1.19 1.54 yes
95 94 0.028 0.040 10.78 7.90 8.78 11.91 0.0378 16 33 70 0.34 1.19 1.54 yes
100 107 106 0.028 0.040 10.92 7.90 9.76 13.36 0.0378 16 33 70 0.34 1.19 1.54 yes
119 118 0.028 0.040 10.85 7.90 10.97 14.88 0.0378 16 33 70 0.34 1.19 1.54 yes
C. Adjusted stream simulation design channel
0 0 0.028 0.040 4.62 4.62 0.05 0.05 0.0378 16 33 70 0.34 1.19 1.54 no
2 2 0.028 0.040 7.43 7.43 0.21 0.21 0.0378 16 33 70 0.34 1.19 1.54 no
4 4 0.028 0.040 7.51 7.51 0.56 0.56 0.0378 16 33 70 0.34 1.19 1.54 no
8 8 0.028 0.040 7.60 7.60 1.03 1.03 0.0378 16 33 70 0.34 1.19 1.54 no
12 12 0.028 0.040 7.69 7.69 1.58 1.58 0.0378 16 33 70 0.34 1.19 1.54 yes
17 17 0.028 0.040 7.78 7.78 2.22 2.22 0.0378 16 33 70 0.34 1.19 1.54 yes
23 23 0.028 0.040 7.86 7.86 2.92 2.92 0.0378 16 33 70 0.34 1.19 1.54 yes
29 29 0.028 0.040 8.06 7.90 3.66 3.73 0.0378 16 33 70 0.34 1.19 1.54 yes
37 37 0.028 0.040 8.33 7.90 4.43 4.67 0.0378 16 33 70 0.34 1.19 1.54 yes
45 45 0.028 0.040 8.60 7.90 5.23 5.69 0.0378 16 33 70 0.34 1.19 1.54 yes
2 54 54 0.028 0.040 8.87 7.90 6.05 6.78 0.0378 16 33 70 0.34 1.19 1.54 yes
63 63 0.028 0.040 9.14 7.90 6.90 7.96 0.0378 16 33 70 0.34 1.19 1.54 yes
73 73 0.028 0.040 9.40 7.90 7.77 9.20 0.0378 16 33 70 0.34 1.19 1.54 yes
84 83 0.028 0.040 9.81 7.90 8.52 10.52 0.0378 16 33 70 0.34 1.19 1.54 yes
95 94 0.028 0.040 10.78 7.90 8.78 11.91 0.0378 16 33 70 0.34 1.19 1.54 yes
100 107 106 0.028 0.040 10.92 7.90 9.76 13.36 0.0378 16 33 70 0.34 1.19 1.54 yes
119 118 0.028 0.040 10.85 7.90 10.97 14.88 0.0378 16 33 70 0.34 1.19 1.54 yes
a. qt = Q / W t , where qt is total unit discharge for the cross section, Q is discharge, and W t is total flow width for the cross section.
b. qa = Qa / W a, where qa is the unit discharge for the active channel (ft 2/s), Qa is discharge in the active channel (ft 3/s), and W a is flow width of the active channel (ft).
c. b = 1.5(D84/D16)-1, where b is the ratio of the D84 percentile particle size (ft) and the D50 percentile particle size (ft).
d. qc-D50 = 0.15 (g)0.5 (D50)1.5 (S)-1.12 , where qc-D50 is the critical unit discharge to entrain the D50 particle size (ft2/s), g is gravity acceleration (ft/s 2), and Sc is bed slope.
e. qc-D84 = qc-D50 (D84/D50)b, where qc-D84 is the critical unit discharge to entrain the D50 particle size (ft2/s).
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Crit. q mobility 3.8%
A. Reference Reach
Step A1: Determine flow hydraulics in the reference reach using HEC-RAS or WinXSPro (this has been done for you).
Step A2: Enter D16, D50, and D84 particle sizes from the reference reach (mm).
Step A3: Calculate b and qc-D50 (these calculations have been done for you).
Step A4: Calculate qc-D84 (this calculation has been done for you).
Step A5: Determine D84 particle mobility by comparing qc-D84 to qc (fill in last column, yes or no).
Note: If qc-D84 is less than qc, the particle is mobile.
3
Step A6: At what discharge is the D84 particle mobilized? SME answer: At discharges greater than 130 ft /s.
D16 (mm) D50 (mm) D84 (mm)
16 33 70
B. Design Channel
Step B1: Determine flow hydraulics in the design channel using HEC-RAS or WinXSPro (this has been done for you).
Step B2: Enter D16, D50, and D84 particle sizes from the reference reach (mm).
Step B3: Calculate b and qc-D50 (these calculations have been done for you).
Step B4: Calculate qc-D84 (this calculation has been done for you).
Step B5: Determine D84 particle mobility by comparing qc-D84 to qc (fill in last column, yes or no).
Note: If qc-D84 is less than qc, the particle is mobile.
Step B6: At what discharge is the D84 particle mobilized? SME answer: At discharges greater than 110 ft 3 /s.
Step B7: Do the particles in the design channel need to be adjusted to achieve similar particle mobility as in the reference reach (if yes, go to C)? SME answer: Yes.
D16 (mm) D50 (mm) D84 (mm)
16 33 70
C. Adjusted Design Channel
Step C1: Determine flow hydraulics in the design channel using HEC-RAS or WinXSPro (this has been done for you)
Step C2: Adjust the D16, D50, and D84 particle sizes by a certain percentage to obtain similar particle mobility in the design channel as in the reference reach.
Step C3: Calculate b, qc-D50, and qc-D84 (these calculations have been done for you).
Step C4: Determine D84 particle mobility by comparing qc-D84 to qc (fill in last column, yes or no).
Note: If qc-D84 is less than qc, the particle is mobile.
Step C5: How much do the particles sizes need to be increased to achieve similar particle mobility in the design channel as in the reference reach? See table below.
D16 (mm) D50 (mm) D84 (mm) Description
16 33 70 initial reference reach particle size
16 33 70 adjusted particle size in design channel
0.00 percent particle size adjustment
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Crit. q mobility 3.8%
Plot of unit discharge versus discharge showing when the D84 particle is mobilized in the
reference-reach channel and the stream simulation design channel. To achieve similar D84
particle mobility in the stream simulation design channel at the same flow as the reference-
reach channel, the D84 particle size was increased from 208 mm to 220 mm.
16
reference reach (XS4)
14 stream simulation design channel (XS7.5D)
12
effective unit discharge (ft2/s)
10 reference reach
qc-D84=8.23 ft2/s
D84=208 mm
8
6
4
prelim bed design
qc-D84=7.28 ft2/s
2 D84=208 mm
0
0 20 40 60 80 100 120 140
discharge (ft3/s)
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Crit. q KeyPieces 3.8
Summary of flow hydraulics and key piece particle stability for the reference-reach channel (XS4) and stream simulation design channel using the critical unit discharge approach. A.
Reference reach (XS4) hydraulics and key piece stability. B. Preliminary stream simulation design channel (XS7.5D) hydraulics and key piece stability. C. Stream simulation design
channel (XS7.5D) hydraulics and adjusted key piece particle sizes to achieve desired key piece particle stability.
Hydraulics Particle Mobility/Stability
Critical Unit
Active
Active Critical Discharge
Channel Particle
Channel to Entrain
Width Total Active Total Unit Size Unit
Recur- Dis- Dis- Flood- Chan- Flow Channel Dis- Unit Dis- Range Disharge D84 Particle D84 Particle
rence charge, charge, plain n nel n Width, W t Width, charge, qt charge, qa Channel D16 D50 D84 Measure, for qc-D50 Size, qc-D84 Stable
3 3
Interval Q (ft /s) Qa (ft /s) Value Value (ft) W a (ft) (ft2/s) a (ft2/s) b slope, Sc (mm) (mm) (mm) bc 2
(ft /s) d 2
(ft /s) e
(yes/no)
A. Reference reach cross section (key pieces):
0.06 0.06 0 0.084 2.11 2.11 0.03 0.03 0.0500 191 305 381 0.75 24.41 28.85 yes
0.36 0.36 0 0.084 3.26 3.26 0.11 0.11 0.0500 191 305 381 0.75 24.41 28.85 yes
0.93 0.93 1 0.084 4.31 4.31 0.22 0.22 0.0500 191 305 381 0.75 24.41 28.85 yes
1.84 1.84 2 0.084 5.36 5.36 0.34 0.34 0.0500 191 305 381 0.75 24.41 28.85 yes
3.13 3.13 3 0.084 6.31 6.31 0.50 0.50 0.0500 191 305 381 0.75 24.41 28.85 yes
4.87 4.87 5 0.084 7.16 7.16 0.68 0.68 0.0500 191 305 381 0.75 24.41 28.85 yes
7.11 7.11 7 0.084 7.79 7.78 0.91 0.91 0.0500 191 305 381 0.75 24.41 28.85 yes
9.79 9.79 10 0.084 8.36 8.36 1.17 1.17 0.0500 191 305 381 0.75 24.41 28.85 yes
12.89 12.89 13 0.084 8.94 8.94 1.44 1.44 0.0500 191 305 381 0.75 24.41 28.85 yes
16.63 16.63 17 0.084 9.30 9.30 1.79 1.79 0.0500 191 305 381 0.75 24.41 28.85 yes
21 21 21 0.084 9.62 9.62 2.16 2.16 0.0500 191 305 381 0.75 24.41 28.85 yes
25 25 25 0.084 9.93 9.93 2.56 2.56 0.0500 191 305 381 0.75 24.41 28.85 yes
31 31 31 0.084 9.96 10.00 3.11 3.09 0.0500 191 305 381 0.75 24.41 28.85 yes
37 37 37 0.084 10.50 10.00 3.53 3.71 0.0500 191 305 381 0.75 24.41 28.85 yes
44 44 44 0.084 11.17 10.00 3.91 4.37 0.0500 191 305 381 0.75 24.41 28.85 yes
2 51 51 51 0.084 11.85 10.00 4.29 5.09 0.0500 191 305 381 0.75 24.41 28.85 yes
59 59 58 0.084 12.52 10.00 4.67 5.85 0.0500 191 305 381 0.75 24.41 28.85 yes
67 67 66 0.084 13.26 10.00 5.05 6.70 0.0500 191 305 381 0.75 24.41 28.85 yes
75 75 74 0.084 15.15 10.00 4.95 7.50 0.0500 191 305 381 0.75 24.41 28.85 yes
85 85 82 0.084 17.17 10.00 4.95 8.50 0.0500 191 305 381 0.75 24.41 28.85 yes
95 95 91 0.084 18.00 10.00 5.28 9.50 0.0500 191 305 381 0.75 24.41 28.85 yes
100 106 106 100 0.084 18.79 10.00 5.64 10.60 0.0500 191 305 381 0.75 24.41 28.85 yes
118 118 110 0.084 19.29 10.00 6.12 11.80 0.0500 191 305 381 0.75 24.41 28.85 yes
B. Preliminary stream simulation design channel (key pieces) for a channel-bed gradient of 3.78%
0 0 0.028 0.040 4.62 4.62 0.05 0.05 0.0378 191 305 381 0.75 33.39 39.47 yes
2 2 0.028 0.040 7.43 7.43 0.21 0.21 0.0378 191 305 381 0.75 33.39 39.47 yes
4 4 0.028 0.040 7.51 7.51 0.56 0.56 0.0378 191 305 381 0.75 33.39 39.47 yes
8 8 0.028 0.040 7.60 7.60 1.03 1.03 0.0378 191 305 381 0.75 33.39 39.47 yes
12 12 0.028 0.040 7.69 7.69 1.58 1.58 0.0378 191 305 381 0.75 33.39 39.47 yes
17 17 0.028 0.040 7.78 7.78 2.22 2.22 0.0378 191 305 381 0.75 33.39 39.47 yes
23 23 0.028 0.040 7.86 7.86 2.92 2.92 0.0378 191 305 381 0.75 33.39 39.47 yes
29 29 0.028 0.040 8.06 7.90 3.66 3.73 0.0378 191 305 381 0.75 33.39 39.47 yes
37 37 0.028 0.040 8.33 7.90 4.43 4.67 0.0378 191 305 381 0.75 33.39 39.47 yes
45 45 0.028 0.040 8.60 7.90 5.23 5.69 0.0378 191 305 381 0.75 33.39 39.47 yes
2 54 54 0.028 0.040 8.87 7.90 6.05 6.78 0.0378 191 305 381 0.75 33.39 39.47 yes
63 63 0.028 0.040 9.14 7.90 6.90 7.96 0.0378 191 305 381 0.75 33.39 39.47 yes
73 73 0.028 0.040 9.40 7.90 7.77 9.20 0.0378 191 305 381 0.75 33.39 39.47 yes
84 83 0.028 0.040 9.81 7.90 8.52 10.52 0.0378 191 305 381 0.75 33.39 39.47 yes
95 94 0.028 0.040 10.78 7.90 8.78 11.91 0.0378 191 305 381 0.75 33.39 39.47 yes
100 107 106 0.028 0.040 10.92 7.90 9.76 13.36 0.0378 191 305 381 0.75 33.39 39.47 yes
119 118 0.028 0.040 10.85 7.90 10.97 14.88 0.0378 191 305 381 0.75 33.39 39.47 yes
C. Adjusted stream simulation design channel (key pieces)
0 0 0.028 0.040 4.62 4.62 0.05 0.05 0.0378 191 305 381 0.75 33.39 39.47 yes
2 2 0.028 0.040 7.43 7.43 0.21 0.21 0.0378 191 305 381 0.75 33.39 39.47 yes
4 4 0.028 0.040 7.51 7.51 0.56 0.56 0.0378 191 305 381 0.75 33.39 39.47 yes
8 8 0.028 0.040 7.60 7.60 1.03 1.03 0.0378 191 305 381 0.75 33.39 39.47 yes
12 12 0.028 0.040 7.69 7.69 1.58 1.58 0.0378 191 305 381 0.75 33.39 39.47 yes
17 17 0.028 0.040 7.78 7.78 2.22 2.22 0.0378 191 305 381 0.75 33.39 39.47 yes
23 23 0.028 0.040 7.86 7.86 2.92 2.92 0.0378 191 305 381 0.75 33.39 39.47 yes
29 29 0.028 0.040 8.06 7.90 3.66 3.73 0.0378 191 305 381 0.75 33.39 39.47 yes
37 37 0.028 0.040 8.33 7.90 4.43 4.67 0.0378 191 305 381 0.75 33.39 39.47 yes
45 45 0.028 0.040 8.60 7.90 5.23 5.69 0.0378 191 305 381 0.75 33.39 39.47 yes
2 54 54 0.028 0.040 8.87 7.90 6.05 6.78 0.0378 191 305 381 0.75 33.39 39.47 yes
63 63 0.028 0.040 9.14 7.90 6.90 7.96 0.0378 191 305 381 0.75 33.39 39.47 yes
73 73 0.028 0.040 9.40 7.90 7.77 9.20 0.0378 191 305 381 0.75 33.39 39.47 yes
84 83 0.028 0.040 9.81 7.90 8.52 10.52 0.0378 191 305 381 0.75 33.39 39.47 yes
95 94 0.028 0.040 10.78 7.90 8.78 11.91 0.0378 191 305 381 0.75 33.39 39.47 yes
100 107 106 0.028 0.040 10.92 7.90 9.76 13.36 0.0378 191 305 381 0.75 33.39 39.47 yes
119 118 0.028 0.040 10.85 7.90 10.97 14.88 0.0378 191 305 381 0.75 33.39 39.47 yes
a. qt = Q / W t , where qt is total unit discharge for the cross section, Q is discharge, and W t is total flow width for the cross section.
b. qa = Qa / W a, where qa is the unit discharge for the active channel (ft 2/s), Qa is discharge in the active channel (ft 3/s), and W a is flow width of the active channel (ft).
c. b = 1.5(D84/D16)-1, where b is the ratio of the D84 percentile particle size (ft) and the D50 percentile particle size (ft).
d. qc-D50 = 0.15 (g)0.5 (D50)1.5 (S)-1.12 , where qc-D50 is the critical unit discharge to entrain the D50 particle size (ft2/s), g is gravity acceleration (ft/s 2), and Sc is bed slope.
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Crit. q KeyPieces 3.8
A. Reference Reach
Step A1: Determine flow hydraulics in the reference reach using HEC-RAS or WinXSPro (this has been done for you).
Step A2: Enter D16, D50, and D84 particle sizes of the key pieces from the reference reach (mm).
Step A3: Calculate b and qc-D50 (these calculations have been done for you).
Step A4: Calculate qc-D84 (this calculation has been done for you).
Step A5: Determine D84 particle stability of the key pieces by comparing qc-D84 to qc (fill in last column, yes or no).
Note: If qc-D84 is less than qc, the particle is mobile.
3
Step A6: At what discharge is the D84 key piece particle mobilized? SME answer: At discharges greater than 370 ft /s.
D16 (mm) D50 (mm) D84 (mm)
191 305 381
B. Design Channel
Step B1: Determine flow hydraulics in the design channel using HEC-RAS or WinXSPro (this has been done for you).
Step B2: Enter D16, D50, and D84 particle sizes of the key pieces from the reference reach (mm).
Step B3: Calculate b and qc-D50 (these calculations have been done for you).
Step B4: Calculate qc-D84 (this calculation has been done for you).
Step B5: Determine D84 particle stability of the key pieces by comparing qc-D84 to qc (fill in last column, yes or no).
Note: If qc-D84 is less than qc, the particle is mobile.
Step B6: At what discharge is the D84 key piece particle mobilized? SME answer: At discharges greater than 370 ft 3 /s.
Step B7: Do the key piece particles in the design channel need to be adjusted to achieve greater stability (if yes, go to C)? SME answer: No.
D16 (mm) D50 (mm) D84 (mm)
191 305 381
C. Adjusted Design Channel
Step C1: Determine flow hydraulics in the design channel using HEC-RAS or WinXSPro (this has been done for you)
Step C2: Adjust the D16, D50, and D84 particle sizes by a certain percentage to obtain greater particle stability in the design channel.
Step C3: Calculate b, qc-D50, and qc-D84 (these calculations have been done for you).
Step C4: Determine D84 particle stability of the key pieces by comparing qc-D84 to qc (fill in last column, yes or no).
Note: If qc-D84 is less than qc, the particle is mobile.
Step C5: How much do the particles sizes need to be increased to achieve greater particle stability of the key pieces in the design channel? N/A
D16 (mm) D50 (mm) D84 (mm) Description
191 305 381 initial reference reach particle size
191.0 305.0 381.0 adjusted particle size in design channel
0 percent particle size adjustment
12/28/2011 2ed4ae45-71ea-4b26-a4da-974e8e93061e.xlsx Crit. q KeyPieces 3.8
e. qc-D84 = qc-D50 (D84/D50)b, where qc-D84 is the critical unit discharge to entrain the D50 particle size (ft2/s).