V = 4.88 m/s
0.0042 V 3
(0.0042) 4.88 3
Dc =
=
= 0.266 m (255 mm)
1/ 2
1/ 2
y
3.66
Critical Depth When the Bed Material Movement Would Stop
(a) Given velocity V of 0.61 m/s and bed material size D50 of 0.305 mm, determine the
critical depth y for no bed material movement.
1.78 x 10 -5 V 6
(1.78 x 10 -5 ) 0.616
y =
=
= 9.86 m
2
2
D
0.000305
(b) Given velocity V of 0.61, 2.44, and 4.88 m/s and bed material size D50 of 152 mm,
determine the critical depth y when bed material movement would stop.
V = 0.61 m/s
1.78 x 10 -5 V 6
(1.78 x 10 -5 ) 0.616
y=
=
= 0.00004 m
D2
0.152 2
There would not be any bed material movement at this velocity.
V = 2.44 m/s
1.78 x 10 -5 V 6
(1.78 x 10 -5 ) 2.44 6
y=
=
= 0.16 m
2
2
D
0.152
V = 4.88 m/s
1.78 x 10 -5 V 6
(1.78 x 10 -5 ) 4.88 6
y=
=
= 10.4 m
D2
0.152 2
Would this depth occur? No. Why not? The coarser material would armor the bed.
3.8 SOLVED PROBLEMS FOR ALLUVIAL CHANNEL FLOW (ENGLISH)
3.8.1 PROBLEM 1 Sediment Properties and Fall Velocities
Generally, sediment sizes are given in mm for the English system. Therefore, the solution to
this problem is identical to the SI solution in Section 3.7.1.
3.61
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