Critical Depth When the Bed Material Movement Would Stop
(a) Given velocity V of 2.0 ft/s and bed material size D50 of 0.305 mm = 0.001 ft, determine
the critical depth y for no bed material movement.
4.94 x 10 -7 V 6
(4.94 x 10 -7 ) 2.0 6
y=
=
= 31.6 ft
2
2
D
0.001
(b) Given velocity V of 2.0, 8.0 and 16 ft/s and bed material size D50 of 152 mm = 0.5 ft,
determine the critical depth y when bed material movement would stop.
V = 2 ft/s
4.94 x 10 -7 V 6
(4.94 x 10 -7 ) 2.0 6
y=
=
= 0.0001 ft
D2
0.5 2
There would not be any bed material movement at this velocity.
V = 8 ft/s
4.94 x 10 -7 V 6
(4.94 x 10 -7 ) 8.0 6
y=
=
= 0.52 ft
D2
0.5 2
V =16 ft/s
4.94 x 10 -7 V 6
(4.94 x 10 -7 ) 16.0 6
y=
=
= 33.28 ft
D2
0.5 2
Would this depth occur? No. Why not? The coarser material would armor the bed.
3.66
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