Critical Velocity for Beginning of Bed Material Movement
(a) Sand Size Bed Material
Given depth y is 3.66 m and bed material size D50 is 0.31 mm, what is the critical velocity Vc?
Vc = 6.19 y1/ 6 D1/ 3 = 6.19 x 3.661/ 6 x 0.000311/ 3 = 0.52 m / s
(b) Gravel Size Bed Material
Given depth y is 3.66 m and bed material size D50 Is 3.1 mm, what is the critical velocity Vc?
Vc = 6.19 y1/ 6 D1/ 3 = 6.19 x 3.661/ 6 x 0.00311/ 3 = 1.12 m / s
(c) Cobble size Bed Material
Given depth y is 3.66 and bed material size D50 is 128 mm, what is the critical velocity Vc?
Vc = 6.19 y1/ 6 D1/ 3 = 6.19 x 3.661/ 6 x 0.1281/ 3 = 3.88 m / s
Critical Size for Beginning of Bed Material Movement
Given depth y is 3.66 m and velocity V is 0.61 m/s, 1.22 m/s, 2.44 m/s, 3.66 m/s, and 4.88
m/s, respectively.
Determine the critical bed material size D50.
V = 0.61 m/s
0.0042 V 3
(0.0042) 0.613
Dc =
=
= 0.0005 m (0.50 mm)
y1/ 2
3.661/ 2
V = 1.22 m/s
0.0042 V 3
(0.0042) 1.223
Dc =
=
= 0.00399 m (3.99 mm)
y1/ 2
3.661/ 2
V = 2.44 m/s
0.0042 V 3
(0.0042) 2.44 3
Dc =
=
= 0.0319 m (31.9 mm)
y1/ 2
3.661/ 2
V = 3.66 m/s
0.0042 V 3
(0.0042 ) 3.66 3
Dc =
=
= 0.108 m (108 mm)
y1/ 2
3.661/ 2
3.60
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