D16 = 2.4 mm
D84 = 6.7 mm
D50 = 4.5 mm
D90 = 7.1 mm
The gradation coefficient is calculated by Equation 3.9:
D50 D84 1 4.5 mm 6.7 mm
1
G=
+
=
+
2
2 2.4 mm 4.5 mm
D16 D50
G = 1.67
Table 3.9. Gravel Bed Material Properties.
Percent of Bed
Percent
Material in this
Geometric
pIDI
Size Range
Finer
Size
Fall Velocity
Mean Size, Di
(pI)
(mm)
(mm)
(m/s)
.125 - 0.250
0.177
0.1
0.1
0.018
0.018
.250 - 0.500
0.354
1.6
1.7
0.566
0.046
.500 - 1.00
0.707
1.7
3.4
1.20
0.088
1.00 - 2.00
1.41
6.3
9.7
8.88
0.198
2.00 - 4.00
2.83
31.8
41.5
90.0
0.335
4.00 - 8.00
5.66
58.5
100.0
331.1
0.518
TOTAL
100
431.9
Pebble Count
The b axis (Intermediate length) of 100 particles were randomly picked up and measured on
a line in and along the flow of the Cache la Poudre River. The sampling was done by
walking in a straight line and picking up and measuring the particle at the big toe at each
step. The b axis lengths in meters are; 0.046, .189, .146, .436, 137, .280, .207 .226, .128,
.256, .262, .067, .088, .195, .259, .216, .177, .055, .226, .113, .201, .098, .134, .082, .016,
.140, .210, .159, .028, .195, .104, .192, .155, .098, .177, .146, .034, .040, .018, .256, .171,
.146, .104, .226, .192, .049, .226, .015, .110, .128, .082, .180, .067, .037, .162, .195, .110,
.128, .232, .021, .046, .159, .226, .177, .235, .192, .122, .015, .082, .223, .195, .070, .040,
.265, .192, .113, .143, .113, .155, .110, .098, .119, .226, .073, .113, .174, .241, .012, .049,
.192, .110, .082, .131, .043, .137, .171, .046, .131, .104, .192
Determine the D50, D16, D84, D90, and G of the bed material.
First decide on discrete size groups and then determine the number of particles in each
group.
Size Range
Class
Percent
(m)
No.
Finer
0.305 - 0.436
1
100
0.244 - 0.305
6
94
0.198 - 0.244
14
80
0.152 - 0.198
24
56
0.091 - 0.152
27
29
0.030 - 0.091
20
9
0.012 - 0.030
8
1
TOTAL
100
3.55
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