The bed material size distribution of a sand bed channel is shown in Table 3.6.

Table 3.6. Sand Bed Material Size Distribution.

Size Range

Percent of Total Weight

(mm)

in Size Range

.002 - .0625

0.8

.0625 - .125

4.4

.125 - .250

14.2

.250 - .500

74.9

.500 - 1.00

5.0

1.00 - 2.00

0.5

2.00 - 4.00

0.2

From the grain size analysis calculate the following statistics: the geometric mean of each

fall velocity of each size range.

The geometric mean is calculated as the square root of the product of the end points of a given

size range.

For the first size range:

Di = [(0.002) (.0625)]1/2 = 0.011 mm.

Likewise for the remainder of the size ranges, the results are summarized in Table 3.7.

The effective diameter (Dm) of the sample distribution is calculated with the use of Equation

3.12 in Section 3.2.4.

n

i=1 pi Dsi

Dm =

100

(0.8) (0.011mm) + (4.44) (0.088mm) + ....(0.3) (2.83mm)

n

i=1 pi Dsi

Dm =

=

100

100

34.2

Dm = 100 = 0.34 mm ; which lies in the sand size.

3.52

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