Figure 7.6. Common pier shapes.
Table 7.1. Correction Factor, K1,for
Table 7.2. Correction Factor, K2, for Angle of
Attack, θ, of the Flow.
Pier Nose Shape.
Shape of Pier Nose
K1
Angle
L/a=4
L/a=8
L/a=12
(a) Square nose
1.1
0
1.0
1.0
1.0
(b) Round nose
1.0
15
1.5
2.0
2.5
(c) Circular cylinder
1.0
30
2.0
2.75
3.5
(d) Group of cylinders
1.0
45
2.3
3.3
4.3
(e) Sharp nose
0.9
90
2.5
3.9
5.0
Angle = skew angle of flow
L = length of pier, m
Bed Condition
Dune Height m
K3
Clear-Water Scour
N/A
1.1
Plane bed and Antidune flow
N/A
1.1
Small Dunes
3> H > 0.6
1.1
Medium Dunes
9> H > 3
1.2 to 1.1
Large Dunes
H>9
1.3
Notes:
1.
The correction factor K1 for pier nose shape should be determined using Table 7.1
for angles of attack up to 5 degrees. For greater angles, K2 dominates and K1
should be considered as 1.0. If L/a is larger than 12, use the values for L/a = 12 as
a maximum in Table 7.2 and Equation 7.8.
7.17
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