Example Problem II-8-2 (Continued)

Appropriate values for *d *and *T *are more subjective. An opposing current amplifies wave height. The amount of

amplification increases as Ω increases (Figure II-8-31). A value for *T *can be determined by considering that any

wave period consistent with the observed events is a likely possibility. Thus the smallest reasonable *T*p (designated

0.025 (Table II-8-13), can be used to estimate *T*pmin as follows:

)

2π *H*0

0.025 '

'

2

max

(II-8-9)

2π

)

)

)

(*H*0 in cm)

0.025 *g*

Return period values of *H*0' are given in Tables II-8-18 and II-8-19. For each return period, a maximum depth

(*d*jetty from Table II-8-18) and a minimum depth (10 m, corresponding to MLLW) were used for calculation, as

summarized in Table II-8-22. Maximum depth cases relate to jetty design and minimum depth cases to toe design.

Values of *R*H ranging from 1.13 to 1.23 indicate that currents could increase wave heights at the jetty head by

between 13 percent and 23 percent. A wave height increase of this magnitude has a major impact on design. Since

available estimates of current speed are speculative and the methods used to assess their impact are highly

simplified (uniform current field, waves coming in opposite direction from current, etc.), a site-specific physical

model study would be required in practice to complete the hydrodynamic design.

2

653

12.9

13.9

-0.26

0.58

1.23

-0.30

0.49

1.18

5

702

13.4

14.1

-0.26

0.56

1.19

-0.30

0.47

1.17

10

737

13.7

14.2

-0.25

0.55

1.17

-0.30

0.46

1.16

25

782

14.1

14.4

-0.25

0.54

1.15

-0.30

0.45

1.15

50

816

14.5

14.5

-0.25

0.53

1.14

-0.30

0.44

1.14

100

850

14.8

14.6

-0.25

0.52

1.13

-0.30

0.43

1.13

Example Problem II-8-2 (Sheet 19 of 21)

Hydrodynamic Analysis and Design Conditions

II-8-53

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