EM 1110-2-1100 (Part II)
30 Apr 02
Example Problem II-8-2 (Continued)
Table II-8-16
Calculation of djetty for Storm Event 1
Water Level Exceedance Frequency (percent)
90
70
50
30
10
H0'/L0
0.0216
0.0216
0.0216
0.0216
0.0216
Jetty head
dijettyA (m)
12.6
12.8
13.0
13.2
13.5
dijettyA/H0'
2.06
2.09
2.12
2.15
2.20
η/H0'
<0
<0
<0
<0
<0
η (m)
0
0
0
0
0
djettyA (m)
12.6
12.8
13.0
13.2
13.5
Nearshore jetty trunk
dijettyC (m)
4.6
4.8
5.0
5.2
5.5
dijettyC/H0'
0.75
0.78
0.82
0.85
0.90
η/H0'
0.053
0.050
0.046
0.043
0.040
η (m)
0.3
0.3
0.3
0.3
0.2
djettyC (m)
4.9
5.1
5.3
5.5
5.7
Estimation of H1/3 at Jetty. Now significant wave heights at the jetty Hsjetty can be estimated. Calculation steps are
listed below and results for Event 1 at the jetty head and nearshore trunk segment are given in Table II-8-17.
(1) Calculate djetty/H0N, where djetty is the combined tide, storm surge, and wave setup water level at the
jetty (Table II-8-16).
(2) Estimate ratio of H1/3 at the jetty Hsjetty to H0N from Figure II-8-25.
(3) Calculate Hsjetty from ratio in step (2). Note in this example that this is a breaking wave. Also note
that the higher H0N values lead to higher H1/3 values in the breaker zone, if d and H0N/L0 are held constant (because
of the gentle slope of the lines in the left portion of Figure II-8-25). Thus the extreme measured Hs values selected
for design analysis can be expected to give extreme nearshore wave heights in the surf zone.
After these calculations are completed for all 33 storm events and 5 water levels, there are a total of 33 5 = 165
event values of Hsjetty at the jetty head and at each of the two trunk sections.
Example Problem II-8-2 (Sheet 11 of 21)
Hydrodynamic Analysis and Design Conditions
II-8-45
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