EM 1110-2-1100 (Part II)
30 Apr 02
Example Problem II-8-2 (Continued)
WAVES:
Measurements. Measurements are available over a period of 17 years from a wave gauge located in
-15.2-m depth MLLW. Events with Hs>6.1 m were selected for design analysis, a total of 33 cases. The maximum
Hs during each event and the corresponding Tp, storm surge, and water depth at the gauge are given in Table II-8-
13.
The data record represented in the table is quite long, and it is considered statistically representative of storm
events to which the site is exposed. It is used as the basis for design. Measured values of Tp can be taken as
representative of both the gauge and jetty locations. Measured values of Hs must be transformed between the
gauge location and jetty. Also, the design water level at the jetty must be estimated because it strongly affects
calculations of Hs.
Estimation of H0'. The equivalent deepwater wave height H0N is calculated as an intermediate step in estimating
wave height at the jetty. Refraction between gauge and jetty locations is assumed to be negligible in this example,
and values of H0N estimated from gauge data are also applicable to the jetty location. Steps in estimating H0N are
listed below and calculation results are given in Table II-8-13. The ACES application "Irregular Wave
Transformation" (Goda's Method) could be used to assist in these and subsequent calculations. It is advisable to
spot-check any ACES calculations with some manual calculations.
(1) Calculate L0 from known values of Tp , L0 = (gTp2)/(2π) = 1.56gTp2 (L0 in m).
(2) Calculate dgauge/L0 .
(3) Calculate Hs/L0 as an initial estimate of H0N/L0 (needed for using the curves in step (4)).
(4) Get shoaling coefficient Ks from Figure II-8-22.
(5) Calculate H0N from significant height at the gauge Hsgauge (Table II-8-13) as
Hsgauge
H0) '
(II-9-7)
Ks
(6) Calculate H0N/L0 to ensure that Ks from step (4) is valid. It may be necessary to repeat steps (4)-(6)
to arrive at a final value of H0N .
Example Problem II-8-2 (Sheet 5 of 21)
Hydrodynamic Analysis and Design Conditions
II-8-39
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