EM 1110-2-1100 (Part II)
30 Apr 02
Example Problem II-8-2 (Continued)
Importance of wave breaking. In estimating design wave conditions, it is important to know whether waves are
breaking. Event values of H0'/L0 from Table II-8-13 plotted with the curve from Figure II-8-13 with bottom slope
of 1/100 show that all values of djetty at the jetty head are very near or smaller than the depth at which Hsjetty reaches
a maximum value during shoaling and breaking (Figure II-8-26). Thus, the jetty head can be considered as inside
the surf zone and subject to breaking waves for all of the storm events. Since the jetty trunk is in shallower water
than the head, it too will be subject to breaking waves for design.
Relationship to Hm0. The significant wave height analysis used in this example is based on statistics of crest-to-
trough wave heights in a train of irregular waves. This wave height parameter can differ significantly from the
energy-based significant wave height parameter Hm0, especially for low-steepness waves in shallow water. Some
design applications may require Hm0 instead of Hsjetty. If so, the event values of Hsjetty may be converted by the
procedure described in Part II-1.
Extremal wave height analysis at the jetty. Extremal wave height analysis is presented here only for the jetty head.
Similar analyses would be needed for jetty trunk sections, but they are omitted for brevity. Since the design waves
are inside the surf zone, water level can be expected to be a key parameter in determining design wave heights.
The equivalent deepwater wave steepness H0'/L0 and H0' also influence Hsjetty. Design wave estimates should
include due consideration of the influence of all three of these parameters: djetty, H0'/L0, and H0'.
The ACES "Extremal Significant Wave Height Analysis" application was applied to the 165 event values of Hsjetty
and the FT-I distribution function was selected as a good fit (Figure II-8-27). Confidence intervals of 95 percent
were also computed, which is approximately equivalent to 2 standard deviations.
Identification of surf zone conditions
Example Problem II-8-2 (Sheet 13 of 21)
Hydrodynamic Analysis and Design Conditions