EM 1110-2-1100 (Part II)
30 Apr 02
(b) Often extreme shallow-water waves are estimated with wave information from an offshore source.
Extreme waves in shallow water are typically greatly transformed from incident (often deepwater) waves due
to a variety of processes discussed in Part II-3 and 4. Consequently, the most extreme incident waves are not
necessarily design conditions when transformed to the shallow-water site. A sufficient range of incident wave
cases must be analyzed to ensure that the most extreme shallow-water cases are identified.
(c) In shallow water, the competing processes of shoaling (tending to increase wave height) and breaking
(decreases wave height in the surf zone) often create a point at which significant height reaches a maximum
value in the outer surf zone. That maximum value can be estimated from Figure II-8-12. It should be noted
that these values are H1/3 rather than the energy-based significant height Hm0 (Part II-1). The water depth at
which the maximum occurs is shown in Figure II-8-13.
(d) Design wave period can be estimated as a representative value for extreme wave conditions, as with
waves in deeper water. However, allowances must be made for a range of wave periods accompanying a
relatively fixed, depth-limited design Hs. In this case, it may be advisable to consider several design Tp values
to adequately represent the range of possibilities impacting design.
(e) Design wave direction is estimated based on measurements, hindcasts, or knowledge of extreme
storm characteristics. Due consideration must be given to shallow-water effects on wave direction (Part II-3).
(5) Extreme individual wave characteristics.
(a) Extreme individual waves can have heights on the order of 2Hs. The Rayleigh distribution function
(Part II-1) is usually sufficient for describing individual wave heights in coastal engineering applications,
even in extreme (but nondepth-limited) conditions. With the Rayleigh distribution function for individual
Hydrodynamic Analysis and Design Conditions