EM 1110-2-1100 (Part II)
30 Apr 02
II-8-7. Interdependence of Processes During Severe Events
a. Design importance.
(1) The interdependence of processes during severe events is a critical consideration for design. For
example, an extreme wave event is usually caused by a severe storm which also typically generates extreme
occurrences of wind, water level, infragravity waves, and currents (Figure II-8-33). The true probability of
occurrence of the combined extremes is higher than would be expected if each of these processes were
analyzed separately and treated as independent of each other.
(2) Without knowledge of the interdependence of processes, designs would be based on a chosen
nonexceedance probability for each process critical to the design. This design condition tends to be
conservatively high, since extremes at the design level of occurrence are unlikely to all occur together.
b. Procedures for estimating realistic design events, probabilities, and return periods. The approach
used in Example Problem II-8-2 illustrates one approach by which data may be used to consider both water
levels and wave heights in design. Another simplified approach which considers wind, surge level, and Hs
is presented in CIRIA/CUR (1991) (pp 223-225). The EST provides a convenient, and more comprehensive,
method for taking advantage of historical information to estimate realistic design events. It is often important
to consider storm duration in estimating design events.
II-8-8. References
American Society of Civil Engineers 1993
American Society of Civil Engineers. 1993. ASCE Standard, Minimum Design Loads for Buildings and Other
Structures, ASCE 7-93, a revision of ANSI/ASCE 7-88, American Society of Civil Engineers, New York.
Battjes 1972
Battjes, J. A. 1972. "Long-Term Wave Height Distribution at Seven Stations around the British Isles,"
Peutchen Hydr. Zeit, Band 25, Hefty, pp 179-189.
Batts, Russell, and Simiu 1980
Batts, M. E., Russell, L. R., and Simiu, E. 1980. "Hurricane Wind Speeds in the United States," J. Struct.
Div., American Society of Civil Engineers, Vol 100, No. STIO, pp 2001-2015.
Blom 1958
Blom, G. 1958. Statistical Estimates and Transformed Beta-Variables, Wiley, New York.
Bowers 1992
Bowers, E. C. 1992. "Low Frequency Waves in Intermediate Water Depths," Proceedings of the 23rd
International Conference on Coastal Engineering, American Society of Civil Engineers, pp 832-845.
Carter and Draper 1988
Carter, D. J. T., and Draper, L. 1988. "Has the North-East Atlantic Become Rougher?" Nature, Vol 332,
No. 7, p 494.
Hydrodynamic Analysis and Design Conditions
II-8-57
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