Frequency of erosion for the combined impacts of tropical and extratropical storms

Figure G8.

Mean value with error limits for frequency of vertical erosion from tropical storms for 8-ft

mound located at 83-ft depth, crest depth of 75 ft

mound at the 83-ft depth. Table G9 summarizes the frequency-of-occurrence of

vertical erosion from extratropical storms for all six mound configurations in the

form of a mean value and +/- standard deviation error that can be added to or

subtracted from the mean value.

Frequency of erosion for the combined impacts of tropical and

extratropical storms

For most sites it is probably only practical (and cost effective) to replace any

lost cap material due to erosion on a yearly basis. Therefore, for sites that

experience both tropical and extratropical storms, the potential for vertical

erosion from the combined impacts of both types of storms over a year's time

must be considered. Proper design of a cap should consider both the episodic

erosion from the less frequently occurring severe storms and the cumulative

erosion from normal storm activity (average intensity storms experienced every

year) experienced over a period of years. If this is not done, then after say 5 to

20 years of annual erosion, the remaining erosion thickness could fall below the

design level (say a 100-year return frequency erosion event).

G25

Appendix G Procedures for Conducting Frequency-of-Erosion Studies