reduction factor, which varied with swl and significant wave height during the

course of each typhoon.

Overtopping-frequency relationships were calculated for 15 profiles along

the project area on the north shore of Cabras Island by application of the EST.

These relationships were computed for maximum conditions at intervals of 5, 10,

25, 50, and 100 years. Input for the EST included maximum overtopping rate

calculated for each of the 30 storms in the training set. The maximum over-

topping rate was calculated as described previously, using 100 independent

simulations of a 100-year time period. Maximum overtopping rates with

100-year return period illustrate variability along the coast (Figure 15). These

values represent mean results from the 100 simulations. Most profiles have

overtopping rates of about 0.07 m3/sec/m (0.7 cfs/ft) for existing conditions and

0.01 m3/sec/m (0.1 cfs/ft) for plan profiles. Existing profiles 6 and 28 have

reduced overtopping rates which are more like the plan overtopping rates, a

consequence of the natural berm present on these existing profiles. Tables of

overtopping-frequency relationship values for each profile are given in

Appendix C. Maximum expected overtopping rate values and standard

deviations are given in the tables for both existing and plan profiles.

Maximum overtopping rates for the full project length can be obtained from

the profile results. Profile overtopping rates are given as cfs per ft width. Since

profiles are at 61-m (200-ft) intervals, each profile overtopping rate can be

multiplied by 61 (200) to give total overtopping rate along the section of coast

represented by the profile. The first and last profiles are considered to represent

an 82-m (270-ft) width so that the full project length is included. Total over-

topping rates along the project area are summarized in Table 9 and Figure 16.

The planned project has a strong impact on reducing overtopping rates.

Stage-frequency relationships were calculated for seven storm surge stations

along the south side of Cabras Island by application of the EST. The relation-

ships were computed for maximum water level at return intervals of 5, 10, 25,

50, 75 and 100 years. Input for the EST included maximum water level calcu-

lated for each of the 30 storms in the training set. Maximum water level was

calculated as the linear superposition of storm surge, tide, and significant wave

effects, as discussed in Chapter 3. Tide levels of mean high water, mean sea

level, and mean low water were used in developing EST probabilities. Tables of

stage-frequency relationship values for each station are given in Appendix E.

In addition to the stage-frequency tables, values of wave parameters and

water level components for each storm at each station are given in Appendix F.

These tables show the relative importance of wave and surge components in

42

Chapter 5

Development of Overtopping and Stage-Frequency Relationships

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