FLORIDA GEOLOGICAL SURVEY
interface elevation but does persist long enough for the beach to be eroded and the coast is attacked by storm waves, 3) the 2combined storm tide does not rise above the beach-coast interface elevation and is short enough in duration so that only the nearshore and beach are affected, and 4) the Hb extreme event remains out at sea so that impact is indirect (i.e., a combined total storm tide does not or only fractionally (m) 0 reaches the shore) and storm waves primarily affect the nearshore and beach.
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The combined total storm tide used here is defined by Dean and others (1989) as the V storm surge due to astronomical tide, wind stress, barometric pressure, and breaker (m) s0 zone dynamic setup, which defines the active phenomena for scenarios 1, 2, and 3 (i.e., the sterm i de event). Scenario 4 40 .... includes only the effects of breaking wave 1 2 3 4 5 6 7 8 9 101112 activity, including dynamic wave setup, and Day is termed the stenn wave event. Scenarios Figure 8. Example of the quick response and 1 and 2 are those which, depending on recovery of the beach to storm wave storm strength, duration, continental slope, activity, Pensacola Beach, Florida, December and approach angle, usually produce the 1974;the storm peak occurred on December design erosion event (Balsillie, 1984,1985a, 7 (data courtesy of James P. Morgan, 1985b, 1986). Probabilistically, the personal communications). frequency of occurrence increases from scenario 1 to 4. 1986; Savage and Birkemeier, 1987), for events described by scenarios 1, 2 and 3 Under certain circumstances of event above. Beach recovery following the effects longevity, astronomical tides, and nearshore of a storm wave event (i.e., scenario 4) was slopes, exceptions can occur. One such recorded by James P. Morgan at his exception occurred when Hurricane Gilbert Pensacola Beach, Florida, home (Figure 8); struck Cancun, Mexico in 1988. Because within a day following storm wave there is essentially no continental shelf and abatement, the beach had recovered to its nearshore slopes are steep, all eroded sand pre-storm width. from Cancun's beaches was removed and natural beach recovery was not possible. The magnitude of seasonal shoreline Potentially, other exceptions can occur change mayvaryfrom year-to-year, since for where, for instance, submarine canyons any site some years may have more frequent might act as a sediment transport conduit and intense storm tide and wave activity and sand is irremeably lost from the littoral than other years. Horizontal shoreline shifts system. For most shores, however, due to direct storm and hurricane impacts continental shelves are wide and nearshore are now usually recorded. However, for slopes gentle enough that beach recovery to storms that do not directly impact the shore pre-storm dimensions following single storm (i.e., are far out at sea, for example Tropical impact occurs in a period of one to several Storm Juan (Clark, 1986) which affected days (Birkemeier, 1979; Bodge and Kriebel, Florida) but generate storm waves that do
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