-- SPECIAL PUBLICATION NO. 43
am- Setiond Destroyed Section
40 section
40
0 Hbl
20 FLAGLER BEACH PIER
w 0
t -. ST SWL
0 Bar ough Envelope-' "
-200 -100 0 100 200 300 400 500 600
Distance from NGVD Shoreline (feet)
Figure 9. Actual damage to the Flagler Beach Pier from the Thanksgiving Holiday Storm of 1984 (Balsillie., 1985c) used to test the Multiple Shore-Breaking Wave Transformation Computer Model for predicting wave behavior, longshore bar formation, and beach/coast erosion (after Balsillie. 1985b).
calculations. intersection of the rising shore and the elevation of 150 percent of the local mean
SEASONAL HIGH WATER CALCULATIONS tidal range above local mean high water ...
(para. 161.053(6)(a)1,F. S.). That is:
In addtion to short-term erosive
impacts due to extreme events, our coasts SHW = ( 1.5 MRT ) + MHW are subject to long-term changes. In 1972,
the State of Florida incorporated
consideration of storm/hurricane erosion in in which MRT is the mean range of tide affixing the location of Coastal Construction (commonly referred to as the mean tide Setback Lines. In 1978, it adopted a posture range). One might assume that the 30-year in which quantitative extreme event erosion erosion projection is to be assessed at the became the primary means by which Coastal SHW elevation. This is simply not true and, Construction Control Lines were located. It in fact, as we have seen earlier would be a was not until 1984, however, that long-term misapplication leading to spatial discontinuity erosion was officially recognized by the introducing computational error (Balsillie and State of Florida (Balsillie and Moore, 1985; Moore, 1985). Rather, the erosion Balsillie, State of Florida (Balsillie and Moore, projection needs to be assessed at MSL. 1985; Balsillie,1985f; 1985g; Balsillie and The required methodology specified by rule others, 1986; etc.,). In 1985, the Growth (para. 16B-33.024(3)(h), F. A. C., Management Amendment required republished as State of Florida, 1992, 62Bassessment of erosion at any coastal site for 33.024(3)(h)1., F. A. C.) specifies NGVD as which a permit application was tendered to the assessment elevation. The original rule, be assessed for a 30-year period, however, was written before compilation of Associated with 30-year long-term erosion datum elevations, foreshore slope, and sea projections is the local SeasonalHigh Water level rise information for the State. (SHWI) defined as ... the line formed by the Subsequent work (Balsillie, Carlen, and
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