- SPECIAL PUBLICATION NO. 43
cause shoreline erosion, such , , erosion is usually not measured, a EXTREME EVENT TYPE
Dolan and others (1988) o Extratropical (Dolan,. Lins, and conducted an extensive study on Hayden, 1988) 1942-1984 extratropical storm activity, a Tropical (Neumann et al.
*Hurricane 1981) 1940-1980
assessed also in terms of storm H ne 1981) 1940-190 wave hours, for 41 years of data g
(1942 to 1984) along the Outer 4 Banks of North Carolina. These .
data (Figure 9) show a concerted 2 seasonal trend. In addition, the Total author extracted from Neumann 3' and others (1981) tropical storms X and hurricanes whose tracks A
E
came within about 250 miles of / the Outer Banks for the period & 21940 to 1980. These latter data, \ also plotted in Figure 9, are added / to the extratropical data (plotted / as a bold, solid line). Hence, the 1 total storm record is nearly represented and, except for only p-a few direct impacts, represent .4- storm wave events (i.e., scenario o ---" $ e-",
4 above). For the mid-Atlantic, JAN FEB MAR APR MAY JMUN JUL AUG SEP OCT NOV DEC about 35 storms occur per year Month on the average (about 26 winter Figure 9. Monthly average occurrences of extreme event events and 9 summer events), wave events for the Outer Banks of North Carolina. 93% of which are extratropical
events. In terms of storm wave duration, Beach Sediments Dolan and others (1988), determined using hindcast techniques that on the average, Beach sediments engender some storm waves occur for about 571 hours per interesting concerns. How we consider year (i.e., 24 days per year) for extratropical sediments depends upon whether storms off of the Outer Banks; winter storm granulometry is applied as a property waves persist for an average of 433 hours element or a response element, which in turn (i.e., 18 days), and summer storm waves has an effect on the dimensional about 156 hours (i.e., 6.5 days). These data configuration of a numerical representation. strongly correlate with the expectation of As an example, equation (1) requires an wider mid-Atlantic east coast summer additional parameter with units of L'1 for the beaches and narrower winter beaches, and equation to be unit consistent. Equation (2) illustrate the important fact that a large was rendered unit consistent by dividing by number... not a few ... winter storm events a granulometric parameter with a length are required to maintain a narrower winter dimension. If this is to be the applied case, beach relative to a wider summer beach. it is useful to note that when sedimentologic grain size is specified in S. I. units, the mean grain size and standard deviation moment measures have units of mm, while
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