SPECIAL PUBLICATION NO. 43
Figure 7. Additional data could have been selected
as well as additional 3 CASE 1
2 Bermtanaf, = 0.085 combinations; however, 2 Len,- =1.7 .t the three illustrated 1 cases will more than
o0- us (SURF RASE)
suffice for our purposes.
.1 <102 f
The profiles of the three examples are plotted so that the MSL (Surf Base) 2 MHW +1.7 ft intercepts define the .- CASE 2 origins of the plots that tI '- te = 0.2
0 *MLt (SURF BASE) they may be compared. 1 .Horizontal differences of MHW intercept locations
are identified by vertical
dashed lines. Deviations f range from 10.2 to 25.6 2 feet, all of which are significant illustrating the CA 3 ML (SU ) inappropriate nature of tm. = 0.os s using MHW for such a
purpose. Again, as with extreme event impact
and seasonal shoreline -4 -I change, MHW shoreline .40 .s 10 0 30o so a So shifts are not comparable MaUrn sr S BASE SSaer (feet) from locality to locality
(the same would hold Figure 7. Long-term shoreine shift analysis. true for other datums
such as MHHW, MLW, MLLW, etc.). In fact, processes. if we evaluated long-term beach changes volumetrically, MHW or any of the other site THE SURF BASE specific extremal variable datums would result in precisely the same non- The preceding application/use examples, comparability problems of the extreme event while rigorously identifying inconsistencies and seasonal shoreline shift examples resulting from the use of extreme datum previously given. planes for coastal science and engineering purposes, have not specifically addressed We can approach the subject from a coastal processes in terms of the forces that different perspective. If MSL is not used as cause beach responses. a reference Surf Base plane, then what should be used? If one selects an extreme In order to understand how the samrf base tidal datum plane such as MHW, does it applies, one needs a basic understanding of represent a base to which aktological force how wave statistics are derived and applied. and response elements can be based? Does At a given water depth a wave train is a it have spatial continuity? Is it applied in a near-periodic set of waves with a conceptually correct sense? All of these characteristic average wave crest height H, questions need be directed toward coastal wave length L, period T, and having a
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