SPECIAL PUBLICATION NO. 43
return the upper portions of the slope to plane that is relevant to the surf base. For a normal slope status. relatively short experiment or field study, MWL or SWL references are suitable to
What point estimator of wave represent the time frame of the experiment parameters, representing the appropriate or study. Such referenced results, however, force element, does one subscribe for an may not be comparable to results referenced extreme average measure of the to MSL at other localities. For this reason, astronomical tide, say for MHW? One does all applicable datums ... MSL, MWL, and not apply such point estimators for wave SWL, where known ... collectively termed transformation synergistic applications, Design Water Levels (DWLs), should be because none would be appropriate. Hence, provided in documentation of results. unless an average sea level (MSL or MTL) is
combined with an average wave height, one SEA LEVEL RISE is mixing "apples and oranges". It is
imperative when undertaking such a task, So far, we have but in passing we render the task to simplest terms. For mentioned the effects of sea level rise, instance, when transforming waves to the recalling that the primary difference between point of shore-breaking, including any wave NGVD and MSL (or MTL) is sea level rise. In reformation and rebreaking, the waves an historical context, the effect of sea level should be expressed as an average wave rise on the current metonic period has, thus height or, perhaps, root-mean-square wave far, been insignificant from a surveying height since these measures include all perspective. Its future effect, however, waves of record. Do not use the significant remains controversial (e.g., Titus and Barth wave height, average of the highest 10 per (1984) and Titus (1987) versus Michaels cent of heights, average of the highest 1 per (1992), to mention but only several cent of wave heights, etc. Whether or not a published works among a vast number on significant zero wave energy component is the subject). Other work indicates details of included depends on the purpose of the work sea level reversals or pulses (Tanner, 1992, (Balsillie, 1993b). Any conversion of the 1993), also characterized as crescendos average wave height to extreme wave height (Fairbridge, 1989). measures of Table 4, say for design
purposes, is accomplished by converting the There are certain applications where average measure, but only after wave temporal specifications of sea level rise are transformation as an average height has of potential consequence. Hence, from a occurred. Kraus and others (1991) note the data management and processing viewpoint, importance of the average wave height and it becomes in certain cases necessary to tout its use to be the "... "Rosetta stone' start with NGVD and calculate the relative for conversion ...", no less important is the date-certain sea level rise component. The proper application of the surf base (MSL) result, of course, becomes the date-certain which becomes the Rosetta Stone for MSL (or MTL). For the 1960-1978 National referencing tide and wave phenomena. Tidal Datum Epoch, the following relationship Another good reason for using averages assessed in British Imperial units is posited: throughout any numerical transformation
process is because one is often unable to MSL0 = NGVD + c (D 1969.5) determine from published results if the
transformation methodology is truly where MSLo is the date-certain value for commutative. MSL (or MTL), c = 0.0060 for Florida's east Coast), c = 0.0064 for Florida's Lower Gulf
MSL is, therefore, the only datum Coast, and c = 0.0069 for the Florida
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