- SPECIAL PUBLICATION NO. 43
size differences are significant. In this study, located to search for a solution (Table 1). however, we shall deal with relatively
straight, ocean-fronting beaches composed First, it might be reasonable to entirely of sand-sized material, inspect the relationship between astronomical tidal conditions and horizontal
DATA AND RESULTS seasonal shoreline shift, Vs, since the tidal condition essentially constitutes a signature
In an investigation of seasonal beach characteristic for each site (i.e., it can vary changes at Torrey Pines Beach, California, considerably depending on the coast under Aubrey and others (1976) state: "No field study). Horizontal seasonal shoreline shift is studies to date have been able to adequately defined as Vs = V.,max -Vmin where Vm. is quantify these wave-related sediment the largest measurement representing the redistributions." In approaching a widest seasonal beach, and V.,i,, is smallest quantitative solution(s) to the problem, it measurement representing the narrowest becomes prudent to identify the force and beach (in this paper V is the distance from response elements involved. Basic force an arbitrary permanent coastal monument to elements are identified to be: 1) astro- the shoreline at any one time). The mean nomical tides, 2) wave height, and 3) wave range of tide, hm, (.e., the difference steepness. Response elements are: 1) vol- between mean low water and mean high ume change, 2) change in beach elevation, water), is plotted against Vs in Figure 1. or 3) horizontal shoreline shift. While the While there is scatter in the plot, a general beach sediment might be viewed as a trend is apparent. response element, given the paucity of
information about temporal/spatial sediment In addition to astronomical tide variation as it impacts this problem, it may conditions, we know that wave climate must be prudent to treat sediment characteristics be considered and that it, like tidal (within the sand-sized range) as a property conditions, varies widely from coast to element (see section on Beach Sediments for coast. Selection of values for variables further discussion). given in Table 1 can be illustrated using time series plots of monthly averages for
The response element used here is shoreline shift and wave data. An example the horizontal shoreline shift. Fortunately, for Torrey Pines Beach, California, is plotted we are dealing with a measure which, in Figure 2, which represents two years of compared to the others, has the largest concurrently observed monthly averages for range in possible values. For example, shoreline position, wave height, wave period, vertical contour changes are less than 1-1/2 and sediment data (Nordstrom and Inman, to 2 meters, and volumetric changes would 1975; Pawka and others, 1976). Further, be 3 to 4 times less than horizontal shift the data have been smoothed by a three("rule-of-thumb" guidance suggested by U. point moving averaging sequence. S. Army (1984) and Everts and others Comparison of horizontal shoreline shifts and (1980)), while horizontal shift may range up wave heights suggests that for the months to tens of meters. from about December through April storm wave activity prevailed, resulting in a
Daft narrower beach, with lull conditions from about May through October coinciding with
While the amount of data available to beach widening. Hence, the average storm quantify seasonal variation in shoreline wave height, Hs, is that occurring from position is not large, 14 data sets for which December through April, and the average lull sufficient information appears to exist were wave height, HL, is that occurring from May
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