VII. MEAN HIGH WATER 
Variations in Height of High Water 
The height to which high water rises varies from day. to day. Primarily these 
variations are related to the varying positions of the moon relative to earth and sun. 
These periodic variations were discussed briefly in Section II, Types of Tide. Super- 
imposed on these periodic variations are non-periodic variations due to the effects of 
wind and weather. The resulting variations from day to day are exemplified in Figure 
38 by the plottings of the heights of high water for the month of October 1947 at At- 
lantic City, Los Angeles, and Pensacola. ‘These represent, respectively, the typical 
variations in the semidaily, mixed and daily types of tide. 
The small circles in Figure 38 give the heights of each high water for the month, 
and to indicate clearly the succession, each high water is joined by a straight line to the 
preceding and succeeding high waters. At Atlantic City it is seen that there were two 
high waters each tidal day, succeeding high waters generally differing by several tenths 
of a foot and sometimes by as much as a foot or even more. For that month the 
lowest high water occurred on the morning of the 7th and the highest on the morning 
of the 31st, the difference between the two being 3.9 feet. The average range of tide 
at Atlantic City during that month, that is the average difference between the high 
and low waters was 4.0 feet, so that the difference between the highest and lowest of 
the high waters was very nearly the same as the average difference between the high 
and low waters. 
At Los Angeles, there were likewise two high waters each tidal day, but the differ- 
ences between succeeding high waters were generally greater than at Atlantic City. 
On the average the difference between the higher high waters and lower high waters 
for that month at Los Angeles was 1.1 feet, but several times this difference exceeded 
2 feet. This difference in the behavior of the high waters at Los Angeles arises from 
the fact that at Atlantic City the tide is of the semidaily type while at Los Angeles it 
is of the mixed type. 
For the month of October 1947, represented in Figure 38, the range of the tide 
at Los Angeles averaged 3.8 feet. The lowest high water occurred on the 6th and the 
highest on the 31st—almost exactly the same dates as for Atlantic City—the difference 
being 3.3 feet. : 
At Pensacola for the greater part of the month of October 1947 only one high 
water and one low water occurred. For the few days when two high waters occurred 
only the higher high water is plotted in Figure 38. The average range of the tide at 
Pensacola for that month, that is, the average difference in height between the higher 
high and lower low waters was 1.2 feet. The highest high water occurred on the 6th 
(with like heights on the 4th and 5th) and the lowest high water occurred on the Ist, 
the difference between the two being 1.4 feet. So that here during this month the 
difference in height between two high waters was greater than the average difference 
between the high waters and low waters of the month. 
The fluctuations in the heights of the high waters pictured in Figure 38 are due 
both to periodic tidal variations and to the effects of wind and weather. The latter 
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