X. HIGHER HIGH WATER 
Definitions 
The existence of daily and semidaily constituents in the tide gives rise to differences 
in consecutive high waters as well as to differences in consecutive low waters. As a 
rule, the two high waters of a day differ in height, the higher being designated the 
higher high water and the lower the lower high water. 
On days when but one high water occurs, the rule for determining whether it 
should be designated as the higher high or lower high is framed in the same way as 
for the similar case of low water. The single high water is given the name opposite 
that of the preceding high water; that is, if the preceding high water was the higher 
high water of the day, then the single high water in question is designated as the lower 
high water, and vice versa. Thus, in the column of high waters in the tabulation of 
Figure 16, the single high water on the 20th will be designated as lower high water, 
since the immediately preceding high water is a higher high water. 
Where the tide becomes diurnal—that is, where but one high and one low water 
occur in a day—the single high water obviously is a higher high water, for it is the 
merging of the lower high water and higher low water that gives rise to the diurnal 
tide. 
Relation to Lower Low Water 
Manifestly the relation of higher high water to the rise of the tide is of a similar 
nature to that which lower low water bears to the fall of the tide. Corresponding 
to low-water diurnal inequality is high-water diurnal inequality, which is the difference 
between high water and higher high water. As distinguished from higher high water, 
high water refers to the average high water, whether for the day, month, or year. 
Diurnal inequality depends on the relative amplitudes of the daily and semidaily 
tidal constituents and also on their phase relations. With given amplitudes of the 
two constituents, the diurnal inequality may exist principally in the high waters, 
principally in the low waters, or equally in the high and low waters, depending on the 
phase relations of the daily and semidaily constituents. At most places the high- 
water and low-water diurnal inequalities differ. As mentioned in the section on lower 
low water, on the Atlantic coast of the United States the high-water inequality is the 
greater, while on the Pacific coast it is the low-water inequality that is the greater. 
However, the daily constituent of the tide has a small amplitude on the Atlantic coast, 
so that, notwithstanding the fact that on this coast the high-water inequality is the 
greater, it is relatively small. 
Variations 
Since the relation of higher high water to the rise of the tide is similar to that of 
lower low water to the fall, it follows that the variations in higher high water will 
be much the same as those in lower low water. These variations may be summarized 
as follows: 
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