Section 8

Tidal Waters

In Canada, daily tide tables are published for reference ports at major coastal locations such as Vancouver and Halifax.

For secondary ports, the differences in tidal heights and times are also published. The tidal times and heights at these locations are obtained by adjusting the reference port data.

Using the Tables

Each volume of the Canadian Tide and Current Tables contains certain tables in addition to the daily predictions. Two of these and the daily tables are used to find the height and time of the tide in secondary ports.

Table 3 lists each secondary port under its reference port. The daily tables for this port are used to calculate the tide at the secondary port. The table also shows the difference in height and time between the secondary ports and their reference ports.

Table 2 shows the ranges of mean, or average, and large tides.

Finding Tidal Predictions for a Secondary Port

To find the height and time of the tide for a secondary port requires five steps. Steps 1 through 5 below answer the question:

Step 1

Outer Wood Island is a secondary port, so the first step is to find its reference port. Table 3, below, indicates the reference port is Saint John because Outer Wood Island is listed among the other secondary ports under "on/sur Saint John".

Make a note of the reference port:

Port Saint John

Step 2

The Saint John Tide Table shows that the morning high tide on July 2 occurs at 0950 AST, and is 7.6 metres above datum. Write this down.

Step 3

Now it must be determined whether the 0950 high tide is mean or large. In other words, is it an average tide or one that is extreme in range?

Table 2 provides a benchmark for mean and large tides, for both high and low tides, at the reference port of Saint John. The height of 7.6 metrest predicted in the tide table is closer to the higher high water mean tide of 7.7 metres than the large tide of 9.0 metres. Thus the 0950 high tide is a mean tide.

Step 4

Having established that the 0950 high tide is a mean tide, return to Table 3 to find the time and height corrections for mean tides for the secondary port of Outer Wood Island.

Step 5

The last step is to apply the secondary port corrections to the time and height of the reference port. If Daylight Saving Time is in effect, Standard Time must be adjusted by adding one hour.

Port Time Height Type Saint John 0950 7.6m mean Outer Wood Is. -15 -2.4m     0935 5.2m      +100     ADST  1035

So, on July 2, the height of the morning high tide at Outer Wood Island is 5.2 metres, and it occurs at 1035 ADST.

Differences in Time Zone

Occasionally the time zone of a secondary port is different from its reference port. In this case, the secondary port's time zone is used in the prediction. The secondary port's time zone is shown in the third column of Table 3 as hours plus or minus Universal Time.

A Review of the Five Steps
to Find Tidal Predictions for a Secondary Port