History of tidal measurements in Canada

Canada has more than 100,000 miles of seacoast and some rather strange tide patterns. Learn about tides and currents, and how Canada developed a system for measuring them.

Importance of tidal records

The early days of tidal and current surveying in the 1930s, 40s and early 50s generally saw less development and funding.

Prior to the late 19th-century, tidal records used to be obtained in several major ports. They were used to provide tidal predictions for other ports based on differences. Halifax was one of the few places in Canada that had well-documented records available from 1851 to 1852, and again from 1860 to 1861.

An increasing number of shipping disasters in the St. Lawrence River and Gulf of St. Lawrence demonstrated the:

necessity of carrying out new tidal surveys
importance of publishing tide tables for Canadian waters

This led to the formation of a committee in 1884 to collect such information. Canada finally authorized further tidal observations in 1890, allowing the purchase of 3 new tide gauges and the processing of available records.

Systematic tidal surveys

Dr. W. Bell Dawson was appointed engineer-in-charge of the tidal survey in 1893. This marked the beginning of a systematic survey of tides and currents in Canadian waters. It would result in:

the ability to produce accurate predictions of tidal occurrences
a much improved understanding of the characteristics of tidal phenomena in Canada

In the late 19th-century, the typical self-recording tidal station was equipped with two stilling wells secured to the side of a wharf or crib. The wells were made of planking. One of the wells served as a float-operated recorder, and the other as a sight gauge.

A shelter was usually built over the well that housed the recorder. In the winter, heat had to be supplied by an oil lamp or small oil stove. These frequently broke and tended to produce smoke and smudge that settled on the clockwork. This meant that:

frequent cleaning and occasional repair was necessary
the gauges required constant monitoring, both to fuel the heat source, and to keep the mechanisms cleaned and working

The timing of the clock also had to be regulated once a week by telegraphic exchange.

Permanent gauging stations also required:

visiting on a regular basis
spirit levels run to yearly benchmarks

Benchmarks and datum references

Dr. Dawson considered establishing benchmarks and datum references important. He worked to re-establish datum references by:

levelling precisely
installing better benchmarks
carrying out tidal observations
documenting and publishing collected information

He later published:

Tide Levels and Datum Planes in Eastern Canada, 1917
Tide Levels and Datum Planes on the Pacific Coast, 1923

Dr. Dawson also saw the need to carry out short period tidal observations at many places to establish the tidal adjustment for secondary port predictions. The 1925 tide tables contained data for approximately 350 secondary ports. The tabulation and analysis of tidal records were time consuming and expensive before the computer age.

The first predictions computed for a Canadian port from harmonic constants were those for Halifax in 1891. Although these were published, they didn’t receive a wide circulation. The tide tables were supplied directly to the leading almanacs without charge in hopes that this would improve distribution.

In the following years, the tide tables were again supplied to almanacs, but were also distributed directly to newspapers and to steamship companies. The first set of tide tables printed for the department were those for Charlottetown, Pictou and St. Paul Island in 1898. The second set were those for Victoria and Sand Heads in 1901. By 1907, the tide tables were printed in 2 volumes, one volume for the eastern coast, and the other for the western coast.

Current surveys

Dr. Dawson also carried out current surveys. In 1894, his first current surveys were carried out in the Strait of Belle Isle and the Cabot Strait. In 1895, he surveyed the entrance to the St. Lawrence Estuary between Gaspé and Mingan. In 1896, he surveyed the channel between Anticosti Island and the Strait of Belle Isle.

The main objective of the surveys was to gather information along the routes of steamship and sailing vessels on the Atlantic coast. Emphasis was placed on surface current measurement up to a depth of approximately 18 feet. This is because these currents had a direct effect on vessel movement.

Dr. Dawson was able to provide needed information to the marine and scientific communities based on his 3 surveys that identified:

direct measurement of currents
other physical water properties

His reports describing current characteristics were supported by the collection of local current knowledge from fishermen and ship captains.

Water levels

Early inland systematic water level gauging of the Great Lakes and the upper St. Lawrence River played an important economic role in Canada.

Staff readings at the Beauharnois Canal near Montréal, though not continuous, date back to 1845. Daily staff readings were first collected on a yearly basis at Lock No. 1 of the Lachine Canal starting in 1856. These were usually recorded by the lock master under the authority of the Department of Canals and Railways.

In 1906, the continuous recording of water levels in the Great Lakes using self-registering gauges was started by the Department of Public Works. This was in support of the Georgian Bay ship canal levelling program.

Self-registering gauges were installed on the:

lower St. Lawrence River in support of the Montréal-Québec Ship Channel Investigation in 1912
upper St. Lawrence River in 1915

By 1930, there were 19 gauges in operation on the Great Lakes, and 25 on the St. Lawrence River. All but 5 of these gauges operated yearly.

The first publication and distribution of monthly and annual water level bulletins occurred in 1925. The distribution of water level information to the public through press releases started in 1929. Unusually high water levels for the Great Lakes in 1929 and 1945 led to the public’s increasing interest in water levels.

Changes to data collection

In the 1950s and 60s, a number of significant changes took place in inland gauging, both in the collection of data and its processing. During this period, the International Great Lakes Datum was created to help inland water gauging. This resulted in a uniform vertical datum for the whole of the Great Lakes and the St. Lawrence River system.

In 1959, strip chart gauges began to replace the older Haskell units. In the early 1960s, dedicated telemetry units were installed for specific users of real-time data. The automation of data processing tasks was well underway. For instance, digital data on a punched tape could be transferred to computer cards and then processed on a computer. In 1962, the first annual summary of gauging station data produced by computer print-out was published.

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