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The History of Tidal Measurements in Canada
The history of tidal, current and water level surveying in Canada for navigational applications has always had a close association with the Canadian Hydrographic Service, (C.H.S.). Prior to the establishment of a formal tidal survey group in the late 19th century, little had been done in Canada in the way of systematic tidal or current surveying. Tidal records had been obtained in several major ports, and 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. In the late 19th century concerns were growing over an increasing number of shipping disasters in the St. Lawrence River and the Gulf of St. Lawrence, so that by 1884 a committee had been formed to collect information on the importance of publishing tide tables for Canadian waters, and the necessity of carrying out new tidal surveys. Under pressure, the government of Canada in 1890 finally authorized further preliminary tidal observations, and allowed the purchase of three new tide gauges, and the processing of the records.
The appointment of Dr. W. Bell Dawson as Engineer-in-Charge of the Tidal Survey in 1893 marked the beginning of a systematic survey of tides and currents in Canadian waters. This would result in a much improved understanding of the characteristics of these tidal phenomena in Canada, and the ability to produce accurate predictions of tidal occurrences.
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, and 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 but in the winter heat had to be supplied by an oil lamp or small oil stove, which frequently mal-functioned and generally produced smoke and smudge which settled on the clock-work necessitating frequent cleaning and occasional repair. It meant 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 and spirit levels run to benchmarks yearly.
Dr. Dawson placed considerable importance on the establishment of benchmarks and datums and he spent a great deal of effort to re-establish datums by installing better benchmarks, carrying out tidal observations, and precise leveling, and documenting and publishing the information. His two publications “Tide Levels and Datum Planes on the Pacific Coast, 1923” and “Tide Levels and Datum Planes in Eastern Canada, 1917” are evidence of this commitment. 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 of tidal records and their subsequent analysis were very 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 did not enjoy a wide circulation. It was subsequently decided to supply the tide tables 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, and the second set were those for Victoria and Sand Heads in 1901. By 1907 the tide tables were printed in two volumes, one volume for the Eastern Coasts, and the other for the Pacific coast.
Current surveys were also carried out by Dr. Dawson. 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 Gaspe and Mingan and in 1896, 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. The emphasis was placed on surface current measurement up to a depth of approximately 18 feet because these currents had a direct effect on vessel movement. From the direct measurement of currents and other physical properties of the waters carried out during these three surveys, Dr. Dawson was able to provide badly needed information to the marine and scientific communities. Dr. Dawson actively solicited local knowledge of currents from fishermen, and ship captains, and used this information extensively in his many reports describing current characteristics.
Inland water level gauging has also played an important role in Canada. In view of the economic importance that navigation on the Great Lakes and the Upper St. Lawrence River system plays it is not surprizing that early systematic gauging of these waters took place. Staff readings at the Beauharnois Canal near Montreal, though not continuous, date back to 1845. Daily staff readings were first collected on a year round 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 in support of the Georgian Bay ship canal leveling program. Self-registering gauges were installed on the lower St. Lawrence River in support of the Montreal-Quebec Ship Channel Investigation in 1912, and on the 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 and all but 5 of theses gauges operated year round. The first publication and distribution of monthly and annual water level bulletins occurred in 1925, and the distribution of water level information to the public through press releases started in 1929. Abnormally high Great Lake water levels in 1929 and 1945 precipitated the public’s increasing interest in water levels.
In the 1950’s and 1960’s a number of significant changes took place in inland gauging, both in the collection of data, and the subsequent processing of this data. Inland water gauging was also helped immensely in the late 1950’s and early 1960 the establishment of the International Great Lakes Datum (IGLD) as 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, and in the early 1960’s dedicated telemetry units were installed for specific users of real-time data. Automation of the data processing task was well underway, and digital data on a punched tape could be transferred to computer cards and then processed on an electronic computer. In 1962 the first annual summary of gauging station data utilizing the computer print-out was published.
The early days of tidal and current surveying in the 19th century under Dr. W. Bell Dawson saw the rapid expansion of new programs under the guidance of dedicated individuals, and in spite of limited funding. The 1930’s, 40’s, and early 50’s generally saw less development, but rather the programs with well defined objectives were being well managed and much Canadian tidal and current data was gathered. The late 50’s and 60’s heralded a period of rapid development in instrumentation and techniques which continued through the 1970’s and into the 80’s and 1990’s. New changing technology offered better methods of performing old tasks.