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.
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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.
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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.
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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.
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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.
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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.
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Reviewed:
2005-03-11
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