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sible to ocean vessels by Fitzroy Channel (12 miles long with width under half a mile : Tidal Streams run 5 knots : Tidal Rise 5 feet : Least water 30 feet at Low Water), hence by OTWAY WATER (47 miles by 16 miles with depth up to 330 fathoms : Tidal Rise 8½ feet) and Jerôme Channel (10 miles by 1 mile wide, deep and Tidal Stream 6½ knots).
Skyring Water is an example of two large Sea Inlets directly connected by a Channel permanently accessible to ocean vessels.
Larger still though similar in essentials are :
(1) the SEA OF MARMORA (110 miles by 40 miles wide over 700 fathoms deep) permanently accessible by the Dardanelles : the channel being 35 miles long with a least width of ¾ mile and a least depth of 25 fathoms, and
(2) the BLACK SEA with a length of 630 miles greatest breadth of 330 miles and a depth up to 1200 fathoms, permanently accessible by the Bosphorus Channel 17 miles long with a width varying from 1½ miles to slightly under ½ mile and a least depth of 20 fathoms. It has been established that both in the Dardanelles and Bosphorus there is a permanent outward flow of the Upper Strata water into the Mediterranean having a velocity of 4 knots, whilst in the lower strata a counter current reaching to near the bottom prevails setting inwards from the Mediterranean having a Density and Temperature of that sea.
VI.
I now propose to consider the nature of the LEVELLING, TIDAL AND CURRENT OBSERVATIONS obtained and the scope of the conclusions to be drawn from them.
Precise Tidal observations were obtained by Canadian Officers continuously throughout two complete Lunar months during August-October 1923, as set out in Part XIV of the Canadian Government Report. Automatic Tide-Gauges, were functioning during this period at two mails Tidal Stations, chosen as reference points of which the first was situated near Lester Point just seaward of the Narrows and the second a short way within Lake Melville on the shore of the north entrance to the Backway.
Although the time available was short, and it was not possible to employ the test of a closure for the actual levelling observations between the two Tidal Stations, the following conclusions as to the determination of the Tide Level Slope between the two Stations mentioned may be accepted as substantially accurate during the period embraced.
(a) That at any instant throughout the period of the observations there was a Definite Slope of the water surface between the two Stations, the Mean Tide Level of the Lake Melville Station being higher than that of the Lester Point Station.
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(b) That the Average Difference between the Mean Tide Levels of the two Stations during this period was 5 inches.
(c) That the Difference was not always constant, but subject to variations at the times of Spring and Neap tides, being greater during the outgoing than the incoming tide, and greatest during the Neap tides.
VII. This Difference of Mean Tide Level determined between August and September is accepted in the Canadian Report as not being an unchanging quantity representing a permanent difference between the level of Lake Melville and Mean Sea Level but the Difference of Level between the Stations for that period. It is in a great measure accounted for by the volume of water in excess of the inflow, due to the accumulation, mostly near the surface, of the fresh water whose progress seaward is arrested after its discharge into Lake Melville ; the water thus held up in Lake Melville is only able to pass out with the Ebb stream ; and the longer duration and greater strength of the Ebb are not sufficient to maintain a common level throughout the system, and restore equilibrium, before the advent of the succeeding Oceanic Tidal Undulation or the commencement of the Flood stream (these two latter features being separated by a considerable interval).
The fact that the Variation of the Surface Slope found between the two Stations or Gauge Points was greatest at Neap Tides, is to a larger extent explained by the variation in the volume of the water that passes in either direction to or from Lake Melville during Spring and Neap Tides. A further contributing cause is that the Times of High and Low Water due to the same Tidal Impulse, differ by some 3¼ hours at the two Stations, the Time of each occurrence being later at the Lake Melville end of the connecting Waterway than at the Lester Point end.
It is natural to suppose (in the absence of more specific observations to determine this point) that the Turn of both Flood and Ebb streams occurs at approximately the same time at each end of the Waterway, so that the upper strata of the water throughout the Waterway must be assumed to run in one direction only at any instant, subject to slight variations near the times of Slack Water at Spring or Neap Tides. Consequently when it is High Water at the Lake Melville end of the Waterway and the Flood stream will continue throughout the Waterway for a further 1½ hours, the Tide (as measured by vertical change) has been falling at the opposite end of the Narrows, for some 3¼ hours. At Low Water the conditions are approximately reversed. Each phase would operate to retard the natural flow of the water outwards from Lake Melville, by producing a cushioning effect there, which would be greatest with the outgoing stream and with the weaker tides. This consequent increase of slope would then diminish as the cycle continued with the 40 restoration of equilibrium at the, ends of the Waterway (where the physical forces operating at any moment are more often dissimilar).
Further Variations in the Slope will arise from temporary and changing local conditions, such as the volume of fresh water which Lake Melville is
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receiving, the strength and duration of the wind in one direction, and any change in the normal turn of the lower strata of water in the Waterway, which, as appears from the observations, generally took place both on the Ebb and on the Flow earlier than the turn of the surface layers.
Doubtless Small Differences of Level such as are here under review occur in portions of other Sea Inlets similar in general configuration and conditions to Hamilton Inlet, and they might prove to be either of a permanent or a seasonal character, if it were expedient or practicable to determine them.
VIII. The Period embraced by the observations must also be carefully noted. They were limited to a Period of two months, at the end of the summer in a particular year, and conclusions correctly drawn for this Period may not be true for other Periods, and should not be taken as a permanent state of the physical conditions that occur. Thus the Difference in Level found may be seasonal only, and due to the fresh water accumulating in the broad expanse of Lake Melville during the summer flood and then making a gradual egress through the Narrows.
Nothing short of a Prolonged Series of Observations would suffice to establish with certainty the existence of any Permanent Difference of Level between the inner and the outer portions of Hamilton Inlet. It would be necessary to exclude all occasional and temporary variations due to the divergent character or effects of physical conditions, natural forces and seasonal changes, and to determine in isolation from all these the true Mean Sea Level of the Sound seaward of the Narrows on the one hand and of the Mean Level of Lake Melville on the other. And they would have to be determined with great precision, when the purpose was to ascertain and account for small differences. At least one year's continuous series of observations and preferably more would be required to determine the Mean Level of the seaward Sound ; and to do the same for Lake Melville, in view of the seasonal
variations in rainfall, snowfall, melting of snow and ice, barometer pressure and winds affecting it, the observations should extend over a Longer Period of time and not be confined to one place in Lake Melville.
IX. When attempting to compare the Slope of the River St. Lawrence with the slope which has been deduced for the Narrows of the Hamilton Inlet, certain cautions should be regarded:—
(a) The levelling observations referred to above were not sufficiently prolonged or extensive to prove the existence of any permanent Slope in the Narrows;
(b) In the case of the St. Lawrence, the Gulf of that name an undoubted Inlet of the Sea, which gradually as it is ascended merges into the well known river system in order to define a division between the two, some more or less arbitrary line of demarcation a choice of criteria must be adopted ; in the case of the Hamilton Inlet, where all
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vessels have natural permanent access from the open sea free of all obstruction, by means of a short deep narrow connecting Waterway to a Sea Basin which is navigable without hindrance to its head, no river enters into the question.
(c) Lake Melville is nevertheless an Arm of the Sea, although owing to its expanse, depth of penetration into the interior of the country and general configuration it possesses the characteristics of a Sea Inlet in a less degree than the Sound seaward of the Narrows, as is manifested by the change in the features of the Flora and Fauna within this Sea Basin.
X. The Marine Character of Hamilton Inlet in its whole extent, including Lake Melville and Goose Bay, is not merely the effect of the Oceanic Tides. If the amplitude of the Tidal Wave impinging on the Labrador coast were very much less than it is (6 ½ feet maximum), doubtless a constant outflow of surface and upper strata water, largely fresh, with a sluggish stream, of a higher temperature than that in the Sound, and liable to freeze, would, in normal weather and in the absence of easterly winds, prevail in the Water-way connecting the Sound with Lake Melville. Lake Melville would then be practically without any Tidal Rise and subject to seasonal changes of level only. At the same time the lower strata of water in this connecting Waterway would be found to be constantly running in from the Ocean, maintaining a general Salinity and Temperature of the sea water standard throughout the lower strata of Lake Melville. The Conditions would then be similar in some aspects to those prevailing in the Dardanelles and the Sea of Marmora (referred to above in paragraph V) and in other Sea Inlets where the Tidal Rise is small. In severe winters the Waterway might freeze throughout, and all passage be barred, as in the case of Lake Melville : all the other features would remain the same.
XI. The Canadian observations establish that the Range of the Tide decreases rapidly during the retarded progress of the Tidal Wave through the Narrows to the entrance of Lake Melville; from there the now diminished Range continues at the same height as the Tidal Wave advances without restriction across the deep and expansive Lake Melville and increases slightly owing to the contracted width of the wave at Goose Bay. These are normal features for a Sea Inlet of this configuration and depth.
The Greater Velocity and Longer Duration of the Ebb Stream than the Flood Stream at Rigolet are equally normal for a Sea Inlet, where a connecting Waterway, with a moderate Tidal Range, expands into a large deep Basin, into which a very extensive drainage falls from the distant watershed of the interior.
The Difference of 3 to 3 ½ hours between the times of High and Low water in the seaward Sound and Lake Melville is of course due to the Retardation of the Tidal Wave in its progress through the Narrows. But on account of natural forces which delay the outflow of water from Lake Melville, the
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water does not attain its maximum height at the entrance, until some time after the arrival of the crest of the Tidal Wave.
Retardation in the advance of a Tidal Undulation is a common feature in Sea Inlets and is dependent in its degree upon the depth, width and sinuosities of any Waterways offering obstruction to its travel.
XII. The observations with regard to the Density of the water established the following conclusions:—
Surface Water (a) at the head of Lake Melville it was almost permanently fresh and fit for drinking ; (b) at the Narrows its average density near the end of the Ebb stream was 58% of the density of standard sea water, and near the end of the Flood stream 76%; (c) in the seaward Sound between Rigolet and Indian Harbour the fresh water impregnation disappeared.
The Lower Strata had the full salinity of sea water throughout the whole extent of the Inlet up to the head of Lake Melville.
The distribution of Fresh Water on the surface, due to the drainage into Lake Melville of rain water and melted ice and snow, may have been abnormally large in the 1923 season, but the presence of fresh water at the head of a Sea Inlet is a constant feature which was well known to early voyagers, was taken advantage of by them for various purposes, e.g. for cleaning the bottom, boiler water, etc., and was continued with the advent of iron and steel vessels until the world wide distribution of docks rendered this expedient no longer an economic one.
The difference in Temperature near the surface of the waters in the seaward Sound of the Inlet and those in Lake Melville may be attributed to the influence of the cold Arctic current which setting permanently southward skirts the Labrador coast, ice in some form here prevails at all seasons of the year, “ field ” and “ bay ” ice during the winter and “ polar bergs ” during the summer. Only a comparatively small quantity of ice in a broken form passes into Lake Melville from the sea.
The severity of Climatic Conditions on the rugged and open sea board of Labrador, fully exposed to the Atlantic, is unique for its latitude (which is the same as the Port of Liverpool) and caused by the continued presence of the ice, the Arctic current and sea fogs, is much modified in Lake Melville where these causes cease to operate. The softening of the Climatic Conditions produces changes in the Fauna and Flora to be found between the mouth of the Inlet and the head of Lake Melville, changes which are paralleled in other Sea Inlets, though the exceptional conditions prevailing on the open sea-board of Labrador together with the large drainage system emptying into Lake Melville heighten the Climatic contrast and make the changes unusually great.
XIII. On consideration of the Hydrographical and Geographical evidence now available, especially the excellent testimony afforded by Chart No. 420
[1927lab]
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