REPLY TO OBSERVATIONS BY VICE-ADMIRAL SIR FREDERICK C. LEARMONTH REGARDING LAKE MELVILLE AND THE NARROWS.
BY DR. W. BELL DAWSON.
In the discussion of the question whether Lake Melville is an arm of the sea or part of a river system, it may be well to note at the outset that this can only be decided by considering the physical conditions which characterize the waters of true inlets and river estuaries. It is thus no mere question of language or an academic discussion of names. This is evident from the names of maps. Take, for example, two bodies of water connected with the ocean by a narrow channel, one in the Queen Charlotte Islands and the other in Cape Breton Island. In any physical geography, these would be classed together because identical in their features ; yet on the maps, one is named an inlet (Masset Inlet) and the other a lake (Bras d'Or Lake). A third very similar one is named a sound (Puget Sound).
The general contention in the “ observations” submitted by Vice-Admiral Sir F. C. Learmonth, is that any body of water into which ships can enter from the ocean, is an Arm of the Sea. The matter is regarded purely from the viewpoint of navigation. The seaman may no doubt consider that any water he can navigate is an extension or branch of the general ocean ; and it does not matter to him whether it is the mouth of a river or a lake, whether it is salt water or fresh, so long as his vessel can get there.
Admiral Learmonth takes this view, and includes all types of inlets and estuaries as “ Arms of the Sea,” so long as they are accessible to ocean-going vessels. The question of navigation is thus made the only criterion. If we take this definition of an arm of the sea, and follow it out, it will become clear that it entirely ignores all physical distinctions in navigable waters. For ocean-going vessels reach Montreal on the St. Lawrence, and ports 2.300 miles from the ocean on the Amazon, and as far as Hankow on the Yang-tze in China. According to the definition, these rivers would have to be classed as arms of the sea up to the head of ocean navigation. Such a view can only be understood from the seaman's standpoint. To the deep-sea captain, a river only begins where his cargo has to be discharged and transferred to river craft.
It will be seen as we proceed, that in the classification of water-areas connected with the ocean, the main distinctions between them must be based on their physical characteristics. A rational classification can thus be made.
The question whether Lake Melville is to be considered as an inlet or arm of the sea, or as part of the Hamilton river system, can then be determined by making a comparison with the various types of inlets and estuaries. The descriptions of inlets given by Admiral Learmonth, are very good so far as they go ; but the primary distinctions between one and another, according to their physical characteristics, are not brought out with sufficient clearness to afford a basis for a decision in the question before us.
In Canadian waters, we find so wide a diversity of characteristics that we have, as it were, a museum containing probably every type that can be imagined ; and we may therefore utilize Canadian inlets and estuaries as examples. Furthermore, the tidal behaviour in all those cited, has been investigated by the Tidal and Current Survey of Canada.
The features and characteristics of inlets and estuaries that we have to consider, are such matters as water-slope, the behaviour of the tide, the outflow to the ocean, and so forth ; and the distinctions between them depend primarily on whether or not they receive a large volume of river water. They may therefore be classified as follows :—
(A) Inlets of the sea which are not modified in their characteristics by river inflow.
(a) The typical inlet is a long arm of the sea, fairly uniform in its width, its sides being approximately parallel. These abound on the coasts of British Columbia and Alaska, and they form the fjords of Norway.
(b) Expanded inlets, connected with the sea by a narrow entrance ; but which receive no river discharge of consequence.
(B) Estuaries of rivers. (To show the bearing of tidal features on the classification, it is noteworthy that where there is little or no tide, a delta is formed at a river mouth instead of an estuary.)
(a) The estuary of the ordinary type where the shores of the river are no longer parallel, but (as a rule) open out towards the ocean. These are well known everywhere.
(b) Expanded estuaries, where the river enlarges to a lake-like area before discharging into the ocean. These are comparatively rare ; but the lower part of the St. John river and the Hamilton river estuary afford characteristic examples. At the one extreme of this class, Lake St. Peter on the St. Lawrence may be cited as an expansion which is just reached by the tide ; and at the other extreme there are bays or ponds at the mouths of rivers at the coast, which are enclosed by bars, or islands.
In this classification, we are dealing throughout with water-areas affected by the tide ; because they are all connected with the ocean. The mere fact that a tidal undulation advances over a water area, does not prove the area to be a part of the ocean. For the tidal undulation may run a long way up
[1st. page following p. 3872]
|INLETS OF THE SEA (Class A. a.)|
Dean Channel, Burke Channel
and arms from them
Knight Inlet, Bute Inlet
|EXPANDED INLETS (Class A. b.)|
Bras d'Or Lake
[2nd. page following p. 3872]
|MAXIMUM RISE OF TIDE IN TIDAL RIVERS AT HEAD OF ESTUARY|
Vertical lines show Rise of Tide at each locality (Same scale in each region)
a river, where the banks are parallel and the water fresh. This is well exemplified by the rivers in any maritime country.
The classes to which such water-areas belong are more clearly indicated than in any other way by the manner in which the tide acts in them. We will describe this as concisely as possible, to explain only those physical differences which are distinctive in their bearing on the Hamilton river system.
The typical inlet (such as those of the British Columbian coast and the fjords of Norway) has approximately parallel shores and is usually deep ; it rims a long way inland (as much as 60 or 80 miles) and it may have branches. Such inlets are properly arms of the sea ; the tide rises fully as high at the head as at the mouth ; and the water is salt throughout their extent. For there is rarely any river discharge of consequence in. these inlets, because of the topography in which they are found. Even when their entrance has become somewhat narrow and shallow (through an exceptional circumstance), as in the case of Burrard inlet, the rise of the tide is not decreased up to the head, and the water is perfectly salt. The typical estuary of any large river, is a complete contrast to this. The rise of the tide increases from the ocean inwards ; and its characteristics differ in many ways that we need not enter upon.
It is the second sub-division in each of the above classes that chiefly concerns us—namely, a large expanse of water connected with the ocean by a narrow entrance. When their physical characteristics are considered, it will be found that the leading influence which dominates them is the amount of river discharge which they receive. This will accordingly justify the primary distinction made in the classification.
As examples of such expanses in the inlet class, there are the Bras d'Or Lakes in Cape Breton Island, and Masset Inlet in the Queen Charlotte Islands. (It has been noted that one is called a lake and the other an inlet, although their characteristics are identical.) They both occupy the central part of islands, so that the river discharge they receive is negligible. [See the outline maps herewith.] Their leading features are :—
(1) They are practically as salt as the sea. (2) The water surface is at the mean level of the outside ocean. (3) The tidal streams outward and inward have the same strength. (4) The rise of the tide is greatly reduced, because the entrance is so narrow and the area so large that it has not time to fill up, during the tidal period. Such an expanse is in reality a part of the ocean ; and the amount of navigation into it will depend chiefly on the depth of the connecting entrance ; and on trade conditions.
As examples in the estuary class of large expanses of water connected with the ocean, we may cite the lower part of the St. John river in New Brunswick, which in the lowermost portion of its course includes several lake -expansions with different appellations. Lake Melville is also a characteristic example of this type. [See the outline maps herewith.] The leading features of the type are :—
(1) The water is less salt than sea water, and it may even be fresh in part. (2) The surface is higher than the mean level of the ocean. (3) The
tidal stream outwards towards the ocean is much stronger than inwards ; and in extreme cases, the current may not reverse at all. (4) The decreased rise of the tide is due to the water slope up which the tidal undulation has to make its way, as well as to the size of the expanse. The contrasting features of the two types may be further considered.
(1) Salt and Fresh Water.— It is usual at the head of the estuarine portions of such rivers for the salt water to flow in along the bottom when the tide begins to rise, because it has a greater density, being salt water and being almost always colder than the river water. The sea water thus acts as a wedge and raises the water level while the surface water is still running out. Very definite examples of this could be given in various river mouths. In this respect the Narrows resemble an estuary and not an inlet of the sea.
(2) Water Slope.— An expanse in a river mouth is always at a higher level than the mean level of the sea ; whereas in a true inlet (though it may have the same general shape) there is nothing to keep the level higher than in the ocean outside. Lake St. Peter, on the St. Lawrence, affords an example of this. In the case of the St. John, there is a rocky barrier at the river mouth which accentuates the differences unduly. The writer calculated the level of Lake Melville above mean sea level, on the assumption that it was part of the Hamilton river system ; the calculation being based on comparison with stretches of the Ottawa and the St. Lawrence ; and the result he obtained was 0.50 of a foot. The difference, as afterwards deter-mined by the levelling was 0.42 of a foot ; and this might have been slightly more if the levels had been extended further seaward as he had recommended when the surveys were undertaken. This certainly corroborates the view that Lake Melville is part of a river system.
Admiral Learmonth reviews quite elaborately the nature of the observations taken, and their interpretation ; but he seems to make the matter unnecessarily complicated. In these observations every precaution was taken to obtain a truly balanced result, as well as to carry out the work under normal conditions. The Hamilton river was not in flood at the time, as the freshet season only lasts about three weeks, and is always over by the middle or end of June at the latest. The result given by the observations cannot properly be challenged therefore on the ground that it might be different under other conditions at other times.
(3) Tidal Streams.— The greater strength of the outward tidal stream through the Narrows is itself a proof, according to the laws of flowing water in hydraulics, that a difference in level must exist ; that is, that the average level of Lake Melville must be higher than sea level. This greater strength of the outward stream was also found to persist throughout the whole of the time during which the observations were made, which corroborates the validity of the levelling results beyond the two months period of observations on which they are based.
Retardation of the Tidal Undulation.— The retardation in the advance
of the tide, which causes high water to be later in time as the tide progresses, is a somewhat complex problem. But when Admiral Learmonth says that “ it is a common feature in sea inlets,” this cannot be accepted as a general statement. For it is remarkable that in the most typical of all inlets, there is practically no retardation, as the time of high water at the mouth and the head is almost simultaneous on a distance of 50 miles.
The following examples from the British Columbia coast will show, that, in truly typical inlets, the time of the tide is practically simultaneous throughout :—
From Hartley Bay, at the entrance, to Kittimat, at the head of Douglas channel, distance 49 miles, the time of high water is 4 minutes later.
From Namu, at the entrance, to Bella-kula, at the head of the inlet, distance 69 miles, the time of high water is 2 minutes later.
From Vancouver, in Burrard inlet, to Port, Moody, at the head, the tide, though it has to pass through Second Narrows, is only 13 minutes later.
Also, the rise of the tide at the head of these inlets is actually greater than in the entrance by 2 to 12 per cent.
These small differences of time were determined by means of registering instruments to record the tide, with the use of chronometers for accurate time.
In contrast with the above the retardation of the tide in an ordinary estuary for an equal distance would be about two hours, as found in the St. Lawrence estuary in its narrower parts. (See the differences of time in the Canadian tide tables.)
The greatest amount of retardation that occurs is therefore in estuaries and as far up a river as the tide extends, where it is chiefly due to the counter-flow of the river and to river slope. In these respects the retardation of the tide in the Narrows and Lake Melville has a closer resemblance to estuarine conditions than to tidal action in any true inlet.
Maximum Rise of Tide.— In any funnel-shaped estuary, the rise of the tide increases from the ocean inwards, and the head of the estuary can be defined (in most cases) as the point where the tide has its maximum range. Beyond this point the tide may still make itself felt a long way up the river, but it gradually decreases in height. On comparing the whole stretch from the outer bay to the head of tide in the Hamilton river with a noteworthy estuary, such as the St. Lawrence, the similarity in this respect is striking, for the maximum rise occurs outside the Narrows, and from this tidal indication these Narrows and Lake Melville within them are to be considered as part of the river system. (See chart accompanying Tidal Survey report, where a comparison with the St. Lawrence is shown, and diagram herewith.)
Supposed Modifications.—In maintaining the marine character of Hamilton inlet, Admiral Learmonth discusses the modifications that would occur if there were no tide on the open coast of that region ; and this supposition is made to institute a comparison with the Black Sea and the Sea of