ANNEX “B” TO No. 1447.
COMMENTS ON THE OBSERVATIONS OF VICE-ADMIRAL LEARMONTH, AND MR. C. TATE REGAN, By H. W. JONES, TIDAL AND CURRENT SURVEY, CANADA.
Comments on the “Observations of Vice-Admiral Sir Frederick C. Learmonth, K.B.E., C.B., on the Hydrographic Survey and Reports by the Canadian Government on Lake Melville, Hamilton inlet, at the Narrows, 1921-23,” and supplementary note respecting criticisms by C. Tate Regan, M.A., F.R.S.
For the purpose of brevity and convenience reference will be made directly to the divisions of Sir Frederick's observations.
II. That the body of water concerned may have been improperly named at the first, through imperfect knowledge of the physical features resulting from incomplete investigation, is not a sound or just reason for confirming the appellation now. That the term “Lake” has been used as well as “Inlet” indicates indecision in the past as to which it really is.
III. The test of accessibility by ocean-going vessels would make of the St. Lawrence river a sea inlet as far as lake St. Peterwhere the first extensive dredging has been done, whereas the Commissioners appointed under the Reciprocity Treaty between the United States and Great Britain, concluded and signed at Washington on the 5th of June, 1854, agreed and decided with respect to the river St. Lawrence that “a line bearing N. 40° W. (magnetic) connecting Cape Chat with Pointe de Monts . . . shall mark the mouth or outer limit of said river,” and that all the waters within or to the westward of this line should be reserved and excluded from the common right of fishing therein under the first and second articles of the said treaty (Moore's International Arbitrations, Volume 1, page 487) ; and in the Royal Proclamation on the 7th of October, 1763, the boundaries of the Province of Quebec as thereby established are defined in part by a limitary line drawn . . . . “from thence (i.e. Cape Rosiers) crossing the mouth of the river St. Lawrence by the west end of the Island of Anticosti terminates at the aforesaid river St. John.” (Canadian Constitutional Documents, 2nd edition, page 164.)
If it be a sound criterion for determining the limit between a river and the sea that the river carries its title down to the point at which it reaches the level of the sea at low tide-this being the level at low tide to which the
[following p. 3856]
waters of the river fall and beyond which the level of the sea never drops-then a determination of the position of the dividing line may be quite approximately made from the tidal record obtained from the self-registering tide gauges.
Taking the mean range of the tide at Indian Harbour as being that of the open ocean and as 100 per cent., the range at Ticoralak Island was found to be also 100 per cent. ; at Broomfield Island 91 per cent. ; at Rigolet 78 per cent., and at Caravalla 23 per cent. of the ocean range. Thus the elevation of the level of the water at low tide is lower at Rigolet than at Caravalla, lower at Broomfield island than at Rigolet, and lower at Ticoralak than at Broomfield island, but from there outward to Indian Harbour it remains the same. From this it is clear that the lowest level to which the waters can is reached somewhere between Broomfield Island and Ticoralak Island, or in the neighbourhood of Ticoralak Point and Turner Headland (see diagram of tidal ranges).
The argument in par. III. premises that no river here comes into consideration, ignoring that the outlet from Lake Melville for a distance approximately 15 miles, after consideration of its physical features, may be judged as such. Its abbreviated length does not make it any the less a river.
It cannot be claimed that the “lake” is accessible at all times by the largest ocean-going vessels except at very great risk. Currents, with tides that were not maximum springs, measured up to 51 knots in the “Narrows” or river stretch opposite Rigolet, and in the passages around Henrietta Island, because of the natural laws where the cross-sectional area is much restricted, they must be much stronger. The figure of 3¼ knots (see III, p. 5) for the strength of the currents that may be expected is certainly in error ; they are likely up to 7 or 8 knots, and possibly more, in these passages on the ebb, when with maximum tides. While the Tidal Survey party lacked the time to make determinations here, the descriptions of the flow through these passages by those who knew them indicated violent currents. A small vessel was said to have foundered in the whirlpools at one time, and the writer had the opportunity of observing the very strong cross-currents between Pike Run and Strathcona Point. Ordinary caution would limit the times to make the passage to the periods at or near slack water.
V. In comparing Lake Melville and its outlet to numerous other water bodies similar in some respects, no discussion is given to the degree of evidence of river water flowing through the discharge. The amount of tidal current itself is dependent upon whether the oceanic tide adjacent is large or small. But the amount of outward discharge and velocity, compared with the inward, is the measure by which we must judge whether the stretch from the lake to the sea is a river or not. The relative densities are also important.
In the case of the Bras d'Or Lakes there are no streams worthy the name of river flowing into them, and the same might be said of Burrard and Masset Inlets. The streams in the outlets are essentially due to the tides. On the other hand, great rivers flow into Lake Melville, and their waters
must find their way through the outlet, giving to this channel more or less—as may be judged—the nature of a river.
A comparison with the St. John River-system of lake basins is suggested. It has an outlet with very strong combined tidal and river currents and through which vessels can pass only at times of slack water. The tidal undulation reaches a distance of ninety miles, but the distance of penetration of sea water has perhaps never been determined. Whether it is found in the sub-strata of the adjacent lakes I cannot say, but have been told on good authority that hake are caught in the Kennebecasis arm. I leave it to the biologists to tell the habits of this fish.
On the other examples cited for comparison, I have not the means at hand to enable me to comment, except as to the Black Sea, which, by its size alone, is perhaps removed from the same class. Also its effluent would be affected by the great evaporation basin of the Mediterranean with which it is connected through the Sea of Marmora.
VII. The fact that river influence, as shown by the Tidal Survey observations, is a sensible quantity, is admitted, and that it accounts “in a great measure” for the difference of level between the gauging stations. I am in agreement with the statement that the cause of the mean level of Lake Melville being higher at neap than at spring tides is the greater volume of water flowing inwards or outwards during the latter than the former periods, but not with the explanation to show that the tidal action is responsible for holding up the mean level of the lake. . . .
That the turn of both the flood and ebb streams occurs “at approximately the same time at each end of the waterway” is very much open to question as concerns the under current, and as to the surface current such is not the case, for, from our point of observation at anchor in midstream, the approach of the current after slack water could be plainly seen at consider-able distance as a ridge of turbulent water, while it was yet stationary in the vicinity of our mooring. Doubtless after a time, as the difference of levels increased more rapidly, the remaining stretch would begin to move almost as a body. In the case of the under current, the factors of momentum and inertia, coupled with the changing in the height of the tide affecting one end before the other, would preclude a simultaneous reversal. Also, if the momentum of the flood current, inwards for 1½ hours after high water tends to bank up the water in the lake, it should also hold true that a similar but even longer and stronger ebb current continuing outward after low water would assist the flow outward to a similar extent or more. For with a greater volume flowing outward, the frictional resistance is proportionately less, and its greater momentum carrying it farther into the open sound (see diagram of Relative Velocities) would have a drawing effect after it on the water from the lake above, and also delay the following flood tide, thus prolonging the duration of the ebb flow. For these reasons the argument presented does not establish that the tidal action has the “cushioning effect” spoken of to hold the lake to a higher level.
On the contrary (since proven by the gauging and levels) the water level in the lake is higher through the periods of neap tides than through the periods of spring tides. Or in other words, the less the amount of tide, the higher is the level in the lake. Thus it appears the tide is responsible for the level of the lake being as low as it is.
VIII. “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 outer portions of Hamilton Inlet.”
The laws of gravitation and inertia alone are sufficient to prove that there is a “permanent difference of level” between the lake and the sea. The gauging and precise levelling are only necessary to prove that the difference is a sensible amount which may be measured. Large rivers flow into the lake. Its area or the local climate is not such that evaporation from its surface need be considered. The water accumulates until, owing to difference of level, the force of gravity overcomes the inertia, and flow results through the short river to the sea. As there is no other escape, so long as the rivers flow, there must be a difference in the mean levels. The dominant flow outward is very pronounced, as shown by the observations.
IX. (a) Dealt with in VIII.
(b) It is said that “no river enters into the question.” Attention is called to the evidence of river influence, and characteristics of a tidal river in the reach known as the Narrows, as shown by the Tidal Survey Report.
X. (No comment.)
XI. (Last paragraph.) The features which are distinctly characteristics of tidal rivers are here said to belong to sea inlets, i.e., those dependent principally upon the element of watershed discharge, but also on the frictional resistance of an attenuated channel and slope.
XII. In this section the percentages of density refer to the excess over unity as compared with the same of sea water and not to the relation between the densities themselves. This was not made sufficiently clear in the original report, and this opportunity is taken to prevent mis-interpretation.
A General Consideration of the Problem.
A shallow strait connecting the sea with a deep inlet into which no streams discharge would have an equal flow each way, of water of uniform sea density, neglecting for the purpose of illustration such modifications as would be caused by barometric disturbance, convection, and other temporary or irregular influences.
The water of a river flowing directly into the sea is also of uniform (fresh) density, but flows all one way, losing itself abruptly at its mouth.
Between these two extremes is the tidal river with its estuary and reaches which are penetrated by the sea water, and pulsate in the manner of flow with the tide. The water of the sea flows and ebbs mainly along the bottom under the water of the river as far as the slope of the river bed permits, and because of agitation caused by obstructions and irregularities of the channel it permeates to a more or less extent the waters of the river. The flood and ebb currents in such a stream show characteristics common to all of them.
Now, if a waterway conducting a river discharge lead from a deep basin, the outlet being like a weir, followed by a channel, so that only at the highest tides would any salt-laden water enter, the water in the lower undisturbed recesses of that lake or basin would be as salt as the sea and the outlet would still have the features of a tidal river.
The case under consideration is such as this only that the outlet, while much restricted in width, is deep enough that all tides penetrate the basin, but the features of river flow and presence of river water are strongly evident.
For illustration, let us revert to the contemplation of the shallow strait connecting the sea with a deep inlet into which no rivers discharge. “Other things being equal,” the tidal flow will be equal in both directions, the water uniform in density, and the mean levels equal. If sufficient streams could be deflected into such an inlet it would be converted into a lake at a higher elevation than the sea, and the strait would become a river.
The purpose of this is to show that whether the outlet from Lake Melville through the Narrows to the “sound” below is a strait or river depends upon the amount of river water present and the nature of the flow
Very large rivers flow into the lake which may not be relatively large, having in mind the Great Lakes and St. Lawrence river, and the flow through the outlet has been shown by the Tidal Survey investigations to resemble less the flow through a strait, than of a tidal river. Per contra, the density of the water is nearer that of sea water than fresh water, but this is also true of nearly all tidal rivers in their lower courses and estuaries.
SUPPLEMENTARY NOTE TO THE ORIGINAL TIDAL SURVEY REPORT REFERRING TO THAT PART CONCERNING THE DENSITY OF THE WATERS.
Mr. C. Tate Regan calls attention to certain figures given as percentages of density of sea water. For the sake of brevity and as the purport is so obvious, the term “density” was used for the “excess-of-density-overunity.” It is this “excess” or difference in density of the numerous samples of water over the density of pure water which indicates the existence of salt water and which is also the measure of its presence. The “percentages” are therefore between zero (density of pure water being 1,000) and 0.024 as 100 per cent., the density of standard sea water being 1.024. Thus a sample of brackish water of specific gravity 1.012 has only 50 per cent. by weight of substances foreign to pure water, that standard sea water bears ;
or, in simple language, it has 50 per cent. the character of sea water as distinguished from fresh water in regard to weight. The figures for the densities are all given, so this particular use of the term is quite obvious.
The use of the term “salinity” is also brought up. It was not my intention to deal with salinity at all, but this word was used instead of “density” in the instance pointed out.
H. W. JONES.