REPORT OF PRECISE LEVELLING IN THE NARROWS (HALIMTON RIVER) BETWEEN LAKE MELVILLE AND LESTER POINT.
By R. H. MONTGOMERY, D.T.S.
The definite object of these operations was to ascertain by direct measurement whether lake Melville was above mean sea level. To determine the exact elevation of lake Melville on mean sea datum was not attempted. Time was not sufficient, nor did the purpose that actuated this expedition require this more exact information.
Available knowledge regarding tide ranges and currents in the Narrows at Rigolet somewhat favoured the supposition that lake Melville was higher than the sea proper. Still it was apparent that the difference would be small and would require levels of the highest order to ascertain it. The very rugged nature of the country adjacent to the Narrows made it extremely doubtful whether such levels could be successfully carried out. However, on account of the urgency of the request, we were warranted in making the attempt at least.
To accomplish this object the work naturally divided itself into two distinct operations, the establishment of automatic gauges at two points and subsequently obtaining the two simultaneous records extending over at least a full lunar period, and, secondly, the connection of the two gauge stations by precise levels. The gauge work was undertaken and carried out by the Hydrographic Survey of the Marine Department. C. A. Price of that Survey, with his assistant, J. R. Dupuis, joined our party at Gaspe and looked after that side of the work. The levelling was undertaken and carried out by the Geodetic Survey. The exact location of the gauge stations and the route between which had to be levelled, were to be selected after a reconnaissance had been first made on the ground.
The north polar expedition sent out by the Dominion Government was due to leave Quebec on July 7th on “ SS. Arctic ” and our instructions were to expedite the organization of our party to enable us, if possible, to leave on the same ship and to be taken by it to Rigolet, Labrador. A launch lying at Gaspe, Quebec, was loaned by the Hydrographic Survey for our use in Labrador and had to be picked up at that point. In spite of the shortness of time, our party and equipment was on board the “ Arctic ” when she sailed on July 9th. On the 13th our launch was taken on board at Gaspe. Our party consisted of the writer, in charge, H. S. Mussell, geodetic engineer, as assistant, a captain and engineer for the launch, two rodmen, umbrellaman, cook and also the two members of the Hydrographic Survey.
On July 19th the “ Arctic ” reached Grady, a small island off the coast of Labrador, about 100 miles from Rigolet, and here it was decided by the officials of the “ Arctic ” that our party should disembark consequently during the night of the 19th and 20th our equipment and supplies were unloaded. On the 22nd we were picked up by the Newfoundland Government mail steamer “ Sagona ” and were landed at Rigolet on the 23rd. Our launch proceeded under its own power from Grady and reached there on the 22nd.
The first two weeks were spent in the erection of the two gauge stations, and August 5th marked the beginning of the simultaneous records of the water level of Lake Melville and the lower part of the Narrows. Various considerations decided the location of these stations probably the most important was the time factor, as the original request required that our records should be in Ottawa by October 1st. To accomplish this meant that only one lunar period could be obtained and the stations were so separated as to assure that in the lunar period the precise levelling connecting them could be accomplished. If more time had been at our disposal, the stations could have been more widely separated and, for reasons stated later, a greater slope would have probably been found.
As soon as the stations were operating the actual levelling was commenced. Our permanent camp was established at Summer Cove, a point on the east side of the Narrows, midway between the gauges and it proved a very convenient location, for, by arranging our work on different sides of camp on alternate working days, the hydrographers were able to visit the gauges regularly. The levelling followed the shore line, except near the Melville gauge, where it was carried over a neck of land, thereby lessening the length of the line of levelling. Bench marks were established near each gauge stations and at prominent points between, as shown on the attached blue print.* These bench marks are of a very permanent nature, being the Geodetic Survey of Canada standard tablet, leaded in bed rock and, in general, referenced by a stone cairn.
The Tidal and Current Survey of the Marine Department also sent a party of six men, in charge of H. W. Jones, to investigate the tides and currents in the Narrows. This party established an automatic gauge at Rigolet and located a permanent bench mark near it. In order to connect their gauge with our levels, we carried our line across the Narrows by a series of reciprocal readings between bench marks 68–K and 73K, as shown on the attached blue print, and tied in with their bench mark at Rigolet, which we designated as 74–K. By making this connection it became possible to co-ordinate the records of their gauge with those obtained by the Hydrographic Survey gauges.
As a result of our levelling we ascertained the elevation of bench mark 72–K, near the Melville gauge, to be 5.301 feet higher than bench mark 66–K, near the. Lester Point gauge, and 14.517 feet higher than the zero mark on the Tidal Survey staff gauge at Rigolet. To deduce the relation between the
*See Map on page 2323 (following Stewart’s Report).
mean water levels at the different gauges, the above information will have to be used in conjunction with the information contained in the reports emanating from the Hydrographic and Tidal Surveys. A list of the permanent bench marks and their elevations, on an assumed datum, is appended hereto.*
The instrument used on this work was the Zeiss level No. 3, being the same as adopted by the British Ordnance Survey for their precise levelling. The staffs were divided into yard, tenths and hundredths of a yard and the rod readings were recorded in thousandths of a yard. In recording and reducing the rod readings, the English practice was followed rather than the American, in that, while the three wire readings were recorded, only the reading of the medial was utilized for determining the differential elevations of the turn points. In the levelling procedure, the same rigorous tests and methods were followed as specified for standard precise levelling on this continent. The discrepancy between the forward and backward line over a section did not exceed ± 0.015 feet M where M is the length of the section in miles. Owing to the nature of the work no external evidence could be obtained as to the accuracy, such as a circuit closure would indicate, still there is no reason to suspect, had a circuit closure been possible, that the standard would have been found wanting.
The levelling was completed by the 1st of September and on the 2nd our party boarded the “ SS. Sagona ” for our return trip. Mr. Mussell remained at Rigolet to look after our launch which had been disabled and which was later brought to Halifax by the “ SS. Nascopie.” Mr. Dupuis remained to look after the gauges in order to get a record of a second lunar period. The “ SS. Sagona ” arrived at St. John's, Newfoundland, on September 13th and the party proceeded overland by rail to Quebec, reaching there on the 17th, when it was disbanded.
We stated in our opening paragraph the elevation of lake Melville, resulting from our operations, is not the true elevation on mean sea level datum. To substantiate this we would advance the following hypothesis.
The peculiar formation of the upper end of the Narrows undoubtedly is the cause of the unusual currents and tide rips for which the Narrows are noted. The outflow of a watershed of roughly 70,000 square miles, has to pass through this channel. Referring to the attached blue print, it may be seen that Henrietta Island divides the Narrows into two channels. The flood tide coming up the Narrows naturally follows the western channel, entering lake Melville near Caravalla cove. This channel has a comparatively wide entrance from the sea and has a shallow and restricted entrance from lake Melville. Our observations revealed that this channel exhibited the same reversing currents and followed the same laws as the Narrows proper near Rigolet. The currents reversed about midtime between the peaks of the tides thus, with neap tides, if high tide occurred at noon, the current would begin to run in about three hours later. Referring to the eastern channel, known as Pike Run, it may be noticed that Holme point has a tendency to deflect the flood tide from this channel, and the wide deep entrance presents
* See Map on page 2323.
an easy outlet for the waters of lake Melville. As our work kept us in the vicinity of Pike Run, it was noticeable how rarely we found the current running into lake Melville by this channel. For these reasons we expect that there is a decided circulatory movement counterclockwise of the waters around Henrietta, or there should be a prevailing east current along the south shore of the island. On this account we are led to believe that, if an automatic gauge had been established on lake Melville west of Caravalla cove, the mean water level at such a point would be appreciably higher than at the Hydro-graphic Survey gauge near Pike Run.
At the lower end of the Narrows the geographical formation would tend to place the head of the Inlet somewhere in the neighbourhood of a line joining Ticoralak and Bloomfield island, and it is probable if a gauge station had been established near Bloomfield island that an ascertainable slope would be found to exist between it and our gauge near Lester point.
The prevailing wind during our stay in Labrador was from the north-east or east. This would have the effect of piling up the waters at the head of Hamilton Inlet and conversely the lowering of the waters at the east end of Lake Melville. Should it be established that the prevailing wind throughout the year is easterly, then the slope in the Narrows ascertained by our operations may be presumed to be the normal slope, but should the above supposition as to the wind’s direction not be correct, a more extended series of observations would naturally reveal a greater difference of elevation than was ascertained.
Thus it would appear that the slope which we ascertained was not the true elevations of lake Melville on mean sea datum but was rather the difference of the elevation of that portion of the Narrows lying between the gauges.
(Sgd.) R. H. MONTGOMERY.
Ottawa, Nov. 26th, 1923.
LIST OF BENCH MARKS ESTABLISHED IN 1923 BY THE GEODETIC SURVEY OF CANADA NEAR RIGOLET, LABRADOR, GIVING DESCRIPTION AND ELEVATION ON ASSUMED DATUM (BENCH MARK 66-K—100 FEET.)
Description of Permanent Bench Marks.
66-KOn south side of the Narrows and 1 mile east of Lester
Point and 4 miles east of Rigolet. On top of first gray
granite outcrop above high water, 30 yards from tree line
and 210 yards west of small creek, and marked by a
stone cairn. Elevation 100.000 feet.
67-K130 Yards west of 66-K, on gray granite outcropping, 75
yards from high water mark and at tree line. Elevation
68-KOn south side of Narrows, 2 miles east of Rigolet, and
1¼ miles west of Lester Point, and on red granite
outcropping 10 feet from tree line and 100 yards west of
Hydrographic Survey signal “ Pinch,” marked by a stone
cairn. Elevation 102.652.
69-KOn east side of Narrows, 4 miles south of Rigolet and 150
yards north of Holme Point—on outcropping of red
granite, 20 yards from high water mark and marked by a
store carin. Elevation 104.765.
70-KOn north shore of Pike run, 3 miles southeast of Holme
Point, at east end of steep outcropping of red granite, 10
feet from high water mark and marked by a store cairn.
71-KOn north shore of lake Melville, 1½ miles east of
unnamed point, at east side of beginning of Pike Run, on
outcropping of red granite, 150 yards east of
Hydrographic Survey station “ Run,” 10 yards from high
water mark and marked by a store cairn. Elevation
72-KOn outcropping of red granite, 50 feet west of 71-K, 10
feet from high water mark. Elevation 105.301.
73-KAt Hydrographic Survey station Burnt, on west side of
Narrows, 14 miles northeast from Rigolet, and 500
yards southeast of Burnt-wood Cove, 10 yards from
high water mark and marked by a stone cairn. Elevation
74-KAt Rigolet, copper bolt embedded vertically in grey granite
out-cropping, 100 yards northwest from Hudson Bay
Company’s wharf, 20 yards from high water mark. This
bench mark was established by the Tidal and Current
Survey. Elevation 103.352.
Zero mark of Tidal and Current Surveys gauge at Rigolet. Elevation 90.784.