TABLE NO. 4.-Coordinates of tertiary triangulation stations in Potagannissing Bay, referred to Harbor Island, in meters. B.-REPORT OF MR. E. E. HASKELL, ASSISTANT ENGINEER. UNITED STATES ENGINEER OFFICE, Sault Ste. Marie, Mich., June 30, 1897. SIR: I have the honor to make the following report upon the discharge measurements made in the St. Marys River at Sault Ste. Marie, Mich., during February and March, 1896: In my last annual report, page 4027, part 6, of the report of the Chief of Engineers for 1896, I gave a brief description of discharge measurements made in St. Marys River during the winter of 1895-96. In the present report we propose to discuss only those observations that were described as having been made on the Spry's Dock section. So few observations were made on the Kemp's Dock section that they have not been reduced, and we do not feel that we have, as yet, all of the data required for a thorough discussion of the observations made from the International Bridge. A few more observations must be made for determining the coefficient to reduce surface velocity measured to the mean of the vertical curve for several of the bridge spans. The St. Marys River from its source, Lake Superior, to its mouth, where it empties into Lake Huron, measured along the main channel line, is 62 miles long. It is a . crooked stream, very variable in width, and is divided at several points by large islands. Beginning at its head it is 4 miles wide. It retains this width for about 5 miles, where it begins to grow narrower, and a distance of 4 miles farther, has reached a width of about half a mile; then it abruptly widens to about 2 miles and retains this width until the head of the St. Marys Rapids are reached, a distance of 14 miles from the starting point. From the best data available, the fall of the river to the head of the rapids is 0.41 of a foot. The St. Marys Rapids are about 1 mile long and half a mile wide, and the mean fall in them-from twenty-five years' observations, 1871 to 1895, inclusive-is 17.68 feet. From the foot of the rapids the river is nearly straight for a distance of 2 miles and has an average width of about three-fourths of a mile, the fall being about 0.2 of a foot. It is in the middle of this reach that the discharge section was located. At the foot of this straight reach the river is divided by Sugar Island into two main channels, known as the Hay Lake and Lake George routes. The present steamboat channel is by the way of Hay Lake; by this route the Little Rapids, which aggregate about one fourth of a mile in width, cover the first 14 miles, and in this distance there is a fall of about 0.75 of a foot. Hay Lake begins at the foot of the Little Rapids, and, measured along the sailing line, is approximately 11 miles long, 2 miles wide, and has a fall of 0.1 of a foot. At the foot of Hay Lake is Neebish Island which helps to form two outlets, the West and the Middle Neebish Rapids. The main channel is by the Middle Neebish Rapids, which are approximately 2 miles long, one-half mile wide, and have a fall of 0.8 of a foot. About a mile below the foot of these rapids, at the foot of Sugar Island, the Lake George branch of the river again joins the Hay Lake branch, after having traversed 26 miles, 16 of which may be called "river" and the remaining 10 "lake," and having divided its waters on the head of St. Joseph Island, a part of them going to Lake Huron by way of the Collingwood channel. From the foot of Sugar Island the main channel passes through Little Mud Lake, 3 miles long and three-fourths of a mile wide, and through the Sailors Encampment reach of the river, 2 miles long and one-fourth of a mile wide, and then empties into Mud Lake. In the 5 miles from the foot of Sugar Island to the head of Mud Lake the fall is about 0.6 of a foot. This route by way of the West Neebish Rapids, from the head of Neebish Island to Mud Lake, is about 7 miles, the first 3 of which may be called a part of Hay Lake, and the remaining 4 rapids and river. The rapids themselves are about 1 mile long and three-eighths of a mile wide. The fall by this route is, of course, the same as that from Hay Lake to Mud Lake by way of the Middle Neebish and Sailors Encampment. From the head of Mud Lake to Lake Huron is 24 miles. This reach of the river is very broad the greater part of its length and has two outlets, one by way of Potagannissing Bay and the other by the main channel. It is so large a stream, in relation to the volume of water it has to carry, that the fall is but slight; a fair estimate would probably be 0.2 of a foot. From the head of the river to Lake Huron, as stated above, is 62 miles, and in this distance the river has fallen 20.75 feet, which represents the difference in elevation between the level of Lake Huron and that of Lake Superior. The results of twentyfive years' observations, from 1871 to 1895 inclusive, show the mean level of Lake Superior to be 601.94, and of Lake Huron to be 581.19, referred to mean tide at New York. The stream is one that would be called permanent in its character, its banks and bed being for the most part rocky. The bed is very irregular from the many shoals that are to be found along it. In consequence of this the flow of water is also very irregular. In the rapids and restricted portions the current is strong, while in many stretches, such as the lakes, it is almost inappreciable. THE DISCHARGE SECTION. The discharge section, located as stated above in the reach of river extending from the foot of the St. Marys Rapids to the head of the Little Rapids, is probably as good a one as can be chosen at any point along the river. All of the flow coming out of Lake Superior has to pass this point. The location of this section is shown on Pl. I, which is a map of the river from the head of the St. Marys Rapids to near the head of Little Rapids, a distance of about 3 miles. On this map can be seen also the location of the gauges used. The section began at the foot of Spry's Dock, on the American side of the river, and ended against Plummer's Dock, on the Canadian side of the river. The amount of water passing behind or underneath these docks is quite inappreciable. The water width of the section is 2,483 feet. The river was frozen over at the time of making the observations, and the section was sounded, and all of the current observations made, through the ice. The section was lined out with a transit and a small stake set every 10 feet, starting from the dock on the American side. An ice auger was then used to bore a hole at each stake, and through this a sounding was made with a sounding reel, using a very heavy lead attached to a No. 18 steel wire. From these soundings the discharge section has been platted and will be found on Pl. I. As great care was taken in laying out the section, marking the distances along it, and in making the soundings, it is not probable that an error as great as 1 per cent exists in the area of the section thus determined. WATER GAUGES. In making the observations four water gauges were used, located as follows: One at the head of the canal, one on the south abutment of the International Bridge, one on the northeast pier of the canal, at the foot of the Rapids, and one on the discharge section on the American side. These locations may be seen on the map, Pl. I. They were all staff gauges and marked to read, directly, the elevation of the water surface above mean tide at New York. The gauge at the head of the canal is the one that has been read daily at noon since January 1, 1871. This gauge gives the level of Lake Superior, less the fall of the river from the lake to the gauge, which, as stated above, is 0.41 of a foot. The gauge on the south abutment of the International Bridge is the one used as a section gauge for the observations made from the bridge. This gauge was read every fifteen minutes, simultaneously with the gauge at the head of the canal, for three days. From these observations the mean fall from the head of the canal to the Bridge was found to be 0.20 of a foot. The gauge on the northeast pier of the canal is practically at the foot of the Rapids. It was used for the purpose of determining the fall between the foot of the Rapids and the Spry's Dock discharge section. The gauge was read every fifteen minutes, simultaneously with the section gauge, for a period of six days, and the observations give a mean fall of 0.12 of a foot. The section gauge was located directly at the end of the discharge section on the American side. This gauge, as well as the one at the International Bridge, was read every fifteen minutes on all days when discharge measurements were in progress. The gauge on the International Bridge was also read simultaneously with the section gauge. CURRENT METER USED. The current meter used was a Haskell, Form E. They belong to the screw or propeller wheel class and are electric recording. They are 16 inches long, have wheels 4 inches in diameter, and weigh 24 pounds. With their low-pitch wheel they will register velocities as low as 0.35 of a foot per second. HYDROMETRIC PENDULUM USED. On the discharge section were three meter stations against the left bank, at which the velocity was too low to be recorded with the meter. After considering the question of how to obtain a measure of the velocity at these stations, we decided to try a hydrometric pendulum. Accordingly, a ball 4 inches in diameter was turned from a block of hard wood and sufficient lead was inserted, as a plug, to render the ball just heavy enough to sink. This ball, with a very fine braided silk cord attached to it, constituted the pendulum. A square board was next made from 1-inch pine large enough to permit striking, from a point near one corner as center, with a 2-foot radius, a quadrant of a circle. Beginning with a radius drawn parallel to one edge of the board, this arc was graduated to half degrees. At the extremity of this arc, in the upper right-hand corner, a plate level from a transit was adjusted to a position in the plane of the board at right angles to the zero radius. Directly underneath this level, on the lower edge of the board, was a screw some 4 inches in length with a spherical head, working in a nut to form a leveling screw. A reel was attached to the side of the board and on this was wound the silk cord of the pendulum, after having passed over a small screw set at the center of the circle. In making observations it was easy enough to estimate the tenth of a degree. RATING OF METER. As stated in my last year's report, a few obervations were made for rating the meter in November, previous to making the discharge measurements that were taken at the International Bridge. The meter was thoroughly rated on completing the discharge measurements on the Spry's Dock section in March, and it is this rating that has been used in reducing all velocities measured. A description of this rating will be given together with the reduction of the rating observations. To make a rating a slit about 8 inches wide and 200 feet long was sawed in the ice, in the canal just above the movable dam. The movable dam was closed at the time and there was no current through the canal. A large sled was selected that would considerably more than span the slit in the ice. Through a hole in the center of the sled was placed a 4-inch gas pipe which was supported in a vertical position by a frame work attached to the sled. This piece of gas pipe was long enough to pass about 2 feet helow the bottom of the ice, and to it the meter was attached in such a manner that it was free to assume the direction in which it was moving. To keep the sled from sliding sideways pieces of 2 by 4 scantling were spiked to the ice on each side of the slit, forming rails between which the runners were confined. The base was 150 feet long, leaving 25 feet at each end for space for starting and stopping the sled in making an observation. The battery, register, and observer occupied a position on the sled, which, with the meter attached, was hauled forward and backward over the course by two men, obtaining the observations which appear in the rating below, Table 1. The method given above can hardly be recommended unless the ice is perfectly smooth. Otherwise there is a continuous trembling of the meter from the jar caused to the sled, and poor observations result. Some difficulty from this source was experienced in making the present rating. Previous to reducing the observations by the rigid method of least squares for the purpose of finding the rating equation, all the observations made were platted on cross-section paper, the time required to traverse the base and the number of revolutions made in that time being used as abscissas and ordinates, respectively. An approximate curve representing a majority of the observations was then drawn on the sheet. Some observations which fell so far from this curve as to indicate that they were greatly in error were rejected. From each of the remaining observations an observation equation of the form y=a+be+cx2 was written, and from them the equation of the most probable curve was deduced by the method of least squares. This equation was found to be y=0.3785-+0.8132 x +0.0834 x2, where x=revolutions per second, giving in feet per second. The probable error of a single observation is +0.0109. All of the velocities measured on the Spry's Dock section fell between zero and 2.2 feet. The rating observations, as seen from the table, are made to cover practically the same limits. TABLE NO. 1.—Meter rating-Meter E, low-pitch wheel. 106 106 113 116 119 124 123 122 122 129 130 127 329.5 0.455 082 .007 .001 ,000 .037 290 .517 .003 .155 .024 .004 290 .001 .080 .012 .517 .159 .025 004 289.5 .001 .082 .013 .004 .001 .081 273.25 .012 .549 216 .047 .010 .002 .119 .026 .628 .293 .008 .192 .058 .013 .219 .074 .035 .012 .215 .070 .127 .029 .344 .119 .041 .014 .228 .079 341 .116 .040 208.25 .014 .233 .079 .028 .294 .027 .296 201 .506.012 .558.009 .602+.002 .662.013 665+.017 .720+.011 .000144 .000081 .566 -.002 . 000004 .000004 .000025 .632 .000 .000000 .000169 . 000004 .000036 000289 .000121 194.75 . 147 .754 -.008 000064 .364 .781 -.011 .172 .000121 000081 .000169 .370 .225 163.25 .919 .649 422 .274 408 .951 .288 .190 .617 .137 .550 .334 .903 +.001 . 000169 .000001 .000484 -.016 .000256 .000064 000625 2.461 64 9.232 2.344 1.984 3.938 2.338 -.030 000900 7.810 15.494 36.288 25.078 27.210 38.052 60.861 34. 793 46.320 008671 |