II. We may throw dams across the channel of the river and convert the rapids into a series of still lakes, and lock directly from one into another.

III. We may combine these methods by canaling around rapids, and using low dams to give the required depth and to drown out currents between the canals.

Sometimes one of these methods is most applicable to a particular locality, and sometimes another; and the judgment of the engineer is shown by his choosing that which best suits the circumstances of the case.

On the lower Ottawa, where the lakes are long and deep, and the shores low and highly cultivated, it would be unwise to attempt to alter the existing levels, for we should drown a arge extent of country, thereby destroying arable land and probably rendering. what was left unhealthy. Whatever plan is proposed will carefully avoid disturbing the long levels.

But fortunately for the project, on the greater part of the river, where the water is required to be raised, the shores are bold and the desired lift would overflow but little land. Here we have only to raise the natural dams or reefs of rocks to the desired height by artificial structures, thus restoring a condition of things which possibly existed before the ceaseless rush of the waters, or glacial action had worn the rock dams down to their present state.

Wherever canaling is resorted to, the canal will follow the shore, and be constructed by embankments rather than in excavation, on account of the great saving of expense over thorough cuts in solid rock of the large dimensions necessary for the navigation.

The whole key to the system of improvement proposed for the Ottawa is comprised in two propositions:

I. Follow the natural bed of the river, and avoid cutting into the rocky shores.

II. Gain the depth required for navigation by raising the surface of the water rather than by submarine rock excavation.

We may lay it down as a general principle that, although on the lower part of the river where the shores are flat and lie upon sedimentary rocks, we could dispense with the use of dams; yet, as soon as we enter upon those portions where the river has cut its bed through crystalline rocks, (which is more than half the distance from Montreal to Lake Huron) the only mode by which a navigation can be made at all is by raising the water by dams.

There is not now depth enough of water; the currents are too strong to be overcome; and as the shores rise almost perpendicular from the water's edge, there is no room to construct canals; moreover, even if there were room, the length of artificial canal required would be so great as to condemn the project; and there can be no doubt of the superiority of a still deep lake from two to three hundred yards wide for purposes of navigation, over a canal of fifty yards in width.

Fortunately every existing condition favors this mode of construct

tion.

The bed of the river consists of hard crystalline rocks, worn smooth and generally free from boulders, and the shores of the same material rise abruptly on either side, diminishing the length of dam required.

Points can be obtained where the water is shallow, and where there are rocky islands which will act as natural buttresses for the structure. Under these circumstances there is no more danger of a properly constructed flat dam being disturbed than one of the islands themselves.

As has been previously said, the Ottawa is not a river subject to sudden rise or extraordinary floods. It never averages over three inches in twenty four hours for any number of days in succession; its common rise is one inch per day. Its rise to its high water mark stand, and subsequent fall, occur every year at nearly the same dates with the utmost regularity. (See Appendix for Table "C.")

There is very little shove of ice in the Ottawa, where dams would be required.

So ample is the volume of water, even in the dry est time, that notwithstanding leakage and the effect of wind blowing down stream, the dams would be always submerged with from one to two feet of water running over their crests.

A very important effect of dams upon the Ottawa will be to diminish the variation between high and low water. This is always proved to be the case wherever they are built, for there is a greater area to be filled up by the flood waters before they can rise, and the discharge over the top of a dam is so free that the water can never rise above it to the same extent that it does in a river channel obstructed by islands and sunken rocks.

In designing a system of dams for the Ottawa improvement, we should have the actual volume of water discharged both at the lowest and highest recorded stages. This would require a series of gauges in different parts of the river, taken for a term of years, until the greatest and least flow was ascertained from actual measurement.

As the time of this survey has been limited to one season, I can. not pretend to have attained such accuracy; nor, merely for the purpose of an estimate of cost, is it necessary. It is only requisite, for that purpose, that what is assumed as the greatest and least volume should cover the extreme limits of variation

The results of several gauges give, for the summer volume of dis charge, at Portage du Fort, 31,000 cubic feet per second, and that of high water, 127,000 cubic feet per second. From anything on record, it does not appear probable that the least discharge ever falls below. 25,000 cubic feet per second, or the greatest over 130,000. These quantities, therefore, have been assumed as a maximum and minimum. (See Appendix, Table "D.")

Where the dams themselves act as waste weirs, it has been thought preferable to raise the masonry of the upper or guard lock, and allow the water to raise as high as it would upon the crests of the dams, rather than to attempt to control it by guard gates in the body of the dams, as this would be introducing a perishable material and mode of construction into the body of the work.

The height at which the water will stand upon the crests of the dams for different volumes of discharge, has been calculated by the formula for weirs, originally due to the investigations of Du Buat.

Let Q be the number of cubic feet per record, and L the length of the overfall of dam be known and we can obtain

H.-The height at which the water will stand above the crest of the dam, from the simple equation.

= ( Q ) #

3.56 L.

By this formula, the table of dams (see Appendix "D") was calculated, and the height of the coping of guard locks established.

It will be seen that these dams will have from 1.34 to 3.51 of water running over them at low water. Yet for purposes of estimating, their crests have been assumed to be as high as the level of water above them which gives excess of material.

One other point demands notice. We know that by dams we can drain out currents in these lakes themselves, strong enough to affect navigation.

The velocity of any current depends directly upon the area of flowage. When that is large in proportion to the volume, the velocity is slow, and as the area diminishes the velocity increases in order that equal volumes may pass in equal times. How great this velocity will be at any point is strictly a matter of calculation, founded on well known hydraulic laws. Without here giving details, it is sufficient to state in general terms that the present area of flow age will be so much enlarged by the depth of water thrown on by dams, that no greater velocity of current need be apprehended than three miles an hour at any point, even during the six or seven weeks of high water, and during the rest of the season the currents will be entirely imperceptible.*

*The investigation of the laws that govern the flow of water over weirs, is one of the most impor tant branches of hydraulic engineering, and has received the attention of many eminent savans, among whom may be particularly mentioned Du Buat, Castel, Poucelet, Lesbois, Dauhuisson, in France: Egleweir, Weisbach, in Germany; the Kennies, Sir John Leslie and Thomas E. Blackwell, in England; and James B. Francis, of Lowell, in the United States.

All the rules and formulæ derived from their investigations are founded on that natural law governing the velocity of fluids, known as the theorem of Tonicelli, modified by co-efficients

III Character of Work and Material in Locks, Dams, Canals, &c.

In accordance with the instructions of the Department, the quality of the work is proposed to be not inferior to the standard of the St. Lawrence canals, and everything has been designed as substantial as possible. It is believed that there will be nothing perishable but the lock gates on the whole line.

Dams, where carried above water, will be of rough but strong rubble masonry laid in cement; wherever the water runs constantly over them they will be flat timber dams composed of solid timber laid up crib-fashion, without framing, fastened with three quarter inch square bolts twenty inches long; at each crossing rock bolts one-quarter inch round, to be filled with loose stones, covered with four inch plank well spiked, and staunched with gravel, similar to those usually constructed by the Department, in connection with timber slides.

In most places the water can be diverted by a rough coffer dam, and the permanent structure commenced directly upon the flat rock. This operation is much facilitated by the numerous channels into which the river is divided at the points selected, by large and small islands. The dams can be run from one island to another, and pas sages left for the discharge of the waters, which can be afterwards closed.

When the water is deep, recourse must be had to the system of sinking cribs. The dams should, where possible, be laid out upon

obtained by comparing the results derived from it with those furnished by experiment. As those experiments have as yet been made on a comparatively small scale, we cannot apply the rules deduced from them to circumstances widely differing from those under which the experiments were made, without discrepancies more or less great being found in the results.

The case with which we have to deal is fortunately one where we proceed from the greater to the less, so that an error, whatever it is, is diminished instead of being increased. Were we calculating the amount of available waterpower from the height on the crest of our dam, a very small error either in observation, or in the co-efficient itself, would give results widely differing from the truth; but where we have already ganged the flow of the stream, and only calculated the height for a given length of dam, we know that the calculated result must, at least, be as close an approximation to mathematical truth, as is the quantity expressing the number of cubic feet of water passing a given area in a second, as obtained from our gauges.

Nevertheless it would be very desirable to have a series of experiments made, with special reference to determining the actual longitudinal section of a large river, dammed entirely across, during different volumes of discharge from extreme high to low water. Such experiments, if properly made, would not only be a very valuable contribution to engineering science, but are almost indispensible to the proper carrying out of a scheme of the magnitude proposed in this report.