In building such a dam as this the difficulties to be contended against
were unusually great. It was required to make it as near perfectly tight
as possible and be, of course, always submerged. Allowing for water used
by canal and slide and the leakage there should be a depth on the crest
of the dam in low water of 2.50 feet and in high of about 10 feet.
These depths turned out ultimately to be correct. The river reaches
its highest about the middle of May, and its lowest in September. It
generally begins to rise again in November. Nothing could be done except
during the short low water season, and some years nothing at all. Even
at the most favorable time the amount of water to be controlled was
large. Then the depth at the site varied in depth from 2 to 14 feet, and
at one place was as much as 23 feet. The current was at the rate of from
10 to 12 miles an hour. Therefore, failures, losses, etc., could not be
avoided, and a great deal had to be learned as the work progressed. I
am not aware that a dam of the kind was ever built, or attempted to be
built across a river having such a large flow as the Ottawa.
The method of construction was as follows. Temporary structures of
various kinds suited to position, time, etc., were first placed
immediately above the site of the dam to break the current. This was
done in sections and the permanent dam proceeded with under that
protection.
In shallow water timber sills 36 feet long and 12 inches by 12 inches
were bolted to the lock up and down stream, having their tops a uniform
height, namely, 9.30 feet below the top of dam when finished. These
sills were, where the rock was high enough, scribed immediately to it,
but if not, they were 'made up' by other timbers scribed to the rock, as
shown by Figs 4 and 5. They were generally placed in pairs about 6 feet
apart, and each alternate space left open for the passage of water, to
be closed by gates as hereafter described. Each sill was fastened by
five 1½ in. bolts driven into pine plugs forced into holes drilled
from 18 inches to 24 inches into the rock. The temporary rock was then
removed as far as possible, to allow a free flow of the water.
In the channels of which there are three, having an aggregate width of
about 650 feet, cribs 46 feet wide up and down stream were sunk. In the
deepest water, where the rock was uneven, they covered the whole bottom
up to about five feet of the level of the silts, and on top of that
isolated cribs, 46 in. X 6 in. and of the necessary height were placed
seven feet apart, as shown at C Figs 2 and 3. At other places similar
narrow cribs were placed on the rock, as shown at D, Figs 2 and 3. The
tops of all were brought to about the same level as the before mentioned
sills. The rock bottom was cleaned by divers of all bowlders, gravel,
etc. The cribs were built in the usual manner, of 12 in. X 12 in. timber
generally hemlock, and carefully fitted to the rock on which they stand.
They were fastened to the rock by 1½ in. bolts, five on each side of a
crib, driven into pine plugs as mentioned for the sills. The drilling
was done by long runners from their tops. The upstream side of the cribs
were sheeted with 4 in. tamarack plank.
On top of these sills and cribs there was then placed all across river a
platform from 36 to 46 feet wide made up of sawed pine timber 12 in.
X 12 in., each piece being securely bolted to its neighbor and to the
sills and cribs below. It was also at intervals bolted through to the
rock.
On top of the "platform" there was next built a flat dam of the
sectional form shown by Fig 1. It was built of 12 in. X 12 in. sawed
pine timbers securely bolted at the crossings and to the platform, and
sheeted all over with tamarack 10 in. thick and the crest covered with
½ in. boiler plate 3 ft. wide. The whole structure was carefully filled
with stone--field stone, or "hard head" generally being used for the
purpose.
At this stage of the works, namely, in the fall of 1881 the structure
presented somewhat the appearance of a bridge with short spans. The
whole river--fortunately low--flowed through the sluices of which there
were 113 and also through a bulkhead which had been left alongside
of the slide with a water width of 60 ft. These openings had a total
sectional area of 4,400 sq. ft., and barely allowed the river to pass,
although, of course, somewhat assisted by leakage.
[Illustration: Fig. 1. CROSS SECTION IN DEEP WATER.]
It now only remained, to complete the dam, to close the openings. This
was done in a manner that can be readily understood by reference to
the cuts. Gates had been constructed with timber 10 in. thick, bolted
together. They were hung on strong wooden hinges and, before being
closed, laid back on the face of dam as shown at B, Figs. 1, 2, and 3.
They were all closed in a short time on the afternoon of 9th November,
1881. To do this it was simply necessary to turn them over, when the
strong current through the sluices carried them into their places, as
shown at A, Figs. 2 and 3 and by the dotted lines on Fig. 1. The closing
was a delicate as well as dangerous operation, but was as successfully
done as could be expected. No accident happened further than the
displacement of two or three of the gates. The openings thus left
were afterward filled up with timber and brushwood. The large opening
alongside of the slide was filled up by a crib built above and floated
into place.
The design contemplates the filling up with stone and gravel on
up-stream side of dam about the triangular space that would be formed by
the production of the line of face of flat dam till it struck the rock.
Part of that was done from the ice last winter; the balance is being put
in this winter.
Observations last summer showed that the calculations as to the raising
of the surface of the river were correct. When the depth on the crest
was 2.50 feet, the water at the foot of the Longue Sault was found to be
25 in. higher than if no dam existed. The intention was to raise it 24
in.
The timber slide was formed by binding parallel piers about 600 feet
long up and down stream, as shown on the map, and 28 ft. apart, with a
timber bottom, the top of which at upper end is 3 ft. below the crest
of dam. It has the necessary stop logs, with machinery to move them, to
control the water. The approach is formed by detached piers, connected
by guide booms, extending about half a mile up stream. See map.
Alongside of the south side of the slide a large bulkhead was built, 69
ft. wide, with a clear waterway of 60 ft. It was furnished with stop
logs and machinery to handle them. When not further required, it was
filled up by a crib as before mentioned.
The following table shows the materials used in the dam and slide, and
the cost:
______________________________________________________________________
| | | Stone | Exca- | |
| Timber, | Iron, | filling, | vation, | Cost. |
| cu. ft. | lb. | cu. yds. | cu. yds.| |
+---------+---------+----------+---------+----------+
Temporary works | 134,500 | 92,000 | 11,400 | | $79,000 |
| | | | | |
Permanent dam | 265,000 | 439,600 | 24,000 | 6,500 | 151,000 |
| | | | | |
Slide, including | 296,500 | 156,400 | 32,800 | | 102,000 |
apparatus | | | | | |
+---------+---------+----------+---------+----------+
| | | | | |
Total | 696,000 | 687,000 | 68,200 | 6,500 | $332,000 |
-----------------+---------+---------+----------+---------+----------+
The above does not include cost of surveys, engineering, or
superintendence, which amounted to about ten per cent, of the above sum.
[Illustration: DETAILS OF THE OTTAWA RIVER DAM, AT CARILLON.]
The construction of the dam and slide was ably superintended by Horace
Merrill, Esq., late superintendent of the "Ottawa River Improvements,"
who has built nearly all the slides and other works on the Ottawa to
facilitate the passage of its immense timber productions.
The contractors were the well known firm of F.B. McNamee & Co., of
Montreal, and the successful completion of the work was in a large
degree due to the energy displayed by the working member of that
firm--Mr. A.G. Nish, formerly engineer of the Montreal harbor.