At the commencement of the rain which caused this flood, the ground was covered with snow to the depth of eighteen inches: the weather became warm and the powerful rain storm continued incessantly for forty-eight hours. Notwithstanding the immense volume discharged at the overfall of the dam, the water was rising, during the night previous to this disaster, at the rate of fourteen inches per hour over the Reservoir, covering an area of four hundred acres.
It occurred on the 8th of January, 1841.
In repairing the breach it was decided to build an extension of solid hydraulic masonry in the place of the portion of embankment which was carried away.
The gate house and wing wall, which is seen on the ridge of the dam, shows where the masonry of the original structure connected with the embankment which extended across the river. The whole length of the overfall is 251 feet. Access to the house over the culvert, is gained by a foot bridge which is seen in the picture. The masonry of the original structure has a rock foundation, and the extension of the overfall which is seen on the left of the house extending across to the embankment has an artificial foundation of concrete.
The masonry of the dam is about 8 feet thick at the top and 65 feet at the base; it is built in a vertical form on the upstream side, with occasional offsets, and the lower face has a curved form such as to pass the water over without giving it a direct fall upon the apron at the foot; this apron is formed of timber, stone, and concrete; and extends some distance from the toe of the masonry, giving security at the point where the water has the greatest action. A secondary dam has been built at a distance of 300 feet from the masonry in order to form a basin of water setting back over the apron at the toe of the main dam so as to break the force of the water falling upon it. This secondary dam is formed of round timber, brush wood, and gravel; it may be seen in the picture directly under the bridge which extends across below the main structure.
On the upstream side of the masonry of the dam, an embankment of earth is filled in, extending 275 feet from the masonry at the base, and extending from the masonry with a slope of 1 foot in 5 on the top.
XII
F. B. Tower.
W. Bennett.