CONSTRUCTION OF DAMS, GATE-HOUSE, CANAL, ETC.

The works at the head require the construction of a reservoir, canal, and a small dam for turning the course of the Berry brook, in order to make the same available.

First, let us consider the construction of the reservoir. Plate I. shows a plan, with the position of dams, gate-house, wasteweir, and inlet of canal indicated.

As has already been stated, the reservoir covers an area of a little more than 50 acres; the banks for the most part are very rocky and quite precipitous, thus affording a site admirably suited by nature for the purpose for which it was chosen. In order to make this area available for the storage of water, the two forks or branches of the Hart-brook meadow, 354 and 222 feet in width, respectively, were dammed.

Plate II. represents an elevation of the sites for the two sections of the dams, and also a plan of the surface as prepared to receive the embankment.

A section of the dam is shown upon Plate VII., and the same drawing also represents a section of the gate-house, of which I will speak later. As is indicated upon the plate and as set forth in the specifications, the dam consists of a core wall surrounded by an embankment of earth. The wall is built of small stone, carefully laid in a good quality of cement mortar, having the inner side thoroughly plastered with cement in order to form an impervious barrier within the embankment. It is four feet wide at the bottom of the foundation, and its width is uniform up to the natural surface of the ground; then it is battered to a uniform thickness of 18 inches at high water line. The wall rests upon bed rock throughout nearly its entire length. There is a short space, however, in the west section, a little east of the center, where the wall does not extend to the underlying stratum of rock. On either side of this narrow space the inclination of the ledge made a sudden dip, and borings proved that it was impracticable to attempt to reach the rock.

At a depth of 17 feet below the surface, an impervious stratum of very fine blue clay was found, which seemed practically almost as impermeable as the rock itself, and upon this as a foundation, the core wall rests for about 30 feet.

On either side of the core is an embankment of earth. It is 15 feet wide on top and built on a slope of one and one half horizontal to one vertical. It was built very closely to the requirements of the specifications, being composed of a very good quality of earth, well moistened, and thoroughly rolled and rammed, as the successive layers-never more than 6 or 8 inches in thickness-were added. The inner slope is to be covered with riprap, 18 inches in thickness, while the top and outer slope are to be covered with soiling to a depth of one foot. Thus the width of dam on top is in all about 18 feet.

The following is the approximate amount of material, exclusive of the grubbing and the preparation of the surface to receive the embankment required for its construction :

The gate-house, or gate-chamber, is built of brick and stone masonry laid upon a bed of concrete, which is at least 18 inches in thickness. The dimensions are as follows::

The house proper, from outside to outside, 13′ 6′′ by 11′ 6′′; concrete extends 18 inches beyond the wall upon either side, making its surface 16′ 6′′ by 14' 6". The outer walls are of rubble masonry, 2 feet in thickness, laid in cement mortar similar to that employed in the construction of the core wall. There is a lining of brick 8 inches thick extending from the the top of the foundation to the high water line; this is shown upon Plates III., IV., and V. Between the inner and outer walls is an inch of cement.