MANCHESTER WATER WORKS.
MASSABESIC lake, whence Manchester, N.H., draws its water supply, is to the east of the city, with its outlet only four and one-half miles from the business centre, and is protected from contamination by the purchase of land on the part of the municipal authorities and by a bold barrier of hills, which lies between it and Manchester. The lake has about 2,400 acres area, with a watershed not less than forty square miles. From the lake is a daily average flow of not less than 40,000,000 gallons a day. When the city’s water system was built this outflowing stream was converted into a 500 h. p. water power for pumping a portion of itself up to a reservoir on the ridge between the lake and the city—there to flow by gratify *hnto the distributing system of the city. To secure the necessary power for working the turbines the dam was built in the brook valtey, about 3,000 feet below the former Inlet of the lake, and its overfall was built up to the level of the lake, thereby increasing the area of the lake to 2,400 acres and three feet draught—equal to about 23,45,000 gallons of water. A little lower down the stream the new dam was built, with an apron of stone, whose mortar joints were preserved from the severe shocks of water falling from the lip of the dam twenty-four and one-half feet perpendicular height, by arranging the front of the dam in a series of steps of increasing projection and decreasing height from the top to the bottom, so designed that the front edges of the steps should nearly touch points in a parabolic curve. By this means the water passing over the overfall strikes upon the fifth,fourth.or third and second steps from the bottom,according to its depth and velocity over the lip, and reaches the apron in a finely divided spray. Thus, except in front of the waste sluice at one end, there is no daugerous scour or undertow. To provide against this the wxste sluice has a width of three feet and a height of five feet ; and has, also, a sluice gate fitted with a geared screw hoisting apparatus. The outlet of the sluice is through the face of the dam near the southern abutment, and the sluice extends from the front of the dam diagonally backwards to the upper end of the abutment, where the gate is locked. The gate stem rises in front of the coping on the upper side of the dam, where it is accessible at all times. On each side of the overfall abutments to the end on the north, and the canal on the south side the dam is constructed of earthwork, and contains a cemented priming wall of stone masonry, two and one-half feet thick at the top, with threeinch batten on each side.
PLAN OF PUMPING STATION AND WALL AT LAKE MASSABESIC HIGH SERVICE, MANCHESTER, N. H
A Georgia pine penstock of six feet clear internal diameter leads from the canal to the turbine wheels within the pump house. The axis of the penstock at the lower end of the canal is twelve feet below the full-water surface of the canal, and the penstock remains under ground throughout all its length, sloping twenty-six feet. The lower end of the penstock is under forty feet head pressure of water. The penstock is constructed of pine staves, four inches in thickness, laid in place so as to break joints in a continuous tube—hooped with screw-bolts, wrought-iron hoops; the hoops having an average distance of eighteen inches between centres. Both edges of the staves as constructed were worked accurately to the radical lines at the same operation by special cutters fitting in a matching machine, and no further dressing was required. The penstock, whose cost for 600 lineal feet at $15.25 was $17,150, is capable of delivering 40.000,000 gallons of water io twenty-four hours, at a velocity not exceeding 135 feet per minute. At the dam is a set of four sluice gates, each of three by five feet opening, controling the flow into it from the canal. Each set of gates is provided with a set of fine copper wire fish screens, easily removable for cleaning.
The Centre reservoir has its water service 152 feet above the city hall. The lift of water from the surface of the lake to the reservoir is 113 feet. It is an earthwork structure, with interior slopes paved below the water surface with hydraulic cement concrete, and above with granite blocks and with exterior soiled and grassed. The full-water area is about three and three-quarter acres, and the depth of water nineteen feet. At its southerly end is an inlet chamber, into which the forcemain delivers its water. The inlet chamber has a measuring weir, over which the water may be passed into the reservoir, and an inlet sluice also, through which the water may be admitted into the reservoir. This chamber has also a wasteweir and sluice. At the northerly end of the reservoir is an out-flow chamber provided with regulating sluices, gates, and fish screens. On this extension of the force-main and on the branch leading to the influent chamber are gates, by which the flow of water from the pumps can be directed into the reservoir or into the supply and distribution pipes independent of the reservoir.
For the high service the pumping station is on the west shore of the westerly part of lake Massabesic, near the northerly end of the lake—a little less than two miles north of the outlet which supplies w’ater to the low service pumping station. The intake pipe is twenty-inch cast iron, extending into the lake 255 feet from the shore wall;the end being covered with a heavy brass screen of three quarters of an inch mesh. The elevation of the top of the dam is 147 feet. The buildings at the pumping station are all of brick, and are all connected. The elevation of the engine house is 158.5 feetjthe boiler room being two feet, eight inches lower. The chimney is circular, and 100 feet, nine inches high; base, eleven feet in diameter; smaller section near top, seven feet, three inches, with cast iron cap made in eight sections, bolted together with composition bolts and weighing three tons and four-tenths. The chimney has an inner shaft four feet inside diameter extending to the top, and the smoke flue enters the chimney eighteen feet above the boiler room floor. The pump well is ten feet, eight inches wide by twenty-one feet, eight inches long, and the elevation of the bottom is 136.5 feet. The bottom is cement concrete and bricks, watertight; the sides, cement rubble masonry.lined with bricks four and eight inches in thickness. In the screen chamber are two sets of copper wire screens of one-quarter inch mesh, and at the end of the twenty-four-inch intake pipe is a sluice gate. The two Worthington high duty pumping engines have each two high pressure thirty-inch cylinders and two double acting water plungers fifteen and one-quarter inches diameter. The two engines will deliver 51.62 gallons per revolution when making the stipulated stroke of eighteen inches, after making a deduction of five per cent, for slip. Each engine was guaranteed to deliver into the reservoir 3,000,000 gallons of water in twenty four hours against a dynamic head of 254 feet—static head,about 250 feet. There are two vertical Manning boilers, s;x feet in diameter, each con taining 180 tubes, two and one-half inches in diameter and fifteen feet in length. The force-main is cast iron and twenty inches in diameter, excepting a short piece at the reservoir which is twenty four-inch. There are two classes of pipe: Class B varies in weight from 2,464 pounds and class A, from 1,980 pounds per length of 12.46 feet. There are seven gates, thirteen hydrants, six air valves, two ten-inch,and five six-inch blowoffs along the main. From the engine house there are 19,076 feet of twenty-inch and eighty feet of twenty-four-inch pipe—total, 3.63 miles.
The high service reservoir has a cement concrete bottom javerage thickness ten inches, including a layer of cement mortar threequarters of an inch thick. The face of the ledge on three sides is concreted to the top. The stone wall is laid in cement mortar and is thirty inches wide at the top under the coping, which is the full width of the wall, one foot thick,and the end joints filled with Portland cement. The corners of the reservoir are circular in shape, except one, which is cut off at an angle of fortv-five degrees, so as to form the front wail of the gate chamber and to give more embankment, thus strengthening the reservoir. The bottom is not a uniform plane: but slopes ‘owards the drainpipe at the gate chamber. Six springs were found along the noith side, and three near the southwest corntr.at which places small iron pipes were built into the masonry. The top of the eastern embankment is ten feet wide, including the masonry, and has an outward slope of two to one. Its elevation is 401 feet and highwater is three feet lower. The inside of the gate chamber is fifteen feet wide by fifteen feet, six inches long and twenty feet deep, ft is divided into two compartments, for the wire and the screens. There are four twenty-inch sluice gates—two of them located eight feet apart vertically, so that water can be drawn from two levels. A permanent weir of southern pine, with its edges of steel, is built into the masonry. The elevation of the crest is 397.29 feet.
The exterior walls of the gate house are of stone, with granite trimmings. The interior of the best face brick laid in red lime and cement mortar: the floor is supported by brick aiches and the top is covered with Portland cement mortar. The ceiling is of Georgia pine, nailed to the rafters and has two coats of hard oil finish. The gate house is nineteen feet, ten inches square, and has a hip roof covered with red slates and terra cotta hip rolls.