THE NEW RESERVOIR AT OAKLAND

THE NEW RESERVOIR AT OAKLAND

Under the supervision of G. H. Wilhelm, chief engineer of the People’s Water Company at Oakland, Cal., the Piedmont Construction Company has just completed a concrete-lined distributing and equalizing reservoir of 150,000,000 gallons capacity. With the exception of some of the minor details the plans were prepared by M. Kempkey, under the direction of A. L. Adams. The recent annexations to the city, giving it a population exceeding 150,000, has made the increase of its water supply imperative, and the new reservoir is said to be the largest on the Pacific coast. It is situated on an elevation of 198 feet above the city. It was made by throwing an earth dam across a former creek bed, the waters of which at one time drained into Sausal creek. Ample provision for the disposal of the surface drainage from above the reservoir is provided by the street sewers in that part of the city. The side slopes of the natural basin were then graded uniformly, and the whole interior of the reservoir, side slopes, dam slope and bottom covered with a layer of concrete. This forms a basin 1,500 feet long by 800 feet wide, covering nearly 20 acres. In all over 200,000 cubic yards of earth were removed and about 100,000 square yards of surface concreted. The water is supplied through a 36-inch riveted steel pipe line a mile and a half long from the Twenty-fourth avenue pumping station, which draws on the company’s main conduits from Lake San Leandro and Alvarado wells. The supply mains to the city are also connected to the discharge of this pumping station, so that central reservoir will fill during periods of low draught, and will supply the deficiency in periods of high consumption, incidentally providing a storage of eight days’ supply under high pressure for all of the lower part of the city of Oakland. The dam is 25 feet wide at the top, 56 feet high and about 900 feet long, with slopes of two horizontal to one vertical on both sides. The outside slope is to be sodded and planted, to prevent erosion, and the inside slope is covered, as noted above, with a 6-inch facing of concrete, terminated at the bottom hy a concrete cut-off wall 2 1/2 feet thick, and varying in depth from 6 feet at the middle to 20 feet at the ends. This wall is bonded well into the concrete lining of the slope face. The paving on the graded slopes is 4 inches thick and is placed in the same manner as that on the dam slope, viz., in 12-foot square slabs, with joints made of “D” grade asphaltum mixed with corbolated lime and run hot. Construction was commenced eighteen months ago, and with the xceptifcn of the short rainy season of the following winter was pursued continuously to completion last October. Test pits were sunk to a depth of 40 feet on the site of the dam and at other parts of the reservoir site and disclosed alternate layers of varying thickness of mixed sand and gravel with clay in large quantities, which, after excavation, placing on the dam, and rolling, formed an excellent and compact day puddle, of which practically the entire dam is built The base of the dam was excavated to a depth of 15 feet below the original surface. Earth was removed at first with a 2 1/2-yard 70 ton steam shovel, emptying into bottom dump wagons which deposited their contents on the dam in layers of 6 to 12 inches in thickness, over which a 12-ton steam roller worked continuously. Later, in the final grading of the side slopes, a 16-horse-drawn gasoline operated grader was used in conjunction with plows and scrapers. For a period of over three months, the steam shovel and dump wagons handled an average of over 1,000 cubic yards daily. All the side slopes of the basin where fills had been made were compacted with a steam roller before the finish grade was set. To eliminate the danger due to exposed pipes in an earth embankment, and to provide for leakage of the same and inspection, a concrete culvert of arch section 8 feet in diameter, with cut-off ribs, runs through the dam and carries, on concrete piers, two 24-inch castiron mains for supply and one 16-inch main for sluicing and drainage of the reservoir. By means of a lead expansion joint embedded in the concrete the culvert is united to a concrete gatetower at the inside toe of the dam. This tower is 6 feet, inside diameter, with 2-foot walls, 56 feet high, and 30×30 Coffin sluice-gates at three levels, operated from the gate-house above by beveled-gcared ball-bearing stands. The tower is surmounted by a rustic-finish modern gatehouse, being reached from the dam over a wooden foot-bridge of two 33-foot spans with a center bent 19 feet high. As the lower part of the gate-tower is in embankment, it was necessary to connect the lower level of the reservoir floor to the outlet tower by a small concretelined tunnel 3 feet by 4 feet in section. The inlet of this tunnel is at an elevation of 146.5, thence it drops on a gradual grade to a sump, where the blow-off pipe is located, and the remaining 20 feet rises to the tower at an elevation of 150 feet. By this plan all the sediment wall be left to the sump, where it can be blown off. The rim of the basin is enclosed by a concrete wall 4 feet high, built in 12-foot sections with joints of building paper and asphaltum. The wall carries an ornamental iron fence and will eventually be surrounded by a driveway. It is the purpose to convert the slopes into public parks. An overflow basin is arranged at an elevation of 198.5 to discharge into a 24-inch terra-cotta drain to a storm sewer. Two springs were uncovered during the process of grading near the center of the reservoir, one of which was excavated to its level bed, from which an 8-inch vitrified drain was laid to the blow-off pipe of the reservoir. This ensures proper sub-drainage and is in no way affected by the opening or closing of the valves. The other small spring was excavated and the hole back filled with tamped clay. This completely checked the flow of the water, and no further trouble was experienced. All structural concrete for the tower, culverts, tunnels, etc., was mixed in proportion of 1: 2: 4. The culvert was reinforced transversely with 3/8-inch round rods spaced 16 inches c. to c. and longitudinally with the same size rods and spacing. Concrete for the lining was mixed in proportions 1: 2 1/2: using an electric-motor-driven mixer of about 18 cubic feet capacity, located on the upper rim of the reservoir, and shifted from time to time to follow the work. For a period of 63 consecutive days an average of 162 cubic yards daily was mixed and placed in nine hours, corresponding to one batch every two minutes. The best day’s work was 246 cubic vards in place. The mixer was fed by a 21 cubic foot loading car hauled up an inclined track, and the mixer discharged into a train of five dump cars of 16 cubic feet capacity, each. From the mixer, the cars were moved by horse to the edge of the slope, and while still in motion the horse was unhitched and the cable of a steam-hoisting engine attached, by means of which the cars ran to any part of the slope. On account of the steep slope of the inner face of the dam. the concrete for its facing was run down a chute instead of employing the cars. The concrete was then dumped on the finished earth slopes into slabs, the only forms necessary being 2×4 1/4 inches surfaced pine boards, 12 ft. c. to c., laid on edge. The concrete was tamped and left rough. When the concrete had set slightly, the forms were removed and a wooden wedge-shaped strip (7/8X5/8X 3 inches) was inserted in its place and the concrete filled in about it. After the concrete was completely set. these strips were removed and the asphalt joint poured. Embedded in the concrete in the bottom of the reservoir is a 3-inch water pipe with hydrant taps for flushing the sides of the reservoir. This was conveniently employed in wetting the concrete lining during setting.

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