STORAGE OF CITY WATER INCREASED BY CONCRETE DAM
The concrete arch dam for the city water supply has been completed and is now ready to be put into service so the supply of stored water will be largely increased. The dam is located six hundred feet above the old dam and is built in the form of an arch spanning the mill pond from bank to bank. The spillway of the new dam is two hundred feet in length which is forty-six feet longer than the spillway of the old dam. The new dam will raise the water behind it four and a half feet higher than the previous level of the pond and will back the water as far as the dam at Milltown. The water in the new pond will overflow forty acres in addition to the area now covered. most of which is located between. Ryder’s Lane and Milltown. The amount of water which was available in the old pond which could be drawn to a depth of five feet below the dam was 87 million gallons. The new dam will add 146 million gallons to the capacity of the pond so there will be an available storage in the Weston’s Mill pond of 233 million. gallons.
The dam is built in the form of an arch. This form where the site is suitable makes it possible to build a dam with greater strength with much. less material than the form of dam which depends on the weight of the structure only to resist the water pressure. The older type of dam usually has a factor of safety of two while the arch dam which has been constructed has a factor of safety of ten. An unusual feature of the dam was that it was constructed in the water of the pond which was over eighteen feet deep and which could not be drained on account of having to maintain the city water supply during the construction of the dam. The construction under these difficult conditions was carried on by building the dam in twenty-five sections which were surrounded by a tight cofferdam of steel sheet piling.
Concrete Poured in Movable Forms.
After pumping out the cofferdam the concrete was poured in movable forms which were used for the whole. structure.
The dam has a spillway with. a length of 200 feet which is held by abutments of twenty-five and thirty feet in length at the two banks. The j dam rests on the solid shale rock and the abutments reach to the shale in each bank. The crest of the dam is three feet wide and the base is nine) feet wide. The height of the dam in the pond is twenty-three feet. The normal difference of water level above and below the dam is four and a half feet but the structure is designed to hold the water for the full height of the dam if the water in the lower pond is entirely drained.
In fixing the location of the structure complete plans and estimates! were made for the dam as built and also for raising the old dam. It was found that it would take more labor and material to raise the old dam than to build an entirely new structure in the adopted location. In addition to the cost of the work there. would be a very great risk of accident during the construction of the dam which might wipe out the pumping station. There would also have! been the work of caring for the ice;” house property which was located Just above the old dam and which would have involved serious expense,
The question of additional storage has been a pressing one for sometime. In 1911 the advisory water commission, the members of which were Drury Cooper, E. P. Darrow, W. H. Benedict, A. A. Titsworia, F. C. Schneider and A. S. March, strongly advised the immediate raising of the present dam three feet to provide the additional storage. They stated. at
that time that this would take care of the immediate need and that additional provisions could be taken after some years had passed. The present structure raising the level of the pond four and a half feet adds over) fifty percent to the additional storage contemplated by their recommendations.
Plans Made in 1914.
The plans for the dam were made! in 1914 at the time of the serious water famine which occurred in:” September of that year and it was strongly urged that the structure be, built at once so sufficient water could be stored to prevent the recurrence. of the shortage. On account of the authority to build being withheld je from the Board of Water Commissioners by the Board of Aldermen, the work was postponed until Commission Government took hold of t matter. The building of the dam was again postponed by the judgment of the advisory water board until after the completion of the filter plant as it was thought that building operations would cause the water to be made turbid. The work was finally started in the fall of 1917, The necessity of the work was shown last fall when all of the storage was used up and temporary pumping was required from the creek below the dam to maintain the necessary amount of water.
During a dry time all the water required beyond that furnished by the flow of Lawrence brook must be taken from storage. The flow of the brook was estimated by the state as given in the report on water supply as a minimum of five and a half gallons a day for the driest period. This estimate is largely in excess of the actual amount which was observed in the dry periods of 1914 and 1918. A careful measurement of the individual streams of the watershed. show that the minimum flow of the Lawrence brook area amounts to only 1,800,000 gallons for 24 hours. The consumption last September, due largely to war conditions perhaps, required seven million gallons a day so five million under these conditions must be taken from storage. City Can Supply 100,000 Population With Water by Damming Near Milltown.
When the water consumption of the city again exceeds the present provision additional storage will have to be sought by a dam somewhere above Milltown or by taking water from the Raritan River. The late Dr. Cook reported on a project for a high dam at a site near Parsons pond which would impound 1,640,000,000 gallons of water. The cost of the dam at that time was $347,000, but under present conditions, it would be two or more times that figure. As everyone has great faith in the steady growth of the city of New Brunswick which is largely dependent on the water supply the necessity of looking! forward is apparent. With the above] storage a population of 100,000 could be supplied with an adequate amount of water.