Brooklyn’s Original Source of Water Supply.
A SATURATED bed, situate about seventy-five feet above tide water, composed of sand and gravel, called Hempstead Plains, terminating by gradual slope on the south side to the Atlantic Ocean from 8 feet to 10 feet per mile and on the north side to a central ridge about 200 feet above tide water. This ridge forms what is termed Ridgewood Hills and is known as the “ back bone ” of Long Island.
Depressions at frequent intervals near tide level in the shape of swamps, and from which strong springs issue and form by their flow short creeks. It is estimated that the flow of these streams are about forty per cent, of the annual and daily discharge of the saturated bed, averaging about 1,200,000 gallons per square mile, and based upon a mean annual rainfall of forty-two inches.
The aqueduct from pump well at Ridgewood to Jamaica creek is nearly four miles in length and its size in cross section measufes eight and two-thirds feet by ten feet; its grade is six inches per mile. The delivering capacity with this slope is 70,000,000 gallons each twenty-four hours with a depth of water equal to five feet deep and when full, its estimated delivering capacity if grade is raised three and two-third feet, about 100,000,000 gallons. The aqueduct extension to Hempstead varies in width from ten feet to eight feet and two inches and its height eight and two-thirds feet to six and five-sixths feet, the grade per mile being six and one-third feet and its length 7.542 miles.
The area of drainage above and north of the aqueduct, which is 12.39 miles in length, is about 85.45 square miles, its estimated annual discharge by streams and springs is said to be about 106,000,000 of gallons daily. Of this amount utilized, the old works obtain by gravity flow into the aqueduct about 20,000,000 gallons of water daily and by driven wells located along the line and south of the aqueduct 35 million gallons of water daily. From this last source (driven and open well supply) the pumping from them has in seasons of drouth, notably in the year 1891, been increased daily, for a length of time, equal to 37,000,000 gallons daily.
In the year 1891, Brooklyn commenced to use water from the new watershed acquired east of Rockville Centre, to the extent of 6,500,000 daily. During the year 1891, the average daily consumption of water was 58,025,000 gallons and
it was the extreme measure of the old watershed necessarily forced to its utmost.
THE NEW WATERSHED TERRITORY,
From Rockville Centre to Massapequa, a distance of 10.05 miles, embiaces the new watershed of 101.20 square miles, of which 12.70 square miles are unused, making available 88.5 square miles in area. It was estimated under plans of the year 1892, the minimum supply would be 20,000,000 gallons daily, and with driven wells established, the same as upon the old watershed, a much larger supply could be obtained.
The present sources of supply are equal to the demands. The extension to new watershed was urged several years ago, and at the time, when the daily consumption did not exceed 35,000,000 gallons; in 1892 it was 58,000,000 gallons.
The old watershed gives about 55.000,000 gallons daily and with the new added to the above figure, it increases to 75,000,000 gallons daily, not estimating supply from driven wells sources on new shed.
THE OLD CONDUIT.
Its delivering capacity when in thorough repair is estimated to be 75,000,000 gallons in twenty-four hours.
The conduit completed in 1892 is a forty-eight inch cast iron main laid alongside of the old brick conduit. It has a cipicityof 2>,oaa,oao gallons delivery in twenty-four hours.
RHJ total conduit capacity now leading to the pump wells at Ridgewood station is therefore 100,000,000 gallons delivery in twenty-four hours.
The total conduit capacity is of necessity more than the average daily consumption and for the reason that during certain months in the year, the daily average consumption is greater than the yearly average consumption.
In brief it will be observed that the old watershed of Brooklyn has been worked up from a surface source of supply of about 20,000,000 gallons daily to 55,000,000 gallons daily, by applying open and driven wells to the territory embraced in the old shed, and south of the old conduit line.
The forty-eight inch new iron conduit is of 25,000,000 conduit capacity; it has been called upon to exercise its maximum conditions. Brooklyn is therefore critically speaking, not provided with supplementary conduit capacity to withstand extraordinary demands for water, when in extreme conditions of demand and in case of accident to the old conduit.
It showed in January, 1893, a daily consumption of 83,000,000 gallons of water.
“ The average daily consumption of water for the year 1892 was 67,555,000 gallons. The greatest daily average for any one month was in July when it reached 72,250,000 gallons.”
“The highest consumption of water in one day in the year 1893, was on February 20, 1893, when it reached 85,705,357 gallons while the average daily consumption was 75,831,705 gallons. The old watershed pressed to its utmost capacity, yielded 60,000,000 per day in wet seasons, as its maximum
capacity and fell to about 46,000,000 gallons in time of drought. Of the 60,000,000 gallons of the old shed about one-half comes from the natural flaw and one-half from pump stations, open and driven wells. It would seem possible to increase the supply from the new extension (now 20,000,000 minimum) by storage ponds and pumping stations so as to make it equal in production to the old watershed.”
The plans for increasing and developing the supply upon the new watershed contemplates the laying of a sixty-inch steel conduit from Mil burn to Ridgewood pumping station, with a delivering capacity of 40,000,000 gallons of water in twentyfour hours and the completion of five driven well plants east of Milburn station. It is estimated that the yield of the driven well plants will approximate 5,000,000 gallons each in twenty-four hours.
When the new sixty-inch steel conduit is completed, the total capacity of all, including the new. will be 140,000,000 gallons in twenty-four hours.
The mechanical features of the new proposed driven well plants,are a great improvement over the old ones, particularly in the character of the tubing used, which will be made of copper or brass and larger in cross sections of area. In the old plants wrought iron tubes were used of two and one-half inch diameter and the work of gradual diminution of area of pipe by oxidation resulted in a short time in partial, if not complete obstruction of the pipes, thus necessitating frequent withdrawal of old tubes and replacement by new ‘and improved ones. There is very little difference so far as it relates to area in square miles between the old and the new watersheds and in fact with regard to the flow of stream sources of supply.
Mr. Van Buren, late chief engineer, estimated the minimum flow of the streams on the new watershed to approximate 20,000,000 of gallons in twenty-four hours, and the yield of the old watershed stream sources of supply, as determined in 1891, a dry year, was about the same figure. The principal and vital question now in process of solution is to ascertain what will be the yield of the saturated bed on the new watershed, without interfering with, or impairing the stream sources of supply. If the underground conditions are the same in essential features, which are yet to be determined by the present work, then from a rational standpoint associated with the experience and skill of the engineers in charge, it may be assumed a reasonable expectation to obtain practically, the same results as have been established by the work upon the old watershed.
The reports of the late Chief Engineer Robert Van Buren show an average daily yield of 55,000.000 gallons from the old water shed. If the new one does as well it will be a hippy consummationof the present plan in progress of construction. When the plans are complete, Brooklyn’s daily supply from the old and new shed,will not be less than 100,000.000 gallons in twenty-four hours.
(To be continued.)