THE SOURCES OF WATER SUPPLY SUITABLE FOR THE FUTURE USE OF

NEW YORK CITY.

BY JAMES H. FUERTES, C. E.

To the Engineering Committee of the New York Merchants' Association, Thomas C. Clarke, Past President Am. Soc. C. E., Chairman :

GENTLEMEN:

On the 16th of December, 1899, instructions were given me by your committee to make the investigations necessary to ascertain from what sources, at what pressure and at what cost, water, as pure as the present Croton water in its best condition, could be obtained for a future supply for the City of New York.

In response to these instructions, I have now the honor, after nearly four months of work, of presenting the results of these investigations.

The work accomplished has been, in brief, the careful investigation of all the possible sources of water supply which could be economically developed by New York City. This has required the location of several hundred miles of aqueduct lines, the selection of sites for filter plants, settling basins, distributing reservoirs, storage reservoirs and their accessory works; the making of surveys of the valleys of the Catskill, Schoharie and Esopus creeks and Wallkill River; the reconnaissance for aqueduct lines in country for which no maps were available; the examination of all stream crossings and other critical points, and the study of the geology of the State with reference to its effect on the cost of the proposed structures. The most exacting part of the work has been the preparation of the detailed estimates of cost of construction and operation of each project, abstracts of which only are presented with this report.

Record maps, on a scale of 500 feet to the inch, have been prepared from the field notes of all the surveyed creek valleys,

reservoir sites and filter sites, and preliminary designs were made for all the filter plants, aqueduct sections and special structures, as a basis for the various estimates of cost. The estimates have been made in as much detail as was desirable, applying prices for materials and labor in the same manner as if the work were to be let by contract. In the estimates of annual cost of operation, your committee instructed me to use a rate of 3 per cent. for interest charges, and to leave out of consideration any charge for a sinking fund. My office force has prepared not only the finished maps published with my own report, but also the maps and diagrams submitted with the reports of Messrs. Croes and Crowell. The work has been carried on by a permanent force of six men, with additional assistants, as circumstances occasionally required. I have been particularly fortunate in having the uninterrupted services of William B. Fuller, M. Am. Soc. C. E., late resident engineer in charge of the construction of the Albany filter plant, to whom was assigned the supervision of the calculations regarding the movement of salt water in Hudson River, and the estimate of the present value of the New York waterworks plant.

The other members of the engineering force were Messrs. Albert J. Himes, M. Am. Soc. C. E.; William P. Boright, C.E.; R. H. Anderson, C.E.; J. F. K. O'Connor, M.E.; A. A. Aguirre and R. H. Cable. The quantity and quality of the work accomplished bear witness to the faithfulness and devotion of the corps.

At this point I wish to express my thorough appreciation of the many courtesies extended me by the members of the Engineering Committee and of the Association.

I.

PRELIMINARY CONSIDERATIONS.

As a basis of work the Engineering Committee specified two quantities of water for the securing of which it was desirable to provide plans and estimates of cost: 250,000,000 gallons daily, and double this amount, 500,000,000 gallons daily. Instructions were also given me to leave out of consideration all streams flowing into other states, and all waters in the Adirondack Mountains. The investigations recounted in this report

are therefore confined to the Hudson River and its tributaries south of the Mohawk River.

A preliminary study of the region north of New York City, on both sides of the Hudson, indicated that waters which could be economically brought to New York by gravity could be delivered at an elevation of 310 feet above sea level; and that the additional quantity which could be delivered at a lower level was quite small. All the gravity projects provide, therefore, for delivering the water 310 feet above sea level at the City line, an elevation sufficient to allow of the distribution of the water to any part of New York, Brooklyn or Staten Island, without pumping.

The watershed areas, for estimating stream flows, have been taken from the topographic maps of the U. S. Geological Survey, from Julius Bien's atlas of the State of New York, and from county maps secured especially for the purpose.

As a basis for calculating the yield of the different streams investigated, it has been assumed that the conditions affecting losses of water by evaporation and seepage on their watersheds are about the same as on the watersheds of the New York and Boston water supply works. It has also been assumed that the dry-year yields of the streams, per square mile of watershed, with different amounts of storage, would be about the same as has been determined for the streams in the Boston, Mass., Croton, N. Y., Perkiomen, Tohickon and Neshaminy, Pa., watersheds, the records of which are the most complete and reliable to be had in the eastern part of the United States. These assumptions are conservative, because the normal annual rainfall on the watersheds under consideration is somewhat greater than on the Boston watersheds. Another compensating factor in the Catskill watersheds is that the valleys through which the creeks flow are filled with gravel and other permeable materials, which will make the available considerably in excess of the visible storage.

In the absence of continuous records of the gaugings of the streams, the assumptions are sufficiently near the truth for the purposes of this study.

The yields obtained under these assumptions will err on the safe side by giving too small rather than too large quantities.

This view is strengthened by Mr. Rafter's estimates of the yield of Schroon reservoir, which are based on gaugings of the

rivers in neighboring territory, using Rochester evaporation data. From these he concludes that the reservoir can easily furnish 500,000,000 gallons a day. The yield, according to the data which I have used, would be about 433,000,000 gallons per day.

The absolute minimum yield of a stream during a series of dry years is exceedingly difficult to estimate with accuracy, even when complete rainfall records have been kept for a great many years in the territory in question. The yield depends, naturally, upon the meteorological conditions and the geological structure of the country, as these affect the natural losses of water, including absorption by plant life, evaporation from surfaces and seepage into the soil.

Evaporation data, including all the above losses, have been collected for some years at several points in this country, and in making calculations for the yields of streams, data from one of these places are generally used, often regardless of whether or not the modifying conditions are similar to those at the point where the data were obtained. As the influence of evaporation is very great, errors in its amount will seriously affect the yield. deduced from its use.

It has always appeared to me, therefore, that to use carefully collected information regarding stream flow from places in about the same latitude, where annual rainfall and temperature conditions are not very different, would give results as nearly correct as it would be possible to approximate in view of the many complex and not easily differentiated conditions.

In order to ascertain the amount of water which could be stored in some of the creeks, it was necessary to survey and prepare contour maps of their valleys, the needed information not being available in published form. These surveys, though hastily made with the aid of many labor-saving devices, covered Esopus and Schoharie creeks, parts of Catskill Creek and the upper thirty miles of Wallkill River, together with the tributaries of each. Although not more than approximate accuracy was desired, various checks were employed whereby errors were kept within definite limits. In addition to surveying the valleys of the principal streams, the various sites for filter beds, pumping stations, settling basins, reservoirs and other works were also surveyed and mapped.

The alignments and profiles of the aqueduct lines were es

1

tablished, in the main, from the United States Geological Survey sheets; the courses of the lines for about one hundred miles, through country for which no maps were available, being located in the field by inspection.

The crossings of the aqueducts over the different streams and valleys have all been inspected and carefully studied on the ground, and the geological structure of the country traversed or occupied by the works has been carefully observed and made a subject of special study.

The aqueducts have been located with the view of securing the shortest lines between the given points consistent with economic construction.

are:

II.

THE BASIN of the LowER HUDSON.

The main branches of the lower Hudson, on the west side,

Murderers' Creek, emptying into the Hudson near Cornwall.

And several smaller creeks, such as Vlaumans Kill, Coey

mans Creek, Plaaterskill Creek and Kaaterskill Creek.

On the east side of the river, above the present Croton watershed, are:

Peekskill Creek, emptying into the Hudson near Peekskill.

Among these streams are some which could not be used because they do not lie at sufficiently high elevations; are al