THE hydraulic engineer in the line of his profession feels more solicitous concerning the characteristics of the above-named features that relate primarily to a water supply, than to any other identified with his work. It is quite a problem to be solved in the several aspects of the case, and peculiar conditions are often met with in the progress of investigation and research, and when least expected.
Light thrown on one particular subject often reveals associate subjects which otherwise would not have been revealed, and which, taken separate or. associated with the original subject of investigation, demand equal consideration. In this case it will be apparent that rain fall, water-shed, and storage capacity are intimate in their relations. A consideration of one without association of the remaining two is of no practical value to the .hydraulic engineer in the prosecution of work in the field of his profession. It occurs to us that the literature evolved during the past few years upon these important subjects is the result of much study and painstaking on the part of the authors. Investigation of recent papers reveals the fact that they are the result of experience and observation rather than of theory or conjecture. F. P. Stearns, chief engineer of the Massachusetts State Board of Health, at the last quarterly meeting of the New England Water-works Association held in Boston, contributed a valuable paper entitled “ Sources of Water Supply,” and accompanied by tables of rain fall, rain fall collected, and percentage of rain fall collected of the Sudbury river water-shed from year 1875 to year 1890, also a diagram showing rain fall on same water-shed from year 1875 to year 1890.
The tables are very complete, and indicate monthly measurements for a period of sixteen years of rain fall.
One table of additional interest also appears, showing the average daily flow from the Sudbury river water-shed for different periods varying from one month to sixteen years, selecting in each case the driest period of given duration. A. Fteley, chief engineer of the New York Aqueduct Commission, also permits a similar table, and for a period of seventeen years, of the flow of Croton river, to be published in the proceedings.
These two tables illustrate the number of gallons per day per square mile, gallons per day per acre, cubic feet per second per square mile.
The noticeable feature of the last-mentioned tables are that the months selected during the sixteen and seventeen year periods were the dry months. In commenting upon the important character of these tables, it is worthy of remark that it would be difficult for one to be disappointed regarding quantity estimated, based upon such common sense figures as are set forth in the tables.
A table upon relation of evaporation to rain fall, by D. Fitzgerald, C. E., Boston, and presented by him to the American Society of Civil Engineers, also appears in the journal of the New England Waterworks Association.
Mr. Stearns has also contributed a table showing the amount of storage required to make available different daily volumes of water per square mile of watershed estimating land surface only, corrected for the effect of evaporation and rain fall on varying percentages of water surfaces not included in estimating the area of water-shed. This table shows at a glance the idea intimated in our early remarks of the association of storage area with the watershed. It is one of the best tables we have yet seen upon the subject, and bears evidence of careful study and consideration of the vital points involved in the question of sources of water supply. A close study of these tables will be a revelation to many, in that it will disturb very many calculations as to the quantity of rain fall which has hitherto been supposed to be capable of utilization.
It is of considerable interest to note the views expressed concerning the storage capacity of the East Jersey Water Company in its relation to contract requirements with the city of Newark, N. J. It is stated by A. Fteley, consulting engineer, that the storage capacity in the Pequannock water shed does not insure a delivery of 50,000,000 gallons of water daily in seasons of drought. In drought season only 35,000,000 gallons can be depended upon.
Prof. Geo. Cook, for many years State geologist of New Jersey, kept the rain fall record of Pequannock water shed.
J. J. R. Croes and George W. Howell in 1879, in a report made to the Newark aqueduct board, gave the mean annual rain fall for a period of twentyfour years, 1846 to 1869 inclusive, as 42.55 inches.
In that period, 1862, 1864 and 1866 were the three driest years, the last mentioned being the lowest, namely, 30.06 inches, and of that amount 49.3 per cent were collectible, which shows but 14.81 inches of the rain fall. Mr. Vermeule, in the last State geological report of New Jersey, confirms the above as substantially correct in result.
Fanning, on “ Water Supply,” remarks, for utilizing the greatest possible portion of the flow is 20 to 25 per cent of the mean annual rain fall. Twenty per cent of the mean annual rain fall, 42.55 inches -f. 5 =8.51 inches, which is available. The watershed of the Pequannock is 65 square miles, and the estimated net result is 9,638,085,660 gallons.
It will appear, judging by Fanning’s lowest figure, namely, 20 per cent of the mean annual rain fall, to furnish the contract requirements to the city of Newark, namely, 50,000,000 gallons per day in dry years, that the storage capacity should be about equal to 9,500,000,000 gallons.
The present storage capacity on the Pequannock water-shed is as follows :
Mr. Fteley, consulting engineer for the city of Newark, takes the position practically that in dry years not more than seven-tenths of the contract figure can be met, and it would seem, in view of all data originated by experts on the subject, and relating to this particular water-shed, that Mr. Fteley is right. It is interesting to note that Fanning, Fteley and Stearns practically agree upon the vital characteristics associated with the features of utilization of rain fall.