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RUNOFF OF HUDSON RIVER AT MECHANICVILLE FOR THE
WATER YEARS 1888-1907, INCLUSIVE.

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Corrected for canal diversion, May to November, inclusive.

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* From advance copies of daily record, kindly furnished by Mr. R. P. Bloss C. E.

ACCURACY OF FORT EDWARD GAGINGS.

The conditions for accurate gaging at Fort Edward are decidedly less favorable than at Mechanicville. The methods followed are much the same at the two places, but at Fort Edward the number of turbines is larger and their uncertainties correspondingly greater, and it is possible that the making of the record is less closely supervised.

The main source of uncertainty in the Fort Edward gagings affects the results only in time of high water. This is due to a flood spillway whose crest is about level with the top of the flash boards, and which is of such irregular form that it caused uncertainty in the computation of the flow through it.

In New York Hydrology, page 375, Mr. Rafter says of the measurement through this flood spillway, that the computations may at times of high water be as much as 25 per cent. in error. (This percentage is understood to apply only to the portion flowing through the flood spillway and not to the larger portion over the main dam 587.6 feet long), and that for a number of years, he was unwilling to publish the record, but has since reviewed it, recomputing a portion.

Mr. H. K. Barrows, Hydrographer, U. S. G. S., considers that the gaging records at Fort Edward are probably from 5 per cent. to 10 per cent. in error at times, owing to the large number of turbines used in the record and the poor condition of the dam for gaging, especially at its right end, but also states that the Mechanicville records are probably accurate inside of 5 per cent., since the Mechanicville dam is in excellent condition, and the records of flow are closely looked after by a competent engineer.

In Water Supply Paper 166, page 18, it is stated that the drainage area above the Fort Edward dam is 2,800 square miles, that the timber dam rests on a slate ledge foundation and has but little leakage, that the crest is straight and nearly level and 287.6 feet long. In other Water Supply papers, it is stated that new and accurate profiles of the crest were made in 1903 and again in 1906, and used in determining the discharge. A photograph of this dam is shown in New York Hydrology, page 628.

In Water Supply Paper No. 65, page 48, it is stated that a record is kept of the height of the flash boards and of the heights of their setting and removal, and that the flow at that time, 1901, was computed by the Mullen, or East Indian Engineers formula.

In Water Supply Paper 125, for 1904, it is stated that for those periods while the flash boards are off, the discharge has in more recent years been computed in accordance with experiments made by the Geological Survey upon a model dam of this form. With flash boards on, the discharge is computed according to the Francis thin edged weir formula.

In the dry season, very little water passes over the dam, all or nearly all passing through the sixty-two turbines in the adjacent paper mill.

These water wheels are stated to be nearly all of modern types which have been tested at the Holyoke flume. A record is kept of the number of hours run by each turbine and of the working head, which is usually nineteen feet.

Check measurements have occasionally been made by current meter at a bridge downstream from the Fort Edward water power. In Water Supply Paper U. S. G. S., page 48, it is stated that check measurement made July 26, 1900, by current meter at bridge below dam, showed 2,704 second feet, while the computed discharge from turbine diagrams varied from 2,420 to 2,720 cubic feet, the average by the turbine diagrams thus being 6 per cent. less than by the current meter gaging.

There are

a few obvious errors in the Fort Edward record, viz., the monthly flows for December 1897, and December 1898. For these periods, interpolations based on the Mechanicville gagings have been used.

RUN-OFF OF HUDSON RIVER AT FORT EDWARD FOR THE
WATER YEARS 1896-1907, INCLUSIVE.

(In inches depth over catchment area.)
(Catchment area -2,800 square miles)

Corrected for canal diversion, May to November, inclusive.

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GAGINGS OF SCHROON RIVER AT WARRENSBURG.

There is available a record of the flow of the Schroon for a few years, which is probably much less precise than that at Mechanicville and somewhat less precise than the Fort Edward record, but since the Schroon is one of the largest tributaries of the Hudson and comes from a watershed of somewhat different characteristics, where according to the isohyetal maps the rainfall is somewhat less than for the Sacandaga or the central and mor elevated portions of the Adirondack plateau, it has appeared wise to make the best possible comparison of the Schroon and Fort Edward gagings as one more check upon our estimates of the Sacandaga yield.

The gaging of the flow of the Schroon is said to have been begun in November 1895, in connection with studies for Adirondack storage, reported upon in the N. Y. State Engineer's report for that year.

The State Engineer's report for 1901, page 541, presents records of daily flow from November 1895 to December 1901, and gives a description of the gagings, substantially thę same as that found in U. S. G. S. Water Supply Paper No. 65, page 45.

In U. S. G. S. Water Supply Paper No. 82, page 100, the daily flows are given for January, February, and March, 1902, and it is stated that owing to a change in management, the data for the remainder of the year were not available at time of publication. Water Supply Paper No. 97, page 222, states that records were maintained during 1903 under the supervision of R. E. Horton, Hydrographer, but publication was withheld awaiting additional data to confirm results.

The original record is understood to consist of a single daily measurement of depth flowing over the dam of the pulp mill at Warrensburg and a daily record of the hours run by the turbines.

The mill dam was of timber, was built in 1893, and stated in Water Supply Paper No. 35, page 58, to then have been "tight as any of its kind,"

but Mr. W. Greenalch, then assistant to Mr. Rafter, considered the estimates of flow at Warrensburg vitiated by the leakage through this dam and by the changes of the flash boards upon it. It appears probable that this leakage increased from year to year.

Mr. G. W. Rafter in New York Hydrology 1905, pages 400-403 gives a summary of the records for the Schroon and states that at the time of his inspection in October, 1895, with the pulp mill shut down and the Starbuckville dam tightly closed, the bed of Schroon river below Warrensburg was nearly dry, the flow not exceeding one to two cubic feet per second. He states that reports indicate that the leakage at a later date might be anywhere from 30 to 50 cubic feet per second.

In 1899, the average low water flow of the Schroon river at Warrensburg was estimated at 150 cubic feet per second, this being the assumed leakage of the Starbuckville dam at that time.

In time of low water, the mill was shut down, and whatever flow was not held back by the storage dam which controls the outlet of Schroon Lake at Starbuckville, came down the river and leaked through the Warrensburg dam. No daily record of flow was kept when the mill was not running.

The leakage of its dam, flash boards and flume on August 9, 1900, measured at a point one-half mile down stream from the dam in the open channel by current meter, was found to be 285 second feet.

This quantity was taken as fairly representative of the average low water flow and leakage in 1901, when making up the estimates published in the reports of the U. S. Geological Survey and the reports of the N. Y. State Engineer, which I have used.

For computing flows over the dam when flash boards are on, the Francis weir formula was used. When there are no flash boards, a formula derived from the Cornell University experiments on a model of similar shape is used. The pulp mill ran twenty-four hours per day for so much of the year as there was water to supply it, and being the only water power upon the Schroon, its owners controlled the flow for the benefit of the pulp mill by a dam on the outlet of Schroon lake, by which it is said water stored to a depth of from four to five feet on an area varjously stated at from seven to nine square miles, is let down as required for use during the summer months. In comparing the curves for Schroon yield with those of the main river, it should therefore be kept in mind that the Schroon has a flow regulated by storage, while the only other storage of which the main river has the benefit is that of Indian lake and perhaps a few lumbermen's dams.

While it is plain from the above description that these measurements of daily or monthly flow on the Schroon are not precise, it has been thought worth while to consider them, but only as checks, in relation to the estimates of Sacandaga yield deduced from the Mechanicville gagings.

GAGINGS OF HOOSIC RIVER AT BUSKIRK.

A study of these gagings also is useful in confirming the estimates of Sacandaga flow, the Hoosic being another of the important tributaries which enter above the main gaging station at Mechanicville. The record of the Hoosic flow is of special interest because this comes from a drainage area

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