The prime requisite to the creation of a water power is the existence
of falling or flowing water. The amount of power which may be available
varies; first, with the amount of water flowing, and second, with the
amount of fall. It requires about one cubic foot of water per second,
falling through a height of ten feet, to make available one theoretical
horsepower. The fall may be either naturally concentrated at one point
in a cascade or it may be artificially concentrated, for the purpose
of development, by combining the fall of several cascades or a series
of rapids. This may be accomplished by either of two methods; first,
by building a dam at the downstream end of the rapids to impound the
water so that the entire fall is concentrated at the dam, or second,
by building a dam at the upstream end of the rapids and conducting
the water through a closed pipe to the lower end of the rapids, where
the resulting water pressure will be exactly the same as in the first
instance. A variation of the latter method consists of diverting the
water from the natural channel at the head of the rapids and carrying
it in a canal, on a slight down grade, along the side of a hill to a
suitable point at which the water is turned into penstocks which run
directly down the slope to the stream, where the power development may
be made. The latter method, involving the construction of a canal, is
open to the objection that considerable trouble is usually experienced
from the accumulation of ice in the winter time. The first two methods
described are the most common.
[Illustration: Cascade on Indian Creek, Warren Co., N. Y. Typical
Example of Undeveloped Water Power]
The amount of water which flows in a stream, in New York State, whether
large or small, is subject to remarkable variation. Only one who has
observed very carefully and continuously, by actual measurement, the
extremes of fluctuation to which a flowing stream is subject, is in a
position fully to appreciate this. Some of the larger rivers of New
York State are subject to such fluctuations of flow that the amount
of water discharged during flood periods is several hundred times as
much as the amount that flows in the extreme dry period. Also in many
instances from one-half to three-fourths of the total runoff of the
stream during the year occurs during a period of a few weeks in the
spring months, when the accumulated snow and ice is melted and runs off
in conjunction with the warm spring rains. Unfortunately, reliable data
relating to the fluctuations of small streams in this State are very
meager. It is, however, a matter of record that the smaller streams for
which records are available are subject to greater fluctuations per
unit of tributary watershed area than are the larger streams. It seems
logical, therefore, to assume that the very small creeks and brooks
are subject to fluctuations relatively greater than those recorded for
streams of only relatively small size. This fact must be borne in mind
by any one who proposes to develop the power on a stream, for if it is
overlooked the project is not so assured of success. For most purposes
power is required in about the same amount for all seasons of the year,
while, as previously stated, the streams run off most of their waters
in the spring. Therefore, in developing the power of any particular
stream, if the power is required to be fairly constant at all seasons
of the year as is usually the case, there are two considerations which
must not be overlooked:
First—Will the minimum flow of the stream—that is, the flow which
occurs in the driest season of a dry year—be sufficient to furnish the
amount of power required?
Second—If the minimum flow is not sufficient, what means are available
for storing the surplus water from the wet season until the dry season?
The subject of equalizing stream flow throughout the year by means of
storage reservoirs has been so thoroughly discussed in the reports of
the Commission that further discussion in this connection does not seem
warranted.
Taking a general average throughout the State of New York, large
streams may be depended upon to produce from one-twentieth to
one-quarter of a cubic foot of water per second per square mile of
tributary drainage area, during the driest period. Streams having
only one or two square miles of drainage frequently dry up entirely
in the dry seasons. If a power development is proposed of such a
character that some considerable sacrifice of power might be made
in the dry seasons with no serious loss, most small streams may be
developed to provide for as much as one-quarter to one-half of a cubic
foot per second per square mile. On the other hand it is often found
practicable to provide a small auxiliary power plant, such as gasolene
or kerosene, to fall back upon in dry weather, or to supply extra power
occasionally, in which case the water-power development need not be
limited to the minimum flow of the stream.
The power of falling water may be applied to practical purposes in
several ways. One of the simplest ways, should it be desired to use
the power of the stream to pump water, is by means of what is known as
a hydraulic ram. This is a device which operates on the principle of
the impact due to the sudden stoppage of flow of a column of water. By
means of this device, or engine, water falling through a very small
height may be used to raise a portion of the same, or a comparatively
small amount of other water, to an elevation considerably higher
than the supply. The mechanical efficiency of the hydraulic ram is
comparatively high under certain conditions but generally is very low,
useful work which manufacturers claim may be realized varying from
38 per cent to 80 per cent. The minimum fall under which a ram will
effectively elevate water is about two feet. This fall will elevate
about one-thirteenth of the supply to a height of twenty feet. Under
the most favorable conditions and a fair amount of fall, a ram may
elevate water as high as 120 feet. The proportion of water which may be
elevated varies from one-twentieth to two-sevenths of the total
supplied; and, accordingly, the proportion of water which must be
wasted at the impetus valve of the ram varies from five-sevenths to
nineteen-twentieths. These proportions both depend upon the ratio of
the amount of supply to the amount to be elevated, that is, a small
proportion may be elevated to a considerable height and vice versa. In
cases where a small brook of suitable quality is available for domestic
water supply, it is often entirely practicable to install a hydraulic
ram which will pump a sufficient proportion of the amount of supply to
furnish a household with all the water necessary for ordinary domestic
purposes, in spite of the fact that the brook may be on a lower level
than the house. Owing to the fact that a hydraulic ram may be applied
only to the purposes of elevating water, it is not generally considered
as a means of developing water power, although in the broadest sense it
does constitute such a development.
On the other hand, the purposes for which power is usually required
are not only for the elevation of water for a water supply, but for
many other and varied requirements. In such cases the power must be
developed in such manner that it may be utilized to operate machinery
near the site of the development, or transmitted for some distance, and
there used to operate machinery or for lighting or heating. To develop
water power in this manner requires some kind of a waterwheel.
There are several types of waterwheels, the principal ones being known
as “undershot,” “overshot,” “breastwheel,” “turbine” and “impulse.” The
overshot wheel is a type very familiar to most readers, being usually
of home manufacture. It consists, usually, of a wooden wheel with water
compartments arranged at regular intervals around the periphery. The
water is fed into the wheel at the top, just off the center. It flows
into the compartment at the top and the weight being exerted on one
side of the supporting axle causes the wheel to revolve, the water
spilling out when the compartment, or water pocket, reaches the bottom.
This type of wheel depends entirely for its power upon the weight of
the water which causes the wheel to revolve.
The undershot wheel is very similar in construction to the overshot
type but depends more for its power on the velocity of the flowing
water which strikes the blades, or buckets, on the under side of the
wheel.
[Illustration: Turbine Type of Waterwheel