estimates of the water power
furnished by expert engineers.

A rough estimate of the volume of a stream may be made by the method
described below:--

Suppose we allow a stream of water to flow through a rectangular
trough; the speed with which the water flows through the trough can be
determined by noting the time required for a chip to float the length
of the trough; if the trough is 10 feet long and the time required is
5 seconds, the water has a velocity of 2 feet per second.

[Illustration: FIG. 123.--Estimating the quantity of water which flows
through the trough each second.]

The quantity of water which flows through the trough each second
depends upon the dimensions of the trough and the velocity of the
water. Suppose the trough is 5 feet wide and 3 feet high, or has a
cross section of 15 square feet. If the velocity of the water were 1
foot per second, then 15 cubic feet of water would pass any given
point each second, but since the velocity of the water is 2 feet per
second, 30 cubic feet will represent the amount of water which will
flow by a given point in one second.

175. Quantity of Water Furnished by a River. Drive stakes in the
river at various places and note the time required for a chip to float
from one stake to another. If we know the distance between the stakes
and the time required for the chip to float from one stake to another,
the velocity of the water can be readily determined.

The width of the stream from bank to bank is easily measured, and the
depth is obtained in the ordinary way by sounding; it is necessary to
take a number of soundings because the bed of the river is by no means
level, and soundings taken at only one level would not give an
accurate estimate. If the soundings show the following depths: 30, 25,
20, 32, 28, the average depth could be taken as 30 + 25 + 20 + 32 + 28
/ 5, or 27 feet. If, as a result of measuring, the river at a given
point in its course is found to be 27 feet deep and 60 feet wide, the
area of a cross section at that spot would be 1620 square feet, and if
the velocity proved to be 6 feet per second, then the quantity of
water passing in any one second would be 1620 x 6, or 9720 cubic feet.
By experiment it has been found that 1 cu. ft. of water weighs about
62.5 lb. The weight of the water passing each second would therefore
be 62.5 x 9720, or 607,500 lb. If this quantity of water plunges over
a 10-ft. dam, it does 607,500 x 10, or 6,075,000 foot po