apid from there
to stake 10, a little less rapid from there to stake 11, and still less
rapid from there to stake 17.

To establish the grade by the profile alone, the proper course would be to
fix the depth at the stakes at which the inclination is to be changed, to
draw straight lines between the points thus found, and then to measure the
vertical distance from these lines to the line indicating the surface of
the ground at the different stakes; thus, fixing the depth at stake 3, at
4 feet and 13 hundredths,(15) the line drawn from that point to the depth
of 2.50, at the silt-basin, will be 3 feet and 62 hundredths (3.62) below
stake 1, and 3 feet and 92 hundredths (3.92) below stake 2. At stake 7 it
is necessary to go sufficiently deep to pass from 7 to 10, without coming
too near the surface at 9, which is at the foot of a steep ascent. A line
drawn straight from 4.59 feet below stake 10 to 4.17 feet at stake 17,
would be unnecessarily deep at 11, 12, 13, and 14; and, consequently it is
better to rise to 4.19 feet at 11. So far as this part of the drain is
concerned, it would be well to continue the same rise to 12, but, in doing
so, we would come too near the surface at 13, 14, and 15; or must
considerably depress the line at 16, which would either make a bad break
in the fall at that point, or carry the drain too deep at 17.

By the arrangement adopted, the grade is broken at 3, 7, 10, and 11.
Between these points, it is a straight line, with the rate of fall
indicated in the following table, which commences at the upper end of the
drain and proceeds toward its outlet:

FROM STAKE, TO STAKE, DISTANCE. TOTAL FALL. RATE OF
DEPTH. DEPTH. FALL. PER
100 FT.
No. No. 246 ft. 2.46 ft. 1.09 ft.
17...4.17 11...4.19
ft. ft.
No. No. 41 ft. 82 ft. 2.00 ft.
11...4.19 10...4.59
ft. ft.
No. No. 91 ft. 2.49 ft. 2.83 ft.
10...4.59 7...4.47
ft. ft.
No. No. 173 ft. 96 ft. 56 ft.
7...4.47 3...4.13
ft. ft.
No. S. Basin 186 ft. 3.47 ft. 1.87 ft.
3...4.13 2.25 ft.
ft.

It will be seen that the fall becomes more rapid as we ascend from stake
7, but below this point it is very much reduced, so much as to make it
very likely that silt