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 will be deposited, (see page 91), and the drain,
thereby, obstructed. To provide against this, a silt-basin must be placed
at this point which will collect the silt and prevent its entrance into
the more nearly level tile below. The construction of this silt-basin is
more particularly described in the next chapter. From stake 7 to the main
silt-basin the fall is such that the drain will clear itself.
The drawing of regular profiles, for the more important drains, will be
useful for the purpose of making the beginner familiar with the method of
grading, and with the principles on which the grade and depth are
computed; and sometimes, in passing over very irregular surfaces, this
method will enable even a skilled drainer to hit upon the best adjustment
in less time than by computation. Ordinarily, however, the form of
computation given in the following table, which refers to the same drain,
(_C_,) will be more expeditious, and its results are mathematically more
correct.(16)
Fall. Depth
Feet and from
Decimals.
Pages:
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134