It will be seen by the plan, that the fall in the line occupied by the main drain is very slight, while the side drains have a fall much greater.
The lateral drains are run in the line of steepest descent, which is, of course, at right angles to the general direction of the contour lines.
The water from the entire system is collected, and escapes at one outlet into the brook.
A peep hole is placed at the intersection of the sub-main drain with the main, which commands about one-half the entire area—the other, half is commanded by the outlet.
Two-inch tile will be laid in the lateral drains, and three, four, and five-inch in the sub-main and main.
It is quite indispensable, to the successful execution of a plan of drainage on land so level as this, that careful measurements be made on the ground with an engineer's level, and such a representation of its surface projected as will show to the eye at a glance what all the natural inclinations are. The work can then be laid out with ease in the best position, and executed in a systematic manner. The time and labor which is devoted to such an examination of the ground is well spent, and, with the knowledge gained by it, the work can be carried on with such economy as to save the original cost of the examination many times over.
Very truly, yours, Shedd & Edson
Hon. H. F. French, Exeter, N. H.