It is true that this portion of the work may be reached and repaired more conveniently than the tiles themselves; but it must be remembered that the decay of the outlet obstructs the flow of the water, produces a general stagnation throughout the drains, and so may cause their permanent obstruction at various points, hard to be ascertained, and difficult to be reached. Considering our liability to neglect such things as perish by a gradual decay, as well as the many accidental injuries to which the outlet is exposed, there is no security but in a solid and permanent structure at the first.
To illustrate the importance attached to this point in England, as well as to indicate the best mode of securing the outlet, the drawings below have been taken from a pamphlet by Mr. Denton. Fig. [37] represents the mode of constructing the common small outlets of field drainage.
Fig. 37.—Small Outlet.
The distinguished engineer, of whose labors we have so freely availed ourselves, remarks as follows upon the subject:
"Too many outlets are objectionable, on account of the labor of their maintenance: too few are objectionable, because they can only exist where there are mains of excessive length. A limit of twenty acres to an outlet, resulting in an average of, perhaps, fourteen acres, will appear, by the practices of the best drainers, to be about the proper thing. If a shilling an acre is reserved for fixing the outlets, which should be iron pipes, with swing gratings, in masonry, very substantial work may be done."
Figures [38] and [39] represent the elevation and section of larger outlets, used in more extensive works.
