20 BULLETIX 724, U. S. DEPARTMENT OF AGRICULTURE. 
even surface. In designing gutters it is well to bear in mind the 
following points : 
1. It is not usually necessary to extend a gutter entirely to the top of a 
grade, because, as examples cited indicate, there usually is not water enough 
flowing in the upper part of the side ditch to cause erosion. 
2. It is not usually economical to vary the size of the gutters on long 
grades so that they will have only the required capacity at all points ; but 
changes may and should be made if any considerable change occurs in the 
required capacity. 
3. All gutters should be sufficiently strong to withstand the impact caused 
by an occasional vehicle being driven into them, but unless they are capable 
of withstanding constant vehicular traffic they - should be designed so as to 
discourage the practice of driving into them. 
4. The grade of gutters should be made as uniform as practicable in order 
to prevent them from becoming partially filled by sedimentation, and should 
not be less than 1 in 200. 
Brief directions for constructing the most common types of gut- 
ters follow : 
COBBLE GUTTERS. 
Cobble gutters are ones constructed of rounded water-worn stones, 
ranging in size from 1 to 8 inches in their longest dimension. The 
stones should be sound, durable, and fairly uniform in shape. The 
construction of the gutter should proceed about as follows : 
First, excavate a trench to receive the gutter. The trench should have a 
width equal to the outside dimensions of the gutter and should be excavated to 
a depth of about 12 or 14 inches below the proposed grade of the gutter. 
Second, spread sufficient broken stone or gravel in the bottom of the trench 
to give a depth of about 6 inches when thoroughly compacted. The broken 
stone or gravel should be of the kind ordinarily specified for macadam or 
gravel roads and should be compacted thoroughly with hand rammers. 
Third, spread a layer of bedding sand over the foundation to such a depth 
that when the cobblestones are bedded into the sand and rammed thoroughly, 
they will form a gutter true to grade, line, and cross section. For cobblestones 
of fairly uniform size a depth of about 2 inches usually is sufficient for the 
sand bedding. 
Fourth, place the cobblestones. In doing this the larger and more nearly 
perfect stones should be selected and placed true to line and grade in the edges 
and in the row which forms the lowest part of the gutter. All stones should be 
laid with their long diameter lengthwise of the gutter and should fit snugly 
one against the other. Each stone should be rammed until it no longer yields 
under the rammer, and any irregularities which may develop should be cor- 
rected by resetting the affected portions. While the ramming is in progress, 
sufficient coarse sand should be spread over the surface to keep the joints 
between the stones well filled. When the ramming is complete, the surface of 
the gutter should be uniformly true to line and grade. Wherever changes in 
the dimensions of the gutter are necessary, they should be made gradually, 
and not by abrupt off-sets. 
Fifth, where the grade of a cobble gutter exceeds about 5 per cent, and the 
volume of water it must carry is at all considerable, the interstices between 
the stones should be filled with Portland cement grout instead of sand, as 
above described. A suitable grout for this purpose may be made by mixing 
