outside and thereby relieve the roadside ditch. Constant-depth ditches (usually 18 in or
0.46 m deep) are desirable. Where used, the minimum pavement profile grades should be
0.24 to 0.48 percent. Where flatter pavement grades are necessary, separate ditch profiles
are developed and the ditch flow line elevations shown on each cross section.
Parallel Channels. Where it is determined that a stream intercepted by the roadway
improvement is to be relocated parallel to the roadway, the channel should be located
beyond the limited access line (or highway easement line) in a separate channel easement.
This arrangement locates the channel beyond the right-of-way fence, if one is to
be installed. Figure 2.21b shows a parallel channel section. This does not apply to conventional
intercepting erosion control ditches located at the top of cut slopes in rolling
terrain.
In areas of low fill and shallow cut, protection along a channel by a wide bench is
usually provided. Fill slope should not exceed 6:1 when this design is used, and maximum
height from shoulder edge to bench should generally not exceed 10 ft (3.05 m).
If it should become necessary to use slopes steeper than 6:1, guiderail may be necessary