1 MARCH 2000
(2) To prevent a significant loss of strength in the subgrade, side ditches must provide ample
capacity and flow rate. The size of ditches will be based on the expected rainfall runoff and the
contribution from other drainage that may empty into the ditches. Guidance for estimating runoff and
ditch size may be found in TM 5-820-4.
(3) To provide adequate capacity, side ditches will be designed for a 10-year storm. To provide an
adequate flow rate, the minimum gradient for side ditches will be 0.30 percent.
(a) While not a desirable practice, there are some areas where the bottom of the ballast section
cannot be installed or raised above the surrounding ground level, and standard side ditches cannot be
dug (or would not provide sufficient flow). In these cases, subdrainage will be installed (figure 6-17).
Figure 6-17. Required Subdrainage where Open Side Ditches cannot be Installed
(1) Chapter 1, part 4 and chapter 8, parts 10 and 13 of the AREMA Manual provide design criteria
and specifications for railroad culverts. All culvert pipe will conform to current AREMA or ASTM
recommendations or specifications for culvert pipe under railroads.
(2) A minimum cover of 2.5 ft should be provided from the bottom of the tie to the top of the culvert.