TM 5-820-3/AFM 88-5, Chap. 3
estimated using the information in figures 5-10 to
5-4. Erosion control at outlet.
5-12. For a given design discharge, culvert di-
There are various methods of preventing scour and
mensions, and tailwater depth relative to the outlet
erosion at outlets and protecting the structure from
invert, the minimum average size of stone (d50) for
undermining. Some of these methods will be
a horizontal blanket of protection can be
discussed in subsequent paragraphs.
determined using data in figure 5-10. The length of
a. In some situations placement of riprap at the
stone protection (LSP) can be determined by the
end of the outlet may be sufficient to protect the
relations shown in figure 5-11. The variables are
structure. The average size of stone (d50) and con-
defined in appendix E, and the recommended con-
figuration of a horizontal blanket of riprap at outlet
figuration of the blanket is shown in figure 5-12.
invert elevation required to control or prevent
localized scour downstream of an outlet can be