TM 5-820-3/AFM 88-5, Chap. 3
CHAPTER 6
OPEN CHANNELS
a. The hydraulic characteristics of the channel
6-1. General.
may be studied by using an open-channel formula
One of the most difficult problems associated with
such as Manning's. Suggested retardance coeffi-
surface drainage facilities is the design of effective,
cients and maximum permissible velocities for
stable, natural, open channels that will not be sub-
nonvegetated channels are given in table 6-1. Re-
ject to severe erosion and/or deposition. Tests
tardance coefficients for turf-lined channels are a
show that performance is poorer and requires more
function of both the turf characteristics and the
costly and more frequent maintenance to provide
depth and velocity of flow and can be estimated by
effective drainage channels. Open channels which
the graphical relations shown in figure 6-1. It is
meet the airfield and heliport's safety and
suggested that maximum velocity in turf-lined
operational requirements will be used since they
channels not exceed 6 feet per second. In regions
provide greater flexibility, a higher safety factor,
where runoff has appreciable silt load, particular
and are more cost effective. Drop structures and
care will be given to securing generally nonsilting
check dams can be used to control the effective
velocities.
channel gradient.
6-2. Channel design.
The following items merit special consideration in
designing channels.
6-1
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