TM 5-820-3/AFM 88-5, Chap. 3
CHANNEL DESIGN PROBLEM
D-1. Design procedure.
D-2. Channel design.
a. Design the desired channel as indicated in the
The following steps will permit the design of a
channel that will satisfy the conditions desired for
the design discharge and one that will ensure no
(1) Assume that a channel is to be provided
deposition or erosion under these conditions.
within and for drainage of an area composed of
medium sand (grain diameter of 0.375 mm) for
drainage basin from representative samples and
conveyance of a maximum rate of runoff of 400
cubic feet per second. Also assume that a channel
b. Determine maximum discharges to be experi-
depth of 6 feet is the maximum that can be toler-
enced annually and during the design storm.
ated from the standpoint of the existing ground-
c. Assume maximum desirable depth of flow, D,
water level, minimum freeboard of 1 foot, and
to be experienced with the design discharge.
other considerations such as ease of excavation,
d. Determine the sizes of material to be trans-
maintenance, and aesthetics.
ported by examining the gradation of the local ma-
(2) From Figure D-1 or the equation
terial (sizes and percentages of the total by weight).
Particular attention should be given to the
possibility of the transport of material from upper
portions of the basin or drainage system and the
the Froude number of flow required for incipient
need to prevent deposition of this material within
transport and prevention of deposition of medium
the channel of interest.
sand in. a channel with a 5-foot depth of flow can
e. Compute ratios of the diameter of the materi-
be estimated to be about 0.12. Further, it is indi-
als that should and should not be transported at the
cated that a Froude number of about 0.20 would be
maximum depth of flow, (d50/D.
required to prevent deposition of very coarse sand
f. Compute the Froude numbers of flow re-
or very fine gravel. Therefore, an average Froude
quired to initiate transport of the selected sizes of
number of about 0.16 should not cause severe ero-
cohesion less materials based on the equation, F
sion or deposition of the medium sand common to
1.88 (d50/D)1/3, to determine the range of F desired
the basin with a flow depth of 5 feet in the desired
in the channel.