TM 5-820-3/AFM 88-5, Chap. 3
(9) The values of D/B and Q/%gB5 can be cal-
(10)
Similar analyses could be made for
culated as 1.67 and 4.52, respectively. Entering
design of stable channels with different sizes of
figure D-3 with these values, it is apparent that
riprap protection should other sizes be available
corresponding values of 4.5 and 0.52 are required
and steeper slopes be desired. This could reduce
for the parameters of SB1/3/n2 and F, respectively.
the number of drop structures required to provide
Assume n = 0.035 (d50)1/6 and calculate Manning's
the necessary grade change equal to the difference
roughness coefficient of 0.25-foot-stone to be
in elevation between that of the local terrain and
0.028. A slope of 0.00245 foot per foot would be
the drop provided by the slope and length of the se-
required for the 5-foot-deep riprap-lined
lected channel design.
trapezoidal channel with base width of 3 feet and
(11)
The feasibility of a paved rectangular
1V-on-311 side slopes. The Froude number of flow
channel on a slope commensurate with that of the
in the channel would meet the 3-inch-diameter
local terrain for conveyance of the design discharge
average size requirement for riprap as well as the
at either subcritical or supercritical velocities
maximum recommended value of 0.8 needed to
should also be investigated. Such a channel should
prevent instabilities of flow and excessive wave
be designed to convey the flow with a Froude
heights in subcritical open channel flow.
number less than 0.8 if subcritical, or greater than
D-6
Previous Page
