FLOOD06940

• County: Statewide
• Basin: Statewide
• Title: Corps of Engineers Riprap Guidance
• Date: 7/1/1970
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Community File

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EM 1110- 2" 1601
1 July 70

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The average local velocity in the vertical at any point should be determined
-
as illustrated in Appendix IV. The subsection width used to determine v
should not be too great. Where there is a significant difference in roughness
over the wetted perimeter, as may occur in a channel with riprap bank revet-
ment and a natural invert, a local effective friction coefficient as determined
from Hydraulic Design Chart 631-4 or Appendix IV should be used in comput-
ing values of v. A graphic solution of equation 32 is presented in plate 32.
(4) Boundary shear in bends. The distribution of local boundary shear
in a bend of a trapezoidal channel with equal bottom and side roughness is
indicated in plates 33 and 34 (compiled from data in refs 53, 54, and 55).
Average boundary shear values obtained by equation 32 should be multiplied
by the indicated ratios of Tb/i' 0 to obtain local boundary shear values in a
bend.

(5) Riprap design shear. The riprap design shear is defined as that
amount of local boundary shear that the in-place riprap will safely withstand.
The design shear for riprap placed on an essentially level channel bottom is
given by reference 56. /

- -

y

T = a (-v s - y) D 50 f-

(33)

where

Ys = the unit weight of stone saturated surface dry (SSD)
coefficient .. a" = 0.040
The design shear for riprap placed on channel side slopes is given by the
following equation taken from reference 3

T' = T (1 _ s~~ q, )0.5 (34)
sm 9

where

cp = the angle of the side slope with the horizontal
9 = the angle of repose of the riprap, normally about 40 deg

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