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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ETL 1110-2-120
14 May 1971

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would result in the local boundary shear being increased somewhat,
the IS-inch layer thickness and first trial riprap gradation should
be adopted. If by model measurement or otherwise it is known that a
velocity of 10 fps will occur 1.0 ft above the riprap toe, then from
Inclosure 4, the local boundary shear equals 2.70 1bs per sq ft.
Thus, the IS-inch riprap layer is satisfactory as the design shear for
the corresponding rip rap gradation is 2.68 lbs per sq ft.

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6. Requested Actions. In general, as evidenced by inordinate
emergency repair costs after major floods in some riprap protected
channels, the design, specificatimls, construction and inspection of
riprap protection needs to be upgraded. The design of riprap pro-
tection resulting from the guidance contained in EM 1110-2-1601 and
this ETL should always be reviewed in the light of experience and
judgment gained with riprap protection projects in particular areas.
In arriving at experience and judgment conclusions, careful consider-
ation should be given to whether or not design flow' conditions have
occurred in the channel protection proj ects. In design memoranda, ,,;,~
letter reports and other media, design considerations and computa-
tions should be presented in sufficient detail to reflect compliance
with EM 1110-2-1601 and ETL guidance or use of procedures which have
been proven by long"time experience to provide adequate riprap pro-
tection in particular localities. If procedures which differ from
those presented in EM 1110-2-1601 and the ETL are used, the riprap
design should be checked against EM 1110-2-1601 and ETL guidance, and
the results of this comparison should be presented. If significant
differences occur, revisions should be made in the design as experience,
judgment mId ETL considerations dictate. Surveillance provisions, as
discussed in EM 1110-2-1601, paragraph l4n, which will be made during
project construction should also be presented in design memoranda,
letter reports, etc.-,

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FOR THE CHIEF OF ENGINEERS:'

5 Incls
As stated

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OSEPH M. CALDWELL
~ Chief, Engineering Division
Civil Works Directorate

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