FLOOD03601

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: Evaluation of and Recommendations for Drop Structures in the Denver Metropolitan Area
• Date: 12/1/1986
• Prepared For: UDFCD
• Prepared By: McLaughlin Water Engineers, Ltd.
• Floodplain - Doc Type: Educational/Technical/Reference Information

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TABLE 1-2
MINIMUM DESIGN THICKNESS CRITERIA
GROUTED SLOPING BOULDER DROPS

Design
Parameter

Drop Height
3 foot or less

Drop Height
Greater than 3 feet

Uniform Rock Size -
Minimum Dimension

1.5 foot

2,0 foot.

Minimum Grout - Thickness

1.0 foot

1.5 foot.

. May use 1.5 rock and LO foot grout for flow depths upstream of crest (normal depth) less than 3 foot.

VERTICAL RIPRAP DROPS - SECTION XII
The design method presented in the 1986 MWE report is based on original research by Smith and
Strang, 1967, later extrapolated by Stevens, 1981. Although this work is still applicable, it has been
climated from the revised USDCM Hydraulic Structures section in favor of a simplified guideline,

Since 1986, UDFCD has reduced the maximum allowable vertical drop height to 3 feet for safety
reasons, To address submergence problems, MWE reviewed several references (Linden, 1963;
Urbonas, 1968; the COE, 1970; Corry, 1975; Little, 1981 and 1982; and SLA, 1986, The simplified
guidelines as presented in the revised structures section of the USDCM, are based on the original
work by Smith and Strange amended to consider submergence and function within the UDFCD
maximum channel flow parameters,

BAFFLE CHUTE DROPS - SECTION XII
Refinements are now available regarding back water effects produced by the first row of baffle blocks
which protrude into the upstream flow area in the standard USBR design, The Fujimoto entrance,
also developed by the USBR, is a modification that can be used to reduce such effects, This and other
information is presented in the revised Hydraulic Structures section of the USDCM,

NOTES REGARDING THE REVISED HYDRAULIC STRUCTURES DESIGN CRITERIA
The theoretical background information presented in the 1986 MWE report has served as a basis for
developing the more simplified design criteria currently included in the 1990 revised Hydraulic
Structures section of the USDCM, Graphical relationships, are now provided which give the basic
drop crest configuration and channel parameters as a function of discharge which will result in
performance at allowable maximum flow conditions, The crest transition configuration is essential
to control the approach velocity acceleration while simultaneously preventing backwater depth from
becoming excessive,

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