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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page XI-3, 3rd paragraph, change heading to read
"Impact and Drag Forces"
and replace the paragraph and equation XI.2 with:
"Water flowing down the drop will directly impact any abrupt rock faces or concrete structure
projecting into the flow. Technically this is a type of drag force which can be estimated by
equation XI,!. Also, the user should compare calculated drag force results with the forces
shown in the revised structures section for baffle chute blocks, A drag coefficient, Cd, of
0.333 was assumed in Equation XI,2 for the drag force of the shape projecting into the flow:
The assumption made under previous paragraph allows the rock to project 25% of the grout
thickness, Dg,

FD = CD P (V2/ 2) (0,25 Dg)

XI,2

Note that this drag is similar to the shear stress discussed earlier, but it differs in that it is a
drag related to the sudden projection into the flow. Impact force caused by debris or rocks,
is more difficult to estimate because ofthe unknown size, mass and time elapsed while contact
is made, Therefore it is recommended that a conservative approach be taken with regard to
calculating water impact (drag force) which generally will cover other types of impact force,
Specialty situations where impact force may be significant must be considered on an individual
basis,"

page XI..4, add after the 3rd paragraph
Dvnamic Pressure Fluctuation
Refer to addendum for discussion.

page XI -4, insert below 4th paragraph,
"Refer to addendum for discussion of safety factor and recommendation to use a minimum
surplus force (weight) as a more meaningful and practical approach."

page XI-4, 5th paragraph, replace last sentence with:
With the toe drain provided, the analysis illustrated that the design would be stable with a
downward surplus force of no less than 30 pounds if the criteria in Table XI-I is satisfied.

page XI-4, 6th paragraph, first line, replace "Figure XI-2" with
"Table XI-I".

page XII-I, 3rd paragraph, insert at the end of the first sentence: "
", and Smith (ref, 69),"

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