FLOOD03313

• County: Denver
• Basin: South Platte
• Title: Drop Structures in the Denver Metropolitan Area
• Date: 12/1/1986
• Prepared For: UDFDC
• Prepared By: McLaughlin Water Engineers, Ltd.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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control (it is impossIble to know if the voids are filled) and aesthetic reasons.
Functionally, the project is satisfactory for a difficult locatIon and a narrow right-
of-way. This was an UDFCD maintenance project designed for 600 cfs.

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Case 28 - Jack Rabbit Gulch near SImms, Lakewood

ThIs development project utIlIzed a SCS vertical stIlling basin for a flow of 220

cfs. The basin IS depressed below the channel Invert and uses a row of baffle blocks

In the basIn which helps to shorten the basin length. A 12-Inch pIpe IS provIded

for basin drainage and to provIde for the trickle flows. The basins, though new,

are fIllIng with debris and there IS some concern as to whether the pipe will plug.

Whenever excess flows occur over the pipe capacIty or there are malfunctions, the

main channel sods wdl become saturated and lead to the eventual creation of a

trickle channel (e.g. the East Harvard Gulch example - Case 4).

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The safety problems are obvious. A chdd could easily slip under the rail (Figure IV-

5), and If a person were swept into the basin With any appreciable flow depth, there

would be no practical escape. It was noted that per SCS gUidelines transition riprap

was not provided.

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Case 30 - Hidden Lake DraInageway at Clear Creek, Jefferson County

Figure IV-6 illustrates this drop, which consists of concrete and grouted rock. The

trIckle channel IS shallow, but In this case, there IS no aggradation because of the

clear water release from the lake. The grouted rock upstream was added as part of

the maintenance Improvements due to vandahsm. It was noted that more contractIon

and better economy could be achieved by USIng a much steeper slope, or even vertical

ends on the crest wall.

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Case 32 - Sanderson Gulch at Navajo, Denver

The drop here IS SImilar to Cases 68.1 and 68.2 on WeIr Gulch which are descrIbed

In this sectIOn. (See discussion of 68.1 where concerns are expressed about the

trickle channel's shallow depth, and rlprap beside the concrete invert In the baSin.)

The riprap was grouted as part of a rehabilitative maintenance program (Figure IV-

16). Though the design called for nprap downstream, aggradation has taken place

to the point where the trickle channel has gained a depth of 18 to 24-inches (Figure

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IV-2

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