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

1I-4

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
'1

This project also illustrates the need for trickle channel provisions. Originally
designed with a low flow!underdrain pipe, it soon became apparent that such a
system had capacity and maintainability problems. Figure 1I-4 shows the upstream
aggradation and the natural trickle channel that was created, much like Niver Creek
(Case 2). The aggradation is greater as one moves upstream. A similar trickle
channel was created downstream (Figure lI-S), and aggradation there was even mOire
significant. Originally, a loose riprap basin was constructed downstream per USBR
guidelines. The UDFCD executed a maintenance project which included a hard-lined
trickle channel and a gl"Outed riprap basin. It directs flow back into the trickle
channel, thereby helping to reduce aggradation caused by low flows spreading out
in the channel bottom. One can also observe that aggradation downstream is still
likel y because of the wide channel which will carry flow having less velocity than
most upstream channels.

Case 5 - Tulsa Small Vertical Drop

Figure 11-6 shows one way of configuring a baffle chute for a smaller vertical drop.

A row of baffles is constructed on the horizontal basin below the drop.

The USBR reports that some designs have successfully used less than 4 rows of
baffles for low drops. It is also practical to use the same basic configuration, but
a flatter slope.

CONCLUSIONS

The baffle apron drop is an excellent choice for a grass-lined channel except for
situations where there are heavy debris flows. Once the hydraulic principles are
clearly understood, the concepts can be applied and modified for many situations.
For example, baffle aprons can be used for small drops and are especially suited to
shallow tailwater and variable bed conditions.

It is important to incorporate a trickle channel into the design. This can be

accomplished by locating the trickle channel between two baffles in the middle of

the apron crest. An 18 to 24-inch depth is recommended. Rock placement in the

stilling basin should be configured for positive drainage and to direct flows into the

trickle channel downstream. When the conventional rock placement guidance by the