Conveyance Channel down steep slope

[cher122976]

I have a proposed trapezoidal stormwater conveyance channel with a capacity of approx 80cfs. I need to get the water down an existing 60'(vertical) 2:1 slope to a river bed from the channel. Does anyone have any ideas on the best way to do this?

Since this is in a desolate area and maintenance is an issue rip rap down the slope is probably the best, but i have seen systems like this undermined in the past. Plus velocity will be an issue

Adding a catch basin at the top of the slope and piping it down the hill is an option. A energy disapator can be installed at the bottom. This system will never be maintained though if the catch basin ever gets covered.

 

[gbam]

Have you considered a concrete spillway? How about a series of drops.

 

[cvg]

dam and irrigation spillways (pipe or chute) are designed for much larger flows than this. concrete lined with stilling basin at the bottom. Look at the USBR "Design of Small Canal Structures" or at "Design of Small Dams" for examples. I would not recommend trapezoidal for the chute.

 

[gbam]

To expand on the series of drops. I have recently designed a cascading spillway using Gabions. Although the fall was not as great; it was only 15-ft +/-. You also may be able to use Gabion mattresses to line it.

 

[chicopee]

GBAM's concrete spillway lined with embedded Rip Rap or stones.

 

[civilman72]

If you're going to consider a concrete spillway, make sure you design for undermining and seepage, especially with this much flow and on this steep of a slope. This requires design of cutoff wall depth, location and number of weep and toe drains, etc.