Energy/Velocity Reducers

[packgrad98]

I have an existing concrete lined trapezoidal channel (2'wide at bottom, 8'wide at top, 2' deep) that drains about 90 acres (Q~150cfs) and is sloped at 5%. All of this equates to a velocity of over 20 fps entering into a 48" dia. culvert. The concrete channel from the culvert to about 60 feet away has broken up and washed away. I intend to put back a concrete channel with a little thicker section. I would like to introduce some sort of energy/velocity reducer that could be inserted in the section to be replaced. My original thought was to install bollard type baffles similar to what might be used at the outlet of a dam or culverts. The other idea was to use "rubble strips" or indentations in the concrete, but I am afraid that this would only work at low flow condition.

I am also thinking it would be beneficial to install some intermediate measures along the 700lf of channel. Any ideas, or suggestions where I might be able to find some design information for the ideas that I mentioned above?

 

[RWF7437]

If anyone has design experience and design guidance in this area it is probably the US Army Corps of Engineers. Try searching their website.

Good Luck

 

[dicksewerrat]

We have used Reinforced concrete bumps in the channel to slow the water down. also a Flat wall perpendicular to the flow. Or use a flat section of channel wider than the pipe and then neck back down to the pipe size. You also might want to put a Trash grate in front of the pipe.

 

[gbam]

OK, if the section you are reconstructing is close to the inlet of the culvert you can use a series of drops to reduce the engery. It would not make sence to have a series of drops in the middle of the reach. If not, you can add baffles per hec 14, FHWA.

Sounds like a fun one, enjoy it!

 

[cvg]

I would recommend a vertical or inclined drop with a flatter section upstream of the culvert. Try to force subcritical flow and keep it that way up to the culvert.

Try reading Bureau of Reclamation Engineering Monograph No. 25, Hydraulic Design of Stilling Basins and Energy Dissipators