Alternative to baffles to attenuate storm manhole damage? 1

[shaneibi]

Howdy,

I have to design a series of 4ft diameter storm manholes along a road with a 65 ft elevation difference (from end to end) and the municipality has insisted on:
1. no more than 6 feet of drop per manhole
2. minimize maintenance due to erosion caused by the high expected flow velocities (approx 12ft/s)
3. NO baffles allowed

In order to reduce the erosion due to the flow slamming into the opposite wall of the manhole I am thinking of a way to produce a drop at the end of the incoming pipe to "guide" the flow straight down. Doing this in the pipe sounds like a pain....perhaps there is a way to accomplish this by modifying the manhole barrel just below the invert of the inlet...perhaps a "ramp" of some kind?

Any suggestions???

Thank you in advance for your help!

Shane in Canada

 

[tincan]

Check with your friends in the sewer business. There are standards for the drop MH that you described. You might start with the public utilities.

Best Tincan

 

[dicksewerrat]

We used what was called a 'Nap curve'. Call the City of Mpls Sewer Design group for formula. 612-673-3000 is the info number. This was a gradual slope that went to the start of a spiral. It started the water in a downward flow instead of straight across. Then you can line the manholes with granite blocks. They wear better than concrete. I don't know if very thick HDPE manholes will wear better, but call Advanced Drainage systems about them. they have an office in Iowa.