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Alternative to baffles to attenuate storm manhole damage?

Alternative to baffles to attenuate storm manhole damage?

Alternative to baffles to attenuate storm manhole damage?

(OP)
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

RE: Alternative to baffles to attenuate storm manhole damage?

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

RE: Alternative to baffles to attenuate storm manhole damage?

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.

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