Storm Sewer Design 1

[Earthmover]

When designing storm sewers, matching crowns seems to be the standard. Is there any opinion that matching the HGL of the pipes to be a better design?
Thanks,
John

 

[BobPE]

Matching EGL (not HGL)is the engineering behind the rule of thumb of matching crowns. That is a good question to as as I see all to often engineers missing the point and designing connections improperly. It is not really a question if it is the right design, it is, it is a question of doing the engineering to make your design work, or just using rules of thimb to make it work....

great question...

BobPE

 

[LHA]

I feel too much gets made of this issue.

Matching the HGL is the most correct and accurate method. But it takes so much iteration and changes so little in most cases, that it is rarely done. I prefer to match crowns, and always find it to be sufficient. Many people just match inverts, and when you get right down to it, that is probably sufficient also.

 

[cvg]

matching inverts is the standard in some areas for both santitary and storm sewers. An example would be Southern California. However, in neighboring Arizona, there really is no standard. The engineering can be made to work either way. Matching crowns may be a way to minimize the trench depth.

 

[BobPE]

Believe it or not cvg, this is what rules of thumb do to us engineers...you may get away with matching inverts with smaller pipes, but even then, not all the time....

If anyone is wondering what I am talking about, then I suggest that you read up on the subjet, or refer the design to a qualified person. Rules of thumb should never be substituted for proper engineering.

BobPE

 

[cvg]

Of course, I do understand that rules of thumb can be dangerous - but only if you don't back up your rule of thumb design with proper analysis. I don't think I ever suggested that proper engineering not be done.

 

[tincan]

when using different diameter pipe entering/leaving a MH, we normally adjust the grades so that the 0.8 diameter points of the pipe are co-linear.

 

[dicksewerrat]

Just remember to form the trough in the manhole to the 80% line. Or all the design work in the world won't help.