Depressed Sewer Design? 2

[drinkchampagne]

Does anyone have any experience in a single barrel depressed sewer design for a sanitary sewer application? Flow will be continuous from a force main upstream. Approx. flow: .3MGD. Elevation difference (inv. to inv.): approx. 30 feet.

Hoping someone could point me in the right direction! Thanks!

 

[rconner]

You may be interested in some information relating to inverted siphons (I suspect that might be a more common terminolgy at least in some areas) contained in ASCE MOP No. 60 (WPCF MOP No. FD-5), as well as in other references like the "Ten States Standards..." e.g. per

http://10statesstandards.com/wastewaterstandards.html

etc.

 

[bimr]

There is a design example for a depressed sewer in Metcalf & Eddy's Collection and Pumping of Wastewater.

Most depressed sewers have multiple pipes because you have to design for variable flow rates, But if the sewer flow is constant, there is no reason that you can not use a single pipe.

Is it possible to extend the force main to eliminate the depressed sewer?

Also, is the flow constant from a force main? Most sewer systems exhibit diurnal flow variations.

 

[drinkchampagne]

Basically, the project is connecting one town with another through a sanitary sewer interceptor for treatment. It starts with a force main pumping wastewater from town "A" to a high point in town "B" and is then gravity to a connection point in town "B". Problem is there is an elevation obstruction about half way to our connection point, hence the need or thought of a depressed sewer.

To answer the question, extending the force main is possible, but town "B" wants to leave it gravity to possibly encourage development and tie ins in the future. A force main would not facilitate this and town "B" would not agree to this, unfortunately.

Since my first post, I have looked into the second edition of ASCE'S MOP 60 (WEF FD-5) as suggested. I have found some useful material going forward in this text.

 

[cvg]

you say town B will not allow the force main, however very few agencies will approve a siphon either. A short force main to cross the obstruction might be better than a siphon.

 

[RWF7437]

Can you post a sketch of the profile ? It is NOT at all clear whether you are talking about a siphon or something else. Phrases like "elevation obstruction" , " flow will be continuous from a force main" (this is almost never true) and "elevation difference ... approximately 30 feet" only add to the confusion.