splitter manhole

[z8e]

Hello,

I need to design a manhole to drop over an existing sewer main to divert a variable portion of the flow to a new main. These seem to be most commonly referred to as "splitter manholes." I intend to make the new invert out the same as the existing invert out but am not sure beyond that. Can't find any literature or details on this. Can someone point me in the right direction?

Thanks.

 

[dicksewerrat]

Use a wier in the manhole to take offthe flow you need to divert.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[RWF7437]

Or use an orifice for one of the outlet pipes.

 

[z8e]

Thank you for the responses. Would the weir be adjustable? Would the orifice trash up with the solids?

 

[dicksewerrat]

The weir will be adjustable if you construct so that it can be. Orifice may plug.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[nackra]

see Figure 6 for another variation

http://www.epa.gov/ednnrmrl/publications/reports/11022dmu0770/00020013-2.pdf

 

[bimr]

What do you mean by variable flow? What you are trying to accomplish?

Assuming that you are using the same invert elevations in the new manhole, there is no reliable method that will split the flows proportionally while the flow changes.

The information submitted by nackra shows overflow devices that will allow the sewer to overflow not split the flow.

Any type of weir that you will install is going to cause backwater in the sewer resulting in solids in the bottom of the sewer.

So maybe you can provide a functional description of your splitter manhole.

 

[z8e]

The need is that the existing line is anticipated to approach capacity in the near future. The proposed solution is to divert some of the flows from the existing line through a new development to another trunk line to the treatment plant. It sounds like from your responses it may be simplest to just decide in advance what the split will be (50-50 or whatever), then construct the manhole base accordingly, with no orifices, gates, or anything else that might cause maintenance problems. I just don't know what the utility will do in the future if they want to adjust the flows. . .

Thanks for the responses, I appreciate it.

 

[bimr]

That is probably correct. Start with the flow split that is desired, then size the flow channels in the manhole to be the same sizes as the discharge pipes on the outlet. That is probably the best that can be done with an existing sewer without a drop through the manhole.

 

[semo]

This can be done many ways depending on how you want to split the flows.

I've done this with a normal flow through manhole containing side overflow weirs so that during normal flow, the flow goes down the main line. Then during high flows when the pipe is full, the excess water can spill over the sides to the eq basin or such.

This does not allow real tight control on the water flowing through the main line.

A modification I've also used is to insert a v-notch weir into the main flow and still have the side overflow weirs. The v-notch keeps the main flow in a pretty tight band.

You just need to size your weirs to meet your needs.