Head over a double sided weir formula?

[emedin]

I'm currently designing an Inlet Works at an existing Wastewater Treatment Works. I've been asked to investigate re-using the existing Inlet Works and to do this I need to calculate the head over a double sided weir in order to determine the depth of flow at the downstream flume.

I can find guidance for calculating the head over a single sided weir but not a double.

Can anyone provide me with guidance or where I can reference material?

Kind Regards,

Ewen

 

[Ryb01]

Could you provide additional information regarding a "double sided weir"?

 

[gbam]

A sketch would be helpful.

 

[DMcGrath]

Perhaps you have a labyrinth weir? Google will kick out a significant amount of info on these.

 

[emedin]

Sketch uploaded as requested.

To explain a bit further: there is an existing rectangular channel with a flume at the downstream end. The flume controls the flows passed forward due to weirs upstream.

The weirs run longitudinally along both sides of the channel and so I've called these "double sided weirs".

I would like to know the method for calculating the head over the a double sided weir.

In the sketch the section shows the channel, flume and weir and omits the storm overflow channel and underpass.

The plan shows the inflow, outflow, flume, weirs and storm overflow channels and underpass.

 

[Ryb01]

One way to determine the head overtop of the wiers may be to consider a simple HEC-Ras model. Within HEC-Ras you can code in a lateral structure (weir) between a couple of cross sections. I believe you can code in a lateral structure on each side of your cross section.

Since the your channel is sloped in relation to the weir, I would recommend using the Hager's lateral weir equation. The standard weir equation assumes the weir is parallel with the water surface, not the case in your scenario. For additional information on this methodology refer to Chapters 8 and 15 of the HEC-Ras reference manual.

You could also produce a similar model in SWMM.

Hope this helps.

 

[gbam]

A spreadsheet can be prepared to evaluate your condition. Refer to Chow open channel Hydraulics Chapter 12, 1959. I have used this approach numerous times and it is straight forward.

 

[emedin]

Thank you very much for your help - I'll have a look at both methods.

Ewen