Open channel with zero slope 1

[DPAJR]

Any suggestions on how to model open channel flow in a channel with zero slope and a drain located about halfway along its length? It is a unifomrly shaped asphalt channel.

Thanks
dpajr

 

[hydrae]

Start with the critical point at the drain, that will give you a starting hgl for the flow rate you are evaulating
then I would use Manning's but each calculation will only be good for a short distance as the 'normal' level will increase to create at false slope the farther you get from the drain. eg there will be a slope in the hgl and egl but it changes as you get away from the drain.

Hydrae

 

[msquared48]

Backwater effect.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ryb01]

The use of a mannings equation will not help you in this scenario.

As msquared48 has said a backwater calculation is probably the way to go, however, you will have to consider how the flow is actually getting to the drain.

Looking at the smaller picture 0% slope= 0 conveyance....

You will probably have to consider a more broader approach considering the flow paths u/s of your area of interest, is there enough momentum u/s to actually carry the flow to your area of interest???? A RAS model may be the way to go...

Hope this helps.

 

[DPAJR]

Thanks to everyone for the quick response.

 

[beej67]

Mannings equation is for uniform flow. The situation you describe is classic "gradually varied" flow.

 

[gte959s]

It can be modeled like a pond. Your flow would be a weir calc or an orifice depending on the head on the inv. Model it like a riser only scenario in your modeling software.

 

[chicopee]

I would model it as a very large diameter tank (not necessarily cylindrical) with an orifice and let the surface area of the pond and flow thru the orifice vary with time.