Hydraflow Storm Sewers / HGL Question 1

[Rookie2]

Hi,
We are designing a storm drain system for a subdivision which ties directly into a system downstream that is currently under construction. The downstream system was designed by others and was supposed to be designed to carry our flow. The engineer of the development downstream was kind enough to provide us with their Hydraflow model. We ran the model and found what we think are issues.

My question is; The model provided does not check for inlet control, and when we ran the model checking inlet control it backs (significantly) out of the system. I was wondering if it is reasonable to assume the HGL is accurate without checking for inlet control, and if so why?

And another question: Based on the hardcopy calculations provided to us the model uses a supercritical starting water surface elevation. The version of Hydraflow we use doesn't even allow this. I know you aren't supposed to use supercritical depths when using the direct step method, but could someone explain why?

Thank You in advance

 

[RWF7437]

Try posting on the Hydraflow forum.

 

[Rookie2]

Sorry,
I searched for a Hydraflow forum prior to posting and browsed through the Engineering Computer Programs directory and found a Hydrocad forum but no Hydraflow forum.

Would you be kind enough to point me in the right direction?

Please forgive my ignorance.

 

[RWF7437]

My fault. I meant HydroCad forum.

Your question, however, is general enough that it may be answered here.

My own guess is that it is unlikely that assuming a tailwater depth equal to some supercritical depth is correct. We would need to know a good deal more about the situation than you have told us though.

You haven't described the "system", the design flows or other details enough to give you a good answer.

As for HydraFlow, I believe it does check for inlet or outlet control. You can still contact the author at Intelisolve but the program has been sold to AutoDesk so formal support may no longer be available.

good luck

 

[elev8848]

My experience:

(1)
Hydraflow 2005 and Hydraflow 2000 are significantly different in calculating HGL.
I don't take their results at face value.

Hydraflow 2005 has the option for checking inlet control, but Hydraflow 2000 does not.

(2)
Assuming supercritical flow at the starting point (outfall/manhole) for me is okey
if there is justification that the pipe downstream flows as supercritical flow for the design
discharge. In other words, if the pipe (or channel) downstream from the first node is steep,
and large, then it will flow with supercritical regime.

(3)
Do you want to share the Hydraflow (filename.stm) file? or just a screenshot of few HGL Profiles?

(Please forgive my ignorance, too.)

 

[Rookie2]

Thank you for your responses. elev88, I agree about taking the results at face value, but we are required by the municipality to provide HGL calculations for the downstream system showing that it works, but we can't reproduce the results. The model was created using version 8.0 we use 2003 (version 10.0). When we run the model without checking inlet control, it still backs out of the structures. The only difference is the starting water surface elevation. Our model defaults to critical depth which is roughly 1.1' higher than the supercritical elevation used in the version 8.0 model. Also I don't know if I am comfortable certifying that the system works without checking for inlet control.

The reason I ask about the supercritical elevation- It's not that I don't think it's possible that the flow is supercritical, but from what I understand when using the direct step method, if the flow is supercritical, calculations are made from upstream to downstream, and downstream to upstream for critical/subcritical flow. That is why I'm wondering if it correct to use a supercritical elevation as a starting water surface elevation. I don't have any experience with Hydraflow versions before or after 2003.

Also, all of the structures are set to manholes in the model. In 2003 the junction loss coefficients are different for round structures and rectangular structures. The coefficients for rectangular structures are higher. Is there a logical reason for doing this in the earlier versions?

Thanks for your help