Flow at far downstream cross section higher than flow at cross section near dam

[Anonymous]

Dear HEC-RAS Helper,

I run unsteady flow on a stream connect to a storage area. Near the connection I set an in line-structure which consider as a dam. I can completely run with unsteady flow with 12 hours time step for one year.

My problem is that the cross sectional flow at far downstream is increasing and even higher than flow from dam. I try many time but cannot understand why it changes the flow like this. Thank you in advance for helping me.

[Robert]

Hello Kong,

In the case when you solve an unsteady flow in the river (upstream c.: flow hydrograph and downstream c.: normal depth, or rating curve or hydrograph), so the hydrograph (wave, dam break wave) should be transform (Translation and Attenuation wave) in the downstream direction.

But you use a storage area for downstream condition. Terefore I don´t know to reply you without view your model.

I suggest you send me your model (URL location) using Debug Report (Hec-RAS- File – Debug report).

regards
Robert

[kong]

Dear Robert,

Thanks for your reply. Please see the attachment of my Hec-RAS- File – Debug report.

PrekTEIrrigation_JD01.zip

[kong]

Dear Robert,

I can get the suitable output now. I just try to change the calculation time step from 1 day to 12 hours. Then, I can reduce theta from 1 to 0.7.

Best Regards,
Kong

[Author]

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