water backing up in sub critical mode

[museo68736]

Hi i was wondering if anyone could help me, i have just started using hec ras and have only been shown once how to go thru and run a full model. I have started a new assignment but the person who showed me how to use the programme has left the company. Anyway i have set up the model as i was shown for some reason when i run it in sub critical mode the water backs up when running down stream for some reason as seen in the image below

when i run it in super cirtical mode though the water doesnt back up at all as shown below

Can anyone tell me why this is as obviously the water wouldnt back up like that as there is nothin to hold the water back. I set up the boundaries as shown before but maybe they are causing water to hold back for some reason, can anyone help wioth this issue?

Thanks

[Hydrojock]

What are you using for your downstream boundary condition? Is it normal depth? If so, is your friction slope reasonable (i.e. does is it roughly equal to the bed slope)?

[museo68736]

yea i have it set up the normal depth value of 0.017 which i got from a drop of 5.074 meters in height over 272 m distance so im not sure why the water backs up as this definately wouldn’t happen, do you have any ideas?

Thanks

[museo68736]

sorry 0.019 even

[Marulke]

On the figure you show, is flow direction from right to left, or left to right.

Normally, on my HEC profile plots, the downstream boundary is to the left.

You could have mixed up cross section numbering so that the most downstream cross section was entered as the US section etc.

Or, I may be completely wrong.

Marulke

[Author]

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