hydraulic illogical jump

[igorce]

Can someone explain why this happened ???

[Chris G.]

No…not by that figure alone. However, you have a 20% slope. Maximum slope suggested in the HEC-RAS user’s manual is 10%. Is this a spillway? In that case, I suggest using boundary layer theory instead of RAS.

[igorce]

Thanks for the reply to my message:
If you look at the new situation, when i expand the channel from 8 to 10m, then there is no problem, even though the slope is retained, and get logical results. I am now confused what is really going on here!?
I’ve seen many projects and designers that use this software to calculate the mixed flow regime through the spillway,with steep slopes, such as slope of 50%.
In my case this is spillway.
how do you think i can use boundary layer theory?
can a few sentences to give me suggestions and any literature that you use.
It would be good to compare the theories used in my country.
Which software to use for this type of problems?

greeting!

[Chris G.]

Please download and read The Corps of Engineers EM 1110-2-1603, Hydraulic Design of Spillways. http://publications.usace.army.mil/publications/eng-manuals/EM_1110-2-1603_sec/toc.htm

Here you will see how to apply the turbulent boundary layer development energy loss to computation of a water surface profile on a spillway crest and chute. In addition, you will see how to incorporate pier end waves, air entrainment and bulking, as well as a cavitation index to your computations.

[Ang May Nee]

Hi,
I am using HEC-RAS version 4.1.0 to run a modeling on spillway. the result shows no hydraulic jump in between from crest to stilling basin but my spillway slope is 17%. may i know the result trustable? can the result represent what actually happen? Thank you very much in advanced for answering my question.

regards,
May Nee

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