HEC-RAS Cross Sections Near a Junction

[chicopee]

Debugging unsteady flow analysis. Warnings pervade my analysis. While reexamining the U/S and D/S cross sections near a main channel/tributary junction, my U/S cross section is cutting thru a tributary. At this junction the results of the analysis become outlandish. Is it permissible to eliminate the valleys from this tributary and flatten out the profile since during high water conditions the WS elevation of the main channel will overwhelm the tributary? Water contribution from this tributary will also be high.

 

[francesca]

You need to modify your cross-section; it should be perpendicular to the flow direction. If it is crossing a tributary it cannot also be perpendicular to the flow in that reach.

There is something on the junction settings that lets you set the length of the junction. A junction is something with area, not a point, so your cross-section may be superfluous.

http://www.bossintl.com/online_help/hec-ras/source/enteringjunctiondata9.htm

If you still want to show the backwater effect in the tributary manually instead of letting HEC-RAS calculate it, then use ineffective flow areas to fill in your valleys.

 

[chicopee]

Francesca, thanks for your input.