HEC-RAS Modeling: Bypass Culvert as Lateral Structure

[djstrick110]

I'm using HEC-RAS to model a floodplain in which a drainage ditch splits at a point, then recombines some distance downstream. I've attached a schematic of the system showing what I'm calling the Main Reach and the Bypass Reach. After the split (XSEC 11+12), the Main Reach routes through a series of open ditches and driveway crossing culverts to my downstream limit. The Bypass Reach is a double-barrel culvert which flows away from the Main Reach, then recombines with the Main Reach at a junction structure (XSEC 6+39). What I'm trying to do is model the Bypass Culvert as a lateral structure in order to calculate the flow split at 11+12, but HEC-RAS won't allow me to direct the diverted flow to XSEC 6+39 after naming 11+12 as the upstream section. It forces me to use the next downstream section as with a normal culvert. Is there a way to "trick" it into letting me name 11+12 and 6+39 as the upstream and downstream cross-sections, respectively? If you see a better way to handle it, any suggestions on how to more effectively approach the system would also be appreciated!

Thanks in advance!

 

[gbam]

Are you looking to model the bypass reach? If so try a junction. If not you should be able to do what you are trying to do. Its been a while for me using the split flow option in RAS; I'm pulling from memory. If I remember correctly, the lateral needs to be between two XSECs and not specifically at one. Try giving your lateral a different River Station (11+11). Remember the headwater at the culvert will be an average of the two XSECs; you may need to insert a XSEC just downstream of the lateral.

 

[jeffd64]

I agree with gbam. You should use a junction to model the split and recombining of the reaches. You can model the flow by using the Flow Optimizations module in the steady flow analysis. (under options)