Hec Ras - Modelling Bridge Parapet.
Hec Ras - Modelling Bridge Parapet.
(OP)
Hello, I am trying to model a bridge replacement case, where the proposed bridge has a larger opening (3-sided culvert), and a parapet wall thats 3' tall. This is causing my WSEL upstream to rise in comparision to the existing. I have modelled the parapet as a deck with the high chord corressponding to the top of the parapet elevation.
Is there an alternate way of modelling the parapet, without having the model assume that the entire width (length when we speak hydraulically) of the bridge is at the same elevation as the parapet. Please advise.
Is there an alternate way of modelling the parapet, without having the model assume that the entire width (length when we speak hydraulically) of the bridge is at the same elevation as the parapet. Please advise.





RE: Hec Ras - Modelling Bridge Parapet.
RE: Hec Ras - Modelling Bridge Parapet.
RE: Hec Ras - Modelling Bridge Parapet.
If that's the case, I think that is probably the best way to model it. If your existing roadway is overtopping and you are placing a solid wall/rail in the flow area, it could be likely that you are reducing weir flow and creating a rise in WSEL.
Unrelated...It would be nice if HEC would throw in an option to model slots or "windows" such as those used in decorative bridge railings.
Good luck!
RE: Hec Ras - Modelling Bridge Parapet.
Also, I am running the bridge comps under Energy Eqn. Any suggestions.
RE: Hec Ras - Modelling Bridge Parapet.
Seriously, though, I had this issue on an in-kind replacement too - only they shifted the bridge 400 ft upstream and I had the same backwater elevation to meet. I guess your options are:
- longer sag curve to extend your weir flow area
- change to a box culvert
- add a secondary culvert on the overbank(s)
RE: Hec Ras - Modelling Bridge Parapet.
RE: Hec Ras - Modelling Bridge Parapet.
RE: Hec Ras - Modelling Bridge Parapet.
It really sounds like you need more bridge opening or potentially lower/change your railing. Your DOT may have approved bridge railings with enough openings that you may be able to increase conveyance.
What is your tailwater condition like? Will downstream grading help your case at all? Depending on your environmental regulations/impacts, lowering the flowline could be an option, if grades allow.
RE: Hec Ras - Modelling Bridge Parapet.