Modeling Unconventional Weirs in HEC-RAS

[alesso]

Since HEC-RAS does not allow a rating curve to be used for an inline struture, does anyone know of a way to work around this?
My problem is I need to model two inline labyrinth weirs across a reach for a LOMR. I have tried creating lateral stuctures with diversion rating curves based on the Tulis equation, but I don't think the water surface elevation is reflected properly. In order to use a lateral weir 100% of the flow would have to go thru the lateral structure and it appears HEC-RAS does not allow this. I don't understand the subroutines in HEC-RAS well enough to figure out a way to "trick" the program into working the way I need it to.

 

[Drew08]

On the inline gate editor, select Gate type = "User Defined Curves", Select "Enter/Edit User Defined Curves", Enter Headwater and Discharge values using Tullis.

Gate opening is somewhat arbitrary as long as it is set equal both in the inline structure and in the steady (or unsteady) Flow Data editor.

This would only be accurate though if the tailwater does not influence the weir flow. I believe Tullis does have a method for accounting for tailwater though.

HEC-RAS won't give you the flow profile through the labyrinth, but should be adequate for upstream backwater analysis.

 

[alesso]

Thank you Drew, that is exactly what I was looking for! This is much better then "tricking".
Luckily, I don't have any influence from backwater so this should work quite well.