HEC-RAS Multiple Opening Scour

[rbutler]

I have a seven opening relief bridge system for which I need to perform a scour analysis on each bridge. I have completed the multiple opening (MO) model, and created individual models of each bridge for the scour analysis (since HEC-RAS wont compute scour for MOs). I truncated each contraction (XS 4) and Expansion (XS 1) section at the computed stagnation points, and entered the computed flow through each bridge (from the MO model).

However, reviewing the MO results, the computed stagnation points seem to be exactly the points I enter, even though I allow the points to migrate greatly between openings. In other words, for opening 1, if I enter a right stagnation point of 500, and for opening 2 I enter a left stagnation point of 200, it computes opening 1's right stagnation point as 200 and opening 2's left stagnation point as 200. If I vary it to 400 and 300, the right and left will be 300. HOWEVER, THE FLOWS, VELOCITIES, ETC ALL REMAIN THE SAME, which is good for the computation of flows through each individual bridge.

My question is, due to the degree of variance (Seeminly based on user input) in the computed stagnation points, will truncating the individual bridge's geometry at these points cause erroneous hydraulic computations for the individual bridge models.

 

[rbutler]

Attached is the output from my model...notice the varying stagnation points (those points represented #s that I entered and varied between the two runs), but the same computed flows, velocities, etc