Adding cross section
Adding cross section
(OP)
My x-section for the entire reach (having bridge at the middle) is the same. Is there disadvantage in accuracy of water surface computation if i provide more x-sections especially near bridge? please can you give me hint or direct a reference?
Thanks
Thanks





RE: Adding cross section
RE: Adding cross section
Thank you in advance.
RE: Adding cross section
1) located far enough downstream so that flow is completely expanded
2) downstream face of bridge (I usally place at toe of slope)
3) upstream face of bridge (Toe of slope)
4) located far enough upstream such that flow width matches the no bridge scenario.
I do on occasion model xsecs between 1 & 2 and 3 & 4; but only in special circumstances changes in manning's, xsec geometry or etc...
Hope this helps.
RE: Adding cross section
Really thank you so much for your attention, I put these 4 sections considering some engineering judgements. However, I put several sections in between section 1&2 and 3&4 by interpolation (the reach has uniform shape). Because i need these points and also i put ineffective flow area locations the same by interpolation b/n 1&2 and 3&4 sections for the interpolated sections. the question is has a negative effect on computation (steady flow WSP)putting more x-sections in between the basic reaches. Another thing is gbam said that section 2&3 usually put at toe of slope, what will be if the embankment is vertical(no slope)?
Thank you.
RE: Adding cross section
As for the placement of Xsecs 2&3 at the toe of slope, by tow of slope I mean the roadway embankment toe of slope. If you have a wall one can set it a couple of feet us or ds. In my area we typically only have brdge wingwalls for short distances away from the channel and then the sloping roadway embankment takes over.
Every scenario may be slightly different. It is up to the engineer to evaluate the condition and come up with the best method for modelling the condition.
RE: Adding cross section
By the way, considering small scale flow systems(Eg. lab. flume flow), is that possible to simulate using HECRAS with the actual scale better than large scale taking a big scale ratio?
RE: Adding cross section
RE: Adding cross section
If you do not mind can i ask another? I saw that the bridge/culvert can skew up to 45 degree only, is that possible to use more than 45 degree mannualy using "cosine value" in excel, and paste it? the mechanism is shown in manual,and it is clear. why HECRAS limit to 45? (I need to check up to 70 degree)
RE: Adding cross section
Do you imagine that the brdge will surcharge? HECRAS will allow caps on xsecs. I have only used this a couple of time but it worked well in my scenario. Hope that helps, I know I did not answer your question directly but it could be a maybe yes or maybe no.